Post on 06-Feb-2018
C0NQ.140.297
MODULAR AUTOMATIC VOLTAGE REGULATOR
GENERAL PRINCIPLE, OPERATION
AND
MAINTENANCE INSTRUCTION
NANJING TURBINE & ELECTRIC MACHINERY (GROUP) CO., LTD.
NANJING CHINA
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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CONTENTS
SECTION TITLE PAGE
1 INTRODUCTION 3
2 MAVR UNIT
4
3 MAINFRAME
9
4 CONTROL CARD 39
5 AUTO POWER CARD 82
6 EXCITATION LIMITER CARD 86
7 POWER FACTOR CONTROL CARD 97
8 EXCITATION MONITOR CARD 114
9 VOLTAGE MONITOR CARD 140
10 MAVR AUXILIARY RACK 156
11 COMMISSIONING 184
12 FAULT FINDING 186
13 INSTALLATION AND MAINTENANCE 195
14 OPERATION 199
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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1. INTRODUCTION
The 'Modular Automatic Voltage Regulator' (MAVR) is designed to
control the excitation of large brushless or statically excited generators.
They are housed in two rack assemblies, named MAVR unit and the
auxiliary rack with external dimensions of 409.5 × 496 × 177 and 365 ×
488 × 266 respectively. MAVR unit has the advantages of a compact
modular construction, enabling a wide range of optional features to be
readily incorporated into the excitation system.
The basic unit for use with brushless generators incorporates the
following plug in modules: auto control bridge; control card (which
includes over flux limiter, diode failure detector and fast acting current
limiter); and excitation limiter card (which includes over and under
excitation limiters). An electronic manual control system in the MAVR
auxiliary rack is used. When used with a statically excited generator,
manual and auto circuits used on a brushless generator are omitted and
the control signal from the static control card is routed to an external
thyristor converter.
The motorized voltage setting potentiometer is incorporated on the
front fixed panel of MAVR unit, which is suitable for manual or remote
operation.
Optional extras include the excitation bias or power factor control
cards, both of which can be used to control power factor or reactive
current. For use on twin AVR systems voltage and excitation monitors
to initiate AVR change-over are also available.
Connections to the unit are via plugs and sockets at the rear of the
rack to facilitate easy removal of the AVR. The outgoing sockets are
connected to multicore cables which require termination in the
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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excitation panel.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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2 MAVR UNIT
2.1 The MAVR unit comprises the mainframe which carries
certain fixed components and into which are plugged various
withdrawable cards.
The mainframe forms the necessary interconnections between the
component parts of the MAVR and provides the required isolation of
input signals. Also included are the power supply components, output
relays and outgoing plug connections. These components are mounted
on two printed circuit boards, the backboard and the backpanel, The
backboard incorporates the sockets into which the various cards are
plugged whereas the backmost printed circuit board, the backpanel,
carries the outgoing plug/socket connections. These two boards are
electrically connected by two plugs in printed circuit boards, called
interconnectors. Connected to the backboard by a small wiring loom is
the power supply transformer (sometimes mounted externally in case of
static excitation systems) and the fixed front panel. The latter unit
houses the sensing and power supply fuses together with the remotely
controllable motorized voltage setting potentiometer and monitor reset
pushbutton, where applicable.
Each plug in card has unique polarizing key positions to prevent
cards being plugged into the incorrect position. The various cards
available, and their position in the mainframe (see fig.2-1) are listed
below separating the basic MAVR, its options and the static excitation
MAVR (see 2.3, 2.4 )
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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O
O
A
Fixed Plate
B C D E F G H
O
O
[ Withdrawable Cards ]
Fig. 2-1 - MAVR Card Positions
2.2 The Basic Brushless System
This system comprises the mainframe together with the following
printed circuit cards:
2.2.1 Auto Power Card-fitted in position H
This is an assembly comprising a single phase half-controlled
thyristor bridge, its heatsink, a surge suppressor, and a semiconductor
protection fuse. This unit accepts the thyristor firing pulses which are
produced by the control card thereby controlling the excitation from
the permanent magnet generator excitation source.
2.2.2 Control Card-fitted in position E
This unit senses the voltage of R to Y and the current of B phase,
and produces thyristor firing pulses to control excitation. Also included
are an over flux circuit to reduced the excitation at reduced speed, a fast
acting field current limiter to prevent sustained high exciter field
current, a "soft start" facility to minimize voltage overshoot on build up,
and a diode failure detector to indicate failure of the rotating diode
assembly. The unit accepts control signals from the excitation limiter
and power factor control cards.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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2.2.3 Excitation Limiter Card-fitted in position D
This unit comprises over and under excitation transducers which
work in conjunction with the control card to prevent the excitation
being controlled above or below preset limits.
The limiter prevents prolonged overexcitation by controlling the
exciter field current, and has an integrating time delay to allow for high
transient field currents. If required, the operating level of the
overexcitation limiter can be temperature compensated to allow for
variation in generator cooling air temperature. The limiter also
prevents underexcitation and high internal load angles due to certain
leading power factor conditions and is quick acting to minimize
transients which could cause pole slipping.
2.3 Optional Extras
A power factor control card is available for use on the Standard
MAVR system, which includes auxiliary rack with electric hand control
board.
Where Twin AVR system is provided by a standby AVR Voltage and
excitation monitors are available, which may be plugged into the standard
MAVR rack.
2.3.1 Power Factor Control Card-fitted in position C
This unit in conjunction with the control card enables a parallel
running generator to be run at a constant power factor or reactive
current by driving the motorized voltage setting potentiometer also
incorporated in the MAVR.
Operation of the unit is initiated by an external signal ( normally
and auxiliary contact on the circuit breaker). An external signal will
also initiate automatic reduction of reactive current - a feature which is
useful when preparing to disconnect a generator from a power system.
A relay mounted in the mainframe may if required be used to inhibit
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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the operation of the controller following manual operation of the
voltage setting control by the external volts raise/lower switch.
2.3.2 Excitation Monitor Card-fitted in position F
This unit comprises over and under excitation transducers which
operate a common monitor relay in the mainframe if the excitation is
controlled to a level outside a preset region.The latched monitor relay
can be used to initiate transfer to an alternative excitation system, and
local latched LED indication of over or under excitation monitor
operation is provided on the card front plate.
When the monitor is fitted to a MAVR a monitor reset pushbutton
would be mounted on the mainframe.
2.3.3 Voltage Monitor Card-fitted in position B
This unit comprises over and under voltage monitors each with an
integrating time delay. When either monitor operates the latched
monitor relay in the mainframe is energized and local latched LED
indication is provided on the card, relay and indication being resetable
by a pushbutton mounted on the mainframe.
The undervoltage monitor includes a circuit which prevents
operation hen the excitation is switched off, or when the generator
current exceeds a level corresponding to a fault at the generator
terminals.
The voltage monitor card would normally be fitted to initiate
transfer of excitation to a standby excitation system.
2.4 Static Excitation Systems
When the MAVR is used as the control element of a static excitation
system the auto power cards are omitted, and a special control card is
fitted in position E, which supplies a d.c. signal to the control circuits of
the thyristor converter, which will usually be situated in a separate
cubicle. Apart from the auto power cards the rest of the basic brushless
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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system is used although various modification are made to the
mainframe such as the removal of the internal power supply. The
options available, as listed in 2.3, are also suitable for use in the static
system.
Due to the high excitation currents associated with static excitation
systems an additional sensing signal is required from the field current
via a D.C. current transformer. The power supply transformer is
mounted externally due to the increased size at the reduced operating
frequency of 50 or 60 Hz.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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3 MAINFRAME
3.1 SPECIFICATION
The mainframe houses the various cards and forms the necessary
interconnections. In addition it carries the ' Remote Volts Setting
Potentiometer ' , sensing fuses, transformers, and output relays.
The overall dimensions of the mainframe are: 177 mm high, 496 mm
wide and 409.5 mm deep. The typical weight of the complete unit is
approximately 14 Kg. It requires access at the back for the four 15-way
plug/socket connectors and adequate clearance above and below for
ventilation; 150 mm is recommended. The unit dissipates up to 200
watts when in operation.
3.1.1 Inputs
1) Voltage sensing supply:
110 V nominal, 50/60 Hz, red to yellow phase at 3 VA, &for the 3
phase
sensing option: yellow to blue phase at 3 VA.
2) Current sensing supply:
5A current transformer input, 50/60 Hz, blue line, burden 5 VA
maximum (with options).
3) Auxiliary supply:
220 V pilot exciter output at 400 Hz, 180 VA for a 50 Hz generator.
264 V pilot exciter output at 480 Hz, 180 VA for a 60 HZ generator.
150 V pilot exciter output at 200 Hz, 180 VA for a 50 HZ generator.
180 V pilot exciter output at 240 Hz, 180 VA for a 60 HZ generator.
220 V supply output at 50 Hz, 180 VA for a 50 HZ generator.
4) Excitation source:
220/264 V 400/480 Hz; 150/180 V 200/240 Hz, (400v on H.I.R.
unit ) pilot exciter output, capability dependent upon excitation
requirements but not exceeding 15 A, 220 V 50 Hz , capability
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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dependent upon excitation requirements but not exceeding 15 A
continuous.
5) Auxiliary D.C. supply:
Selectable by internal links (on the backpanel ) for:
24 v + 25% ~ -20%
48 v + 25% ~ -20%
125v + 25% ~ -20%
220v +10% ~ -10%
Current rating 150 mA at all voltage taps.
3.1.2 Relay Outputs
Three relay outputs are available; one for the limiter card, one for the
various monitors, and one for the Diode Failure circuit.
1) Contact arrangement:
Normally open or normally closed all relay.
2) Contact rating:
220 V a.c./d.c., 100watts, 5 A, non-inductive.
3.1.3 Auxiliary Control Inputs
1) An external single pole changeover switch with centre 'OFF'
position is required to drive the internal motorized voltage setting
potentiometer.
Rating 150 V D.C. at 150 mA.
2) 'Field Application Contactor Auxiliary' for 'soft start' and 'under
voltage monitor override' ( single pole, normally open ). Rating 30V
D.C. at 10 mA.
3) Grid breaker auxiliary (single pole, normally open ) for use with
'Power Factor Control Card' . Rating 30 v d.c. at 10 mA.
4) VAr shed signal (signal pole, normally open ) for use with ' Power
Factor Control Card ', if required. Rating 30 v d.c. at 10 mA.
5) Smooth Changeover ' Signal ' ( single pole, normally open ) for use
with twin AVR schemes to reduce changeover shock with '
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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Excitation Bias ' and ' Over Excitation ' units.
Rating 30 v d. c. at 60 mA.
6) A normally open contractor to give self-centering of MVSR Rating
150V d.c. at 150 mA.
3.1.4 Optional Input/Outputs
(1) Remote 'Level' potentiometer for' Excitation Bias/P.F. Control
Card '.
(2) External temperature compensation for over excitation limiter.
(3) Latching path for P.F. Control over-ride.
(4) Internal MVSR for twin AVR schemes.
(5) Smooth changeover single outputs/inputs for twin AVR schemes.
(6) Main amplifier input and output signals.
3.1.5 Ambient Temperature Range
Operating : -25 ℃ to + 65 ℃
Storage : -40 ℃ to + 100℃
3.1.6 External Connections
External connections are made by up to four 15 way plug/sockets, the
loose Plugs being wired to 3 metres of individually numbered 15 core
multicore cables, cross sectional area 1.0 mm2.
3.1.7 Extender Card
An extender card will be supplied mounted in the mainframe to give
access to test points on the various cards.
3.2 DESCRIPTION OF OPERATION
3.2.1 Introduction
The mainframe is the basic rack with all the plug in cards
withdrawn. The unit comprises the 19" rack assemble fitted with two
printed circuit boards, called the backpanel and backboard; fixed front
panel; and a power supply transformer which is fixed to the left hand
side plate of the rack.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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Interconnection between the backpanel and the backboard is made by
two printed circuit boards called interconnectors; and the backboard is
connected to the fixed front panel and power supply transformer by a
small wiring loom and a plug/socket to enable the fixed front panel to
be removed.
To select the various options available links are fitted on the
backpanel-these being set according to the specified contract
requirements.
3.2.2 Backpanel
The backpanel receives the plug/socket external connections and
carries the sensing transformers and auxiliary components as detailed
below.
Circuit
Reference Function
T1 Voltage sensing transformer energized via sensing
Fuses FS3 and 4 mounted on fixed front panel.
T2
Optional voltage sensing transformer used for three
phase sensing facility (not fitted on standard unit,
fitted on H.I.R. Unit)
T3,Z1,Z2,LK1
Sensing C.T. for excitation bias (EB) or power factor
control (PFC) card. Z1,Z2 provide C.T. load when
card withdrawn. CT is shorted by LK1 when EB or
PFC cards not fitted.
T4,Z3,Z4,LK2
Sensing C.T. for excitation monitor (EM) card.
Z3,Z4 provide C.T. load when EM card withdrawn.
C.T. is shorted by LK2 when EM card omitted.
T5,Z5,Z6 Sensing C.T. for excitation limiter (EL) card. Z5,Z6
provide C.T. load when card withdrawn.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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T6,Z7,Z8,LK3,
4,5,6
Sensing C.T. for control (c) card. LK3,4 will
normally be fitted and LK5,6 omitted to provide
quadrature current compensation (QCC) For
external reactance compensation LK3,4 will be
omitted and LK5,6 fitted. Z7,Z8 provide C.T. load
when C card is withdrawn.
R1,R2,LK8
AVR stabilizing resistors. R1,R2,LK8 fitted on single
AVR system; R1,LK8 only fitted on twin AVR system
when R1 on main and standby units are paralleled.
R3 Load resistor across output of Field rectifier to assist
thyristor turn on.
D1,D2,D3,D4
Flywheel diodes across output of Field rectifier, for
connector protection if power cards inadvertently
withdrawn during AVR operation.
RL1,R12,D5 Limiter operating relay, series dropper and Flywheel
diode.
RL2,R13,D6 Monitor operated relay, series dropper and flywheel
diode.
RL3,Z11,D7
Power supply monitoring relay. Energizes and causes
AVR transfer on a twin system if main AVR supply
fails. Energizes and causes AVR transfer to hand
control in the single AVR system if AVR supply fails.
RL4,D10,11,
12,R14,
R18
P.F. control inhibit latching relay. Relay is energized
through D11 or D12, and latched by RL4-1 and
external circuitry to inhibit p.f. control. Only used
when p.f. control card fitted.
R4,5,6,7,9,10
LK9,10,11,12,
13,14
Dropper resistors and voltage selection links for
internal motorized potentiometer.
Fit links LK9 & 10 for 24/30v dc supply.
LK11 & 12 for 50v dc supply.
LK13 & 14 for 125v dc supply.
LK13 & 14 for 220v dc supply.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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Z9,Z10 Stabilizing zeners for motorized potentiometer.
LK19,20,21 LK20,21 fitted only when P.F. control card is
supplied. LK19 is not fitted.
LK22,23
Both links are normally omitted. When fitted the
AVR amplifier input and pulse circuit input become
available at outgoing socket 4, pins 6 and 5
respectively.
R15,R16,D15,
D14,
C1,Z12
To effect a trip to hand control excitation on loss of
power supply with back-up excitation systems.
RL5,R17,D13,
LK26,
LK27
Diode Failure operated relay, series dropper and
flywheel diode, LK26 gives N/O contacts and LK27
N/C contacts.
LK28A,LK28B
Enables the Power Factor Control card option to be
used on 24/30v and 50v D.C. supplies. Fit neither
LK28A or LK28B for 120v D.C. Fit LK28A for 50v
D.C. Fit LK28B for 24/30v D.C.
INTERCHANGEABILITY
NOTE: LK24 and LK25 to be fitted only when replacing an original
version backpanel (G.A. B9602928 - PCB9602927). The 'Type A'
backpanel then becomes interchangeable, requiring no external wiring
changes.
3.2.3 Backboard (refer to fig. 3-3)
The backboard performs the function of interconnecting the various
printed circuit boards, transformer and fixed front panel. It provides
the stabilized D.C. supply for the cards and has various other auxiliary
components as detailed below.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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Circuit
Preference
Function
D1,2,3,4,C1,2 Power supply diodes and smoothing capacitors
Z1,2,C3,4
AVR power supply stabilizing zeners and smoothing
for control card electronics.
Z3,4,C5,6,R8,9
Auxiliary power supply stabilizing zeners and
smoothing for electronics not included on the
control card.
RL1,D5,6,VT1,
2,Z5,R3,4,5,6,7,
C7
Time delay circuit to inhibit transient operation of
Limiter, DFI and monitor relays immediately after
supplies connected to AVR RL1 will energize after a
delay provided the D.C. exceeds a pre-set level.
D7,Z6,R10 Provide feed to inhibit under-voltage monitor when
line current exceeds preset level.
LK1 Link which is removed when reset monitors
pushbutton fitted. This will usually be made on the
fixed front panel plug
3.2.4 Power supply Transformer (T1)
This unit isolates the electronics from the a.c. supply and provides
the correct voltage for the D.C. supply stabilizing circuit incorporated
on the backboard. It is also used to provide the phase reference and
frequency sensing signals for the control card.
An external transformer is used on some static excitation systems.
The primary tap used depends on the generator frequency and pilot
exciter viz:
R/B wire to TM2 for 200/240 Hz. 190v Newton PMG.
R/B wire to TM3 for 3,000 r.p.m. 220v Brush PMX exciter.
R/B wire to TM4 for 3,600 r.p.m. 264v Brush PMX exciter.
3.2.5 Fixed Front Panel (refer to fig 3-4)
This unit incorporates the volts setting potentiometer, monitor
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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reset-pushbutton and supply/sensing fuses as detailed below.
Circuit
Reference Function
FS1,FS2
Auxiliary a.c. fuses in primary of transformer T1 or
in a.c. supply to power supply bridge on static
excitation systems
FS3,FS4,(FS5)
Voltage sensing fuses in primary of back panel
mounted sensing transformer T1 (FS5 is not
normally fitted but will be fitted when AVR
incorporates 3 phase sensing and T2 is fitted to back
panel).
RV1,RV2
Voltage setting potentiometer. On a twin AVR
system, the standby unit incorporates the voltage
setting control for both unit units. RV2 sets the
voltage of the main AVR.
(RV2 may not be fitted in a single AVR system).
M,LS1,LS3
Motor assemble for driving voltage setting control
incorporates limit switches LS1 and LS3. M, RV1,
RV2 will not be fitted on the main AVR of a twin
MAVR system.
LS2 & LS4 Limit switches for driving the voltage setting control
to the centre of its range (i.e. selfcentering).
PB1 Reset monitors pushbutton fitted to AVR's
incorporating latched Fault monitors.
The components fitted on a particular unit will vary according to
contract requirements, typically FS1,2,3 & 4, RV1,M,LS!,2,3 & 4 are
fitted on a standard unit.PB1 is normally fitted in place of M, RV1 and
2, LS1,2,3 & 4 in the case of the main unit of a twin system whereas the
standby unit is usually a standard unit.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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3.3 COMMISSIONING PROCEDURE
This section describes the commissioning procedure for the
mainframe and should be read in conjunction with the general
commissioning procedure, section 11 and any specific contract
commissioning instructions
IMPORTANT:
(1) Check that the correct links are fitted on the backpanel as
detailed in the test records for MAVR tested with a test
generator. (sub-section 6)
(2) Check that the correct power supply transformer tap has been
selected.
In general the majority of the commissioning procedure of a MAVR
unit is covered by the procedure for the individual cards, see the
appropriate instructions. However prior to running the set the
following static checks should be carried out.
1) Check all connections associated with the mainframe are sound and
tight.
2) Check all external wiring to 0NQ.359.019 MAVR Excitation system
circuit diagram paying particular attention to the phasing of the P.T.
and C.T. feeds.
3) Apply the D.C. supply to the mainframe and check corrector
operation of the motorized voltage setting potentiometer, i.e.
clockwise rotation for a 'raise' signal and vice versa.
3.4 FAULT FINDING PROCEDURE
This section describe the fault finding procedure for the mainframe
and should be read in conjunction with the general fault finding section
12.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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IMPORTANT:
(1) The majority of excitation faults are caused by incorrect connections
- thoroughly check all connections are correct to the circuit diagram.
(2) Check the correct links are fitted as detailed in the test records for
MAVR tested with a test generator. (sub-section 6)
Before commencing fault finding on the mainframe exhaust all the
pertinent faults given in the general fault finding section 12 and the
detailed faults given in the individual card sections.
The following tables give the required signals on each finger of the card
sockets and the path from those fingers to the source or output. Card
fingers/sockets are referred to as bracketed numbers, output
connections as socket number/pin number and each card is abbreviated
thus:
Control C
Auto Power AP
Excitation Limiter EL
Excitation Monitor EM
Power Factor Control PFC
Volts Monitor VM
Interconnector I1-5 & I9-6
By tracing through the signals present on the socket of a suspected
faulty card the nature of the fault can be deduced and corrective action
taken.
Table 3-1 CONTROL CARD
SKT Title Required Signal Path Possible
Fault
1 If pick-up
O.165v/A
excitation w.r.t.
C(29) - brushless
only.
Via I9-6(3)
to R1/R2 &
1/14.
R1/R2
faulty.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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2 AVR Amp
i/p Zero w.r.t. C(29)
Via I1-5(3)
& LK23 to
4/6
Control card
faulty
3 QCC
C.T.M
1.53v/A sensing
current w.r.t.
C(6) Maximum
Q.C.C
Via I1-5(6)
& LK3 or
LK6 to T6
T6 or control
card faulty.
4 42v a. c.R.
42v a.c. @105v.
Sensing volts
w.r.t.C(6)
Via I1-5(8)
to T1
T1 of control
card faulty.
5 42v a.c.B.
42v a.c. @105v.
Sensing volts
w.r.t. C(4)-three
phase sensing
only.
Via I1-5(10)
to T2
T2 or control
card faulty.
6 42v a.c.Y. See(4) Via I1-5(12)
to T1
T1 or control
card faulty.
7 +ve AVR
P.S.
+15v D.C. w.r.t.
C(29)
To Z1
(Backboard)Z1 faulty.
8 Not used
9 Not used
10 SCR1
cathode
Negative pulse
w.r.t. C(13) To AP(12)
Auto power/
control card
faulty.
11 P.S. A.C 54v a.c. w.r.t.
C(29)
To T1
terminal(5) T1 faulty.
12 P.S. A.C 54v a.c. w.r.t.
C(29)
To T1
terminal(7) T1 faulty.
13 SCR1 gate Positive pulse
w.r.t. C(10) To AP(13)
Auto power/
Control card
faulty.
14 Not used.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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15 Pulse CCT
O/R
±0.7v D.C. w.r.t.
C(29)
Via I1-5(27)
& LK22 to
4/5
Control card
faulty.
16 Not used.
17 SCR2
cathode
Negative Pulse
w.r.t.
C(18)
To AP(14)
Auto power/
Control card
faulty.
18 SCR2 gate
Positive pulse
w.r.t.
C(17)
To AP(15)
Auto power/
Control card
faulty.
19 -ve Unreg. -76v D.C. w.r.t.
C(29)
To C2,D2,D4
(backboard)
T1 or C2,D2,
D4 faulty.
20 +ve Unreg. -76v D.C. w.r.t.
C(29)
To C1,D1,D3
(backboard)
T1 or C1,D1,
D3 faulty.
21 -ve AVR
P.S.
-15v D.C. w.r.t.
C(29) To Z2 Z2 faulty
22 AVR Amp
Com. Zero w.r.t. C(29)
Via I1-5(42)
to 4/10
Control card
faulty.
23 Internal
MVSR2
500 ohm w.r.t. to
C(29) at
minimum set
volts with
control card
removed.
To fixed
front panel
via BK/O
wire &
I1-5(43) to
4/11.
RV1 faulty.
24 Reset 1 +15v D.C. w.r.t.
C(29)
To PB1 or
T1 via O/BN
wire.
PB1 faulty
or O/BN not
shorted to
O/GN on T1.
25 U.V.
override Zero w.r.t. C(29) To VM(28)
Control card
or Z6,D7 on
backboard
faulty.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
22�
26 FAC Aux. +15v D.C. w.r.t.
C(29)
Via I1-5(28)
to 2/11
Control card
faulty.
27 Not used.
28 D.F.I. Relay
+15v D.C. w.r.t.
C(29) when
D.F.I. operating
Via I1-5(50)
to RL5 &
R17.
D.F.I. faulty.
29 common Zero
Via
I9-6(51-60)
to R1/R2
Mainframe
faulty.
Table 3-2 AUTO POWER CARD
SKT
No. Title Required Signal Path
Possible
Fault
(1-5) Field +ve
Field voltage
(+ve) w.r.t.
AP(29)
Via I9-6(5 to
11) to 1/1 &
1/2.
Auto power
card faulty.
(6-1
0)
Common
A.C.
220/264v(150/180
v) a.c. (400v on
H.I.R.unit.) w.r.t.
Ap(20)
Via I9-6(13
to 19) to 1/3
& 1/4
External
fault.
(11) Not used.
(12) SCR1
Cathode
Negative pulse
w.r.t. AP(13) To C(10)
Auto Power/
Control card
faulty.
(13) SCR1 Gate Positive pulse
w.r.t. AP(12) To C(13)
Auto Power/
Control card
faulty.
(14) SCR2
Cathode
Negative pulse
w.r.t. AP(15) To C(17)
Auto Power/
Control card
faulty.
(15) SCR2 Gate Positive pulse
w.r.t. AP(14) To C(18)
Auto Power/
Control card
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
23�
faulty.
(16) Not used.
(17) Not used.
(18) Not used.
(19) Not used.
(20-
24) Auto A.C
220/264v(150/180
v) a.c.w.r.t. AP(6)
Via I9-6(42
to 49) to 1/7
& 1/8
External
fault
(25-
29)
Output -ve
(Common)
Negative voltage
w.r.t. AP(1)
Via I9-6 (51
to 69) to
R1/R2
Mainframe
faulty
Table 3-3 EXCITATION LIMITER CARD
SKT
No. Title Required Signal Path
Possible
Fault
(1) Reset 2 +15v D.C. w.r.t.
EL(29)
To RL-1
(Backboard
and PBI or
T1 via O/GN
wire
RL1 faulty.
(2)
If pick-up
0.165v/A
excitation w.r.t.
EL(29)-
brushless only.
Via I5-6(3)
to R1/R2 &
1/14
R1/R2
faulty.
(10) OEL Temp
comp 3 Not used.
Via I5-6(48)
to 3/13 Not used
(11) Not used.
(12) Limiter
O.R.
+15v D.C. w.r.t.
EL(29) when
Monitor O.R.
given to 3/7
Via I1-5(29)
to 3/7
Limiter/
Monitor or
external
signal faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
24�
(13) SCO
Selector
+15v D.C. w.r.t.
EL(29) on twin
system when on
other AVR.
Not used on
single AVR
Via I1-5(29)
to 4/3
External
faulty
(14) -ve Aux.
P.S.
-15v w.r.t.
EL(29)
To Z4
(Backboard)Z4 faulty
(15) Pulse cct
O/R
+0.7v D.C. w.r.t.
EL(29)
To C(15) and
via I1-5(27)
& LK22 to
4/5
Control/
Excitation
Limiter
faulty.
(16) +ve Aux.
P.S.
+15v D.C. w.r.t.
EL(29)
To Z3
(backboard) Z3 faulty
(17) Limiter
Relay
+15v D.C. w.r.t.
EL(29) when
Limiter
operating
Via I1-5(25)
to R12/RL1 R12/RL1
(18) Ext. OEL
Amp
Not used on
single system ±
10v D.C. w.r.t
EL(29) on twin
system
Via I1-5(51)
to 3/12
Other AVR
faulty
(19) -ve Unreg. -76v D.C. w.r.t.
