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15.10 NUMERICAL BUSBAR PROTECTION

SCHEMES

The application of numerical relay technology to busbar

protection has lagged behind that of other protection

functions. Static technology is still usual for such

schemes, but numerical technology is now readily

available. The very latest developments in the

technology are included, such as extensive use of a data

bus to link the various units involved, and fault tolerance

against loss of a particular link by providing multiple

communications paths. The development process hasbeen very rigorous, because the requirements for busbar

protection in respect of immunity to maloperation are

very high.

The philosophy adopted is one of distributed processing of

the measured values, as shown in Figure 15.20. Feeders

each have their own processing unit, which collects

together information on the state of the feeder (currents,

voltages, CB and isolator status, etc.) and communicates

it over high-speed fibre-optic data links to a central unit.

For large substations, more than one central unit may be

used, while in the case of small installations, all of theunits can be co-located, leading to the appearance of a

traditional centralised architecture.

For simple feeders, interface units at a bay may be used

with the data transmitted to a single centrally

located peripheral unit. The central unit performs the

calculations required for the protection functions.

Available protection functions are:

a. protection

b. backup overcurrent protection

c. breaker failure

d. dead zone protection

In addition, monitoring functions such as CB and isolator

monitoring, disturbance recording and transformersupervision are provided.

Because of the distributed topology used,

synchronisation of the measurements taken by theperipheral units is of vital importance. A high stability

numerically-controlled oscillator is fitted in each of the

central and peripheral units, with time synchronisation

between them. In the event of loss of thesynchronisation signal, the high stability of the oscillatorin the affected feeder unit(s) enables processing of the

incoming data to continue without significant errors

until synchronisation can be restored.

The peripheral units have responsibility for collecting the

required data, such as voltages and currents, and

processing it into digital form for onwards transmissionto the central unit. Modelling of the CT response is

included, to eliminate errors caused by effects such as CTsaturation. Disturbance recording for the monitored

feeder is implemented, for later download as required.

Because each peripheral unit is concerned only with anindividual feeder, the protection algorithms must reside

in the central unit.

The differential protection algorithm can be much more

sophisticated than with earlier technology, due to

improvements in processing power. In addition tocalculating the sum of the measured currents, the

algorithm can also evaluate differences betweensuccessive current samples, since a large change above a

threshold may indicate a fault the threshold being

chosen such that normal load changes, apart from inrushconditions do not exceed the threshold. The same

15

BusbarProt

ection

N e t w o r k P r o t e c t i o n & A u t o m a t i o n G u i d e 2 5 1

Figure 15.20: Architecture for numerical protection scheme

Personal

Computer

PU

CT

CBPU CB

CT

PU CB

CT

Feeder 1 Feeder 2

CU

Central Unit

PU

Fibre optic link

System Communication Network

PU: Peripheral Unit

CU: Central Unit

CB

CT

Chap15-232-253 17/06/02 9:54 Page 251

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considerations can also be applied to the phase angles ofcurrents, and incremental changes in them.

One advantage gained from the use of numericaltechnology is the ability to easily re-configure theprotection to cater for changes in configuration of thesubstation. For example, addition of an extra feeder

involves the addition of an extra peripheral unit, thefibre-optic connection to the central unit and entry viathe MMI of the new configuration into the central unit.Figure 15.21 illustrates the latest numerical technologyemployed.

15.10.1 Reliability Considerations

In considering the introduction of numerical busbarprotection schemes, users have been concerned withreliability issues such as security and availability.Conventional high impedance schemes have been one of

the main protection schemes used for busbar protection.The basic measuring element is simple in concept andhas few components. Calculation of stability limits andother setting parameters is straightforward and schemeperformance can be predicted without the need forcostly testing. Practically, high impedance schemes haveproved to be a very reliable form of protection.

In contrast, modern numerical schemes are morecomplex with a much greater range of facilities and amuch high component count. Based on low impedancebias techniques, and with a greater range of facilities toset, setting calculations can also be more complex.