EL(29)
To C2,D2,D4
(Backboard)
T1 or C2,D2,
D4 faulty.
(20) +ve Unreg. +76v D.C. w.r.t.
EL(29)
To C1,D1,D3
(Backboard)
T1 or C1,D1,
D3 faulty.
(21) 2.5v A.C.
R-Y
2.5v D.C. w.r.t
EL(29)
Via I1-5(46)
to T1 T1 faulty.
(23) Int OEL
Amp.
±10v D.C. w.r.t.
EL(29)
Via I1-5(52)
to 3/10
Excitation
Limiter
faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
25�
(24) OE. Temp
Comp. 2
-1v to -5v D.C.
w.r.t. EL(26)
when external
temp. Comp.
Unit fitted
Via I1-5(53)
to 4/12
Main Frame
faulty or
external
temp. Comp
unit faulty
(25)
Exc.
Lim/Mon
Link
As EL(26) To EM(25) Mainframe
fault
(26) OE Temp
Comp. 2
+1v to +5v D.C.
w.r.t. EL(24)
when external
temp. Comp.
Unit fitted
Via I1-5(54)
to 4/13
External
temp. Comp.
Unit fault or
main frame
fault.
(27) UEL C.T.L.
4.5v/A-sensing
current. W.r.t.
EL(28)
Via I1-5(55)
to T5 T5 faulty.
(28) UEL
C.T.M.
4.5v/A-sensing
current. W.r.t.
EL(27)
Via I1-5(56)
to T5 T5 faulty.
(29) Common Zero
Via
I9-6(51-60)
to R1/R2
Mainframe
faulty.
Table 3-4 POWER FACTOR CONTROL CARD
SKT
NO. Title Required Signal Path
Possible
Fault
(1) P.F. +ve P.F.C. +ve
auxiliary D.C.
Via I1-5(1)
to 3/9
External
wiring
(4) Ext. Pot. H
Remote PFC
level only. 5
kohms w.r.t.
PFC(6) with
card removed.
Via I1-5(4)
to 4/4
External
wiring fault.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
26�
(5) Ext. Pot. A
Remote PFC
level only. 5
kohms w.r.t.
PFC(6) with
card removed
and dependant
on pot position
Via I1-5(5)
to 4/2
External
wiring fault.
(6) Ext. Pot. L
5 kohms w.r.t.
PF(4) when card
removed.
Via I1-5)(7)
to 4/1
External
wiring fault.
(7) PFC Raise PFC-Raise signal
to MVSR
Via I1-5(9)
to 3/3 and
via LK20 to
Z10 &
MVSR
Other AVR
fault
PFC faulty
(8) PFC Lower PFC-Lower
signal to MVSR
Via I1-5(11)
to 3/1 and
via LK21 to
Z9 & WVSR
PFC faulty
(9) Grid C/B
Aux.
+15v D.C. w.r.t.
PFC(29)
Via I1-5(13)
and
LK19/RL4-3
to 2/3.
External
fault
(10) VAr shed
+15v D.C. w.r.t.
PFC(29) when
VAr shed
selected.
Via I1-5(15)
to 2/3
External
fault
(11) PFC CTM
6.0v/A-sensing
current w.r.t.
PFC(12)
Via I1-5(18)
to T3 T3 faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
27�
(12) PFC CTL
6.0v/A-sensing
current w.r.t.
PFC(11)
Via I1-5(16)
to T3 T3 faulty
(13) SCO
Selector
PFC-not used
EB-+15v D.C.
w.r.t. EB(29)
when other AVR
selected.
Via I1-5(19)
to 4/3
External
fault
(14) -ve Aux P.S. -15v D.C. w.r.t.
PFC(29)
To Z4
(Backboard)Z4 faulty
(16) +ve Aux
P.S.
+15v D.C. w.r.t.
PFC(29)
To Z3
(Backboard)Z3 faulty
(21) 2.5v
A.C.Y-R
2.5v a.c. w.r.t.
PFC(29)
Via I1-5(46)
to T1 T1 faulty
(25) -ve Unreg. -76v D.C. w.r.t.
PFC(29)
To C2,D2,D4
(backboard)
T1 or
C2,D2,D4
faulty
(26) +ve Unreg. +76v D.C. w.r.t.
PFC(29)
To C!,D1,D3
(backboard)
T1 or
C1,D1,D3
faulty
(29) Common Zero
Via
I9-6(51-60)
to R1/R2
Mainframe
Faulty
Table 3-5 EXCITATION MONITOR CARD
SKT
No. Title Required Signal Path
Possible
Fault
(2) If Pick-up
0.165v/A-excitati
on w.r.t. EM(29)-
brushless only.
Via I9-6(1)
to R1/R2 &
1/14
R1/R2 faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
28�
(9) Monitor.
Relay
+15v D.C. w.r.t.
EM(29) when
monitor
operating
Via I1-5(14)
to R13 &
RL2
Monitor or
RL2 faulty
(14) -ve Aux.
P.S.
-15v D.C. w.r.t.
EM(29)
To Z4
(Backboard)Z4 faulty
(16) +ve Aux.
P.S.
+15v D.C. w.r.t.
EM(29)
To Z3
(Backboard)Z3 faulty
(18) Exc. Mon.
O.R.
+15v D.C. w.r.t.
EM(29) when
Monitor override
signal given to
3/7
Via I1-5(29)
to 3/7
Monitor or
external
signal faulty.
(19) UEM
C.T.L.
4.5v/A-sensing
current w.r.t.
EL(20)
Via I1-5(44)
to T4 T4 faulty
(20) UEM
C.T.M.
4.5v/A-sensing
current w.r.t.
EL(19)
Via I1-5(45)
to T4 T4 faulty
(21) 2.5v A.C.
R-Y
2.5v a.c. w.r.t.
EM(29)
Via I1-5(46)
to T1 T1 faulty
(22) +ve Unreg. +76v D.C. w.r.t.
EM(29)
To C1,D1,D3
(Backboard)
T1 or
C1,D1,D3
faulty
(23) -ve Unreg. -76v D.C. w.r.t.
EM(29)
To C2,D2,D4
(Backboard)
T1 or
C2,D2,D4
faulty
(24) Reset 1 +15v D.C. w.r.t.
EM(29)
To PB1 or
T1 via O/BN
wire
PB1 faulty
or O/BN not
shorted to
O/GN on T1.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
29�
(25)
Exc.
Lim/Mon
Link
As EL(26) when
EL fitted To EL(25) Main frame
(29) Common Zero
Via
I9-6(51-60)
to R1/R2
Mainframe
faulty.
Table 3-6 VOLTAGE NONITOR CARD
SKT
No. Title Required Signal Path
Possible
Fault
(2) Volts Mon
O.R
+15v D.C. w.r.t.
VM(29) when
Monitor override
signal give to
3/11
Via I1-5(2)
to 3/11
Monitor or
external
signal fault
(8) Monitor
relay
+15v D.C. w.r.t.
VM(29) when
monitor
operating
Via I1-5(14)
to R13 and
R12
Monitor or
RL2 faulty
(12) -ve Aux.
P.S.
-15v D.C. w.r.t.
VM(29)
To Z4
(Backboard)Z4 faulty
(13) +ve Aux.
P.S.
+15v D.C. w.r.t.
VM(29)
To Z3
(Backboard)Z3 faulty
(20) Sensing
R105v
105v a.c. w.r.t.
VM(22)
Via FS4 Y
I1-5(39) to
T1
FS4 or main
frame faulty
(22) Sensing
Y105v
105v a.c. w.r.t.
VM(20)
Via FS3 Y
I1-5(34) to
2/9
FS3 or main
frame faulty
(24) Reset 1 +15v D.C. w.r.t.
VM(29)
To PB1 or
T1 via O/BN
PB1 faulty
or O/BN not
shorted to
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
30�
O/GN on T1.
(25) -ve Unreg. -78v D.C. w.r.t.
VM(29)
To C2,D2,D4
(Backboard)
T1 or
C1,D2,D4
faulty
(26) +ve Unreg. -+8v D.C. w.r.t.
VM(29)
To C1,D1,D3
(Backboard)
T1 or
C1,D1,D4
faulty
(28) U.V.
Override
Zero w.r.t.
VM(29) To C25
Volts
monitor/
Control card
faulty or
Z6,D7 on
Backboard
faulty.
(29) Common Zero
Via
I9-6(51-60)
to R1/R2
Main frame
fault.
Table 3-7 OUTGOING SOCKET NO.1
SKT
No.
Title Required Signal Path Possible
Fault
1/1
&
1/2
Field +ve Field Voltage
w.r.t. 1/10
Via
I9-6(5-11) to
AP(1-5)
Mainframe
faulty
1/3
&
1/4
Common
A.C.
220/264v(150/180
v) a.c. w.r.t. 1/7
and 1/8
Via
I9-6(13-19)
to AP(6-10)
Mainframe
faulty
1/7
&
1/8
Auto A.C.
220/264v(150/180
v) a.c. w.r.t. 1/3
& 1/4
Via
I9-6(43-49)
to AP(20-24)
Mainframe/e
xternal
wiring faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
31�
1/9 MVSR
Raise +ve
Auxiliary D.C.
+ve when raise
signal given
Via D8, Z10,
I-5(36) to
MVSR
Faulty
MVSR, D8
or Z10
1/10
Field
-ve/Commo
n -ve
-ve Field voltage
w.r.t. 1/1 or 1/2 To LK8
Mainframe/
Link
omission
fault
1/11 Aux. A.C. 220/264v(150v/1-
80v) a.c. w.r.t. 3/6
Via I1-5(20)
to FS2
External
wiring fault
1/12 MVSR
Lower +ve
Auxiliary D.C.
+ve when lower
signal given
Via D9, Z9,
I1-5(35) to
MVSR.
Faulty
MVSR, D9
or Z9.
1/13 Blue C.T.M. Passes sensing
current
To 1/15 via
T3, T4 or
LK2, T5 &
T6
External
wiring
fault/LK2
omitted if T4
not fitted
1/14 Field -ve -ve field voltage
w.r.t. 1/1 or 1/2 To R1/R2
Mainframe
failure
1/15 Blue C.T.L. Passes sensing
current
To 1/13 via
T3, T4 or
LK2, T5 &
T6
External
wiring
fault/LK2
omitted if T4
not fitted.
Table 3-8 OUTGING SOCKET NO.2
SKT
NO.
Title Required Signal Path Possible
Fault
2/1 Grid
Breaker
Aux.
+15v D.C. w.r.t.
1/14 when PFC
operation
selected
Via
LK19/RL4-3
& I1-5(13) to
PFC(9)
LK19/RL4-3
faulty
2/2 Monitor RL Short circuit to To RL2-1 RL2 faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
32�
n/c 2/4 when no
monitor
operating
2/3 VAr shed
selector
+15v D.C. w.r.t.
1/14 when 'VAr
shed' selected
Via I1-5(15)
to PFC(10)
External
fault.
2/4 Monitor RL
com
See 2/2 & 2/6 To RL2-1 RL2 faulty
2/6 Monitor RL
n/o
Short circuit to
2/4when a
monitor is
operating
To RL2-1 RL2 faulty
2/7 Incoming
Y105v
105v a.c. w.r.t.
2/9
Via I1-5(32)
to FS4
External
fault
2/8 Limiter RL
n/o
Shirt circuit to
2/10 when the
Limiter is
operating
To RL1-1 RL1 faulty
2/9 Incoming
Y105v
105v a.c. w.r.t.
2/7
Via I1-5(34)
to FS3
External
fault
2/10 Limiter RL
com.
See 2/8 & 2/12 To RL1-1 RL1 faulty
2/11 FAC Aux. +15v D.C. w.r.t.
1/14 when FAC
closed
Via I1-5(28)
to C26
External
fault
2/12 Limiter RL
n/c
Short circuit to
2/10 when the
limiter is not
operating
To RL1-1 RL1 faulty
2/13 Astatic
C.T.L
1V/A sensing
current w.r.t.
2/15 - Maximum
Q.C.C.
To T6 T6 faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
33�
2/13 Astatic
C.T.L
1V/A sensing
current w.r.t.
2/15 - Maximum
Q.C.C.
To T6 T6 faulty
2/14 MVSR
Supply-ve
Auxuiliary D.C.
-ve
To LK9 to 14
and RL4
External
fault
2/15 Astatic
C.T.M.
See 2/13 To T6 T6 faulty
Table 3-9 OUTGOING SOCKET NO.3
SKT
No. Title Require Signal Path
Possible
Fault
3/1 PFC Lower
±7.5v D.C. w.r.t.
4/10 -PFC-Lower
signal to MVSR
Via I1-5(11)
to PFC(8) &
Via LK21 to
Z9 & MVSR
PFC Faulty
3/2 P.F. Control
Latch
Auxiliary D.C.
+ve unless
resetting
To RL4 via
RL4-1
External
fault
3/3 PFC Raise
±7.5v D.C. w.r.t.
4/10 -(twin
system only)
PFC-Raise signal
to MVSR
Via I1-5(9)
to
EB/PFC(7)
& via LK20
to Z10 &
MVSR
EB-Other
AVR fault
PFC-PFC
faulty
3/4
Standby
select RL
com twin
system or
hand
control sel
RL com
single
system
+15v D.C. w.r.t.
4/10
To D7,Z11 &
RL3
Other AVR
faulty Hand
control
faulty
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
34�
3/5 Trip Supply
To PMG 50%
Tap or Hand
Control supply
To D14 (&
LK25) &
associated
components
External
fault
3/6 Aux. A.C.
Com. See 1/11
Via I1-5(24)
to FS1
External
wiring fault
3/7 Ecx. Mon
O.R.
+15v D.C. w.r.t.
4/10 when
monitor override
signal given to
3/7
Via I1-5(29)
to EM(18)
EM or
external
fault
3/8 MVSR
Centre
Aux. D.C. +ve
when
self-centering
required
Via I1-5(60)
to MVSR
Faulty
MVSR or
external
signal
3/9 PF +ve +ve auxiliary dc
Via I1-5(1)
to
EB/PFC(1)
External
fault
3/10 Int. OEL
Amp.
±10v D.C. w.r.t.
4/10
Via I1-5(52)
to EL(23)
Excitation
Limiter
faulty
3/11 Volts Mon
O.R.
+15v D.C. w.r.t.
4/10 when
monitor override
Signal give to
3/11
Via I1-5(20)
to VM(2)
Monitor or
external
fault
3/12 Ext. OEL.
Amp
Not used on
single system ±
10v D.C. w.r.t. to
4/10 -on twin
system
Via I1-5(51)
to EL(18)
Other AVR
fault
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
35�
3/13 OEL Temp
Comp 3.
Zero voltage
w.r.t. 1/14 if E.L
fitted
Via I1-5(48)
to EL(10)
Mainframe
faulty or EL
faulty
3/14
3/15
DFI Relay
DFI Relay
N/C if link LK27 fitted to RL5
via LK26
N/O if link LK26 fitted to LK27
Link missing
or RL5
faulty
Table 3-10 OUTGOING SOCKET NO.4
SKT
No. Title Require Signal Path Possible Fault
4/1 Remote PFC
pot. L
5 kohms w.r.t. 4/4
with PFC card
removed
Via I1-5(7) to
PFC(6)
External
faulty
4/2 Remote PFC
pot. A
0-5 kohms w.r.t. 4/4
with PFC card
removed
Via I1-5(5) to
PFC(5) External fault
4/3 Common
SCO selector
+15v D.C. w.r.t.
1/14 when other
AVR selected twin
system only
Via I1-5(19)
to PFC(13) &
EL(13)
External fault
4/4 Remote PFC
pot.H. See 4/1
Via I1-5(4) to
PFC(4) External fault
4/5 Pulse cct.
O/R
± 0.7v D.C. w.r.t.
1/14
Via LK22 &
L1-5(27) to
C15
Control card
fault. LK22
not normally
fitted
4/6 AVR amp. i/p Zero w.r.t. 1/14 Via LK23 &
I1-5(3) to C2
Control card
fault. LK23
not normally
fitted
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
36�
4/7 External
MVSR2
500 ohms w.r.t. 4/8
at minimum volts
set & external
wiring removed
Via I1-5(30)
to MVSR
Mainframe
fault
4/8 External
MVSR1
500 ohms w.r.t. 4/7
at minimum volts
set & external
wiring removed
Via I1-5(31)
to MVSR
Mainframe
fault
4/9 Incoming
B105v
105v a.c. w.r.t. 2/9
& 2/8 when 3-c
sensing fitted.
Via I1-5(33)
to FS5 External fault
4/10 AVR Amp.
Com. Zero w.r.t. 1/14
Via I1-5(42)
to C(22)
Mainframe
fault.
4/11 Internal
MVSR2
500 ohms w.r.t. 4/10
at minimum volts
set & control card
removed
Via I1-5(43)
to C(23)
Mainframe
fault.
4/12 OEL temp.
Comp.2
Zero volts w.r.t.
1/14 if E.L. fitted.
Via I1-5(53)
to EL(24)
Main frame or
E.L. frame
fault
4/13 OEL Temp.
Comp.1
1v to 5v D.C. w.r.t.
1/14 when temp
comp. connected
externally.
Via I1-5(54)
to EL(26) External fault
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4. CONTROL CARD
4.1 SPECIFICATION
4.1.1 Steady State Voltage Regulation
The generator voltage is maintained within ±1% of the selected
operation voltage subject to the following conditions:
1) The ambient temperature must not deviate by more than ±15℃
from that temperature at which nominal voltage is first set.
2) The frequency deviation must not exceed ±10% of the nominal
frequency (50 or 60Hz).
3) The sensing voltage supplied to the unit must be a constant
proportion of the generator output.
4) The current limit circuit is not operating.
The generator voltage will be maintained within ±0.5% of the
selected operating voltage when the generator load is switched from
no-load to full-load provided there is zero quadrature current
compensation.
4.1.2 Nominal Detector Supply Voltage
Within the range 100~120 volts.
4.1.3 Operating Voltage Range
An adjustment of ±10% on nominal voltage is provided by the
voltage setting rheostat which is controlled either manually or remotely.
A larger voltage setting range is available but is non-standard.
4.1.4 Parallel Operation
An internal current transformer is provided, an isolated primary
winding of which is supplied from the 5 amp. Secondary winding of an
instrument current transformer in the generator output. The internal
current transformer and its load represents a burden of less than 1 VA.
Two modes of parallel operation of the generator are normally available;
the quadrature current compensation and astatic compensation, and
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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the degree of stability of reactive current is determined by the setting of
a rheostat in the AVR.
To convert to astatic compensation, a third winding is provided on
the AVR internal current transformer and these should be connected in
a operated in parallel.
In the quadrature current compensation mode 15% droop at full
load zero power factor is available. For compensation of external
reactance the droop can be inverted by internal links to give up to
15% external reactance compensation.
If the nominal CT current is less than 5 amps, the amount of
compensation will be reduced in proportion.
4.1.5 Frequency Fall Off
1) The fall off frequency is set to:
42.5 Hz on a 50 Hz system ) selected by
51 Hz on a 60 Hz system ) internal links
2) The fall off frequency does not vary by more than 2% of the setting
provided the temperature variation is less than ±15℃ from
ambient and the pilot exciter output voltage is within ±25% of
nominal voltage tap selected on power transformer.
3) The generator output will be linearly reduced to between 50% and
30% of nominal at 50% of the falling frequency set point.
4) Below 50% speed the characteristic is less predictable but over
fluxing will be prevented.
4.1.6 Diode Failure Indicator
1) This unit detects field current ripple and gives an output signal to a
relay mounted in the mainframe and also gives local indication
when the ripple exceeds a preset proportion of the field current.
2) Normal Sensitivity (with link 12 and 13 omitted). The relay will
operate when the negative peak of ripple in exciter field current
exceeds 20% of the d. c. level.
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3) Increased sensitivity (link 12 fitted and 13 omitted). The ripple to operate
the relay is adjustable using RV6 from 20% to 12% of the d. c. level.
4) Reduced sensitivity (link 12 omitted and 13 fitted). The ripple to operate the
relay is adjustable using RV6 from 20% to 40% of the d. c. level.
4.1.7 Current Limiter
1) This circuit is incorporated to limit the maximum continuous field
current, and has a quick acting inverse timer delay characteristic
for short circuit current limiting.
2) The field current limit can be set within the range 5 to 25 A; the
time delay is fixed at 20% second ±10%.
3) A link can be changed to increase the sensitivity by a factor of 10 (±
0.5) as a commissioning aid.
4.1.8 Soft Start Circuit
This circuit uses an external ‘Field Application Contractor’
auxiliary contact to detect excitation build up and utilizes this to slowly
ramp up the voltage reference to minimize over shoot on build up.
4.1.9 Ambient Temperature Range
Operating: -25℃ to 65℃
Storage : -40℃ to 100℃
4.1.10 Power Supply Requirements
The card draws its ±15volt power supplies from the mainframe.
The power supplies are adequate from 120% to50% of nominal
frequency and nominal pilot exciter voltage range of 120% to 40%.
4.1.11 Input Signals
The unit requires a single phase, 100 to 120 volts, B to A phase
supply of 2 VA rating. It also requires a 5A current transformer input of
1VA rating in the C phase.
4.1.12 Remote Voltage Setting Potentiometer
Fine adjustment (±10%) on the nominal voltage is provided by a
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500 ohms 1W potentiometer that is either mounted in the mainframe or
mounted externally.
4.1.13 Controls and Indications
1) Set V: A front access multi-turn potentiometer to set the nominal
voltage.
2) Q.C.C. A front mounted single turn potentiometer with a calibrated
dial scaled 0 ~ 10 which sets the level of quadrature current
compensation.
3) Set Q: A front access multi-turn potentiometer that adjusts the
stabilizing signal magnitude.
4) Set P: A front access multi-turn potentiometer that adjusts the
stabilizing signal phase.
5) Test DF: A front mounted pushbutton to test the ‘Diode Failure
Indicator’ circuit operation.
6) D.F.I.: A front mounted ‘Light Emitting Diode’ to give indication
of rotating diode failure.
7) Set DF: A front access multi-turn potentiometer to set the sensitivity
of the ‘Diode Failure Indicator’.
8) If LIM: A front access multi-turn potentiometer to set the maximum
continuous field current controlled by the ‘Current Limit’.
9) Step: A pushbutton mounted on the printed circuit board that can
be used to provide a 10% step to AVR reference.
Can be used when setting up response during commissioning.
4.2 DESCRIPTION OF OPERATION
(Numbers in brackets ( ) refer to printed circuit board edge
connections, and all voltage levels are relative to TP1.)
The unit is supplied with –15V(21), 0V(29), +15V(7) stabilized rails
derived from Z1, Z2, C3, C4, on the backboard. When the control
card is inserted in the rack, R1, R2, R5, R6 supply current to the power
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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supply zeners on the backboard.
4.2.1 The Detector and Amplifier
Sensing voltage is supplied to DB1 at (3) (4) (6) from T1 and T6
mounted on the back panel. RV1 adjusts the voltage across (3) and (6)
and the amount of quadrature current (or external reactance)
compensation, i.e. drooping (or rising) voltage with increasing lagging
vars.
The sensing voltage is attenuated, smoothed and compared with a
reference signal produced by Z1 and R14, and the resultant error
supplied to the AVR amplifier, IC1, which is gain stabilized by R16.
RV2 provides coarse voltage adjustment and RV1 on the fixed front
panel connected across (22) and (23), the fine adjustment.
4.2.2 Auxiliary Control Signals
Auxiliary control signals can also be supplied to the input to the
voltage error amplifier via (2). If this facility is utilized the signal,
which should be isolated, should be supplied to the multi-core 4/10 and
4/6, and link LK23 on the back panel fitted.
4.2.3 Pulse Circuit
VT1, 2, 3, PUT1, T1 and associated components form the pulse
circuit.
At the beginning of each half cycle of the permanent magnet
generator (PMG) output waveform, the voltage TP3 to TP1 is
approximately 0.5 volts negative due to D6 and D7 being forward
biased by R22. When the PMG voltage increases from zero, D8 is
forward biased by R21 and D9 or D10 and D6 is charged from –0.5
volts towards the amplifier output voltage at TP2, through resistor R17.
After a delay dependant on the voltage at TP2, VT1 will be turned on,
VT2 turned off, causing the voltage at the anode of PUT1 to rise. When
the voltage at the anode of programmable injunction transistor PUT1
reaches a level set by the ratio of R25 and R29, the PUT switches on,
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and the voltage across R28 rises rapidly to a level set by R24 and R28.
Transistor VT3 is turned on for a short period by a pulse or current
through R27 and C8 and C9 rapid discharges through the primary
winding of pulse transformer T1 and VT3. A pulse is produced across
each secondary winding of T1 that is connected to SCR1 gate via (13)
and (10) and SCR2 gate via (17) and (18).
At the end of the half cycle of PMG output waveform, D8 becomes
reverse biased and D6 and D7 forward biased by R22, the voltage at
TP3 falling to –0.5 volts. VT1 turns off, VT2 on, and the voltage at the
anode of the PUT falls to a low level, in preparation for the next pulse,
which occurs during the next half cycle. When VT3 ceases conduction,
C9 is charged to approximately +15 volts via R26.
The time taken to charge C6 is dependent on the amplifier output
voltage, which varies according to the firing angle of the thyristors.
Figure 4-1 shows the capacitor and output voltage waveforms for high
and low amplifier output voltage.
An additional feed to C6 via (15) makes it possible for the
excitation limiters to over-ride the amplifier output signal there by
preventing over or under excitation beyond preset limits.
In addition, when LK6 is inserted in the control card, the earliest
possible firing angle can be limited by the output of IC2b, the field
current limit amplifier.
4.2.4 AVR Stabilizing
On a brushless generator the voltage control loop is stabilized by
transient feedback from exciter field current.
The voltage from the stabilizing resistor (R1, R2 on back panel) is
supplied to the input of IC1 via (1), LK1, C1, C2, RV3 and R12. RV4
adjusts the amplitude of the stabilizing signal, and RV3, the phase. LK2
is not fitted:
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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4.2.5 Field Current Limit
When the current in the exciter field exceeds a level depending on
the setting of RV5, the voltage at the output of IC2b begins of fall.
D17 begins to conduct, and current flows through LK6 and R53,
thereby reducing the rate at which C6 is charged and delaying the
firing angle. The output voltage of IC2b settles at a value whereby the
voltage at the wiper of RV5 is controlled to the voltage at pin 6 of IC2b,
which corresponds to a preset field current.
4.2.6 Falling Frequency (Over Flux) Protection
The output of the supply transformer is fed via R33 and (11) to a
frequency sensitive circuit. On alternate half cycles, C14 is charged to a
positive value via D12, and C13 is charged to a negative value via D11.
As the frequency reduces, the voltage at the anode of D13 becomes most
positive and at the cut off frequency, D13 begins to conduct, tuning off
VT4 for a period that increases as the frequency reduces further.
The collector of VT4 begins to pulse to a negative value, producing
pulses of current through R38, causing the output voltage of IC2a to
become positive. The effect of current flow through D15, D14, R43,
R42 and LK5 to the input of IC1 is to reduce the reference current at
IC1 input, thereby causing a reduction in the level of controlled voltage,
to a value depending on the frequency of the generator. LK3 and LK4
select the knee point (the frequency at which the over. flux circuit
begins to operate). An additional feed is taken from TP4 via R76 and
D25, which is used to inhibit the action of the under voltage monitor
when the over flux protection is operating, and R49 is used to inhibit
the diode failure detector when the over flux protection is operating.
4.2.7 Diode Failure Detector
Diode or fuse failure in the rotating assembly is detected by sensing
ripple induced in the exciter field current, caused by misbalance load
on the exciter output.
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The voltage from the stabilizing resistors (R1, R2 on back panel) is
supplied to the diode failure circuit where it is attenuated and smoothed
by R57, RV6 and C16. This signal, which now represents
approximately 80% of the average input, is fed to the inverting input of
IC2c. The input signal is also fed via R55, with minimal smoothing by
C18, to the non-inverting input of IC2c. The output of IC2c is
normally high and goes low only when the negative peaks of the
unsmoothed input fall bellow 80% of the average input signal. The
output of IC2c is fed via D18 and R61 to the input of IC2d that turns on
VT5 after a time delay generated by R64 and C20, zeners Z4 and Z5
clamp the output of IC2d. VT5 turns on VT6 energizing the back panel
mounted diode or fuse failure relay via D21, LED1, LK7 and 28.
Pressing PB1 that injects current via R56 to the input of IC2c tests the
detector. The light emitting diode LED1 provides local indication that
the detector is operating
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If local indication only is required, LK7 should be removed and
R69 fitted. In the majority of applications the fixed sensitivity described
above will be suitable. This standard sensitivity will accept a normal
negative going peak ripple of 20% of the D.C. level.
LK12, when fitted, provides adjustable sensitivity from
approximately 20% to 12% of the D.C. level, sensitivity increasing as
RV6 is turned clockwise.
LK13, when fitted, provides adjustable sensitivity from
approximately 20% to 40% of the D.C. level, sensitivity being reduced
by turning RV6 clockwise.
4.2.8. Soft start circuit
When the generator is run up with the excitation switched on,
voltage will build up slowly due to the falling frequency circuit. A
circuit is incorporated which limits the rate of rise of output voltage,
when the excitation is applied suddenly at rated speed by closing the
field contractor or switching on the PMG supply.
Assume that the set is running which the MAVR energized but the
field contractor open. The auxiliary contact on FAC (across 2/5 and
2/11) is open and RL1 is de-energized. The MAVR is energized but
since RL1-1 is open, the voltage across C23 is low, D23 and D24 being
reversed biased. VT7is turned on by R70 and current flows through
R74 and (25) to prevent operation of the under voltage monitor.
RL1-1 closes and the voltage at TP7 become positive, returning to
the negative rail potential as C23 is charged through R73. During the
period that TP7 is positive, a transient current flows through and the
under voltage monitor (if fitted) is inhibited by a transient current
through D24, R75 and (25).
If FAC is initially closed and excitation is applied by switching the
PMG output to the MAVR, the transient feeds through D23 and D24
occur in the same manner since the initial charge on C23 is zero, and
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RL1-1 will close, when the MAVR is energized.
In both cases, VT7 is turned off during normal running due to
RL1-1 being closed.
If for any reason, the auxiliary contact on FAC is not used to
provide soft start, multi-cores 2/5 and 2/11 should be linked.
4.2.9. Three Phase Sensing
When this option is included the C phase sensing voltage is
supplied to D1, D2 via (5) and to cater for the increased input voltage,
link LK9 should be removed.
4.2.10. Link Identification
LK1 Selects transient feedback from exciter field current as
used for stabilisation on brushless generators.
When fitted LK2 must be omitted.
LK2
Selects transient feedback from the error amplifier
output as used for stabilisation on statically excited
generators.
When fitted LK1 must be omitted.
LK3 Selects falling frequency knee point at 42.5Hz for 50Hz
generators.
When fitted LK4 must be omitted.
LK4 Selects falling frequency knee point at 51Hz for 60Hz
generators.
When fitted LK3 must be omitted.
LK5 Selects falling frequency circuit operation.
LK6 Selects field current limit circuit operation.
LK7 Selects diode failure detector circuit operation.
LK8 Selects soft start circuit operation.
LK9 Selects single phase sensing. When removed the unit is
suitable for three phase sensing.
LK10 Selects the normal level of field current limit.
LK11 Selects a field current limit level of one tenth of the
normal level (used during commissioning).
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LK12
LK13
Not normally Fitted
LK12 brings RV6 into operation to increase sensitivity,
i.e. circuit will operate with a lower level of ripple.
LK13 brings RV6 into operation to decrease sensitivity,
i.e. circuit will operate with a lower level of ripple.
4.3 COMMISSIONING PROCEDURE
This section describes the commissioning procedure for the control
card and should be read in conjunction with the general commissioning
procedure, section 13 and any specific contract commissioning
instructions.
IMPORTANT:
(1) The short circuit field current limit potentiometer, IFLIM, has
been set to the correct level at the factory and should not require
any on-site adjustment.
(2) Check that the correct links are fitted as detailed in the Setting
Records for MAVR tested with test generator (sub-section 6).
(3) Check operation on hand control prior to operation in auto
control.
4.3.1 Basic voltage control and soft start circuits
Set the mainframe front mounted motorized voltage setting
potentiometer to mid rang and the control card ‘Set V’ control fully
anti-clockwise.
Run the generator up to rated speed and switch the excitation to
‘auto’ control. The generator voltage should up slowly, due to the soft
start circuit action, to a stable voltage below nominal.
If the generator voltage is unstable the stabilizing controls should
be adjusted as described in sub-section 4.3.6. Adjust the ‘set V’
control to bring the generator voltage to its nominal value. Check by
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rotation of the motorized voltage setting potentiometer that the
generator voltage can be varied by ±10% from its nominal value and
reset it to this value.
Switch off the excitation for 2 minutes to allow the soft start circuit
to reset. Check that on re-selecting ‘auto’ excitation control the
generator voltage builds up slowly to nominal with minimal overshoot.
4.3.2. Falling Frequency Circuit
Inhibit any speed switch signal, where applicable, to maintain
‘auto’ excitation control at reduced frequency.
Reduce the generator speed and check that line voltage is reduced
in sympathy with the generator frequency below 85% of nominal
frequency. Run up set from low speed with the excitation switched on.
Check voltage builds up at approximately 40% speed and increases
gradually to nominal when 85% speed is reached.
4.3.3. Parallel Operation
To ensure reactive load sharing between AVR controlled generators
operating in parallel and to ensure stable control when paralleled to a
large supply system, it is necessary to provide quadrature current
compensation (Q.C.C.). Q.C.C. is phase sensitive and it is necessary to
carefully check the phasing of the sensing voltage and current to the
contract schematic diagram.
When synchronizing the generator for the first time the procedure
shown below should be followed: -
1) Synchronizing to a large supply system:
Set the Q.C.C. (RV1) control fully clockwise and carefully
synchronies are ensuring minimal mismatch in system and
generator voltage. Increase the motorized voltage setting
potentiometer and check that a lagging KVAR load is taken on the
generator.
2) Synchronizing to another generator:-
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Connect the other generator to the bus-bars with hand controlled
excitation and synchronies to it the set being commissioned with
‘auto’ excitation to give 25% reactive circulating KVAR. The
bus-bar voltage should reduce by approximately 4%.
3) Set the Q.C.C. control, i.e. RV1, to give the required droop.
4.3.4. Diode Failure Circuit
1) Check that the diode failure test pushbutton gives local LED
indication after approximately 2 seconds delay. The generator
should be operating on no load, with MAVR operation. If possible,
fully load generator at rated power factor and check that no diode
failure indication is given.
2) To be certain that the diode failure relay operates. When a rotating
diode failure occurs the most appropriate test is to temporarily
replace one of the brushless rectifier fuses by an open circuit (blown)
fuse (N.B. it is essential on high-speed machines to maintain
mechanical balance by fitting an equivalent fuse). Run the
machine and excite an open circuit at nominal volts. Indication of
diode failure should be given. On identical machines it is
acceptable to perform this test on one machine only. Do not
attempt this test unless the blown fuse is a direct mechanical
replacement to the healthy one.
3) In unusual cases, the inherent ripple in exciter field current may be
too high under healthy conditions, and the relay may operate
continuously, In this case fit LK13 and rotate RV6 clockwise from
the fully anti-clockwise position until the relay de-energizes.
Rotate RV6 two further turns clockwise. In this case it is
recommended that the test in (2) above be performed to confirm
relay operation on an actual fault.
4) In the unlikely event of the test in (2) above not resulting in
operation of the relay, fit LK12 and increase the sensitivity of the
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relay by rotating RV6 clockwise from the fully anti-clockwise
position until the relay operates, then rotate RV6 two turns further.
4.3.5 Field Current Limit Circuit
This circuit is incorporated to limit the steady state short circuit
fault current to a defined safe level and has been preset at the factory to
be required level. It should not be altered unless absolutely necessary.
If the level needs to be reset or checked this can best be achieved at low
excitation levels on open circuit as follows: -
Remove LK10 and fit LK11. In this state the If limit circuit will
operate at one tenth of its normal level. Set RV5 to give a limiting
excitation level one tenth of the desired level and finally remove LK11
and replace LK10.
4.3.6. Stabilizing Circuit Adjustment
The stabilizing controls are: -
Set Q – Quantity or magnitude of stabilizing signal (RV4)
Set P – Phase of stabilizing signal (RV3).
If it is necessary to adjust the stabilizing the following procedure
should be carried out:
1) Adjust ‘set P’ to 10 turns clockwise and ‘Set Q’ to 15 turns
clockwise.
2) With the generator running at rated speed, select ‘auto’ excitation.
The voltage should build up and stabilize.
The generator voltage must now be disturbed by means of suddenly
changing the setting of the motorized voltage setting potentiometer or
operating PB2 the ‘STEP’ pushbutton after fitting the control card
into the rack using the extender card.
3) If the voltage recovery is sluggish, turn ‘Set P’ anti-clockwise by a
small amount. Reset ‘Set q’ by turning it anti-clockwise until the
voltage becomes unstable and then clockwise until just stable.
4) If the voltage recovery is oscillatory, turn ‘Set P’ clockwise by a
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small amount. Reset ‘Set Q’ as in (4).
5) Having optimized the stability to voltage reference changes it
remains to finally optimize the response by load application and
rejection. Repeat step (4) and (5) using load changes until the
optimum is reached.
Optimum stabilizing is achieved when the voltage overshoots the
final steady value once following load application.
The response as indicated by the generator output voltmeter would
be affected by the damping of the meter movement. A more
accurate indication can be obtained from a multi-meter connected
across the exciter field.
If definite recovery time following a particular load change should
not be exceeded, an oscillogram of generator output voltage should be
taken on a suitable recorder having a high frequency response.
4.4 FAULT FINDING PROCEDURE
This section describes the faultfinding procedure for the Control
Card and should be read in conjunction with the general fault finding
section 14.
IMPORTANT
1) The majority of excitation faults are caused by incorrect
connections – thoroughly check all connections are correct to
0NQ.359.019 Excitation System Circuit Diagram.
2) Check that the correct links are fitted as detailed in the setting
records for MAVR tested with test generator, sub-section 6.
In general faults associated with the Control card can be separated
into four categories, viz.
1. Over Excitation (Table 4-1)
2. Under Excitation (Table 4-2)
3. Instability (Table 4-3)
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4. Operational Faults (Table 4-4)
Refer to the appropriate section for corrective action.
Table 4-1 Over excitation Faults
No. Possible Fault Test Remedial Action
1 Loss of voltage
sensing
Check FS3,4(&5)
and all external
fuses and wiring
Measure sensing
voltage (2/7 to 2/9)
on hand control
Replace blown fuses or
correct as necessary.
2 Q.C.C. Circuit
Failure
Check Q.C.C. feed
to 1/13 & 1/15
Correct as necessary
3 Mainframe
Failure
See mainframe
failure finding
procedure.
See section 2.4
4 Limiter Card
Failure
Remove Limiter
Card
See excitation limiter
card failure finding
procedure.
5 Auto Power
Card Failure
See Auto power
card failure
finding procedure.
See Auto power card
failure finding
procedure.
6 Control Card
Failure
Interchange
Control Card with
a spare
Replace Control Card
and return faulty card
to the Works for repair
Table 4-2 Under Excitation
No. Possible Fault Test Remedial Action
1 Wiring Fault Check all external
wiring
Correct as necessary
2 Q.C.C. Circuit
Failure
Check Q.C.C. feed
to 1/13 & 1/15
Correct as necessary
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3 Loss of
Auxiliary
Power Supply
Check FS1&2 and
any external fuses
and wiring to
auxiliary supply.
Replace blown fuses or
correct as necessary.
4 Mainframe
Failure
See mainframe
failure finding
procedure.
See Section 2.4
5 Limiter Card
Failure
Remove Limiter
Card
See Section 6.4
6 Auto Power
Card Failure
See Auto power
card failure
finding procedure.
See Section 5.4
7 If Limit too
low/faulty
Remove link 6 Reset as in Section 4.3.5
or if faulty repair
Control Card
8 ‘Frequency Fall
Off’ circuit
operating
Remove link LK5 Check correct links
fitted, if faulty repair
Control Card. Check
capacitors C11&12 on
Control Card are
correct.
9 ‘Soft Start’
Circuit faulty.
Remove Link LK8 If correct with LK8
removed, repair control
card.
⒑ Pilot exciter
faulty
Check Pilot exciter
output
Check and repair pilot
exciter
⒒ Control Card
Failure
Interchange
Control Card with
a spare
Replace Control Card
and return faulty card
to the Works for repair
Table 4-3 Instability
No. Possible Fault Test Remedial Action
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1 Incorrect
stabilizing
circuit link
selected.
Check LK1 is
fitted for Brushless
generators, or LK2
fitted for directly
excited generators.
Select correct link.
2 Incorrectly set
Stability
controls.
See Section 4.3 See Section 4.3
3 Main-frame
faulty
No field current
pick up signal to
control card
(1)&(29)-should be
150 mV to 1V 0n
no-load.
See Section 2.4 & 3.4
4 Power System
instability
Refer to operating
chart to ensure
stability limits are
not exceeded.
Check stability of
excitation limiters if
operating.
5 Governor
instability
Check excitation
stable on hand
control
Reset governor
stabilizing…
Table 4-4 Operational Faults
No. Symptom Possible Fault Test Remedial
Action
1 Over fluxing at
reduced speeds
Frequency
Fall Off
Circuit faulty
or link LK5
omitted/incor
rect Lk3/4
fitted
Check LK5
is fitted and
LK3 for
50Hz or
LK4 for
60Hz set.
Fit Link 5, if
omitted or
repair
control card
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2 Limited lagging
capability or
sluggish
on-load
response
If limit set too
low or faulty
Check again
after
removing
LK6
Reset level
as in Section
4.3 or if
faulty repair
Control
card.
3 Diode failure
indication
permanent-ly on
Diode has
failed DFI too
sensitive or
faulty
Check
rotating
diodes or
DFI
sensitivity
Refer to
Section 4.3
Replace
faulty diode,
reset DFI
sensitivity or
repair
control card
if faulty
4 Diode failure
circuit in
operative
LK7 is
omitted or
R65 is not
fitted. DF1
not sensitive
enough.
Check LK7
or R65 is
fitted
Fit LK7or
R65. If still
faulty repair
control card
5 Excessive
overshoot on
excitation
build-up
Soft Start
Circuit is
faulty, LK8 is
omitted, or
external
wiring is
incorrect
between 2/5
and 2/11.
Incorrect
stabilizing
adjustment.
Check as
necessary
Correct as
necessary
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5. AUTO POWER CARD
5.1 SPECIFICATION
5.1.1 Maximum continuous ratings within the temperature range : 25℃ to
+50℃:
(1) 50 Hz to 576 Hz (i.e. to 480 Hz +20% over speed).
(2) 15A D.C. output (12.5A at 65℃).
(3) 350 volts RMS input at +20% over speed, open circuit.
5.1.2 In addition, to meet short circuit excitation levels, the following rating
applies for 3 seconds maximum: 25A D.C. output.
5.1.3 Storage temperature range: -40℃ to +100℃
5.1.4 Maximum (D.C.) output volts =RMS input volts ×0.9.
5.2 DESCRIPTION OF OPERATION
(Numbers in brackets ( ) refer to printed circuit board edge
connections).
The PMG excitation source is supplied to the half controlled
thyristor bridge, THB1, via the fuse, FS1, at (6)(7)(8)(9)(10) and
(20)(21)(22)(23)(24).
The thyristor control signals, coming from the control card, are
supplied to (12) (13) for SCR1 and (14) (15) for SCR2. The phasing of
these control signals with respect to the PMG voltage varies the mean
D.C. output of the bridge which appears at (1) (2) (3) (4) (5) positive
and (25) (26) (27) (28) (29) negative.
The two resistors R1, R2, are incorporated to ensure a low
impedance gate circuit to avoid false thyristor triggering due to pick-up.
The suppressor, CL1, is fitted to protect the bridge against spurious
voltage transients.
5.3 COMMISSIONING PROCEDURE
This section describes the commissioning procedure for the auto
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power card and should be read in conjunction with the general
commissioning procedure, section 11 and any specific contract
commissioning instructions.
As the auto power card converts the output of control card into the
required generator excitation the commissioning procedure follows that
of the control card. As a precautionary measure check that the fuse,
FS1, and the half-controlled thyristor bridge, TM1, DM1, connections
are physically sound.
5.4 FAULT FINDING PROCEDURE LT
This section describes the faultfinding procedure for the Auto
Power Card and should be read in conjunction with the general fault
finding section 12.
IMPORTANT:
(1) The majority of excitation faults are caused by incorrect
connections – thoroughly check all connections are correct to
the 0NQ.359.019 Excitation System Circuit Diagram.
(2) To reduce electrical stress on the edge connectors, if at all
possible the power cards should only be withdrawn with the
generator unexcited, or being controlled by a standby AVR.
If it is absolutely necessary to remove an auto or hand power card from
a MAVR, which is in use, first select the alternative card.
Never withdraw a card that is supplying excitation since this may
damage the connections.
Table 5-1 AUTO POWER CARD FAULTS
No Symptom Possible Fault Test Remedial
Action
1 No
excitation
a) Control Card
Fault
b) FS1 failure
c) External fuse
See section 4.
Check FS1.
Check
external fuses,
See section 4
Replace, if
necessary, with
20ET fuse
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failure, wiring
fault, or pilot
exciter failure.
d)Field circuit
incomplete
e)Thyristor bridge
failure
wiring and
pilot.
Check field
continuity.
Check TM1 &
DM1 bridge as
detailed below.
link.
Replace/correc
t as necessary.
Correct as
necessary.
Replace card if
faulty
2 Over
excitation
a) Control Card
Fault
b) Thyristor
bridge failure
c) Wiring fault
See section 4
Check
thyristor
bridge as
detailed below.
Check wiring
See section 4
Replace card if
faulty
Correct as
necessary
THYRISTOR BRIDGE TESTS
The thyristor bridge consists of TM1 thyristors and DM1 diodes
mounted in an encapsulated module. The drives can be individually
checked however with the unit assembled on the card (withdrawn from
the mainframe) as described below.
1) Thyristors
Connect the circuit as shown:
(1) Initially, with the switch S open and not having previously been
closed, ensure that the ammeter registers zero current.C
(2) lose S and observe that the ammeter now registers
approximately 3/4 amp.
(3) Re-open S and observe that the ammeter continues to register
–ideally as in (b) above.
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Figure 5-1 thyrisistor Test Circuit
If any one of these three tests is not satisfied for the thyristor,
the Auto Power Card should be replaced.
N.B. To reduce the current to zero after the thyristor has been
triggered-as in (b) above – the battery circuit must be disconnected.
2) Diodes
The diodes can easily be checked by measuring the forward
and reverse resistance, with an ohmmeter e.g. AVO meter model 8
etc.
Each diode should exhibit a low resistance in the forward
direction, typically 20-50 ohms, and a very high resistance in the
reverse direction.
If either diode has zero or wary low resistance in both
directions or infinite or very high resistance in both directions, it is
faulty and the Auto Power Card should be replaced.
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6. EXCITATION LIMITER CARD.
6.1 SPECIFICATION
6.1.1 Over Excitation Limiter
1) Limiting level
The limiting level is adjustable within the range 5 to 15 A in the
brushless system or an input voltage of between 0.8 and 2.5 volts in the
case of a static excitation scheme.
2) Increased Sensitivity feature
An internal link enables the sensitivity to be increased by a factor of
4 (±2.5%) to allow setting up without overexciting the generator.
3) Temperature Compensation Facility
By use of an external 100 ohm or 130 ohm Resistance Temperature
Detector (RTD) situated in the machine air inlet, temperature
compensation may be achieved.
Compensation temperature range –25 ℃ to +55 ℃ (RTD
temperature).
Compensation level –0.2 to –1% of O.E.L. level/℃ rise.
Compensation Characteristic ±1% linearity.
Providing that.
(1) The local ambient temperature is within 15℃ of that at which
the unit was set.
(2) The ideal RTD characteristic i.e. linear and having a
39.2x0.0001 p.u/℃ temperature coefficient.
(3) The RTD has 3 lead termination, the individual lead resistance
being less than 50 ohm.
4) Differential Feature
Two links can be selected: one selects 80% (±2.5%)differential, the
other 70%(±2.5%) differential. Dependent upon which link is selected,
the limiter will control excitation to 70% (or 80%) of nominal limiting
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level and only reset when excitation reduces below the controlled level.
The feature will normally be inhibited by an internal link.(100%
differential).
5) Time Delay
An adjustable ‘integrating delay’ is incorporated giving delays from
1000%-seconds to 100%seconds. This corresponds to a range of 10 to 1
seconds for a 100% error, i.e. excitation twice the nominal limiting level.
6) Temperature Range
-25℃ to +65℃: Operating
-40℃ to +100℃: Storage
7) Accuracy
Limiting level ± 2%
repeatability
Time delay ± 5%
repeatability
Provided temperature is within ±15℃
of the temperature at which the unit
was set, and with no temperature
compensation.
6.1.2 Under excitation limiter.
1) Characteristic
(1) MVAr limit at Zero power, this is set by the ‘Xd’ control. When
the input voltage and current supplied to unit are nominally
105V and 5A the ‘Xd’ control gives a MVAr limit ranging from
12.5% to 100% of the rated MVA. This is equivalent to a
generator reactance range from 8 to 1 p.u.
(2) Limiting Level Curvature, this is set by the ‘Xe’ control. When
the input voltage and current supplied to the unit are nominally
105V and 5A the ‘Xe’ control compensates for external
reactance effects (e.g. unit transformers) in the range 0 to 0.8
p.u.
2) Stabilization
Two controls are incorporated for stabilizing : quantity and phase
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For a brushless generator the limiter is stabilized from exciter field
current whilst for
a static excitation system stabilizing is obtained from the error
amplifier output.
3) Temperature Range
-25℃ to +65℃: Operating
-40℃ to +100℃: Storage
4) Accuracy
Limiting level: ± 2%
repeatability
Provided temperature is within
±15℃ of that at which the
unit was set.
5) Input Signals
6) It requires a 5A current transformer input of 1 VA rating in the
blue phase. The voltage sensing is derived from the red to yellow
sensing signal.
6.1.3 Controls and Indications
1) Set Q: A front access multi-turn potentiometer which adjusts the
stabilizing signal magnitude of the under excitation limiter.
2) Set P: A front access multi-turn potentiometer which adjusts the
stabilizing signal phase of the under excitation limiter.
3) OE Delay: A front mounted, single turn potentiometer with a
calibrated dial scaled 0 to 10 which adjusts the time delay of the
over excitation limiter.
4) Set Xd: A front mounted, single turn potentiometer with a
calibrated dial scaled 0 to 10 which adjusts the operating level of the
unit at zero power.
5) Set Xe: A front mounted, single turn potentiometer with a
calibrated dial scaled 0 to 10 which adjusts the curvature of the
limiter characteristic.
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6) Set If: A front access multi-turn potentiometer which adjusts the
over excitation limiter field current limit.
7) Set Bal.: An internal access multi-turn potentiometer which
adjusts the temperature compensation bridge balance point.
8) Set T.C.: An internal access multi-turn potentiometer which
adjusts the temperature compensation range.(i.e. effective
compensation achieved in %/℃)
9) OE On: A front mounted ‘Light Emitting Diode’ to give
indication of the over excitation limiter.
10) UE On: A front mounted ‘Light Emitting Diode’ to give indication
of operation of the over excitation limiter.
11) Relay output: For remote indication of an over or under excitation
limiter operating condition a common relay mounted in the
Mainframe in energized.
6.2 DESCRIPTION OF OPERATION
(Number in brackets ( ) refer to p.c.b. edge connections, and all
voltage levels are relative to TP1.)
6.2.1 Over Excitation Limiter
(This is shown on the lower half of the Schematic Diagram Fig 6.4)
On a brushless excitation system field current is sensed across the
MAVR stabilizing resister, R1, R2 mounted on the back panel, and the
signal is supplied to the limiter at (2) and (29).
On a static excitation system the signal is derived from a DC
current transformer measuring rotor current.
A current proportional to the field current is compared to the
stabilized reference current flowing through R56. When the field
current exceeds a preset level determined by the reference current and
the setting of RV5, the output voltage of IC3b begins to fall, and when it
becomes negative current flows through R65, D20, LK12 and (15),
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reducing the change rate of C6 on the control card thereby reducing the
excitation.
IC3a and associated components provide the temperature
compensation facility. The external RTD is the temperature sensor in a
detector bridge (comprising R39, R42, R43, R70 and RV8) RV8
adjusting the balance points of the bridge. Components Z4, R40, R41,
FS1 and D26 are the stabilized power supply for the detector bridge.
The misbalance of the bridge, which bears a direct relation to the
temperature change, is amplified by IC3a and effects the limiter
reference current via RV7, R55 and LK5. Adjustment of RV7 alters the
degree of compensation achieved. To facilitate commissioning of the
unit links I3, I4, I5, I6, I7 are used to test the temperature compensation,
catering for both 100 ohm and 130 ohm RTD’s at both 0℃ and 40℃.
Removal of LK5 inhibits the temperature compensation circuit effect.
IC3a output is routed to the excitation monitor card via (25) to provide
temperature compensation on that card if required. In general in the
generator with closed cycle ventilation system, the temperature
compensation unit should not be used.
If the RTD fails and shorts to earth, to protect the operation of the
limiter THY1 is ‘fired’ by D31, D30, D29 (depending on Fault location),
Z9 and R86, This momentarily shorts the supply rail rupturing FS1,
therefore disconnecting the supply to the detector bridge. IC3a output
rises to 6.2V. It is clamped by Z8 which corresponds to an RTD
temperature of about 55℃.
When the voltage at TP6 become negative transistor VT6 is turned
on via R45, and if LK9 or LK10 is fitted, part of the reference current is
diverted through VT6. Thus, the field current can be limited to a level
lower than that required to cause the limiter to operate.
Either LK11, LK10 or LK9 may be fitted (one link only) which will
make the limiting level 100%, 80% or 70% of the operating level
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respectively.
As a commissioning aid the sensitivity of the limiter can be
increased by fitting LK7, which reduces the reference current and the
operating level of the limiter by a factor of four. The differential links
LK9 or LK10 should be removed when using this facility, as should the
temperature compensation link LK5.
Indication of limiter operation is provided by IC3c output going
positive. TP6 voltage becomes negative .VT3 and VT4 are switched on
and an output signal via LED2 and D23 provides local indication and
energizes RL1 in the back panel via(17) providing remote indication of
limiter operation. The integrating time delay is provided by C10 and
RV6.
On the standby AVR of a twin AVR system the output of the OEL
amplifier TP6 is disconnected from the OE delay control by RL1-1, and
the voltage on the delay circuit is linked via RL1-1, (18) on the standby,
to the output of the controlled limiter via the back board and (23) on
the controlling limiter. This is to prevent surges in excitation due to the
high gain of standby and controlling limiters when control is switched
to the standby unit.
Twin System with Differential Facility
When transferring control to a standby AVR from a unit with its
over excitation limiter operating, a transient surge in excitation may
occur since it may be necessary to allow the excitation to reach the
standby limited operating level, prior to excitation being reduced to the
controlling level.
6.2.2 Under Excitation Limiter
This is shown on the upper half of the schematic diagram. Fig 6.4.