However, studies of the comparative reliability of

conventional high impedance schemes and modernnumerical schemes have shown that assessing relativereliability is not quite so simple as it might appear. Thenumerical scheme has two advantages over its oldercounterpart:

a. there is a reduction in the number of externalcomponents such as switching and other auxiliaryrelays, many of the functions of which areperformed internally within the softwarealgorithms

b. numerical schemes include sophisticatedmonitoring features which provide alarm facilities

if the scheme is faulty. In certain cases, simulationof the scheme functions can be performed on linefrom the CT inputs through to the tripping outputsand thus scheme functions can be checked on aregular basis to ensure a full operational mode isavailable at all times

Reliability analyses using fault tree analysis methodshave examined issues of dependability (e.g. the ability tooperate when required) and security (e.g. the ability notto provide spurious/indiscriminate operation). Theseanalyses have shown that:

a. dependability of numerical schemes is better thanconventional high impedance schemes

b. security of numerical and conventional highimpedance schemes are comparable

In addition, an important feature of numerical schemesis the in-built monitoring system. This considerablyimproves the potential availability of numerical schemescompared to conventional schemes as faults within theequipment and its operational state can be detected andalarmed. With the conventional scheme, failure to re-instate the scheme correctly after maintenance may notbe detected until the scheme is required to operate. Inthis situation, its effective availability is zero until it isdetected and repaired.

15.11 REFERENCES

15.1 The Behaviour of Current Transformers subjectedto Transient Asymmetric Currents and theEffects on Associated Protective Relays. J.W.Hodgkiss. CIGRE Paper Number 329, Session15-25 June 1960.

15

N e t w o r k P r o t e c t i o n & A u t o m a t i o n G u i d e 2 5 2

Figure 15.21: Busbar protection relay using thelatest numerical technology (MiCOM P740 range)

BusbarProt

ection

Chap15-232-253 17/06/02 9:54 Page 252

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The MiCOM P740 numerical busbar protection

scheme provides complete protection for all

types of extra / ultra high voltage busbar

configurations.

Built on a number of innovative techniques,

including CT saturation detection and dynamic

topology processing algorithms, the P740 offers

a unique combination of security, speed and

sensitivity.

With a typical operating time of 15ms, the P740

protection is one of the fastest in its class and

meets the most stringent requirements of extra /

ultra high voltage transmission systems.

The substation replica processing algorithms

ensure that P740 adapts to the dynamically

changing topology of the busbar.

The MiCOM P740 busbar differential protectionscheme can be engineered to provide a

centralized or a distributed architecture. It also

supports easy maintenance, operation and future

expansion of the busbar.

Customer benefits

Fast fault trip(typically 15ms)

Adaptable to any busbarconfiguration.

Can operate with differenttypes of CT.

Fibre optic cable used forcommunication betweenCentral and Peripheral Units:- Ensures high

communication speed- Eliminates insulation

problems

AREVA T&D

MiCOM P740Numerical Busbar Protection

PROTECTION

MiCOM P741 in 80TE

MiCOM P743 in 60TE

MiCOM P742 in 40TE

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APPLICATION

The MiCOM P740 numerical busbar protection scheme

has been designed to protect a wide range of busbar

configurations. The modular scheme comprises of three

relays:

Central Unit - P741

Peripheral Unit - P742 / P743

These units, interconnected using optic fibre cables

together with the topology configurator software allow

application to all types of busbar configurations.

The Central Unit co-ordinates the scheme, receiving

signals from all the peripheral units associated with the

protected busbars and acting on these signals, initiating

a buszone protection trip when necessary. A single

Central Unit can accommodate upto,

8 Zones

28 Peripheral Units

One Peripheral Unit is associated with each

CT location, usually one per incomer/feeder and one

or two for each bus coupler/bus section, depending on

number of CT (1 or 2). The Peripheral Units acquire

the analogue signals from the associated CT and the

binary signals from the auxiliary contacts of circuit

breakers and isolators.The Peripheral Units also

incorporate the main circuit breaker failure logic

together with backup protection.

The difference between the P742 and P743 is in the

number of I/O that each can accommodate. The P743

allows for increased I/O, this is particularly useful in

double busbar applications. Especially where single

pole breakers and transfer busbar are employed, in

these applications the I/O requirements are large in

comparison to those required for a single busbar

application where a P742 may be more suitable.