The under excitation limit of a generator operating in parallel with a
system is determined by the generator and system reactance, and can be
represented on the generator operating chart. Figure 6.1 shows a typical
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operating chart and the effect of differing external reactance between
the generator and the infinite systems. Such a system could be due to
transformers
Figure 6-1. Generator Operating Chart
If the excitation is reduced to a level that wound cause the
generator to operate at a power factor more leading than is shown on
the chart, the angle by which the internal emf of the generator leads the
system voltage will exceed 90°and loss of synchronism may occur.
So that the operation of the limiter can be understood, it is necessary to
be aware of the relationship between the simplified vector diagram of
the generator and the generator operating chart.Figure 6-2 below shows
the equivalent circuit and vector diagram of the generator paralleled to
an infinite system.
I = generator current
Et = generator terminal emf
Vt = generator terminal voltage
eIXIXtEV d
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V∞ = system voltage
Xd = generator synchronous
Xe =external reactance
Fig 6-2 The simplified Vector Diagram
The condition is drawn for line current Ⅰ,at Φ leading. The
under excited limiter occur when the internal Emf, Et. Leads the
voltage of the infinite system by 90°。
It can be seen that when Xe=0, the limit is a straight line
corresponding to constant leading VAr’s of 1/Xd per unit, and that as
Xe increases the MVAr limit reduces with increasing power.
The under excitation limiter incorporates circuits in which the
internal emf of the generator and the system voltage, are simulated
and a control signal is produced to maintain the excitation above a level
that would cause the 90° load angle to be exceeded.
Operation
(All voltage levels are relative to TP1).
The unit senses line voltage at (21) (29) which is nominally 2.5 volts
rms supplied from T1 on the back panel, and line current at (28) (27)
nominally 28mA supplied by T5 on the back panel. The phasing of these
signals is such that the current leads the voltages by 90°when
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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generating at unity power factor.
The input circuit compressing R1, R5, R9, RV1, RV2, is arranged
so that voltages corresponding in phase and amplitude to the internal
emf of the generator, and the system voltage are produced at TP3 and
TP4 respectively. IC1a, IC1b, IC1c, and IC2 form a circuit which
produces a mean positive voltage across C3 when the voltage at TP3
leads that at TP4 less than 90℃, and a mean negative voltage when
the voltage at TP3 leads that at TP4 by more than 90°.
The latter case corresponds to an under excited condition, current
through R19, causing the output of IC1d to rise producing a signal
which is fed to (15) on the control card via D9, R25, LK6 and (15). The
operation of the limiter is to ensure that C6 on the control card is
changed fast enough to prevent the field voltage from being reduced a
level that would correspond a load angle in excess of 90°.
It is necessary for the limiter to respond rapidly to an under excited
condition and therefore stabilizing is required which is achieved by
transient feedback via R22, RV3, RV4, and C6. The stabilizing signal is
obtained from exciter field current (via LK4 and (2)) on a brushless
AVR, and from the output of IC1d (via LK3) on a static excitation
system. Local indication of limiter operation is provided by LED1 and
RL1 on the back panel (via 17) which operate when VT1 and VT2 are
turned on by the output of IC1d.
CMOS QUAD Solid State Switch (4016) IC2
This is a 14 pin package which contains four solid state switches.
Consider one switch; when a positive voltage is applied to say pin 5, the
signal present at pin 4 is internally connected to pin 3. Thus, with pin 5
positive, 4 and 3 can be considered as a closed switch, and with pin 5
negative, 4 and 3 can be considered as an open switch.
6.2.3 Link Identification
Link LK1 Fitted for 100 ohm RTD. When fitted omit LK2
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Link LK2 Fitted for 130 ohm RTD. When fitted omit LK1
Link LK3 Selects transient feedback for the under excitation limiter
from the amplifier output. This is used for stabilization on statically
excited generators. When fitted LK4 must be omitted.
Link LK4 Selects transient feedback for the under excitation
limiter from exciter field current as used for
stabilization on brushless generators. When fitted LK3
must be omitted.
Link LK5 Selects temperature compensation on the over
excitation limiter.
Link LK6 Selects the under excitation limiter relay outputs.
When fitted LK6A must be omitted.
Link LK6A Inhibits the under excitation limiter relay outputs.
When fitted LK6 must be omitted.
Link LK7 Selects an increase of sensitivity by a factor of 4 on the
over excitation limiter for commissioning purposes
only.
When fitted LK8 must be omitted.
Link LK8 Selects the normal operating sensitivity of the over
excitation limiter. When fitted LK7 must be omitted.
Link LK9 Selects 70% differential on the over excitation limiter.
When fitted LK10 and LK11 must be omitted.
Link LK10 Selects 80% differential on the over excitation limiter.
When fitted LK9 and LK11 must be omitted
Link LK11 Selects 100% differential on the over excitation limiter.
When fitted LK9 and LK10 must be omitted
Link LK12 Selects the over excitation limiter relay outputs. When
fitted LK12A must be omitted.
Link
LK12A
Selects the over excitation limiter relay outputs. When
fitted LK12 must be omitted.
Link LK13 Test facility for 130 ohm RTD at 0℃.Not normally
fitted.
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Link LK14 Test facility for 130 ohm RTD at 40℃.Not normally
fitted.
Link LK15 Test facility for 100 ohm RTD at 0℃.Not normally
fitted.
Link LK16 Test facility for 100 ohm RTD at 40℃.Not normally
fitted.
Link LK17 Test facility for temperature compensation. Not
normally fitted.
Link LK18 Fitted for normal operation.
6.3 COMMISSIONING PROCEDUCE
This section describes the commissioning procedure for the
excitation limiter card and should be read in conjunction with the
general commissioning procedure, section 9, and any specific contract
commissioning procedure.
IMPORTANT
(1) The potentiometers, ‘OE Delay’, ‘Set If’, ‘Set Xd’, ‘Set Xe’, ‘Set
TC’ have been set to the correct level at the factory and should not
require any on site adjustment.
(2) Check that the correct links are fitted as detailed in the setting
record for MAVR testing with test generator sub-section 6.
(3) Complete commissioning of the control card prior to commissioning
the excitation limiter card. Temporarily remove the Excitation
Monitor card, if fitted, to avoid transfer of excitation to another
source.
6.3.1 Over Excitation Limiter –X4 Level
(1) Determine the limiter parameters, (over excitation limit X1 and
X4, differential, delay and temperature compensation) from
setting record for MAVR testing with test generator sub-section
2. In the absence of these, typical settings are the X1 limit 10%
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higher than the continuous full load rating of the exciter : the
differential to 100% (link 11): the time delay to 400% seconds:
and the temperature compensation to 80% of the 0℃ level for a
temperature rise of 40℃.
(2) Remove limiter card and re-insert together with the extension
card, Fit link LK11 and remove LK9 or LK10 if applicable, and
LK5.
(3) Select the X4 increased sensitivity feature by removing link LK8
and fitting LK7, thereby enabling the approximate operating
level of the unit to be checked at a low excitation level. Insert a
suitable ammeter in the field circuit if one is not already
available.
(4) Run the generator up to rated speed, unparalleled, and on
no-load with ‘auto’ excitation selected.
(5) Check that no external limiter operation signal is given(i.e. an
open circuit between outgoing multicore 2 wires 8 and 10) and
the ‘OE On’ LED is off. This assumes that the no-load excitation
is less than 25% of the preset over excitation limit.
(6) Increase the excitation to above the preset 0℃ over excitation
limit divided by 4 (to allow for the X4 increase in sensitivity) by
adjusting the motorized voltage setting potentiometer fully
clockwise and if necessary the ‘Set V’ potentiometer on the
control card. The over excitation limit should operate (i.e. a
short circuit between outgoing multicore 2 wires 8 and 10,
together with the ‘OE On’ LED coming on), and control the
excitation to the required 0℃ limit divided by 4, after a
significant time delay - approximately 160 seconds for a 10%
error in field current or 4 times the required percentage -
seconds delay. Note the operation of the limiter will be
accompanied by a reduction in line voltage.
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NOTE:
If the no - load excitation is greater than 25% of the 0℃ over
excitation limit, the limiter will operate to reduce line voltage
below nominal. If this is the case check that the field current is
controlled to 25% of the required limit ±2.5%, and that the
'OE On' LED is illuminated and the appropriate external signal
given.
(7) If the controlled level is incorrect by more than ±2.5 then the
'Set If' potentiometer has been reset since the unit left the
factory and requires readjustment, To increase the over
excitation limit rotate the 'Set If' potentiometer clockwise and
vice versa.
(8) The over excitation limiter is now set to limit field current to
approximately the required level when the X1 sensitivity is
reselected by removing link LK7 and fitting LK8. This will
allow the control card to control the generator voltage which
can be reset by setting the motorized voltage setting
potentiometer to mid-range and adjusting the control card 'Set
V' potentiometer to give nominal line voltage.
1) Over excitation Limiter. Check on Temperature Compensation
Facility X4 Sensitivity.
When the temperature compensation facility provided on the
over excitation limiter is utilized the preliminary checks outlined
below should be carried out.
(1) Perform tests AI) to VIII) above.
(2) Remove links 1,2,18.Fit link 17.
Fit link 15 if the RTD resistance is 100 ohms at 0℃ or Fit link
13 if the RTD resistance is 130 ohms at 0℃.
(3) Connect a dc. voltmeter across TP16 (+ve) and TP1 and check
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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that the meter indicates 0 volts ±0.25 volts, adjusting RV8
(set bal.) if necessary to obtain correct reading.
(4) Fit link 16 if the RTD resistance is 100 ohms at 0℃.
Fit link 14 if the RTD resistance is 130 ohms at 0℃.
(5) Determine from the setting record for MAVR testing with test
generator the percentage reduction in excitation for a 40℃ rise
(typically a 20% reduction) and check that the voltage
measured at TP16 (+ve) w.r.t. TP1 is equal to (% reduction in
excitation x 0.22) volts dc. ±15%. i.e. if the 40 ℃ limiter
setting is to be 80% of the 0℃ setting the reduction is 20% and
the voltmeter should read
(20 x 0.22) = 4.4 ± 0.66 volts dc.
Adjust RV7 if necessary to obtain the required reading .
(6) Remove links 17, 13, 14, 15, 16
Fit links 18 and 1 for a 100 ohm RTD
Or 2 for a 130 ohm RTD
(7) Check that the reading obtained on the dc. voltmeter connected
across TP16 (+ve) and TP1 corresponds to the ambient
temperature at location of the RTD.
The voltmeter should indicate
ambient temperature (℃) X Voltmeter reading in test (V)
40
(This test is not applicable at temperature below zero).
Fit link LK5.
6.3.2 Over Excitation Limiter -X1 Level
1) Synchronize the generator to the system and lightly load the
generator (5-10% of rated power). Connect a 10 volt dc voltmeter
(20 kohm per volt or more) across TP6 (+ve) and TP1, and check it
registers greater than 9 volts.
2) Gradually increase the excitation by clockwise adjustment of the
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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motorized voltage setting potentiometer to an excitation level
approximately 5% over the recommended over excitation limit. The
voltmeter should indicate a slowly falling reading. When the meter
starts to read negative (approximately - 1 volt) the limiter should
come into operation and give local and remote indication. If
difficulty is encountered in reaching the required excitation level
rotate the control card 'Q.C.C.' potentiometer anti-clockwise.
3) If necessary trim the 'Set If' control to give the required excitation
limiting level; clockwise rotating increasing the limit and vice versa.
Reduce the excitation level to nominal.
6.3.3 Over Excitation Limiter - Differential
1) If 100% differential is required omit this section and proceed to
subsection 6.3.4.
2) Whilst still in parallel with the system and on the over excitation
limit select the appropriate differential link - LK9 for 70% and
LK10 for 80% (±2.5%) of the previous limiting level depending on
link selection- LK9 or LK10 respectively.
6.3.4 Over Excitation Limiter - Temperature Compensation (if applicable)
1) Leave RV7 (set TC) as set at the works and select or omit links as
follows:
100 ohm RTD fit LK15 & 17 omit LK1,2,13,14,16,18
130 ohm RTD fit LK13 & 17 omit LK1,2,14,15,16,18
Leave all other links as selected. Check RTD connections are
correct. Connect a 10V dc. voltmeter (20 kohm/v or more) between
TP15 (+ve) and TP1.
2) If necessary adjust RX8 (Set Bal.) to bring the voltmeter reading to
zero. Reconnect the multimeter to TP6 (+ve) and TP1.
3) Synchronize and lightly load the generator, increase the excitation
and check that the limiter operates as in section BII. Check that this
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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limit is within ±1% of the required 0℃ over excitation limit.
4) Reduce the excitation to nominal and reselect links as follows:
100 ohm RTD Remove LK15 and fit LK16
130 ohm RTD Remove LK13 and fit LK14
5) Increase the excitation and check that the limiter now operates at a
lower level corresponding to the 40V over excitation limit ±2%, If
necessary adjust RV7 (Set TC) to achieve this, If no figure is
available for this limit assume a value of 0.8 x 0℃ Limit. Clockwise
rotation of RV7 increases the temperature compensation, i.e. reduce
the 40V Limit.
6) Reduce the excitation to nominal and reselect links as follows:
100 ohm RTD Remove Links 16&17 and fit Links 1&18
130 ohm RTD Remove Links 14&17 and fit Links 2&18
7) Increase the excitation and check that the limiter operates at a new
level dependant the external RTD temperature, 't'. Knowing this
temperature check that the limiter 'I' is
Where I0 = 0℃ limit I40 = 40℃ limit
If incorrect check the nominal RTD resistance and its connections
are correct.
6.3.5 Over Excitation Limiter - Time Delay
1) Whilst still in parallel with the system and on the over excitation
limit short out TP8 to TP1. This shorts out the over excitation
limiter sensing input so that the limiter resets - indicated by the
voltmeter resetting to above 9 volts - and excitation reverts to its set
level. Remove link LK9 or LK10, if fitted, and fit LK11.
2) Set the excitation to 'X%' above the over excitation limit
(preferably 10% or more - but at least 5%), Time the period taken,
't seconds', between removing the short between TP8 to TP1 and
%2}40
)({ 400
0
tII
II
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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the unit limiting excitation. The product, 'X'x't', gives the over
excitation limiter time delay expressed in %-secs.
3) If necessary trim the 'OE Delay' control to give the required %-secs
delay; clockwise rotation increasing the delay and vice versa. When
rechecking the time delay allow the limiter to fully reset, i.e. the
voltmeter reading above 9 volts, before removing the shorting link
and retiming.
4) Refit the appropriate differential link LK9, 10 or 11.Rest the Q.C.C.
potentiometer to the required setting if it was adjusted. Reduce
excitation by turning the motorized voltage setting potentiometer
anti-clockwise to give unity power factor. Remove the voltmeter
between TP6 and TP1.
6.3.6 Under Excitation Limiter - zero Power Limit
1) Determine the under excitation limiter parameters ('Xd' And 'Xe'
levels) from the setting record for MAVR Testing with Test
Generator sub-section 2. In the absence of these reference should be
made to the generator operating chart, the 'Xd' control should be
set to 10% less leading VAr's than the machine capability and the
'Xe' control to any quoted external reactance figure or a safe level -
say 0.1 p.u. reactance, 'Xe' can also be measured by synchronizing
the generator to the system and adjusting the power to zero; by
nothing the per unit change in reactive loads (Q) for a given change
in system voltage (V p.u.) of say 0.05 p.u. caused by changing the
motorized voltage setting potentiometer, Xe can be calculated as:
To simulate an exact under excitation limit reference should be
made to Fig. 6-3 below. The limiting level is given by a circle:
..upQ
VXe
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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Thus knowing the required circular characteristics center and
radius the two parameters 'Xd' and 'Xe' can be deduced.
Fig. 6-3 Under Excitation Limit Characteristic
2) With the machine running in parallel with the system on 'auto'
excitation, set the generator output power to zero. Reduce the
excitation by slowly rotating the motorized voltage setting
potentiometer anti-clockwise and check that the limiter operates
when the generator leading reactive power reaches the required set
level. Operation is indicated by the 'UE On' LED coming on and a
short circuit between multicore 2 wires 8 and 10. Check that the
limiter operation is stable and that a further reduction of the
motorized voltage setting potentiometer does not increase the
generator leading reactive power beyond the required limiting level.
Adjust if necessary the limiting level by adjustment of the 'Xd'
potentiometer, clockwise rotation decreasing the limiting level and
vice versa.
upXdXe
center
upXdXe
redius
.}}
11{
2
1
..}}
11{
2
1
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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3) If the limit is unstable adjust the two stabilizing controls 'Set Q' and
'Set P' as necessary, but first ensure that the limiting level is within
the generators capability as this can give rise to apparent
instability (actually pole swinging) when the machines limit is
exceeded or even reached. In generator to stabilize the limiter
increase clockwise the 'Set Q' control and if still unstable turn the
'Set Q' control anti-clockwise.
To check the response turn the motorized voltage setting
potentiometer first clockwise (off the limit) and then quickly
anti-clockwise (onto the limit). The limiter should quickly come into
operation and settle with minimal oscillatory action.
6.3.7 Under Excitation Limiter -'Xe' Control
1) Take the generator off its under excitation limit and set to unity
power factor by clockwise rotation of the motorized voltage setting
potentiometer. Remove the excitation limiter card from the rack.
2) Knowing the required external reactance, Xe, calculate from the
following the required resistance of the 'Xe' potentiometer
R = 60 x 5(Xe p.u)/(1 p.u Sensing CT current)ohms
Where 1 p.u sensing CT current = rated current/Sensing CT ratio
(nominally 5A)
3) Check using a digital ohm-meter that the resistance between TP2
and TP4 agrees with that calculated. If it is 'incorrect adjust the
'Xe' control, clockwise rotation will increase the resistance and vice
versa. Replace the excitation limiter card after first removing the
extender card.
6.3.8 Under Excitation Limiter - Operating Characteristic
1) To check the operating characteristic throughout its range bring the
limiter into operation by turning the motorized voltage setting
potentiometer fully anti-clockwise and check the under excitation
limiter is operating. Increase the generators output power from
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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zero to maximum and check that the reactive power is varied in
sympathy with power as indicated on the generator operating chart.
2) If the operating chart is not available or 'Xe' could not be check as
detailed in sub-section 6.3.7 the following procedure should be
adopted. Knowing 'Xd' and 'Xe' per unit values, calculate the
radius and center of the limiter circular characteristic as shown in
Fig. 6.3. Referring to figure 6.3 for any generator output power
'OX', the corresponding limiter reactive power 'XY', can be
calculated as follows:
Reactive power 'XY' p.u =
3) From the above calculations the theoretical and practical limiting
curves can be compared and errors compensated for by
appropriate adjustment of the 'Xd' and 'Xe' potentiometers.
In general the 'Xd' control sets the zero power limit and the 'Xe'
control the curvature of the characteristic.
NOTE: The generator operating chart is normally drawn for
operation, at nominal voltage, although the actual limiting curve of
the generator and system reduces in proportion to the square of line
voltage, and the limiter incorporates this characteristic.
If the limiter characteristic is being checked, the readings of MVAr
should be divided by (per unit volts) squared, at line voltages other
than nominal.
6.4 FAULT FINDING PROCEDURE
This section describes the fault finding procedure for the Excitation
Limiter card and should be read in conjunction with the general fault
finding section 10.
IMPORTANT
)().()( 22 CenterOApowerOXpurediusAC
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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1) The majority of excitation faults are caused by incorrect
connections -thoroughly check all connections are correct to
0NQ.359.019 excitation system circuit diagram.
2) Check that the correct links are fitted as detailed in the setting
record for 'MAVR Testing with Test Generator', sub-section6.
In general faults associated with the Excitation Limiter Card can be
separated into two main categories (Over and Under Excitation Limiter)
viz:
Over Excitation Limiter - Inoperative (Table 6.4.1)
- Continuous operation (Table 6.4.2)
- Operational Faults (Table 6.4.3)
Under Excitation Limiter - Inoperative (Table 6.4.4)
-Continuous operation (Table 6.4.5)
-Operational Faults (Table 6.4.6)
Refer to the appropriate section for corrective action.
Table 6.4.1 Over Excitation Limiter Inoperative
No Possible Fault Test Remedial Action
1 Incorrect output
link selected
Check link LK12 if
fitted and LK12A
omitted
Correct as
necessary
2 Loss of power
supply
Check FS1&2 and any
external fuses and
wiring to auxiliary
supply.
Replace blown
fuse or correct as
necessary
3 RTD short circuit
or associated
wiring fault
Remove LK1 or 2 and
check correct
operation. Check RTD
and wiring.
Correct as
necessary
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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4 Mainframe failure No fired current
pick-up signal to
limiter cards(2)&(29) -
should be 0.165V/A -
sensing current - or
internal power supply
failure.
See 6
5 'Set If' control set
too high
Check level as in 6.3.2 Reset level, if
necessary, as in
6.3.2
6 Limiter card faulty Interchange Limiter
card with a spare
Replace limiter
card and return
to the works for
repair
Table 6.4.2 Over Excitation Limiter-Continuous Operation
No Possible Fault Test Remedial Action
1 Increased
sensitivity link
selected
Check link LK8 if
fitted and LK7
omitted
Correct as
necessary
2 'Set If' control set
too low
Check level as in 6.3.2 Reset level, if
necessary, as in
6.3.2
3 RTD open circuit
or an associated
wiring fault
Remove LK5 & check
correct operation.
Check RTD and
wiring.
Correct as
necessary
4 Control
card/sensing
failure saving rise
to an over excited
condition
See 4 See 4
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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5 Mainframe failure Field current pick-up
signal excessive
(should be nominally
0.165V between (2)
and (29 ) per amp of
excitation).
See 3
6 Limiter card
failure
Interchange Limiter
card with a spare
Replace limiter
card and return
to the works for
repair
Table 6.4.3 Over Excitation Limiter - Operational Faults
No symptom Possible Fault Test Remedial
Action
1 Limiter
operates when
machine on
load
'Set If'
control set too
low
Check level as
in 6.3.2
Reset level, if
necessary, as
in 6.3.2
2 Limiter
operates
transiently on
load application
'OE Delay'
set too short.
Check level as
in 6.3.5
Reset delay,
if necessary,
as in 6.3.5
3 Operation at
high loads
causes leading
power factor
operation on
limiter
operation
'Set If' level
too low or
differential
link(LK9,10
or 11)
incorrect or
excessive
temperature
compensation
Check level,
temperature
compensation
and
differential
required as
detailed in.
Correct as
necessary
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
89�
4 Limiter
operates but
does not give
indication
Mainframe
failure
Limiter relay
faulty (RL1
on
mainframe)
Replace
relay RL1
5 Time delay can
not be
lengthened
Smooth
change over
circuit
permanently
energized
Check
external
wiring to 2/3
to 2/5
Correct as
necessary
6 Limiter level
too low at high
ambient.
Excessive
temperature
compensation
.
Check as
detailed in
6.3.4
Correct as
necessary
Table 6.4.4 Under Excitation Limiter - Inoperative
No Possible Fault Test Remedial Action
1 Incorrect output
link selected
Check link LK6 is
fitted and LK6A
omitted
Correct as
necessary
2 Loss of power
supply
Check FS1&2 and
any external fuses and
wiring to auxiliary
supply.
Replace blown
fuse or correct as
necessary
3 Mainframe failure Loss of sensing
signals(sensing volts,
2.5V,(21) to (29) and
sensing current, 22.5V
at 5A (27) to (28).
See 3
4 'Xd' and 'Xe'
controls set too low
Check level as in
6.3.6/7
Reset level, if
necessary, as in
6.3.6/7
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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5 Limiter card faulty Interchange Limiter
card with a spare
Replace limiter
card and return
to works for
repair
Table 6.4.5 Over Excitation Limiter-Continuous Operation
No Possible Fault Test Remedial Action
1 CT and/or PT
sensing phasing
incorrect.
Check to contract
circuit diagram.
Correct as
necessary
2 Control card
failure giving rise
to an under excited
condition
See 4 See 4
3 Limiter card faulty Interchange Limiter
card with a spare
Replace limiter
card and return
to the works for
repair
4 Mainframe failure All other tests fail to
clear fault.
See 3
Table 6.4.6 Under Excitation Limiter - Operational Faults
No symptom Possible Fault Test Remedial
Action
1 Generator
loses
stability
before
limiter
operation.
Limiter level
set too high.
Check
operation level
as detailed in
6.3.6/7
Reset levels, if
necessary, as in
6.3.6/7
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
91�
2 Generator
unstable
on Under
Excitation
Limiter
operation
Stabilizing
controls
incorrectly set,
or too close to
stability limit
(pole swinging)
Check
stabilizing
controls and
correct link
fitted(LK4 for
Brushless, LK3
for Direct
excitation) or
check operating
level.
Reset
stabilizing
controls or
level.
3 UEL
operates
briefly
during run
up or
when
excitation
switched
on
Incorrect
settings of
UEL stability
controls
Reduce stab Q
setting &
increase stab P
setting
4 Under
Excitation
Limiter
gives
spurious
indication
on load
changes.
Stability
control not
optimized.
Check
stabilizing
control as in
6.3.6
In general
decrease
stabilizing Q
and increase P
consistent with
stability
5 Limiter
operates
but does
not give
indication
Mainframe
failure
Limiter relay
faulty (RL1 on
mainframe)
Replace relay
RL1
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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7. POWER FACTOR CONTROL CARD
7.1 SPECIFICATIONS
7.1.1 Range of Control
1) Power Factor Control:
0.6 PF lagging to 0.9 PF leading
2) Reactive Current Control;
100% rated current lagging to 50% leading
(rated current =5A)
7.1.2 Accuracy of Power Factor Control
The phase angle is controlled to within ±1°at full load current (5A)
and ± 5 ° at 20% rated current (accuracy being approximately
inversely proportional to current) provided:
1) The frequency is within ±10% of nominal.
2) The line voltage is within ±20% nominal.
3) The temperature is within ±15℃ of initial value.
4) The line current does not contain more than 2% harmonics.
5) The line voltage is free of even harmonics and does not contain more
than 10% required power factor.
6) Odd harmonics.
7.1.3 Accuracy of reactive current control
The reactive current is controlled to within ±2% of rated current
provided:
1) The frequency is within ±10% of nominal.
2) The line voltage is within ±20% of nominal.
3) The temperature is within ±15℃ of initial value.
4) The line current does not contain more than 2% harmonics.
5) The line voltage is free from even harmonics and does not contain
more than 10% odd harmonics.
6) The 'Motorized Volts Setting Rheostat' has sufficient range to give
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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the required reactive current.
7) The line current is in excess of 10% rated.
7.1.4 Temperature Range:
-25℃ to +65℃ :operating
-40℃ to +100℃ :storage
7.1.5 Input Signals
The unit require a 5A current transformer input of 1VA rating in
the C phase. The voltage sensing is common to the 'Control Card' B to
A voltage sensing signal.
A normally open contact is required to bring the unit into operation
when the generator is parallel, and another to give a VAr shed signal (i.e.
control to unity power factor).
7.1.6 Operation Indication
Local Indication is given when the unit is in operation and when in
the VAr shed mode.
7.1.7 Mode Selection
Selection of 'Power Factor' Or 'Reactive Current' mode of
operation is made by selection of internal links.
7.1.8 Remote Level Control
The operation level in either mode can be controlled by an
externally mounted 5k.ohm,1watt potentiometer. Internal/external
control is selected by internal links.
When a remote potentiometer is used to set the operating level, the
internally mounted potentiometer acts a fine trim on the level set by the
remote potentiometer. This facility is used on twin AVR systems to
equalize the controlling point of standby and main power factor cards.
7.1.9 Controls and Indications
1) Level: A front mounted single turn potentiometer with a
calibrated dial scaled 0 to 10 which adjusts cosφ or Isinφ
(dependent upon the internal links selected).
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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2) Slug : A front access multi-turn potentiometer which adjusts the
period between MVSR pulses.
3) PFC on: A front mounted 'Light Emitting Diode' to give indication
that the circuit is operating.
4) VAr shed: A front mounted 'Light Emitting Diode' to give indication
that the circuit is operating in the VAr shed mode.
5) Gain: A front access multi-turn potentiometer which adjusts
the pulse width to the MVSR.
7.2 DESCRIPTION OF OPERATION
(Number in brackets ( ) refer to printed circuit board edge
connections and voltage levels are relative to TP1).
The unit senses line voltage at (21) (29) which is nominally 2.5 volts
rms supplied from T1 on the back panel, and line current at (11) (12)
nominally 28 mA supplied from T3 on the back panel.
The phasing of these signals is such that the current lag the voltage
by 90°when generating at unit power factor.
7.2.1 COMS QUAD Solid State Switch (4016,IC1,IC2)
This is a 14 pin package which contain 4 solid state switches.
Consider one switch, when a positive voltage is applied to pin 5, the
signal present at pin 4 is internally connected to pin 3.Thus with pin 5
positive, 4 and 3 can be regarded as a closed switch, and with pin 5
negative, 4 and 3 can be regarded as an open switch.
VT1 and 2 are switched on by alternate half cycles of the sensing
voltage producing gating signals at pin 5 and pin 6 of IC2. The switch
associated with pin 6 (IC2) is arranged to produce a gating signal to pin
13 (IC2) in antiphase to that at pin 5 (IC2).
The output of the detector at TP4 is proportional to Isinφ and is
zero at unity, negative at lagging, and positive at leading power factor.
This signal is smoothed by R23, C6 and R24, and compared to a
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
96�
reference current flowing through R25. The difference between the
detector output and the reference signal is amplified by IC3 whose
output is a d.c.. level which may be positive ,negative, or zero.
Consider an under excited condition where the output of the
detector exceeds the reference current through R25. The voltage at TP5
becomes negative reaching a level determined by R39,R41,R43, when
VT7,VT8 and RL4 are switched on. PFC card(1) (7) are linked
applying auxiliary d.c.. supplied to multicore 3/9 to the voltage setting
potentiometer motor via LK20 on the back panel.
When RL4 is energized, D13 becomes forward biased and a current,
dependent on the setting of RV3,flows through R30, If this current
exceeds the error signal, the voltage at TP5 will rise until VT7,VT8 and
RL4 turn off, at a point determined by R39,R41 and R42, and the
feedback through R30 is removed.
The overall effect is to produce a series of pulses which drive the
potentiometer motor to its optimum position with the minimum of
overshoot.
For a particular error,RV2 and C10 determine the delay before a
motor pulse is given and RV3 sets the pulse width for a certain setting
of RV2.
When an over excited condition exists the voltage at TP4 becomes
negative the output of IC3 becomes positive and the circuit associated
with VT5, VT6 and RL3 operates to pulse the potentiometer motor to a
lower position through PFC card (1) (7) and LK21 on the back panel.
The VAr shed facility is initiated by linking multicores 2/5 and 2/3 thus
applying the +15V supply to RL2 to RL2 via (10) and LED2 which
provides local indication.
RL2-2 close which reduces the referenced current to zero, which
corresponds to zero VAr’s. This facility can be used as a means of
reducing line current to zero prior to shutting down a set.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
97�
The power factor controller is switched into operation by linking
multicore 2/5 and 2/1. This energizes RL1 on the power factor
controller via (9) and LED1 which provides local indication.
7.2.2 Remote Latch and Reset Facility
By fitting the appropriate links and external connections, the power
factor controller can be switched out of service an operator attempts to
adjust the voltage setting control during parallel operation.
Back panel relay RL4 is energized via D11 or D12 when a voltage
raise/lower signal is applied to multicores 1/9 or 1/12.
RL4-1 closes latching RL4 energized via a normally closed external
contact connected between the 125 volt positive supply and multicore
3/2.
RL4-3 opens and, provided LK19 is omitted, the power factor
controller is switched out of operation for the period that RL4 remains
energized. Figure 7-2 shows the simplified arrangement.
Power factor control can be re-selected by disconnecting the d.c..
supply from multicore 3/2.
Figure.7-1 Simplified PFC Latch Circuity
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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7.2.3 Link Identifications
LK1 &
LK4
Selects the ‘power factor’ mode of operation.
When fitted LK2 and 3 should be omitted.
LK2 &
LK3
Selects the ‘reactive current’ mode of operation. When
and 4 should be omitted.
LK5 &
LK7
Selects the remote ’level’ potentiometer. When fitted
LK6 and 8 should be omitted.
LK6 &LK8 Selects the internal ‘level’ potentiometer. When fitted
LK5 and 7 should be omitted.
LK9 Selects the output to pulse the motorized voltage setting
potentiometer.
7.3 COMISSIONING PROCEDURE
This selection describe the commissioning procedure for the power
factor control card and should be read in conjunction with the general
commissioning procedure, section 11, and any specific contract
commissioning instructions.
IMPORTANT
1) Check the correct links are fitted as detailed ‘a setting record for
MAVR
testing with test generator’.
2) Complete commissioning of the control card prior to commissioning
the power factor card.
3) Check External Connections according to “0NQ.359.019 MAVR
Circuit diagram” and “0NQ.162.118 MAVR back panel scheme”
7.3.1 Open loop operational checks
1) Remove the power factor controls card from the rack and refit
together with the extension card. Remove LK9 and connect a d.c..
voltmeter (20 kohms per volt or more) on the 10V d.c.. range
between TP5 (-Ve) and TP1. Remove LK2 and LK3. Fit LK1and
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LK4.
2) Run the generator up to speed, synchronism with the system and set
the output power to approximately 20% of rated power. Set the
generator power factor to unity by adjustment of the motorized
voltage setting potentiometer if necessary.
3) Turn either the local or remote ‘level’ potentiometer, whichever is
applicable, fully clockwise and check that the voltmeter registers
between 6 and 8 volts positive.
4) Reverse the voltmeter connections and turn the level potentiometer
fully anti-clockwise. Check that the voltmeter registers between 6
and 8 volts positive.
7.3.2 Power Factor control mode of operation checks (if applicable)
1) Adjust the ‘level’ potentiometer to bring the voltmeter reading
down to zero –a slight drift is unavoidable duo to an integrating
action. Refit lK9.
2) Select power factor control operation if not already selected,
(shorting multicore 2 wires 1 and 5 together) by the appropriate
selector switch or breaker auxiliaries and note the ‘PFC On’ LED
on.
Manually adjust the motorized voltage setting potentiometer and
check the power factor is controlled to unity by the motorized
voltage setting potentiometer being pulsed back to its original
position. Any overshoot or slow response indicates the stabilizing
controls need optimizing as detailed below in sub-section 7.3.4.
3) It is normally to latch off the power factor control circuit following a
remote raise or lower signal to the motorized voltage setting
potentiometer, thereby reverting to manually power factor
adjustment. During the commissioning procedure this should be
avoided by disconnection of external wiring to multicore 3/2 and
multicore 1/9 & 1/12 until required in sub-section 7.3.5.
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4) Adjust the ‘level’ potentiometer to give the required power factor.
Vary the generator output power from 10% to full power and check
that the steady state power factor is kept constant. Note that if the
motorized voltage setting potentiometer reached an end stop, power
factor can no longer be maintained.
7.3.3 Reactive Current Control mode of operation checks (if applicable).
1) Adjust the 'level' potentiometer to bring the voltmeter reading
down to zero --a slight drift is unavoidable due to an integrating
action. Refit LK9, remove LK1 and LK4 .Fit LK2,LK3.
2) Select power factor control operation if not already selected,
(shorting multicore 2 wires 1 and 5 together) by the appropriate
selector switch or breaker auxiliaries and note the ‘PFC On’ LED on.
Manually adjust the motorized voltage setting potentiometer and
check the reactive current is controlled to zero by the motorized
voltage setting potentiometer being pulsed back to its original
position. Any overshoot or slow response indicates the stabilizing
controls need optimizing as detailed below in sub-section 7.3.4.
3) It is normal to latch off the power factor control circuit following a
remote raise or lower signal to the motorized voltage setting
potentiometer, thereby reverting to manually reactive current
adjustment. During the commissioning procedure this should be
avoided by disconnection of external wiring to multicore 3/2 and
multicore 1/9 & 1/12 until required in sub-section 7.3.5.
4) Adjust the ‘level’ potentiometer to give the required power factor.
Vary the generator output power from zero to full power and check
that the steady state power factor is kept constant. Note that if the
motorized voltage setting potentiometer reached an end stop then
the reactive current control can no longer be maintained.
7.3.4 Optimization of response
1) Two controls('Slug' and 'gain') are incorporated on the unit to allow
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response optimization. The 'slug' potentiometer slows the response
of the unit to system transients whilst the 'gain' potentiometer
adjusts the width of the output pulse for a given error. By
adjustment of these two controls the motorized voltage getting
potentiometer can be made to quickly close-in the final position by
continuous movement finally being 'inched' in with shorter duration
pulses thereby avoiding overshoot or excessive pulsing.
2) To check the response turn the motorized voltage setting
potentiometer approximately 1 quarter of a turn away from its
initial position and watch the response in returning to the final
position. The initial movement should be continuous until nearly
back to its final position when it should be pulsed, the length of
pulses getting shorter as the final position is reached. If the pulses
are too short turn the 'gain' potentiometer clockwise and vice versa.
If frequent correction pulse are being given once the initial error
has been overcome this could indicate too long a pulse or
insufficient slug, in this case first decrease the 'gain' and then
increase (turn clockwise) the 'slug'. If the overall response is very
slow decrease the 'slug' by turning the potentiometer anti-clockwise.
It is important that excessive pulsing is avoided as this will
inherently reduce the system reliability.
7.3.5 Power Factor Control Inhibit Latch(if applicable)
1) As already described this circuit is included to enable cancellation of
the power factor control circuit by operator intervention. The
circuit detects either an external raise or lower pulse given to the
motorized voltage setting potentiometer which latches a relay to
inhibit the power factor control card. Return to automatic operation
is achieved by breaking the external latching path. This circuit is
incorporated on the 'back panel '.
2) Reconnect the external wiring to multicore 3/2 and multicore 1/9
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and 1/12. Select power factor control operation and verify correct
operation. Give an external raise signal to the motorized voltage
setting potentiometer (i.e. auxiliary d.c. positive to multicore 1/9)
and check no corrective action is initiated by the power factor
control card until the latching circuit is broken by the appropriate
external logic (i.e. breaking the auxiliary D.C.. positive feed to
multicore 3/2). Repeat this procedure but with an external lower
signal to the motorized voltage setting potentiometer (i.e. auxiliary
d.c.. positive to multicore 1/12).
7.3.6 VAr shed operational check (if applicable)
1) With the generator in parallel with the system and power factor
control operation selected (either in power factor or reactive current
control mode) takes up 20% to 50% of rated load.
2) Select 'VAr shed' (shorting multicore 2/3 and 2/5 together) by the
appropriate selector switch or control logic and note that 'VAr shed'
LED comes on simulations with a reduction of generator output
VArs to zero, i.e. unity power factor.
3) Vary the generator output power from zero to full load and check
that the VArs are controlled to zero, or power factor to unity. Switch
off the VAr shed signal and check return to normal operation.
7.3.7 Remote Level control on twin systems (if applicable)
1) When the remote 'level' potentiometer is selected the internal 'level'
potentiometer is connected across it via series resistors. This feature
enables any mismatch between the two MAVR units 'level'
potentiometers to be compensated for. To minimize this error run the
generator in parallel with the system with power factor control
selected and local 'level' potentiometers set to 5.0 both MAVR's.
2) Set the remote 'level' potentiometer to the normal operating level
and note the controlled power factor or reactive current. Select the
other MAVR unit and check its quiescent controlled power factor or
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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reactive current . If the latter controls to a more lagging level turn its
local 'level' potentiometer say 1.0 division clockwise, and if to a more
leading power factor in the opposite direction. Repeat the transfer
between MAVR units and again check the quiescent controlled levels,
minimizing any mismatch by adjusting the local 'level'
potentiometers as described.
7.4 FAULT FINDING PROCEDURE
This section describes the fault finding procedure for the power
factor control card and should be read in conjunction with the general
fault finding section 10.
IMPORTANT
1) The majority of excitation faults are caused by incorrect
connections -thoroughly check all connections are correct to the
0NQ.359.019 MAVR circuit diagram.
2) Check that the correct links are fitted as detailed in the setting
record for 6.
In general faults associated with the power factor control card can
be separated into two categories:
Non-operation (Table 7)
Mal-operation (Table7)
Table 7-4.1 Non-operation
No. Possible Fault Test Remedial Action
1.Output not selected CheckLK9 is fitted Correct
2.External signal to
select operation not
given
Check external wiring
between 2/1 and 2/5
should be shorted for
PFC unit operation.
Correct as
necessary
3.Positive of auxiliary
D.C.. not connected to
card.
Check positive of
auxiliary D.C.. is
connected to 3/9.
Correct as
necessary.
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4. Card latched out of
operation by external
signal.
Break latching path to
3/2 and check RL4 is
de-energized.
Check external
logic and correct as
necessary.
5.Links selecting
mode of operation
(power factor or
reactive current) &/or
local remote
adjustment links
missing.
Check links fitted as
detailed in section 7.3.2
& 7.3.3
Correct as
necessary
6.insufficient output
pulse duration to
MVSR.
Check 'gain' control
setting
Correct as detailed
in 7.3.4
7.Loss of power
supply
Check FS1 & 2 and any
external fuses and
wiring to he auxiliary
supply.
Replace blown fuse
or correct as
necessary.
8.PF Control card
faulty.
Interchange card with a
spare
Replace card and
return to the Works
for repair.
9. Main frame failure Loss of sensing signals
(Sensing volts,2.5V a.c.
(21) to (29) & sensing
current,30V @5A,(11)
to (12), Loss of power
supplies.
See 3.
Table 7-4.2 Non-Operation
No. System Possible Fault Test Remedial
Action
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1. Control is to
unity power factor
only
a. VAR shed
selected
(VAR shed
LED is on)
b. Incorrect links
selected
c. External
wiring fault.
Check external
wiring between
2/3 &2/5
should be open
circuit
Check links
7.3.2 & 7.3.3
Check wiring
to 4/1,4/2,4/4
Correct as
necessary
Correct as
necessary
Correct as
necessary
2.Control is to
extend units range
a. C.T and /or
P.T sensing
phasing
incorrect
b. External
'level' pot.
Connections
incorrect
remote control
only
c. Incorrect links
selected.
Check to
MAVR circuit
diagram.
Check to
MAVR circuit
diagram.
See section
7.3.2 & 7.3.3
Correct as
necessary
Correct as
necessary
Correct as
necessary
3.Response very
slow or unstable
'Slug & gain'
control
incorrectly
crossed.
Check links
7.3.3 & 7.3.2
See section
7..3.4
Correct as
necessary
4. Unit has wrong
range of control.
Power factor
/reactive current
links crossed.
Check links
7.3.2 & 7.3.3
Correct as
necessary
5. 'Remote' or
'Local'
potentiometer
ineffective.
Local/Remote
links missing or
crossed.
Check links
7.2.2
Correct as
necessary
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6. 'Volts Set'
potentiometer
motored prior to
synchronous to
system
PF Control
operation
permanently
selected.
Check external
wiring between
2/1 & 2/5
should be open
circuit during
single running
Correct as
necessary
7. Manual
intervention does
not cause PF
Control lockout.
PF Control
latching path
open circuit
Check external
wiring between
3/2 & auxiliary
d.c. positive
should be short
circuit.
Correct as
necessary
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8. EXCITATION MONITOR CARD TYPE A
8.1 SPECIFICATION
8.1.1 Over Excitation Monitor
1) Tripping Level
The tripping level is adjustable within the range 5 to 15A, or an
input voltage of between 0.8 and 2.5 volts in the case of a static
excitation scheme.
2) Increased Sensitivity Feature
An internal link enables the sensitivity to be increased by a
factor of 4(±2.5%) to allow setting up without overexciting the
generator.
3) Temperature Compensation Facility
Temperature compensation of the monitor tripping level can be
achieved from the ‘Excitation Limiter’ card, the level of
compensation being independently controllable. The specification
of this facility is identical to the ‘Excitation Limiter’, see section
3.5.1.3.
4) Time Delay
An adjustable ‘integrating delay’ is incorporated giving delays
from 1000%-seconds to 100%-seconds. This corresponds to a range
of 10 to 1 seconds for a 100% error, i.e. excitation twice the nominal
tripping level.
5) Temperature Range
-25℃ to +65℃ : Operating
-40℃ to +100℃ : Storage
6) Accuracy
Tripping level ±2% repeatability provided the temperature is
within ±15℃
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Time delay ±5% repeatability of that at which the unit was
set, and with no temperature
compensation.
8.1.2 Under Excitation Monitor
1) Characteristic
(1) MVAr Limit at Zero Power, this is set by the ‘Xd’ control. When
the input voltage and current supplied to unit are nominally
110V and 5A the ‘Xd’ control gives an MVAr trip level ranging
from 12.5% to 100% of the rated MVAr. This is equivalent to a
generator reactance range from 0.8 to 1.0 p.u..
(2) Tripping Level Curvature, this is set by the ‘Xe’ control. When
the input voltage and current supplied to the unit are nominally
110V and 5A the ‘Xe’ control compensates for external reactance
effects (e.g. unit transformers) in the range 0 to 0.4 p.u.
2) Time Delay
An adjustable integrating time delay is incorporated in the unit
for use on monitors to avoid transients causing spurious operations.
3) Temperature Range
-25℃ to +65℃ : Operating
-40℃ to +100℃ : Storage
4) Accuracy
Tripping level ±2% repeatability provided the
temperature is within ±15℃
Monitor Time delay ±5% repeatability of that at which the
unit was set.
5) Input Signals
It requires a 5A current transformer input of 1VA rating in the
yellow phase. The voltage sensing is derived from the red to blue
sensing signal.
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8.1.3 Common – Controls and Indications
Slug UE: A front access multi-turn potentiometer which adjusts the
under excitation monitor time delay.
OE Delay: A front mounted, single turn potentiometer with a calibrated
dial scaled 0 to 10 which adjusts the time delay of the over
excitation monitor.
Set Xd: A front mounted, single turn potentiometer with a calibrated
dial scaled 0 to 10 which adjusts the operating level of the
unit at zero power.
Set Xe: A front mounted, single turn potentiometer with a calibrated
dial scaled 0 to 10 which adjusts the curvature of the
monitor characteristic.
Set If: A front access multi-run potentiometer that adjusts the over
excitation monitor field current tripping level.
Set T.C.: An internal access multiturn potentiometer which adjusts
the temperature compensation range (i.e. effective
compensation achieved in %/℃.)
OE Trip: A front mounted ‘Light Emitting Diode’ to give indication of
operation of the over excitation monitor.
UE Trip: A front mounted ‘Light Emitting Diode’ to give indication of
operation of the under excitation monitor.
Relay Output : For remote indication of an over or under excitation
monitor trip Condition a common relay mounted in the
mainframe is energized.
8.2 DESCRIPTION OF OPERATION
(Number in brackets ( ) refer to printed circuit board edge connections).
8.2.1 Over Excitation Monitor
(This is shown on the lower half of the schematic diagram).
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On a brushless excitation system field current is sensed across the
back panel mounted stabilizing resistor R1, R2, and the signal is
supplied to the monitor at (29) and (2).
On a static excitation system the signal is derived from a D.C.
current transformer-measuring rotor current. On the units supplied
before 1981 the output of the C.T. feeds the MAVR at multicore
terminals 1/10 and 1/7 and is routed to monitor (2) (29) via LK16 and
LK7 on the backpanel. On the type A mainframe the C.T. supplies
MAVR terminal 1/14 and 1/10, LK8 being fitted on the backpanel.
A current proportional to the field current is compared to the
stabilized reference current lowing through R56. When the field current
exceeds a preset level determined by the reference current and the
setting of RV5 the output voltage of IC3b begins to fall, causing IC3c to
rise and turning on VT3 and VT4 producing local indication of monitor
operation by LED2, and energizing the common monitor relay, (RL2 on
the back panel) via D23 and (9).
D21 and R67 provide positive feedback that latches VT3 and 4 on,
once the monitor has operated. The output can be reset by removing the
D.C. supply from (24) by depressing the ‘monitor reset’ pushbutton,
which is fitted to the fixed front panel on a MAVR incorporating fault
monitors.
When LK7 is fitted, the sensitivity is increased by a factor of four,
which facilities commissioning of the monitor at reduced levels of
excitation.
RV6 and C10 provide an adjustable integrating time delay, before
the monitor operates.
The temperature compensation signal is derived from the excitation
limiter via (25), potentiometer RV3 providing adjustment of the level of
compensation fed to IC3b via R55 and LK4. LK4 inhibits this signal
when removed.
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8.2.2 Under Excitation Monitor
(This is shown on the upper half of the schematic diagram).
The under excitation limit of a generator operating in parallel with
a system is determined by the generator and system reactance, and can
be represented on a generator operating chart.
If the excitation is reduced to a level that would cause the generator
to operate at a power factor more leading than is shown on the chart,
the angle by which the internal emf of the generator leads the system
voltage will extend 90 and loss of synchronism may occur.
Figure 8-1 shows a typical operating chart and the effect of
differing external reactance between the generator and the infinite
system. Such a reactance could be due to transformers.
Figure 8-1 Generator Operating chart
So that the operation of the monitor can be understood it is
necessary to be aware of the relationship between the simplified vector
diagram of the generator and the generator-operating chart.
Figure 8-2 below shows the equivalent circuit and vector diagram of the
generator paralleled to an infinite system.
I = generator current
Et = generator internal emf
Vt = generator terminal voltage
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V = system voltage
Xd = generator synchronous reactance
Xe = external reactance
Figure 8—2
Figure 8—3 shows how the vector diagram can be related to the
generator-
operating chart.
The condition is drawn for line current I, at φ leading. The under
excited limit occurs when the internal Emf, Et, leads the voltage of the
infinite system by 90 degree.
It can be seen that when Xe=0, the limit is a straight line
corresponding to constant leading MVAr’s of 1/Xd per unit, and that as
Xe increases the MVAr limit reduce with increasing power.
Figure 8—3
IXe Xd Et V
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8.2.3 Operation
(All voltage levels are relative to TP1).
The unit senses line voltage at (21) (29) which is nominally 2.5 volts
rms supplied from T1 on the back panel, and line current at (28) (27)
nominally 28mA supplied by T5 on the back panel. Whose center tap
also feeds (21). The phasing of these signals is such that the current lags
the voltage by 90 degree, when generating at unity power factor.
The input circuit comprising R1, R5, R9, RV1, RV2, is arranged so
that voltages corresponding in phase and amplitude to the internal emf
of the generator, and the system voltage, are produced at TP3 and TP4
respectively. IC1a, IC1b, IC1c, and IC2 form a circuit that produces a
mean positive voltage across C3 when the voltage at TP3 leads that at
TP4 by less than 90 degree; and a mean voltage when the voltage at TP3
leads that at TP4 by more than 90 degree. The latter case corresponds
to an under excited condition, current through R19 causing the output
of IC1d to rise, turning on VT1 and VT2 and producing a local
indication of monitor operation by LED1, and energizing the common
monitor relay, RL1 on the back panel, via D14 and (9). D12 and R26
provide positive feedback that latches VT1 and 2 on, once the monitor
has operated. The output can be reset by removing the D.C. supply
from (24) by depressing the ‘monitor reset’ pushbutton that is fitted on
the fixed front panel of a MAVR incorporating fault monitors.
The output of the monitor can be inhabited by linking multicore 2/5
and 3/7 which ensure that the output of IC1d remaining negative due to
a feed through R71 and D25. This facility can be used to inhibit the
monitor under certain single running condition to increase the overall
reliability.
RV4 and C6 provide an adjustable delay that should be set to
prevent the relay tripping due to transient swings in load angle.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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8.2.4 Link Identification
Link LK1 Selects the under excitation relay output. When fitted
LK1A must be omitted.
Link LK1A Inhibits the under excitation relay output. When fitted
LK1 must be omitted.
Link LK2 Selects the over excitation relay output. When fitted
LK2A must be omitted.
Link LK2A Inhibits the over excitation relay output. When fitted
LK2 must be omitted.
Link LK3 Selects monitor override on under excitation monitor.
Link LK4 Selects temperature compensation.
Link LK7 Selects an increase of sensitivity by a factor of 4 on the
over excitation monitors for commissioning purposes
only. When fitted LK8 must be omitted.
Link LK8 Selects the normal operating sensitivity of the over
excitation monitor. When fitted LK7 must be omitted.
8.3 COMMISSIONING PROCEDURE
This section describes the commissioning procedure for the
excitation monitor card and should be read in conjunction with the
general commissioning procedure, Section D, and any specific contract
commissioning instructions.
IMPORTANT
(1) The potentiometers 'OE Delay', 'Set If’, 'Set Xd', 'Set Xe', and 'Set
TC' have been set to correct level at the factory and should not
require site adjustment.
(2) Check that the correct links are fitted as detailed in the test record--
'MAVR Tests with Test Generator' subsection 6, or by reference to
sub-section 8.2 of the handbook.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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(3) Complete commissioning of the control card prior to commissioning
the excitation monitor card. Temporarily remove the excitation
limiter card during commissioning of the monitor card except when
checking temperature compensation. If applicable, inhibit the
monitor relay from causing transfer to an alternative excitation
source.
8.3.1 Over Excitation Monitor x4 level
(1) Determine the limited parameters. (Over excitation limit x1 and
x4, differential, delay and temperature compensation) from test
record--'MAVR Tests with Test Generator' section. In the
absence of these, typical setting are: the x1 limit 10% higher
than the continuous full load rating of the exciter or main field
of the generator, the differential to 100% (Link 11), the time
delay to 400% seconds, and the temperature compensation to
80% of the 0℃ level for a temperature rise of 40℃.
(2) Remove the monitor card and re-insert together with the
extension card, the latter is behind one of the MAVR blank
front panels. Connect a 10-volt D.C. voltmeter (20 Kohm per
volt or more) across TP6 (+ve) and TP1. Remove LK4 if fitted.
(3) Select the x4 increased sensitivity feature by removing link LK8
and fitting LK7, thereby enabling the approximate operating
level of the monitor to be checked at a low excitation level.
Insert a suitable ammeter in the field circuit if one is not
already available.
(4) Run the generator up to rated speed, single running and on no
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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load with "auto' excitation selected.
(5) Check that no external monitor operation signal is given (i.e. an
open circuit between multicore 2 wires 4 and 6, and the 'OE
Trip' LED is off). This assumes that the no-load excitation is
less than 25% of the preset over excitation trip level. In the
event of it having tripped reset the circuit by the reset
pushbutton on the left hand side of the mainframe.
(6) ncreases the excitation to above the preset over excitation trip
level divided by 4 (to allow for the x4 increase in sensitivity) by
adjusting the motorized voltage setting potentiometer and if
necessary the ‘set V’ potentiometer on the control card. Note
that the voltmeter reading slowly reduce indicating correct
operation, adjust the excitation as necessary to maintain the
voltmeter reading at zero – a slow drift is unavoidable due to
the integrating acting. The excitation current is then at the x4
trip level.
(7) If this level is incorrect by more than ±2.5% then the ‘Set If’
potentiometer has been reset since the unit left the factory and
requires readjustment. To increase the over excitation trip level
rotate the ‘Set If’ potentiometer clockwise and vice versa. In the
event of a trip signal being given reduce excitation and reset the
unit by the reset pushbutton.
(8) Increase the excitation above the x4 trip level and check that
monitor operating is given, (i.e. a short circuit between
multicore 2 wires 4 and 6, and the ‘OE Trip’ LED on). Reduce
the excitation to below the x4 trip level and check that monitor
operation is still indicated until the reset pushbutton is
depressed.
(9) The over excitation monitor is now set to trip at approximately
the required level when the x1 sensitivity is reselected by
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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removing link LK7 and fitting link LK8. Readjust the
motorized voltage setting potentiometer to mid-range and
adjust the control card ‘Set V’ potentiometer to give nominal
line voltage.
1) Over excitation Monitor. Check on Temperature Compensation
Facility x4 Sensitivity
When the temperature compensation facility provided on the
over excitation limiter is utilized, the operating level of the over
excitation monitor is also compensated according to temperature.
The compensation circuit fitted to the limiter card feeds into the
monitor card (pin 25).
(1) Perform tests 8.3.1.5 to 8.3.1.9 above.
(2) Confirm that the over excitation limiter has been commissioned
according to section 6-3 parts A and AA.
(3) Determine the dc voltmeter reading obtained in test 6—3 and
check that the voltage measured across TP10 (+ve) and TP1
corresponds to the ambient temperature at the location of the
RTD.
The voltmeter should indicate
Ambient Temperature (℃) X
Voltmeter reading in test C5-3 AA.V
40
(Test not applicable at ambient temperature below zero).
Adjust RV3 to provide required reading if necessary.
3) Refit link LK4.
8.3.2 Over Excitation Monitor - x1 level
1) Synchronize the generator to the system and lightly load the
generator (5 - 10% of rated power).
2) Gradually increase the excitation by clockwise adjustment of the
motorized voltage setting potentiometer to an excitation level just in
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excess of the recommended x1 trip level. The voltmeter should
display a slowly falling reading indication correct operation. Adjust
the excitation as necessary to maintain the voltmeter reading at zero
- a slow drift is unavoidable due to the integrating action. The
excitation current is then at the x1 trip level. If difficulty is
encountered in reaching the required excitation rotate the control
card ‘Q.C.C’ potentiometer anti-clockwise.
3) If necessary trim the 'Set If' control to give the required excitation
level with a zero reading on the voltmeter. Clockwise rotation
increases the trip level and vice versa.
8.3.3 Over Excitation Monitor – Temperature Compensation (If applicable)
1) Remove LK12 and fit LK12A on the excitation limiter card, together
with the following:
100 ohm RTD Fit LK15 & 17 Omit Links 1, 2, 13, 14, 15,
18
130ohm RTD Fit LK13 & 17 Omit Links 1,2,14,15,16,18
Leave all other links as fitted and replace the limiter card.
2) Synchronize and lightly load the generator, increase the excitation
and check that the monitor operates as in section 8.3.3. Check that
the trip level is within 1% of the required 0℃ Over Excitation
Monitor level.
3) Reduce the excitation to nominal, reset the monitor and reselect the
links on the limiter card as follows:
100 ohm RTD R Remove LK15 Fit LK16
130 ohm RTD Remove LK13 Fit LK14
4) Increase the excitation and check that the monitor now trips at a
lower level corresponding to 40℃ over excitation monitor trip level
±2%. If necessary adjust RV3 (set T.C.) on the monitor card to
achieve this. If no figure is available for this limit assume a value of
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0.8x the 0℃ monitor level. Clockwise rotation of RV3 increases the
amount of temperature compensation i.e. reduce the 40℃ monitor
level and vice versa.
5) Reduce the excitation to nominal, reset the monitor and reselect
links on the limiter card as follow:
100 ohm RTD Remove LKs 16 & 17 and fit LKs 1& 18
130 ohm RTD Remove LKs 14 & 17 and fit LKs 2 & 18
The external RTD is then selected.
6) Increase the excitation and check the monitor operates at a new
level dependant upon the external RTD temperature, ‘t’. Knowing
this temperature check that the trip level, ‘I’ is
Where I0 = 0℃ limit
I40 = 40℃ limit
If incorrect check that the nominal RTD resistance and connections
are correct.
Refit LK12 and remove LK12A on the Limiter card and leave this
card out.
8.3.4 Over Excitation monitor –Time Delay
1) Whilst still in parallel with the system short out TP8 to TP1 with a
temporary link. This shorts out the over excitation monitor sensing
output so that the monitor reset – indicated by the voltmeter
resetting to above 9 volts.
2) Set the excitation to ‘X%’ above the over excitation trip level
(preferable 10% or more – but at least 5%). Reset the monitor if
necessary. Time the period taken, ‘t seconds’, between removing the
short between TP8 and TP1 and the monitor giving trip indication.
2%
40
t*I40-I0*I0 I
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The produce ‘X’ x ‘t’, give the over excitation monitor time delay
expressed in %-SEC’s.
3) If necessary, turn the ‘OE Delay’ control to give the required
%-SEC’s delay; clockwise rotation increasing the delay and vice
versa. When rechecking the time delay allow the monitor to fully
reset, i.e. the voltmeter reading above 9 volts, and cancel the trip
signal by the reset pushbutton.
4) Reset the Q.C.C potentiometer to the required setting if it was
adjusted. Reduce excitation by turning the motorized voltage setting
potentiometer anti-clockwise to give unity power factor. Remove the
voltmeter between TP6 and TP1.
8.3.5 Under Excitation Monitor –Zero Power Level
1) Determine the under excitation monitor parameter (‘Xd’ and ‘Xe’
levels) from the test record- ‘MAVR Tests with Test Generator’
subsection 5. In the absence of these reference should be made to the
generator operation chart, the ‘Xd’ control should be set to the
machine loading capability at zero power and the ‘Xe’ control to any
quoted external reactance figure or a safe level – say 0.1 p.u.
Reactance. ’Xe’ can also be measured by synchronizing the
generator to the system and adjusting the power to zero: by noting
the per unit change in reactive load(ΔQ) for a given change in
system voltage (ΔV p.u.) of say 0.05 p.u. caused by changing the
motorized voltage setting potentiometer, Xe:
To simulate an exact under excitation tripping characteristic
reference should be made to
Fig.8-4. below. A circle gives the tripping level.
p.u. Xd
1
Xe
1
2
1radius
p.u. Q
V Xe
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Thus knowing the required circular characteristics centre and radius
the two parameter
‘Xd’ and ‘Xe’ can be deduced.
Fig 8-4 Under Excitation Monitor Characteristic
2) Connect a 10-volt D.C. voltmeter (20 kohm per volt or more). Across
TP5 and TP1 (+ve). With the machine running in parallel with the
system on ‘auto’ excitation, set the generator output power to zero.
Reduce the excitation by slowing rotating the motorized voltage
setting potentiometer anti-clockwise and check that the monitor
operates when the trip level is exceeded. Operation is indicated by
the ‘UE trip’ LED coming on and a short circuit between multi-core
2 wires 4 and 6. Increase the excitation to below the limit and check
that indication is given until the test pushbutton is operated. Reduce
the excitation again and set to a level that corresponds to a zero
reading on the voltmeter – a slow drift being unavoidable due to the
integrating action. The excitation is then set to the tripping level,
check that this corresponds to the required level and adjust the
p.u. Xd
1 -
Xe
1
2
1centre
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tripping level, if necessary, by adjustment of the ‘Xd’ potentiometer,
clockwise rotating decreasing the level and vice versa.
8.3.6 Under Excitation Monitor – ‘Xe’ Control
1) Increase the excitation to give unity power factor by clockwise
rotation of the motorized voltage setting potentiometer. Remove the
excitation monitor card from the rack.
2) Knowing the required external reactance, Xe, calculate from the
following the required resistance of the ‘Xe’ potentiometer:
(This figure is given in ‘MAVR Tests with Test Generator’ Section
QC48, subsection 7, page1).
Check using a digital ohm-meter that the resistance between TP2 and
TP4 agrees with that calculated. If it is incorrect adjust the ‘Xe’ control,
clockwise rotation will increase the resistance and vice versa. If a digital
ohm-meter is not available the ‘Xe’ control setting can be checked as
detailed in subsection 8.3.8 (Below). Replace the excitation monitor card.
8.3.7 Under Excitation Monitor – Tripping Level Characteristic
1) To check the tripping level characteristic throughout the range
adjust the excitation to give a zero reading on the voltmeter at
various generator output power from zero to maximum. By
checking the reactive power at these levels a comparison can be
made with the generator operating chart when it shows the under
excitation monitor tripping level.
2) If the operating chart is not available or shows insufficient
information, or ‘Xe’ could not be checked as detailed in subsection
F the following procedure should be adopted. Knowing ‘Xd’ and
ohms
current) C.T. p.u.sensin (1
Xe.p.u.*5*60R
5) (nominally ratio C.T. Sensing
current line ratedcurrent) C.T. sensing p.u. (1 Where
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‘Xe’ per unit values, calculate the radius and centre of the tripping
level circular characteristic as shown in Figure 8-4. Referring to
figure 8-4, for any generator output power, ‘OX’, the corresponding
tripping level of reactive power, ‘XY’, can be calculated as follows:
3) From the above calculations the theoretical and practical tripping
level curves can be compared and any errors compensated for by
appropriate adjustment of the ‘Xd’ and ‘Xe’ potentiometers. In
general the ‘Xd’ control sets the zero power trip level and the 'Xe'
control the curvature of the characteristic.
NOTE: The generator-operating chart is normally drawn for
operation at nominal voltage, although the actual limiting
curve of the generator and system reduces in proportion to
the square of line voltage, and the limiter incorporates this
characteristic.
If the limiter characteristic is being checked the reading of
MVAr should be divided by (per unit volts) squared, at line
voltages other than nominal.
8.3.8 Under Excitation Monitor – Time Delay
1) Remove the voltmeter and extender card. Replace the excitation
limiter card in the rack and adjust the excitation to unity power
factor.
2) At various generator output power from zero maximum check that
a sudden reduction in excitation caused by quickly rotating the
motorized voltage setting potentiometer fully anti-clockwise cause
the excitation limiter to operate before the under-excitation monitor
trips. If the monitor operates first rotate the ‘Slug UE’
potentiometer clockwise until the above condition can be set.
3) Reconnect the excitation monitor output relay to revert to the
OA centreOXpower p.u.AC reactivep.u. XY''power Reactive 22
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normal operational scheme.
8.4 FAULT FINDING PROCEDURE
This section describes the fault-finding procedure for the Excitation
Monitor card and should be read in conjunction with the general fault
finding section E.
IMPORTANT
(1) The majority of excitation fault are caused by incorrect connections-
thoroughly check all connections are correct to the contract
schematic diagram.
(2) Check that the correct links are fitted as detailed in the test record –
‘MAVR Test With Test Generator’ subsection, or by reference to
subsection 8-2 of the handbook.
In general faults associated with the Excitation Monitor Card can
be separated into two categories (Over and Under Excitation Monitor) viz:
Over Excitation Monitor – Inoperative (Table 8.4.1)
- Continuous operation (Table 8.4.2)
- Operator faults (Table 8.4.3)
Under Excitation Monitor- Inoperative (Table 8.4.4)
- Continuous operation (Table 8.4.5)
- Operator faults (Table 8.4.6)
Refer to the appropriate section for corrective action.
NOTE: If any card is returned to the Works for repair please quote the
Type/Model/Contract numbers which appear inside the MAVR
front door, and on the right hand side of the mainframe
together with the nature of the fault.
Table 8.4.3 Over Excitation Monitor – Operational Faults
No
.
System Possible
Fault
Test Remedial
Action
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1. Monitor
operates when
machine on
load.
Set If control
set too low.
Check level as
in Section
8.3.2
Reset level, if
necessary as
in Section
8.3.2
2. Monitor
operates due to
transient on
load
applications.
‘OE Delay’
set too short.
Check delay as
in Section
8.3.4
Reset delay, if
necessary as
in Section
8.3.4
3. On a twin
system the
monitor causes
transfer before
limiter
operates.
Relative
levels and
time delays
of limiter
and monitor
incorrect.
Check levels &
delays as
detailed in 6.3
and 8.3
Reset as
necessary as
in Section 6.3
and 8.3.
4. Local
indication
given but relay
output
inoperative.
Mainframe
failure.
Monitor relay
faulty (RL2 on
Mainframe).
Replace relay
RL2.
5. Monitor
operates but
does not give
latched
indication.
Monitor
failure.
Interchange
monitor card
with a spare.
Replace
monitor card
and return to
Works for
repair.
6. Monitor low at
high
temperatures.
Excessive
temperature
compensatio
n.
Check as
detailed in
Section 8.3.3.
Correct as
necessary.
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Table 8.4.4 Under Excitation Monitor – Inoperative
No
.
Possible fault Test Remedial Action
1. Incorrect
output link
selected.
Check link LK2 is fitted
and LK2A omitted.
Correct as
necessary.
2. Loss of Power
Supply.
Check FS1 & 2 and any
external fuses and wiring
to auxiliary supply.
Replace blown
fuse or correct as
necessary.
3. Mainframe
failure.
Loss of sensing signals
(Sensing volts, 2.5v, (21) to
(29) & sensing current,
22.5V at 5A (19) to (20)).
See Section 8.4
4. ‘Xd’ & ‘Xe’
controls set too
low.
Check level as in 8.3.5&
8.3.6.
Reset levels, if
necessary, as in
Section 8.3.5 &
8.3.6.
5. Monitor Card
Faulty.
Interchange Monitor card
with a spare.
Replace Monitor
card and return
to the Works for
repair.
Table 8.4.1 Over Excitation Monitor – Inoperative
No
.
Possible fault Test Remedial Action
1. Incorrect
output link
selected
Check link LK1 if fitted
and LK1A omitted.
Correct as
necessary.
2. Loss of power
supplies.
Check FS1& 2 and any
external fuses and wiring
to auxiliary supply.
Replace blown
fuse or correct as
necessary.
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3. RTD short
circuit or an
associated
wiring fault or
limiter card
faulty.
Remove LK1 or 2 on
limiter card & check
correct operation. Check
RTD and wiring. Check
limiter card temperature
compensation.
Correct as
necessary.
4. Mainframe
failure.
No field current pick up
signal to monitor card (2)
& (29) – should be 150mV
to 1V on no load – or
internal power supply
failure.
See Section C1-4.
5. ‘Set If’ control
set too high.
Check level as in section
8.3.2.
Reset level, if
necessary, as in
section 8.3.2.
6. Limiter card
faulty.
Interchange monitor card
with a spare.
Replace monitor
card and return
to the Works for
repair.
Table 8.4.2 Over Excitation Monitor – Continuous Operation
No
.
Possible Fault Test Remedial Action
1. Increased
sensitivity link
selected.
Check link LK8 is fitted
and LK7 omitted.
Correct as
necessary.
2. ‘Set If’ control
set too low.
Check level as in Section
8.3.2.
Reset level, if
necessary, as in
section 8.3.2.
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3. RTD open
circuit, on
associated
wiring fault or
limiter card
faulty.
Remove LK4 & check
correct operation. Check
RTD wiring & Limiter
card temperature
compensation.
Correct as
necessary.
4. Control
card/sensing
failure giving
rise to an over
excited
condition.
See Section 4.4. See Section 4.4
5. Mainframe
failure.
Field current pick up
excessive (should be
nominally 0.17V between
(2) and (29) per amp of
excitation.
See section 3.4.
6. Monitor card
faulty.
Interchange monitor card
with a spare.
Replace monitor
card and return
to the Works for
repair.
7. Temperature
Compensation
Unit faulty.
Disconnect & check
monitor on its own.
Replace TCU &
return to Works
for repair.
Table 8.4.5 Under Excitation Monitor – Continuous Operation
No
.
Possible Test Remedial
1. C.T. and /or
P.T. sensing
phasing
incorrect.
Check to contract scheme. Correct as
necessary.
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2. Control card
failure giving
rise to an
under excited
condition.
See Section 4.4. See Section 4.4
3. Monitor Card
faulty.
Interchange Monitor card
with a spare.
Replace Monitor
card and return
to the Works for
repair.
4. Mainframe
failure.
All other tests fail to clear
fault.
See Section 3.4
Table 8.4.6 Under Excitation Monitor – Operational Faults
No
.
System Possible Fault Test Remedial
Action
1. Generator
loses stability
before limiter
operation.
Monitor level
set to low I.e.
outside
generator
capability.
Check
operating level
as detailed in
8.3.4 & 8.3.5.
Reset levels,
if necessary,
as in Section
8.3.5 &
8.3.6.
2. On a twin
system the
monitor causes
transfer before
limiter
operates.
Relatives level
and time
delay/stabilizi
ng of limiter
and monitor
incorrect.
Check levels
and
delay/stabilizin
g as detailed in
6.3 and 8.3.
Reset as
necessary as
in Sections
6.3 and 8.3.
3. Local
indication
given but relay
output
inoperative.
Mainframe
failure.
Monitor relays
faulty (RL2 on
mainframe).
Replace
relay RL2.
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4. Monitor
operates due to
transient
voltage
changes.
‘Slug UE’ set
too short.
Check slug as
in section 8.3.8.
Increase
‘Slug UE’ as
in section
8.3.8.
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9 VOLTAGE MONITOR CARD
9.1 SPECIFICATION.
9.1.1 UNDER VOLTAGE MONITOR SPECIFICATIONS.
1) OPERATING LEVEL
The operating level is adjustable between 70% and 100% of
nominal voltage (110V).
2) Time delay.
An adjustable integrating time delay is incorporated having a range
of 2.5% --second to 25%--second (i.e. 100% error gives 25 ms to
250 ms delay).
9.1.2 OVER VOLTAGE MONITOR SPECIFICATIONS.
1) OPERATING LEVEL
The operating level is adjustable between 100% and 130% of
nominal voltage (110V).
2) TIME DELAY
An adjustable integrating time delay is incorporated having a
range of 10% --second to 100%--second (i.e. 100% error gives 100
ms to 1 second delay).
9.1.3 COMMON SPECIFICATIONS
1) ACCURACY
The operating level is maintained within ±1% of the selected
operating level subject to the following conditions:
(1) The temperature is within ±15℃ of the initial value.
(2) The frequency is within ±20% of nominal.
2) Input signals.
The unit requires a single phase, 110 volt nominal supply of
1VA rating at 50/60 Hz, separate to the control card sensing.
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3) Ambient Temperature Range.
Operating: -25℃ to +65℃.
Storage: -40℃ to +100℃
9.1.4 CONTROLS AND INDICATIONS.
1) Set OV: A front access multi-turn potentiometer which adjusts the
over voltage trip level.
2) Set UV: A front access multi-turn potentiometer which adjusts the
under voltage trip level.
3) OV delay: A front mounted single turn potentiometer with a
calibrated dial scaled 0 to 10 which adjusts the over voltage time
delay.
4) UN delay: A front mounted single turn potentiometer with a
calibrated dial scaled 0 to 10 which adjusts the under voltage time
delay.
5) OV trip: A front mounted ‘Light Emitting Diode’ to give
indication that the over voltage monitor has tripped.
6) UV trip: A front mounted ‘Light Emitting Diode’ to give
indication that the under voltage monitor has tripped.
9.2 DESCRIPTION OF OPERATION
(Numbers in brackets ( ) refer to printed circuit board edge
connections, and all voltage level are relative to TP1.)
Sensing voltage supplied to multi-cores 2/7 and 2/9 is supplied to
(20) (22) via sensing fuses FS3, 4.
The sensing signal is isolated and rectified to produce a d.c. voltage
at TP7 that is used for both under and over voltage monitors.
9.2.1 Under Voltage monitor.
The input signal produces a current in R11 that compared with an
adjustable stabilized reference current flowing through R14. When the
input signal exceeds the reference, the output of IC1 (TP3) is negative,
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and VT3, 4 are non-conducting and no output signal is given. When the
input signal is less than the reference signal, the output of IC1 rises at a
rate determined by the error, and setting of RV2, and when TP3
becomes approximately 0.5 volt positive, VT3 and VT4 turn on
energizing the monitor relay R12 on the back panel via (8) and LED1
which provides local indication. Positive feedback via D5 and R22 keep
VT3 and VT4 on, even if the sensing voltage rises causing the voltage at
TP3 to fall.
The monitor relay R12 remains energized until the reset monitors
pushbutton (on the fixed front panel) is pressed which removes the +15
volt supply from (24).
The under voltage monitor can inhibited by a positive signal at (28)
which turns on VT1, VT2 producing a current through R12 which
over-rides the error signal, preventing the output of IC1 becoming
positive. This facility is used during operation of the falling frequency
protection and soft start facility where the line voltage is intentionally
controlled to a lower level.
9.2.2 Over Voltage Monitor
The input signal produces a current through R18 that is compared
with an adjustable stabilized reference current flowing through R26.
When the input signal exceeds the reference, the output voltage of IC2
(TP4) begins to rise at a rate determined by the error and setting of
RV4, and when TP4 becomes approximately 0.5 volt positive VT5, VT6
are turned on and the monitor relay R12 on the back panel is energized
via (8) and LED2 which provides local indication.
Positive feedback via R32 and D10 latch in the relay driver circuit
which cad be reset by operating the reset monitors pushbutton which
removes the +15 volt supply from (24).
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Inhibit monitors
Over and under Voltage monitors can be inhibited by applying +15
volts d.c. to (2), ensures that the output of both amplifiers remains
negative. This can be achieved by linking multi-cores 3/11 and 2/5 and is
sometimes used to increase the overall reliability of the fault monitor
when operating in parallel with a large system.
Link Identification
Link LK1 Selects the under voltage monitor output.
Link LK2 Selects the over voltage monitor output.
Link LK3 Selects the under voltage override input.
9.3 COMMISSIONING PROCEDURE.
This section describes the commissioning procedure for the voltage
monitor card and should be read in conjunction with the general
commissioning procedure, section D and any specific contract
commissioning instructions.
IMPORTANT
(1) Check the correct links are fitted as detailed in the setting records
for MAVR tested with Generator sub-section 6.
(2) All potentiometers on the unit have been set to the correct level at
the factory and should not require any on-site adjustment.
(3) Complete commissioning of the control card prior to commissioning
the voltage monitor.
9.3.1 Over Voltage Monitor – Operating Level
1) Determine the over voltage parameters (level and time-delay) from
the test record ‘MAVR Tests with Test Generator’ section QC48,
sub-section 6, page 1. In the absence of these, typical settings are the
over voltage level 15% above the nominal line voltage and a time
delay of 20%-seconds although certain site operating conditions
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might require different settings.
2) Remove the voltage monitor card and re-insert together with the
extension card. Connect a voltmeter (20K ohms per volt or more)
on the 10V d.c. range between TP1 (+ve) and TP4. Inhibit any
transfer of excitation to a standby source due to monitor operation,
if applicable.
3) Run the generator up to speed and select ‘Auto’ excitation. Set the
motorized voltage setting potentiometer fully clockwise and adjust
the ‘set V’ control on the control card to give a line voltage of 105%
(in preparation for setting the time delay) of the over voltage trip
level.
4) Reduce the generator line voltage by turning the motorized voltage
setting potentiometer fully anti-clockwise and reset the voltage
monitor, if necessary, depressing the reset pushbutton on the left of
the mainframe.
5) Adjust the motorized voltage setting potentiometer until the
voltmeter indicates a slowly falling voltage, finally adjusting to give
a reading of zero on the voltmeter – a slow drift being unavoidable
due to an integrating action. The line voltage is then at the set level
of the over voltage monitor.
6) Due to sensing VT differences or adjustment of the set ‘OV’
potentiometer it may be necessary to reset the level. To increase the
level turn the ‘set OV’ potentiometer clockwise and vice versa.
Repeat the above procedure (AV) until the set level is correct.
7) Increase the voltage above the set level and check that the over
voltage monitor operates (i.e. a short circuit between multi-core 2
wires 4 and 6, and the ‘OV Trip’ LED on). Reduce the voltage below
the set level and check that monitor operation is still indicated until
the reset pushbutton is momentarily depressed.
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9.3.2 Over Voltage Monitor –Time Delay.
1) With the voltage below the set level and the monitor reset suddenly
turn the motorized voltage setting potentiometer fully clockwise and
measure the delay ‘t sec's’ (Using a stopwatch) before the ‘OV Trip’
LED is turned on.
2) The time delay is given by the product, 5 x ‘t’%-sec's (the error
being set to 5% in sub-section AIII). This time-delay should
correspond to that quoted in the test record.
3) If the time delay is incorrect then the ‘OV Delay’ potentiometer has
been reset since the unit left the factory and requires readjustment.
To increase the delay turns the ‘OV Delay’ potentiometer clockwise
and vice versa. Repeat the above procedure (BI & II) until the time
delay is correct.
9.3.3 Under Voltage monitor – operating level.
1) Determine the under voltage parameters (level and time delay)
from the test record – ‘MAVR Tests with Test generator’ section
QC48, sub-section 6, page 1. In the absence of these, typical settings
are the under voltage level 15% below the nominal line. Voltage and
a time delay of 10%-secs. , Although certain site operating
conditions might require different settings.
2) Set the motorized voltage setting potentiometer fully anti-clockwise
and adjust the ‘set V’ control on the control card to give a line
voltage of 97.5% of the under voltage trip level (in preparation for
setting the time delay). Connect a voltmeter (20 Kohms per volt or
more) on the 10V d.c. range between TP1 (+ve) and TP4 and
remove link LK3.
3) Increase the generator line voltage by turning motorized voltage
setting potentiometer fully clockwise and reset the voltage monitor,
if necessary by depressing the re-set pushbutton on the left of the
mainframe.
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4) Adjust the motorized voltage setting potentiometer until the
voltmeter indicates a slowly falling voltage, finally adjusting to give
a reading of zero on the voltage – a slow drift being unavoidable
due to an integrating action. The line voltage is then at the set level
of the under voltage monitor.
5) If this level is incorrect then the ‘set UV’ potentiometer has been
reset since the unit left the factory and requires read just-ment. To
increase the level turn the ‘set UV’ potentiometer clockwise and vice
versa. Repeat the above procedure (CIV) until the set level is
correct.
6) Decrease the voltage below the set level and check that the under
voltage monitor operates (i.e. a short circuit between multi-core 2
wires 4 & 6, and the ‘UV Trip’ LED on). Increase the voltage above
the set level and check that monitor operation is still indicated until
the reset pushbutton is momentarily depressed.
9.3.4 Under Voltage monitor – time delay.
1) With the voltage above the set level and the monitor reset suddenly
turn the motorized voltage setting potentiometer fully clockwise
and measure the delay, ‘t sec’s’, (using a stopwatch) before the ‘UV
Trip’ LED is turned on.
2) The time delay is given by the product, 2.5 x ‘t’%-sec’s (the error
being set to 2.5% in sub-section CII). This delay should correspond
to that quoted in the test record.
3) If the delay is incorrect then the ‘UV Delay’ potentiometer has been
reset since the unit left the factory and requires adjustment. To
increase the delay turn the ‘UV delay’ potentiometer clockwise and
vice versa. Repeat the above procedure (DI & II) until the time
delay is correct.
9.3.5 Under Voltage monitor –Override.
1) refit link LK3, set the line voltage to just above the under voltage
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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trip level (the voltmeter indicating a slowly rising voltage) and
switch off the excitation.
2) Switch on the excitation after 2 minutes, the control card ‘soft start’
circuit having then reset, and check that the under voltage monitor
does not operate during build-up.
3) Reduce the generator speed to zero and check that the under voltage
monitor does not operate whilst on the frequency fall off
characteristic.
9.3.6 Voltage Monitor Inhibit Circuit (if applicable).
1) With the set running at rated speed on ‘Auto’ excitation inhibit the
voltage monitor by the appropriate external logic (shorting
multi-core 3 wire 11 to multi-core 2 wire 5).
2) Adjust the voltage above the over voltage trip level and below the
under voltage trip level and check that neither gives a trip signal.
9.3.7 Final Notes.
1) Reset the motorized voltage setting potentiometer to mid range and
adjust the control card ‘set V’ potentiometer to give the required
nominal line voltage.
2) Reconnect any logic that was disconnected to inhibit transfer of
excitation on monitor operation.
3) Remove the voltmeter and extender card and refit the voltage
monitor card.
9.4 FAULT FINDING PROCEDURE.
This section describes the fault finding procedure for the voltage
monitor card and should be read in conjunction with the general fault
finding section 9.4.5.
IMPORTANT.
(1) The majority of excitation faults are caused by incorrect
connections thoroughly check all connections are correct to the
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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contract circuit diagram.
(2) Check that the correct links are fitted as detailed in the test record
‘MAVR Tests with Test Generator’, sub-section6, or by reference to
sub-section 9.2 of the handbook.
(3) In general faults associated with the voltage monitor card can be
separated into six main categories viz.:
Over Voltage monitor Inoperative (Table 9.4.1)
Continuous Operation (Table 9.4.2)
Maloperation (Table 9.4.3)
Under Voltage Monitor Inoperative (Table 9.4.4)
Continuous Operation (Table 9.4.5)
Maloperation (Table 9.4.6)
Refer to the appropriate section for connective action.
NOTE:
If any card is returned to the works for repair please quote the
Type/Model/Contract numbers that appear inside the MAVR front
door and on the right had side of the mainframe together with the
nature of the fault.
Table 9.4.1 Over Voltage Monitor – Inoperative.
No. Possible Fault. Test. Remedial Action.
1. Output link
not selected.
Check link LK2 is fitted. Correct as
necessary.
2. Trip level set
too high.
Check level as detailed in
9.3.
Reset level if
necessary.
3. Trip signal
overridden
Check wiring between
3/11 & 2/5 – should be
open circuit.
Correct as
necessary.
4. Loss of Power
Supply.
Check FS1 & 2 and any
external fuses and wiring
to the auxiliary supply.
Replace
blown-fuse or
correct as
necessary.
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5. Monitor card
faulty.
Interchange the monitor
card with a spare.
Replace monitor
card and return
to the works for
repair.
6. Mainframe
failure.
No sensing voltage to
card, 110V a.c. (nominal)
to (20) and (22).
See section 3.4.
Table 9.4.2 Over Voltage monitor – Continuous Operation.
No. Possible Fault. Test. Remedial Action.
1. Trip level set
too low.
Check level as detailed in
section 9.3.
Reset level if
necessary.
2. Control
card-sensing
failure giving
rise to an
over-voltage
conditions.
See section 4.4. See section 4.4.
3. Monitor card
faulty.
Interchange the monitor
card with a spare.
Replace monitor
card and return
to the works for
repair.
4. Mainframe
failure.
See section 3.4. See section 3.4.
Table 9.4.3 Over Voltage monitor – Maloperation.
No. Symptom. Possible Fault. Test. Remedial
Action.
1. Monitor
operates due to
machine off
‘O.V. Delay’ set
too short.
Check delay
as in section
9.3.
Reset delay
if necessary.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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load transients.
2. Monitor
operates but
does not giving
latched
indication.
Monitor
failure.
Interchange
the monitor
card with a
spare.
Replace
monitor
card and
return to
the works
for repair.
3. Local
indication
giving but
relay output.
Inoperative.
Monitor
failure.
Monitor
relay faulty
(RL2 on
Mainframe).
Replace
relay RL2
Table 9.4.4 Under Voltage Monitor – inoperative.
No. Possible Fault. Test. Remedial Action.
1. Output link
not selected.
Check link LK2 is fitted. Correct as
necessary.
2. Trip level set
too low.
Check level as detailed in
9.3.
Reset level if
necessary.
3. Trip signal
overridden
a) Check wiring
between 3/11 & 2/5 –
should be open
circuit.
b) Remove link LK3.
Correct as
necessary.
If operating when
LK3 removed
then either volts
monitor faulty or
control card is
giving an
overriding output
due to ‘F.F.O.’ or
‘soft start’
circuits-see
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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section 4.4.
4. Loss of Power
Supply.
Check FS1 & 2 and any
external fuses and wiring
to the auxiliary supply.
Replace
blown-fuse or
correct as
necessary.
5. Monitor card
faulty.
Interchange the monitor
card with a spare.
Replace monitor
card and return
to the works for
repair.
6. Mainframe
failure.
See section 3.4. See section 3.4.
Table 9.4.5 Under Voltage Monitor –Continuous Operation.
No. Possible Fault. Test. Remedial Action.
1. Trip level set
too high.
Check level as detailed in
section 9.3.
Reset level if
necessary.
2. Loss of sensing
signal
Mainframe
failure.
See section 3.4. See section 3.4.
5. Monitor card
faulty.
Interchange the monitor
card with a spare.
Replace monitor
card and return
to the works for
repair.
Table 9.4.6 Under Voltage monitor – Maloperation.
No. Symptom Possible Fault. Test. Remedial
Action.
1. Monitor
operates due to
‘U.V Delay’ set
too short.
Check delay
as in section
Reset delay
if necessary.
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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machine on
load transients.
9.3.
2. Monitor
operates on
buildup,
and/or
run-down.
Link LK3
missing – no
override
during these
conditions.
Check link
LK3 is
fitted.
Correct as
necessary.
3. Monitor
operates but
dose not give
latched
indication.
Monitor
failure.
Interchange
monitor
card with a
spare.
Replace
monitor
card and
return to
the works
for repair.
4. Local
indication
giving but
relay output.
Inoperative.
Monitor
failure.
Monitor
relay faulty
(RL2 on
Mainframe).
Replace
relay RL2
9.5 LIST OF PARTS (CON'D).
Com-po
nent
Ref.
Descrip-ti
on.
Value. Toleran
ce.
Manuf
actures
rating.
Manufac
turer &
Type
Brush
Ref.
IC1,2 Integrate
d Circuit
ZLD74
1
28781-74
3
RV1 Potentio
meter
5
kohm
±
10%
1W
25
turn
Allen
Bradle
y 80
26564-69
0
RV2, 4 Potentio
meter
10
kohm
±
10%
1W Cloven
clr1206
26631-74
7
RV3 Potentio 2 ± 1W Allen 26564-68
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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meter kohm 10% 25
turn
Bradle
y 80
0
LED1, 2 LED 100m
A/3V
Litroni
x 21-02
28241-25
1
T1 Transfor
mer
240:
12-0-
12
R.S
196-27
4
25122-37
8
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10 MAVR AUXILIARY RACK
10.1 INTRODUCTION
The MAVR auxiliary equipment rack contains item which are
associated with any standard MAVR excitation system but which are
not housed in the MAVRE unit.
The rack contains the following main items:
Electronic manual control system;
Auto follower;
Null balance circuit (an external indicator is required);
Exciter field suppression contactor and resistor;
Auto-manual changeover contactor;
Auxiliary d.c. supply fuses;
Terminals for excitation system connections and all MAVR
multicore cables;
Slave relays for MAVR limiter and fault signals.
This handbook section covers the auxiliary equipment rack for use
on single MAVR system in which manual control is selected either
manually by an operator or automatically if AVR d.c. supply fails, or
excitation monitors are fitted to the AVR.
10.2 SPECIFICATION
10.2.1 Excitation Supply Voltage
The unit will accept nominal supply voltages in the following ranges;
150V 200Hz ±15%
180V 240Hz ±15%
220V 400Hz ±15%
264V 480Hz ±15%
220V 50Hz ±10%
Refer to section 8.3 for correct links selection.
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10.2.2 D.C. auxiliary Supply
The unit will accept d.c. auxiliary supplies in the following ranges:
24V +15% -20%
48V +15% -20%
125V +15% -20%
220V +10% -10%
Refer to section 8.3 for correct link selection.
10.2.3 Output Rating
1) current
15 amps continuous at 65℃
18 amps continuous at 55℃
2) Voltage
The maximum output voltage is the lowest of the following:
(1) 0.4 X a.c supply voltage
(2) 100V d.c. (LK7 omitted)
(3) 75V d.c. (LK7 fitted)
3) The generator power factor: lag 0.6-lead 0.9
10.2.4 Field Voltage Control
1) Adjustment Range
The controller regulates the exciter field voltage to a constant level
which is continuously adjustable between zero and the maximum
specified in section 8.2.3 2).
2) Remote Adjustment
Adjustment of excitation field voltage is achieved by energizing
either a 'raise' or 'lower' relay on the unit. These relays should be
energized from the d.c. auxiliary supply.
3) Local Adjustment
As a commission/testing aid, miniature pushbuttons are provided on
the printed circuit to raise and lower the set point.
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4) Travel Time
The time taken for field voltage to be adjusted between minimum
and maximum limits in 60 seconds.
5) Automatic Reset to Minimum
When the unit is energized during run up, the set point will be
automatically set to zero.
10.2.5 Auto Follower
In the normal operating mode, When the excitation is being
controlled by the MAVR, The output of the manual controlled is
automatically adjusted to match the output of the MAVR, enabling
control to be switched from the AVR to manual with negligible shock to
the system.
While either manual raise or lower control is being operated The
action of the auto follower is temporarily inhibited.
The accuracy of the auto follower for a temperature variation of ±
15℃ will be better than
1) ±2 % at 100 volts output from the AVR.
2) 10% at 10 volts output from the AVR
Where VLA = line voltage on AVR control just before select manual
control
VLM = line voltage on manual control
10.2.6 Inhibit Follower Facility
A relay is provided which, When energized from the auxiliary d.c.
supply, will inhibit the operation of the auto-follower.
This relay is normally energized when manual control is selected and if
an AVR excitation limiter operates when in auto control. When this
relay is energized, the set point of the manual controller will remain
constant unless adjusted by raise/lower controls.
%)(100VLA
VLAVLMaccuracy
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10.2.7 Minimum position Indication
A relay is fitted which is energized if the manual controller set point
is at minimum and the manual output is zero.
10.2.8 Null Balance Indication
An output is provided for a 0.5-0-0.5 mA, center zero ammeter.
When the output of the manual controller is matched to the output
of the AVR, balance is indicated by the meter reading zero.
10.2.9 Isolation
There are three groups of terminals on the unit VIZ
1) a.c. supply terminals
2) d.c.. auxiliary supply terminals
3) relay output terminals
These groups of terminals are electrically isolated, both from each
other and from the earth terminal on the frame.
10.2.10 Auxiliary Contactors
Auxiliary contactors are provided for indication/monitoring of the
excitation system. The function and ratings of these contacts are shown
below.
Function Type and Rating
Excitation Tripped
Manual/Auto selected
AVR fault monitor tripped
AVR limiter operating
Manual at minimum position
Changeover 200V 0.07A D.C.. time
constant ≤40 ms
10.3 DESCRIPTION OF OPERATION
(Reference is made to 0NQ.162.121 and 0NQ.351.018)
[Number is brackets( ) refers to printed circuit board edge connections,
and all voltage levels are relative to TP1]
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10.3.1 Electronics Power Supply (T1,DB1,Z2,Z3,Z4,RL1,etc)
The a.c supply for the Electronics Power supply is derived from the
PMG This voltage is applied to the primary of transformer T1 via fuse
FS1, links LK1 to LK5 being used to select the PMG voltage as
following:
Nominal PMG
voltage (±
15%)
Fit Links Omit links
264V LK5,LK4 LK1,LK2,LK3
220V LK5,LK2 LK1,LK3,LK4
110V LK1,LK2,LK3 LK4,LK5
The secondaries of T1 are used via diode bridge DB1 to provide
positive and negative unregulated and three stabilized rails.
R53,C14,R49and Z2 provide the positive unregulated supply for the
pulse circuit and the +15V regulated supply (TP2) for IC1 and IC2.
R51,C15,R52 and Z3 provide the negative unregulated supply for RL2
and the -15V regulated supply (TP3) used for IC1 and IC2.
The -6.2V rail (TP4) is derived from the -15V rail via R50, C13 and
the contact of relay RL1. The coil of RL1, with R48 in series, is
connected between the +15V and -15V rails. This ensures that the -6.2V
rail, which is used for the digital reference and logic, is only available
when the 15V positive and negative rails have been established.
10.3.2 Manual Control Regulator (IC2, T2,VT1,VT2,SCR1,etc)
The manual control regulator output is derived from the PMG
supply and takes the form of a half wave, phase controlled supply. The
current path during the period when the terminal 3 is positive WRT
terminal 4 is as follow:
From terminal 3 via FSC-1 and FS3 to thyristor SCR1 then via
ECC-1, DB1 and the contacts FSC-4, 3 and 2 to terminal 5 and the
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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exciter fields.
From terminal 2F2 of the field, the path is the MAVR field pick-up
resistors and back via terminal 24 and DB2 to terminal 4.
Phase control of SCR1 is achieved as follows:
IC2 is an operational amplifier arranged as a high gain inverting
amplifier. The input is connected to the manual output via the
attenuating and filtering components R30,R31,R32,R33 and C6. This
provides a positive input which is balanced against the negative input
provided by the digital reference from IC6,IC7 and IC8.
The output voltage of IC2 is determined by the difference between
the manual output and reference voltage, a low manual output
producing a high voltage at TP5, and conversely, a high manual output
producing a low voltage at TP5.
The output voltage of IC2, measured at TP5 is limited between
approximately -0.5 volts and +10 volts by D5,D6,Z1 and R39.
The thyristor firing pulse is produced when VT1 is turned on which
can only occur during the period that the thyristor is forward biased.
The phase reference signal supplied to terminal 23 on the electric
board is connected to the anode of the thyristor. When this is negative,
transistor VT2 is turned on via R41, and the voltage at TP8 is clamped
to approximately -0.5 volts due to current flowing through D9,VT2 and
R40 to the negative rail. This prevents VT1 from being turned on.
During the period that the thyristor is forward biased, D13 conducts
and VT2 is turned off.
This allows the voltage at TP8 to rise, at a rate determined by the
output voltage IC2, and the time constant set by R35 and C7.
An increase in the voltage at output of IC2 due to a low output from
the manual regulator, cause VT1 to turn on earlier, and the thyristor to
fire earlier. This tends to restore the manual output to the correct level,
at which point the manual and reference signals at the input to IC2 are
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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balanced, and the output voltage of IC2 falls to a steady state level.
The pulse circuit operation is described below:
As the base of VT1 begins conduct at approx. 0.5 volts, collector
current starts to flow. Positive feedback via the pulse transformer T2,
causes VT1 to turn on rapidly which produces a positive pulse in the
output winding which fires the thyristor via terminal 8 on the printed
circuit board.
The pulse energy is provided mainly by C9 and as the voltage
across the pulse transformer falls a point is reached when there is
insufficient feedback to hold VT1 on. A this point the collector voltage
begins to increase, which is followed by rapid turn off due to the effect
of the feedback. Diode D11 provides a path for the stored energy in the
core of the pulse transformer. Meanwhile C9 charges up again through
R49 and as soon as the pulse transformer winding reverse voltage
reaches zero, the cycle repeats itself and another pulse is given.
As a result a train of pulse is applied to the gate of the thyristor.
10.3.3 Digital Reference (IC6,IC7 and IC8)
IC6,7 and 8 form a twelve bit up-down counter controlled by the
raise/lower section.
The 12 outputs, Q1 to Q4 on each IC, are connected to a network of
resisters R76 to R95. The arrangement provides reference signal which
is adjustable in 4096 steps from 0 to approx. 400 micro amps. The
power supply used in both the digital reference and raise/lower logic is
-6.2V so a logic '1' state is at 0V and a logic '0' state is represented by
-6.2V relative to TP1. The up-down counter is in the fully 'up' state
when all of its outputs are a logic 1 but in this state the digital reference
will provide zero current drain and therefore from the point view of the
manual control, it is at the minimum level. Equally when the counter is
in its fully 'down' state the outputs will be at logic 0(-6.2V) and provide
the maximum current for the reference. The above means that an 'up'
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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count reduce the reference current and thus reduces the manual output
while a 'down' count increases the manual output. Notwithstanding the
above all the controls provide for the unit are arranged and labeled
such that for instance a 'raise' signal will increase the manual output
even through it has to generate a 'down' count to do so.
The resistors R76 to R95 are arranged to give a virtually monotonic
output to the counter. They are chosen to give powers of 2 reductions
from the Q4 output of IC6 (the most significant bit) right down to the
Q1 output of IC8(the least significant bit).
10.3.4 Raise/lower and Logic (IC3 to IC5, DN1,RL3 to RL5)
The digital reference described in the previous section needs to be
adjusted, while the unit in use , in several different ways. The
requirement of this logic function are as follow:
(1) While Operating in Auto
The auto-follower raise/lower output must function but will be
inhibited temporarily by the operation of the manual
raise/lower controls both remote and local. The auto-follower
output must also be inhibited by the operation of the MAVR
excitation limiter.
(2) Operating in manual
In this case the auto-follower output will be inhibited
completely and only the manual raise/lower controls both local
and remote will adjust the reference.
Note: Throughout the following description, the terms 'logic
1' and 'logic 0' will be used in the normal way but it must be
kept in mind that the actual voltages:
Logic 1 is 0V
Logic 0 is -6.2V
1) Reset Circuit
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IC5 (d) together with R37 and C31 are arranged such that as
the logic power rail establishes (as RL1 energized -see section 8.3.1)
the output of IC5 (d) will go to logic 1 for a short time before
dropping to and remaining at logic 0. This signal is connected to the
preset enable pins of the counter IC6 to IC8 and has the effect of
setting the counter to the state determined by its 'Jam' input, in this
case to full count which represents the minimum hand control
output.
2) Clock and Gate Circuit
IC5(c) generates a continuous train of clock pulses the
frequency of which is determined by C29, R70 and RV4. These
pulses are routed through the gate IC4 (d) to the clock input of the
counters IC6 to IC8. Pin 12 of IC4(d) gives control of the gate.
Logic 1 on this pin enable the gate and allows the clock pulses
through and logic 0 will prevent the passage of clock pulses.
3) Latch Circuit
IC5(a) and IC5(b) are arranged to give a latch circuit. The
output from this latch from pin 3 of IC5(a) is fed to the up/down
inputs of the counter IC6 to IC8.
The latch is such that a momentary logic 0 at pin 1 of IC5(a)
will give a logic 1 on the latch output and cause the counter to count
up. The latch output will remain in this state until a logic 0 is
momentarily applied to the other latch input on pin 6 of IC5 (b) in
which case the output will become logic 0 and cause the counter to
count down.
If a logic 0 input is applied to both inputs of the latch then the
output will be a logic 1 and give an up count on the counter.
R68 and R69 are pull-up resistors so that, in the absence of
inputs to the latch, both inputs are held at logic 1.
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4) Relay Buffers
Relay RL3,RL4 and RKL5, which are on the p.c. board, are
used as buffers between the external signals and the electronics.
They are energized from the auxiliary d.c. supply to the unit.
Provision is made with LK8 to LK13 for three d.c. supply voltages.
D.C.. SUPPLY FIT LINKS OMIT LINKS
125V +15%/-20% ----- LK8,9,10,11,12,13
48V +15%/-20% LK9,10,12 LK8,11,13
24V +15%/-20% LK8,11,13 LK9,10,12
Relay RL3 is energized from pin 12 on the PCB. When an
external 'lower' signal is given.
5) Raise/Lower and Inhibit Circuit
(1) Operation in Auto (Auto follower operation)
In the absence of any external raise or lower signals, the
output of both IC3(b) and IC3(c) will be at logic 1.
In auto RL3 will be de-energized unless the excitation limiter
operates, and the output of IC3(a) will be at logic 1. This
enables IC3(d) and IC4(a).
The output of the auto follower comparator at IC1(b) pin
1 is applied to the input of IC4(a) at pin 2. When the output of
the auto is most negative, the output of IC4(a) will be at logic 1.
This will produce a logic 0 output from IC3(d) resulting in
(i) a Logic 1 at the output of IC4(c) which enables the clock
gate.
(ii) The latch IC5(a) and (IC5(b)) gives an 'up' signal to the
counter.
If the output of the auto follower comparator is positive,
IC4(a) output will be logic 0 which will cause the latch to give a
'down' signal to the counter and again enable the lock gate via
IC4(b).
MAVR GENERAL PRINCIPLE OPERATION AND MAINTENANCE INSTUCTION C0NQ.140.297
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While operating in the auto follower mode as described
above, the counter is operating continuously and the up/down
signal is alternating every few clock pulses as the system keeps
the manual output matched to that of the MAVR. The slight
oscillation may be visible on the null balance meter.
Auto follower operation can be interrupted in several
ways:
(i) The counter may reach the fully down or fully up state. In
either case the 'carry out' pin 7 of IC6, goes to a logic 0 and,
via D23, clamps further clock pulses until released by the
up/down signal being reversed.
(ii) A MAVR limiter may operate or control may be
transferred to manual by a external signal.
(iii) An external (or logical) raise or lower signal RL4-1 or PB2
will close and IC3(c) will produce a logic 0 output which
disables IC3(d) and IC4(a) again inhibiting the auto
follower action. A lower signal produced the same effect via
IC3(b)
(2) Operation in Manual
As explained in (ii) above, relay RL3 will be energized
when operating in manual and the auto-follower action will be
inhibited. An external raise signal will energized RL4 and
RL4-1 will close producing a logic 0 at the output of IC3(c).
This will operate the latch (IC5(a) and IC5(b)) causing it to give
a down signal and at the same time, via IC4(b), enable the clock
gate. Clock pulses will continue to reduce the counter level until
the external raise signal is removed.
An external lower signal will energized RL5 and RL5-1 will
close. This produces a logic 0 at the output of IC3(b) which
operate the latch (IC5(a) and IC5(b) causing it to give a up
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signal and at the same time, via IC4(c) enable the clock gate.
Clock pulses will continue to increase the counter level until the
external lower signal is removed.
These raise and lower operations can be accomplished
locally by operating the pushbuttons on the PC board.
Simultaneous operation of raise and lower controls gives an
up count causing a reducing a reduction of manual output.
When the counter reaches fully up or fully down state, the
same process occurs as explained in 8.3.4. 5) (1) to inhibit
further clock pulses.
10.3.5 Auto Follower
IC1(a) is an amplifier the gain of which is adjustable using
potentiometer RV1. The input to this amplifier is supplied from the
MAVR output attenuated and filtered by R1,R2 and C3. The output,
Which is inverted, is fed via R6 to the inverting input of IC1(b).
The manual output, attenuated and filtered by R7, R8 and C4, is also
applied via R9 to the input of IC1(b). This amplifier is arranged as a
high gain inverting amplifier and acts as a comparator. The difference
between the auto and manual outputs thus appears at the output of
IOC1(b). This output is fed via R11 to IC4(a) where it provides the
raise/lower signal for the digital reference.
Two controls are provided to set up the balance between the
outputs of the AVR and manual regulator. RV1 adjusts the gain IC1(a)
and is used to compensate for component tolerances in the attenuation
circuits. RV2 can be used to give a constant negative bleed to the input
of IC1(b)
which is adjustable, and in most applications will be set to minimum, or
close to minimum.
10.3.6 Null Balance Detector (IC1 (c), IC1(d) etc.)
IC1(c) is arranged as a low gain, inverting amplifier which is
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supplied from the auto output after attenuating and filtering with
R18,19 and 20 and C23. The inverted output is fed via R23 to the input
of IC1 (d). The manual output after attenuation and filtering with
R24,R25,R26 and C25 is also fed to the input of IC1 (d) which is
arranged as a high gain inverting amplifier. IC1(c) and (d) are
analogous in operation to IC1(a) and (b) in the auto follower circuit but
the output of IC1 (d) supplies via R28, an external center zero
millimeter. This instrument must be a moving coil type with a sensitivity
of 0.5 – 0 – 0.5 mA.
As described in Section 10.3.5, potentiometers RV3 and RV2 are
used to achieve satisfactory balance throughout the working range of
the unit.
10.3.7 Minimum Position Indicator (IC9 VT3 VT4 RL2 etc.)
This circuit gives a relay output signal and local LED indication
when the manual output is at the minimum level.
The eight most significant of the twelve outputs from the digital
reference are taken to an eight input and gate IC9. When all eight
inputs are at logic 1 then the reference counter is virtually at the
minimum position and the output of IC9 will be at logic 0.This will turn
or transistor VT4 via VT3. LED1 and RL2 will be energized given local
and remote indication that the reference is at the minimum position.
R99, R100 and C32 provide a signal to VT3 base, which is proportional
to the output of the manual regulator. This ensures that minimum
position indication is only given when the digital reference and the
manual regulator output voltage are at minimum.
10.3.8 Field Suppression
Incorporated in the rack is a block contactor (FSC) and a resistor
(FSR) used for suppression of the exciter field. Three contacts of FSC in
series are used, each of these contacts having a section of FSC connected
across it.
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As these contacts open to suppress the field, the current flows
through the resistor FSR giving rapid decay of exciter filed current. A
fourth contact of FSC is used to break the A.C supply from the
PMG.
The contactor is mechanically latched so that a failure in the coil
supply will not product any change in the contactor state.
When the contactor is in the tripped condition, (recognized by the
button on the latching mechanism being ‘in’ ) the field is suppressed.
10.3.9 Smooth Transfer
As described in the previous sections, the auto follower action
ensures a smooth transfer from auto to manual but smooth transfer
from manual to auto is not provided as standard. However it can be
achieved as follows:
When operating in manual control, contact ECC-7 is open to
remove the PMG supply to the MAVR power circuit. (The MAVR
electronics supply is remains energized via terminals 3/6 and 1/11).
To obtain smooth transfer, a switch (arranged with a spring
return to open mechanism) should be connected between terminals 26
and 27 on the unit. When the switch is closed , the supply is restored to
the MAVR power circuit and the AVR output will be present at terminal
25 on the unit.
The null balance indication facility will now operate although
when operating in manual control , the indicator will invariably settle at
either end of the indicator scale.
To transfer from manual to auto with minimum shock the MAVR
datum should be adjusted to correspond to the generator or bus bar
voltage. At this point, the null balance indicator reading will suddenly
reverse. By making slight adjustments to the AVR datum and observing
the null balance indicator it is possible to confirm that the AVR and
manual regulator are set to give the same output voltage at this point
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transfer to the AVR will be achieved with minimum system shock.
10.4 COMMISSIONING
This section should be read in conjunction with the general
commissioning procedure, section 11.
10.4.1 Preliminary Tests
1) Remove front cover of auxiliary rack and retain for subsequent
replacement.
Check that the correct links are fitted by reference to ‘ The Setting
Record of MAVR Testing with Test Generator’ item 6.
2) Care should be taken before connecting any supplies to ensure that
all the connection to the unit and MAVR are correct by reference to
the contract schematic diagram. The polarity of the D.C supply
should also be checked.
3) Connect the D.C supply to the excitation system.
4) Operate the manual/auto switch (local and remote). When
‘manual’ is selected the button on the latch of ECC should be
‘out’ and relay ECCS should be energized and its indicator ‘ON’ –
when ‘auto’ is selected the ECC latch button should be ‘IN’ and
relay ECCS should be de energized and its indicator ‘OFF’. Check
that any external indication of excitation mode are correct.
5) Operate the protection relay or arrange by temporary wiring to
provide ‘Excitation ON’ and ‘Excitation Trip’ signals. When
excitation is ‘on’ the button on the latch of FSC should be ‘OUT’
and relay FSCS should be energized and its indicator ‘ON’. When
excitation is tripped the FSC latch button should be ‘IN’ and FSCS
should be de energized, its indicator off.
While carrying out these tests check the operation of local and
remote excitation ON/OFF indications.
6) With the excitation mode switch in ‘Manual’ use AVO meter or
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equivalent to check that the ‘Transfer’ Switch (if fitted) is correctly
connected in that rack terminals 26 and 27 are linked only when
the switch is operated.
7) Operate the manual raise/lower switch and check with an AVO set
to the appropriate D.C. voltage range, that with respect to terminal
2 (-ve) terminal 11 is (+ve) when a ‘raise, signal is given, and that
terminal 12 is (+ve) when a ‘lower’ signal is given.
10.4.2 Manual Control
1) Remove and isolate the exciter field connections from the MAVR
and the MAVR auxiliary rack. These are :
(1) The positive connection at terminal 5 on the M.A.V.R.
auxiliary rack.
(2) The negative connection at terminal 1/14 on the multi core
connection terminals of the auxiliary rack.
2) Connect an AVO or similar suitable meter set to 100V D.C. range,
positive to terminal 5, negative to terminal 1/14. By operating the
excitation mode switch select the ‘Manual’ mode (ECCS energized
and check that) FSC is in the ‘ excitation ON’ state (FSCS
energized).Turn the excitation off using the switch in the PMG
supply.
3) Run the generator up to rated speed and by using the switch in the
PMG supply switch the excitation on. The output voltage on the
AVO meter should be zero and local (LED on P.C. board) and
remote indication of ‘manual at minimum ‘ should be given.
4) By operating the manual raise / lower control switch check that the
output voltage can be adjusted from zero to a level at least equal to
the full load exciter field voltage.
The generator output voltage during this test should remain low at
the residual level since the exciter field is disconnected.
5) With the output at 30 volts switch the excitation off using the PMG
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supply switch and check that the output is reduced to zero. Check
that when the PMG supply switch is switched ON the output
remain at zero.
Turn the switch to OFF.
6) Shut down the generator and replace the field connections removed
in 1) above .Run the generator up to speed, turn the excitation on ,
and check that smooth control of the generator output voltage is
obtained using the manual raise / lower switch.
Proceed with section 10.4.3 following commissioning of the MAVR.
10.4.3 Final Commissioning (To be completed following commissioning of
MAVR.)
1) Smooth Transfer Auto to Manual
Run the generator at rated speed and rated voltage in auto control.
Take a careful note of the line voltage. Use the excitation mode
switch to transfer to manual. Note the new line voltage and if
necessary adjust RV1 on the MAVR auxiliary rack P.C. board.
Slightly to reduce the auto / manual line voltage difference.
Clockwise adjustment of RV1 increases the manual output and vice
versa. RV2 is normally set fully anti-clockwise.
Switch control between manual and auto, and optimize RV1 to
produce minimum change in line voltage when switching between
both mode of control.
Select ‘auto’ and adjust RV3 as necessary to obtain zero (mid scale)
reading on the null balance meter.
Run in AVR control.
Load the generator either individually or by paralleling to a larger
system.
Check that as excitation changes, the null balance indicator is
maintained at the zero position. If necessary, operate the voltage
setting control on the MAVR to vary the VAR’ s, to confirm the auto
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follower action.
Select manual control and check that there minimum change in
excitation on switching from Auto to Manual.
To obtain smooth transfer from manual to auto, the procedure
described in 2) should be followed.
2) Smooth Transfer Manual to Auto.
This may be achieved by using a smooth transfer switch which
should be connected between terminals 26 and 27 on the auxiliary
rack . The switch must be arranged so that it is spring loaded to the
open state.
The following sequence should be carried out starting in manual
control:
(1) Check that the machine line voltage is within 5% of nominal.
(2) Turn the motorized voltage setting rheostat (MVSR) on MAVR
fully anti- clockwise.
(3) The null balance meter should read fully to right or left. Note
its position.
(4) Close the smooth transfer switch and hold it closed.
(5) Slowly increase MAVR until the reading on the null balance
meter suddenly reverses. Then adjust MVSR until the null
balance meter reading is zero.
(6) Select auto control and release the smooth transfer switch.
Excitation will be change from ‘Manual’ to ‘Auto’ smoothly.
10.5 FAULT FINDING PROCEDURE
Before attempting to trace suspected faults on the M.A.V.R.
auxiliaries
rack, the basic tests outlined on section 13.should be followed. In
the event of the auxiliary equipment rack being suspected faulty, the
following tables should assist in locating the fault and effecting a
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remedy.
The faults full generally into three categories:
Contactor and Relay faults Table 10.5.1
Faults occurring when in manual control Table 10.5.2
Fault associated with the Auto Follower and Table 10.5.3
Null Balance indicator.
10.5.1 CONTACTOR AND RELAY FAULTS
No. Symptom Check Remedial Action
1) FSC closed (button
on latching unit
OUT FSC closed)
If closed check all field
circuit wiring. If not
closed perform 2). 3).
4). 5).
2) Check PMG fuses and
links in pilot exciter
terminal box
Replace if necessary
3) D.C supply to terminal
1 (+ve) and 2
Ensure supply present
and correct voltage.
4) D.C fuses FS1 &FS2 Replace if blown
5)FSC control switches
or contacts
Correct as necessary
1. Cannot
Excite machine
on manual or
auto.
6) Check FSC latches
closed when close signal
given
If D.C. volts applied to
close coil of contact,
contactor should close
& lated. If not-
contactor is faulty
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2. Excitation
will not trip
1).Volts applied to FSC
trip coil when trip signal
given.
If correct volts present
and contactor does not
trip (button on latching
unit goes IN).
Contactor is faulty .If
volts not
present ,perform
checks 10.5.1 1. 3). 4).
5).
1).ECC latches closed
when manual select
switches operated
2). As 10.5.1 1. 3). 4).
3). Check ECC control
switches / contacts
If ECC closes check
wiring in rack
associated with manual
power circuit.
3.Cannot select
Manual
4).Check ECC latches
closed when manual
select switch operated.
If D.C volts applied to
close coil of contactor it
should close & latch .If
not- contactor is faulty.
1). Check MAVR
monitors are reset
Reset monitors before
attempting to select
Auto.
4. Cannot
select Auto
2). Check ECC latches
open when Auto select
switch operated.
If D.C. volts applied to
trip coil of contactor it
should trip. Ensure
that continuous
Manual select signal
not being given.
1).Check FRS energizes
when fault monitor
operates.
5. Manual not
selected when
MAVR fault
Monitor
operates.
2). Check FRS-1 ECC-6
circuit.
Check wiring from
MAVR to FRS
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1).ECCS energizes when
manual selected
6. Auto
follower not
inhibited when
in manual.
2). ECCS-3 closes to
apply +ve D.C to
energized RL3 on P.C.
board.
Check & rectify wiring
as necessary
1). Ensure LRS
energized when MAVR
limiter operates.
7.Auto follower
not inhibited
when MAVR
limiters
operate.
2) Ensure LRS-1 closes
to apply +ve D.C. to
energize RL3 on P.C
board.
Rectify as necessary
10.5.2 FAULTS OCCURRING WHEN IN MANUAL CONTROL
No. Symptom Check Remedial Action
1). Check correct links
fitted.
Alter if necessary.
2). Check semiconductor
fuse FS3 in rack.
Replace if
necessary
3). Check fuse FS1 on P.C
board.
Replace if
necessary
4). Check ECC energized,
the button on the
contactor being ‘OUT’.
Check contactor
control wiring.
1. Zero output.
5). Check FSC closed, the
button on the contactor
being ‘OUT’
Check contactor
control wiring
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6). Operate raise PB2 on
P.C board
If this produces
output, check
remote raise switch
wiring energizes
RL4 on P.C board.
Rectify as
necessary.
7). Check remote switches
not giving permanent
lower signal.
Rectify if necessary.
8). Test thyristor ref.
Section 5.4.
Replace if
necessary.
1). Check that local
adjustment operates.
If local adjustment
operational check
remote control
switches energize
RL4 (raise) and
RL5 (lower) on P.C
board. Rectify as
necessary.
2. Remote
adjustment
non-operational.
2). Check voltage selector
links.
Rectify if necessary.
1). Test thyristor ref.
Section 5.4
Replace if
necessary.
3. Excitation flat
out.
2). Check LED 1 come on
when unit is switched on
indicating ‘Manual reset
to minimum’
If not, P.C board
faulty .Fit
replacement.
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3)Check continuous raise
signal is not being given
by remote switches
causing RL4 on P.C
board to be continuously
energized.
Rectify wiring if
necessary.
4. Cannot obtain
full load
excitation.
1).Check that link 7 is
fitted.
Lower output if
fitted.
1). Check exciter field
voltage is constant. If this
is so line volts fluctuating
will be due to speed or
load variation.
5. Line voltage
fluctuates when on
manual control.
2). Check all wiring is
sound no loose
connections.
Replace as
necessary.
10.5.3 AUTO FOLLOWER FAULTS
No. Symptom Check Remedial Action
1. Line voltage
changes following
transfer to manual
at light loal.
1). Check load steady and
that null balance
indicator is stationary
prior to transfer.
Refer to section
10.4.3. 1). to set up
RV1 on P.C .board.
1). Check load steady and
that null balance
indicator is stationary
prior to transfer.
2. Line voltage
changes following
transfer to manual
when load.
2).Check RV2 fully
anti-clockwise.
Reset and repeat
10.4.3. 1). If
necessary.
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3). Check whether voltage
change gets worse when
transferring to manual at
hight loads.
Rotate RV2 on P.C.
board 10%
clockwise then
reset RV1 to give
minimum voltage
change on transfer
to manual. Increase
setting of RV2 to
improve further if
necessary.
3. Null balance
indicator not at
zero when output
of manual
controller
matched to output
of AVR.
1).Set up RV3 on P.C.
board.
Refer to 10.4.3. 1).
10.6. CONSTRUCTION TRANSPORT AND INSTALLATION
10.6.1 CONSTRCTION
The unit is housed in a standard equipment rack 19” wide. See
drawing C11-1. All equipment is mounted on a steel back plate and an
anodized aluminium plate provides the front cover of the unit.
Perforated metal cover are fitted to the top and bottom of the unit.
Two rows of terminals type D1 are fitted to the rear panel which
are suitable for cables up to 6 mm2.
These terminals are for M.A.V.R. multi core terminations and
other connections to excitation system.
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10.6.2 INSTALLATION
The unit any be installed in a cubicle directly above or below its
associated M.A.V.R. unit.
It is recommended that at least 150mm of free space is provided
above and below the unit, or if mounted with the M.A.V.R., above and
below the pair of units. This is necessary to provide adequate air
circulation for cooling. It must be noted when installing that the multi
core between M.A.V.R. and rack is 3m long.
10.6.3 TRANSPORT
If the cubicle is to be transported with the rack installed; the rack
should be supported underneath to relieve the stress on the mounting
flanges. It may be seperately packed for transportation.
10.6.4 WEIGHT
The complete unit weight 17kg.
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11 COMMISSIONING
11.1 GENERAL
Prior to commissioning the M.A.V.R. unit it is important to
complete commissioning of the protection system for generator and
associated power equipment. Having verified that these are correct the
following preliminary checks should be made on the excitation system:
1) Check the PMG output or alternatively the excitation transformer
is correct wired.
2) Check the sensing signals (C.T’ s and P.T’ S) are correct in polarity
and phasing.
3) Check the exciter field is correctly wired.
4) Check all wiring external to the M.A.V.R. is correct to the contract
circuit diagram, and sound.
5) Check excitation contactors, logic, manual control and any other
auxiliary equipment have not been disturbed in transit and that
wiring is sound.
6) Visually check the M.A.V.R. unit has not been physically damage on
transit to site, ensure that outgoing plug in cards are correctly
aligned and inserted fully.
7) Check that the correct links are fitted in the M.AV.R. unit as
detailed in the setting record for M.A.V.R. Testing With Generator
sub- section 6.
11.2 THE MAVR UNIT IS THEN READY FOR
COMMISSIONING
11.2.1 COMMISSIONING A SINGLE EXCITATION SYSTEM WITH
M.A.V.R AUXILIARY RACK (ELECTION MANUAL CONTROL)
1) With the generator at standard, complete the following section:
(1) 3.3 Commissioning of the MAVR mainframe.
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(2) 5.3 Commissioning of the Auto Power Card.
(3) 10.4.1 Preliminary Commissioning of the MAVR Auxiliary
Rack.
3) Commissioning the manual control of MAVR Auxiliary rack as
described in section 10.4.
4) Commissioning MAVR Control card, section 4.3.
5) Commissioning MAVR Excitation Limiter Card, section 6.3.
6) Commissioning MAVR Power Factor Control Card, section 7.3.
7) Commissioning MAVR Auxiliary Rack, section 10.4.
8) Having complete all the appropriate sections above a final check
should be made to ensure that all external controls and indication
function correctly.
Note: The above procedure must be followed during
commissioning.
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12 FAULTY FINDING
12.1 GENERAL
If a MAVR unit does not function correctly, a test sequence is
recommended in which the generator and external wiring are first
thoroughly checked before it is assumed that the fault lies in the
electronic equipment .The fault finding procedure is designed to enable
faults to be found quickly. It is essential, therefore, to follow the order in
which they are presented. In the event of finding a fault on any part of
the MAVR the company strongly recommends that no attempt is made
to repair the unit, but is replaced by a spare which should be
re-commissioned according to the relevant section of this handbook.
The fault unit should be returned to the Works for repair.
12.2 PRECAUTIONS
Meggers Flash Testers and Bell Sets must not be used to check any
equipment connected to or incorporating semiconductor.
If these instruments are to be used to check any equipment,
isolation from all semiconductor devices must first be ensured. In the
case of the MAVR either remove all the plug in multi cores from the
rack or short together all the individual cores of all the multi cores.
When the MAVR auxiliary rack is fitted , it is recommended that ,
when on site flash testing is required ,all outgoing cables are
disconnected and the terminals at the rear of are linked together prior
to flash testing.
12.3 PROCEDURE
Before commencing fault finding on the MAVR unit the following
preliminary checks should be carried out.
1) Check correct operation of the generator, i.e. PMG output available
( if applicable ), the field and sensing signals are correct etc.
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2) Check all wiring associated with the excitation system.
3) Check all contactors switches and other external components
associated with the MAVR rack(s) or plate.
4) Check that the correct links are fitted in the MAVR unit as detailed
in the test record ‘MAVR Tests with Test Generator ’ sub-section 6.
Having completed these preliminary checks the fault can be
assumed to be internal to the MAVR unit. In this event the nature
of the fault will generally fall into one of the following categories:
(1) Loss of excitation in ‘manual’ control: for rack mounted
auxiliaries with electronic manual control. (see Table 10.5.2)
(2) Over excitation in ‘manual’ control: for rack mounted
auxiliaries with electronic manual control. (see Table 10.5.2)
(3) Excitation fluctuates in manual control: for rack mounted
auxiliaries with electronic manual control. (see Table 10.5.2)
(4) Loss of excitation in ‘auto’ control. (see Table 12.3)
(5) Over excitation in ‘auto’ control. (see Table 12.3)
(6) Instability (see Table 12.3)
(7) Parallel operation instability (see Table 12.3)
(8) Limiter mal operation (see Table 12.3)
(9) VAR control mal operation (see Table 12.3)
(10) Monitor mal operation (see Table 12.3)
(11) General system operation faults (see Table 12.3)
Each category has an associated table which details the
appropriate action to be taken, cross referring to the individual
MAVR unit fault finding sections. By following the sequence
through the source of the fault should be located and the cause
remedied.
In the event of the fault not being located, or in cases of
difficulty or doubt, contact:
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Table 12.3.1 Loss of Excitation in ‘Auto’ Control
No. Check Remedial Action
1. PMG output to MAVR input
(1/3 to1/7 )should be 220V A.C
Correct wiring, excitation
switch or blown fuse as
necessary
2. MAVR output voltage present
at 1/1 and 1/10.
1) Auto power card fault
–see section 5.
2) Control card fault –see
section 4.
3) Mainframe fault –see
section 3.
3. Field current flows when
MAVR field output high
Correct field circuit
connection
4. Check generator Possible rotating diode
failure or open circuit field.
Table 12.3.2 Over Excitation in ‘Auto’ Control
No. Check Remedial Action
1. Check sensing voltage to
MAVR nominally 105V A.C
Correct as necessary
2. Check FS3,4 on MAVR ( i.e.
sensing fuses )
Replace blown fuses
3. Check ‘Auto’ control
components
1) Auto Power card fault -see
section 5.
2) Control card fault –
section 4.
3) Mainframe fault – see
section 3.
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Table 12.3.3 Instability – Single Running
No. Check Remedial Action
1. Check if unstable on manual
control (Electronic manual
system).
Refer to table 10.2.
2. If unstable in auto control
check stabilizing setting.
If stability cannot be reset
satisfactorily then control
card fault – see section 4.4 or
mainframe fault –see section
3.4
Table 12.3.4 Parallel Operation Instability
No. Check Remedial Action
1. Check C.T &P.T phasing. Correct as necessary.
2. Check correct mode links
selected i.e. ‘Q.C.C’ or ‘Line
Drop Comp.’
Correct as necessary.
3. Correct control card and
mainframe.
Control card – see section 4.4
and mainframe – see section
3.4.
4. Check that machine running
within the limits of the
operating chart.
Refer to section 3.4, 6.4, 10.4
and re-adjust if necessary
5. Check stability setting of
limiters
6. Check stability on manual
control.
Refer to section 10. If
electronic manual fitted.
.
Table 12.3.5 Limiter Mal-operation
No. Check Remedial Action
1. Check limiter settings. See section 6.3
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2. Check limiter setting are
consistent with the site re-
quirements.
Confirm with the Works any
revised setting and adjust as
in section 6.3.
3. On a twin system check the
‘smooth changeover’ logic if
over excitation faulty.
Correct as necessary.
4. Check C.T & P.T phasing if
‘Under Excitation’ mal
operating.
Correct as necessary.
5. Check external field current
pick-up signal if ‘Over
Excitation ‘ mal operating –
Direct excitation system only.
Correct as necessary.
6. Check limiter card and
mainframe.
Excitation limiter card – see
section 6.4. Mainframe – see
section 3.4.
Table 12.3.6 VAR Control Mal-operation
No Check Remedial Action
1. Check C.T &P.T phasing Correct as necessary.
2. Check Q.C.C setting on
control.
Adjust if necessary – see
section 2.3
3. With P.F. Control card –
check the auxiliary D.C
supply and PFC latching path
to the MAVR.
Correct as necessary.
4. Check the ‘slug’ and ‘gain’
stabilizing settings of the P.F
Control card.
P.F Control card – see section
7.3
5 On twin system check the
‘smooth changeover’ logic.
Correct as necessary.
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6. Check P.F. Control card P.F. Control card – see
section 7.4
7. Check system voltage is within
±10% of the AVR set point.
Correct on volts settings/
Q.C.C controls if necessary.
Table 12.3.7 Monitor Mal-operation
No. Check . Remedial Action
1. Check monitor settings Voltage Monitor – see section
9.3. Excitation Monitor -
see 8.3.
2. Check monitor settings are
consistent with the site
requirements.
Confirm with the Works any
revised settings and adjust as
in section 9.3 voltage monitor
and 8.3 excitation monitor.
3. Check external override logic
if monitor inoperative.
Correct as necessary.
4. Check external field current
pick-up signal if ‘Over
Excitation’ mal operating –
direct excitation system only.
Correct as necessary.
5. Check C.T & P.T phasing if
‘Under Excitation’ mal
operating.
Correct as necessary.
6. Check monitor cards and
mainframe.
Excitation Monitor card – see
section 8.4. and Voltage
Monitor card – see section
9.4 and see mainframe – see
section 2.4.
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Table 12.3.8 General System Operation Faults
No. System Check Remedial Action
1. System
response
unsatisfactory.
Check control card
stability settings.
Reset controls – see
section 4.4.
2.Excessive
overshoot on
build-up.
Check FAC auxiliary
contact between 2/5 and
2/11.
Correct as necessary.
3.On-load
response
sluggish.
‘If limit’ set too low or
stabilizing too slugged.
See section 4.4
4.Generator
VAR capability
too limited.
Check limiter settings. See section 6.3
5. Single running
voltage droop
excessive.
Excessive Q.C.C Reset Q.C.C as in 4.3
6. Monitor
operation with
voltage or load
transients
Check monitor delays. Reset delay : Voltage
monitor – 9.3
Excitation monitor –
8.3.
7. Monitor
operation before
limiter
operation.
Check relative levels and
delays.
Reset as necessary :
Excitation limiter –
5.3
Excitation Monitor –
6.3
8. VAR control
range limited.
Check system droop is
not greater than 10%.
If less than 10% then
P.F control card is
fault see 7.4.
9.Line volts /
VAR’ s change
excessively.
Check setting up of
balance and offset
controls
Refer to section
12.3.4.
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1).Check voltage
matching between units.
Reset as necessary as
in 4.3
2) Check smooth
changeover logic if
occurring on Excitation
limiter operation.
Correct as necessary.
3). Check operating
levels of Excitation
limiters if occurring
when in operation.
Correct as necessary.
Excitation limiter –
5.3
10. Excessive
shock on
transfer between
AVR’ s on a twin
system.
4). Check auxiliary
supply of standby AVR is
present prior to
changeover.
Correct as necessary.
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13 INSTALATION AND MANTENCE
13.1 MECHANICAL DATAILS
The overall dimension of MAVR and Auxiliary rack are given in
fig 13-1 & fig 13-2 and they are designed for front panel mounting. The
mainframe is aluminium construction with a smoked ‘perspex’ door
hinged on the left hand side. Access to the with draw able cards is by
turning the quarter-turn fastener anti-clockwise and opening the door.
This then reveals the fixed front panel and with draw able cards, the
latter also being secured by quarter-turn fasteners. The fixed front
panel, on the left hand side, caries the fuses and motorized voltage
setting potentiometer (if applicable) and is not intended the
quarter-turn fastener anti-clockwise and pulling the card out. The auto
power card may be damaged if with drawn from the unit whilst the
card is supplying excitation and replacing electronic plug-in cards. To
replace a card first turn the quarter-turn fastener fully anti-clockwise
until tight. For commissioning purpose an extender card and plug onto
the required card and replace the whole into the appropriate card
socket.
The outgoing terminating of the MAVR unit are by up to 4 rear
mounted plugs / sockets to 3 meter of 15 way multi core. To enable a
sound earth to be made to the MAVR mainframe an earthing stud is
also made on the back of the unit.
There are two lines of terminal on the rear of AUX. Rack . One is
designed for connection with cable between MAVR and AUX. Rack.
Anther is used for the outgoing terminations of MAVR unit. An
earthing stud is also made on the rear of AUX. Rack.
The weight of MAVR and AUX. Rack is 17 kg respectively.
13.2 INSTALLATION
The MAVR unit is primarily designed for mounting into any
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sturdy panel with a suitable cut-out. It is strongly recommended that
where the unit is to be fitted a cut-out that some form of vertical
stiffening is incorporated behind the panel at each side of the cut-out to
support the cantilevered weight of the unit. The unit also can be
mounted on other appropriated place. It is recommended that at least
150mm above and free space is provided between the main and
Auxiliary racks to provide adequate air circulation for cooling when
packed together. The two units can also be mounted separately.
However, a free space at least 150mm above and below the unit is also
recommended to provide for cooling. The four (or less) multi cores used
interconnect the MAVR unit with the external panel of the excitation
system must have each core individually terminated at a terminal block
whether they are or not. To avoid the eventuality of the outgoing sockets
vibrating loose or being inadvertently pulled loose the retainer should
be pulled over the socket hoods. The 3 meter length of multi cores
should not be shortened excessively as a sufficient length of ‘ free’ multi
core should be left to allow the rack to be with draw prior to the multi
cores being disconnected. As the individual cores of the multi core each
indelibly marked (numbered 1to 15 by words and numerals), if they are
shorted the identification is not lost. If required the earth wire should
be run from the MAVR back mounted stud, with the multi cores to the
earthing bar.
13.3 MAINTENANCE
The MAVR unit is essential completely static apart from the relays,
push buttons and motorized voltage setting potentiometer, and as such
requires very little maintenance.
Every six mouths or during routine station maintenance periods
remove the MAVR unit and visually inspect that it is free of dust and
any other debris In particular check that the motorized voltage setting
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potentiometer, associated limit switch and back panel plug-in relays are
function correctly. In the event of excessive dust build-up it should be
carefully removed using a soft brush.
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14 OPERATION
After all commissioning procedure of Mainframe and Auxiliary
Rack have been finished and all Parameters have been set. M.A.V.R
may be operated with a Generator.
14.1 EXCITATION SYSTEM COMMISSION AND OPERATION
14.1.1 Confirm that system is either in constant power factor control or in
constant reactive current control prior to commission. In general the
constant power factor control is selected . However if the capacity of the
grid is small or large VAR is needed. The constant reactive current
control, LK4,LK1 should be omitted with LK2 ,LK3 fitted. If neither of
the control modes is selected .Power factor controller should be latched
during operation.
If the generator is running in single or a few Generators, similar in
capacity, running in parallel. The power factor controller should be
latch.
NOTE: When the N /O contactors of Auxiliary relay ZJ1, connected
between multi cores 2/1 and 2/5 are used for parallel operation, with
circuit breaker closed , multi cores 2/1 and 2/5 will be short- circuited.
Then the power factor control card will go in operation. If no N/O
contactors are used, the power factor control card will not be selected.
14.1.2 Operate “ Auto Excitation” control switch SW4 and set MVSR to preset
level position.
14.1.3 Turn “ Excitation Selector” switch SW1 to “Auto” ,and set the Single /
parallel running control switch SW5 to appropriate position.
14.1.4 There are two mode for Generator voltage build up.
1) Switch on the excitation control switch SW3 as the Generator runs
up to its rated speed, voltage will build up with speed rising . When
the Generator is up to 85% rated speed, voltage reaches its set
voltage.
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2) Run the Generator up rated speed. Then switch on SW3 voltage
will build up quickly with overshoot less than 5% of rated voltage.
14.1.5 After Generator voltage has build-up, use “Automatic Synchronizing
Unit ” or “Hand synchronizing Unit” to hook up the Generator to grid.
14.1.6 When the Generator is running in parallel the set value of power factor
(or VAR power) can be adjusted by ‘level’ potentiometer power factor
control card front panel. Care must be taken that in constant power
factor control the set power factor should not exceed the that on the
Generator name plate; While in constant reactive current control, it
should ensure the Generator not to be overloaded at rated output.
If the power factor control card is switch out of operation, adjusting
MVSR can b change the power factor or reactive current of the
Generator.
14.1.7 Two ways to transfer ‘Auto’ to ‘Manual’ during operation:
1) If power supply fails or Monitors relay operates, ‘Auto’
automatically transfer to ‘Manual’.
2) ‘Auto’ can be manually transferred to ‘Manual’ by turning SW1
(Excitation Mode Selector Switch) to ‘ Manual’.
14.1.8 In ‘Manual’ mode the Generator operation can be controlled by
operating ‘Manual Excitation’ control switch.
NOTE: In ‘Manual mode, the hand of the Null Balance Meter will not
be at the center.
14.1.9 Procedures to transfer ‘Manual’ to ‘Auto’ are as follows:
Push hold button YA operate SW4 (Auto Excitation Switch) to change
MAVR output till the Null Balance Meter AT ZERO, TURN sw1 TO
‘Auto’. Then release button YA.
14.2 FIELD SUPPRESSION
14.2.1 When the Generator is not running properly, output relay on the
Generator panel will operate and ECC contactor trips to suppress the
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magnetic field of the Generator automatically.
14.2.2 Two ways can be followed to suppress the field for Generator running
in parallel:
1) When the P.F. control is selected and before the Generator is cut off
from grid, energize Auxiliary ZJ2 relay to close the N/O contactors
connected between the multi core 2/3 and 2/5 .In about 30 seconds
M.A.V.R will reduce Generator VAR to 0 automatically. Then the
Generator can be cut off from grid automatically. Switch off SW3
for field- suppression.
2) Manually adjust voltage setting potentiometer (MVSR) or ‘Manual
Excitation’ control switch SW2 to reduce VAR to 0 (the active
power should be 0 preferably). Then open the Main Breaker to cut
the Generator off the grid. Switch off the SW3 for field suppression.
14.2.3 For single running Generator, switch off SW3 for field suppression,
when the Generator has been unloaded.
14.2.4 After field suppression, the Motorize Voltage Setting Potentiometer
(MVSR) should be turn to zero position (i.e. at 12 o’clock position) to
prepare for the next starting.
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