2>3

Complete flexibility to suitany busbar configuration

P740 scheme

applied for protecting

double busbar with transfer bus

BB1

Central UnitOptical fibre Peripheral UnitsPeripheral Units

BB2

BB3

BB4

TransferBus

2 P742 or2 P743

P742 P743 P741 P742P743

PROTECTION

FUNCTIONS

OVERVIEW P74 P74 P743

87BB / P Phase segregated biased current - -differential high speed busbar protection

87BB / N Sensitive earth fault bias current controlled - -busbar protection

87 CZ Check zone element (supervision) - -50 / 51 / P Phase overcurrent protection (2 stages) - 50 / 51 / N Earth overcurrent protection (2 stages) - 50ST Dead zone protection (short zone between CTs and CBs) - -CTS Current transformer supervision 50BF Breaker failure protection (LBB) ISL Isolator discrepancy alarm -

Fibre optic signalling channel Digital inputs 8 16 24

Output relays 8 8 21

Front communication port (RS232) Rear communication port (RS485) Time synchronisation port (IRIG-B) * option - -

* Refer data sheet for model selection

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MANAGEMENT FUNCTIONS

In addition to the protection and control elements, the

P740 scheme provides a wide range of measurement,

monitoring, post fault analysis and self-diagnostic

features:

Circuit breaker control

Trip circuit supervision (using PSL)

On-line measurement

Plant status monitoring 4 alternative setting groups

Programmable scheme logic (PSL)

Sequence of event recording (SOE)

Comprehensive disturbance recording (waveform

capture)

User configurable LEDs

Local and remote communication ports

Time synchronisation

Fully customisable menu texts

Multi level password protection

Test facilities

Power-up diagnostics and continuous self-monitoring

of relay.

User friendly setting and analysis software

Speed, Sensitive & Secure:P740 the ultimate in busbar protection

X

/

/

/ /

Fault records

Measurements

PSL

Local

Communication

Remote

comm. port

Busbar protection scheme

Peripheral Unit P742 / P743

LEDsBinaryInput / output

Self monitoring

50/

51/P

50/

51/N

50ST

Disturbance

Record

Fibre optic

signaling

channel

50BF CTS

Fault records

Measurements

PSL

Local

Communication

Remote

comm. port

Busbar protection schemeCentral Unit P741

LEDsBinaryInput / output

Self monitoring

87BB

/ P

87BB

/ N 87CZ

Disturbance

Record

Fibre optic

signaling

channel

50BF CTS

ISL

FUNCTIONAL OVERVIEW

(Description of ANSI code nos. see Protection Function Overview)

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The P740 employs biased differential algorithms, in

which the differential current is compared with a bias

current. This characteristic ensures stability of the

protection for external fault even with differing CT

tolerances and errors which otherwise could lead to

spurious operation.

To increase the security of the differential protection,

the biased differential element is supervised by a

global check zone element. This ensures stability

even under erroneous status of the auxiliary contact of

plant isolators and circuit breakers.

The MiCOM P740 also employs an innovative, ultra

high-speed, secure CT saturation detection

algorithm. This ensures stability when CTs become

saturated, particularly under external fault conditions.

This algorithm combine a simulation of the flux built up

in the core of the CTs with a recursive consistence

variation control.This technique can detect CT

saturation in less than 2ms.

4>5

i (t)bias

I > 2Di3 in

i2i1

I > 1D

Ispe

rcenta

gebias

-k=20t

o90%

Tripping

Area

Restrain

area

i (t)diff nodeDifferential current : = + + i n1 2 iii 3 + ....... +

i (t)diffOperating current : = = i

i (t)diff

i (t)bias i 1 i 2 i 3 i nRestraining current : =+ + + ....... + = i

i (t)diff node

Universal on-line topology processing

Bias differential characteristics

CT saturation detection

To ensure adaptability of the relay to any type of

busbar configuration the P740 is built with a universal

topology processing algorithm. This algorithm

determines the optimum tripping zone on-line based

on the status of the plant isolator and breakers.

This ensures that minimum part of the busbar is

isolated for any fault in it.

BUSBAR DIFFERENTIAL PROTECTION

The primary protection element of the P740 scheme is

the phase segregated biased current differential

protection. The technique is based on the numerical

application of Kirchoff's Law for the selective detection

and ultra high-speed isolation of a faulty section of the

busbar.

The analysis is carried out in the Central Unit (CU)

which communicates with the Peripheral Unit (PU) to

get the current flowing in individual circuits and to

implement the tripping of circuits as decided by it.

This reliable, high speed communication is achieved

via a direct optical connection utilising a 2.5 Mbps

data rate.

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DUAL CHARACTERISTICS

To provide stability for severe through faults and at the

same time detect low current internal faults, the P740

is equipped with dual characteristics. One phase

segregated differential protection and another

sensitive earth current differential protection.

MULTIPLE TRIPPING CRITERIA

The MiCOM P740 maintains the highest level of

stability, under all conditions including a hardware

failure and incoherent signals applied from external

plant equipment or generated by power system.

Any tripping order must therefore be made conditional

on the simultaneous occurrence of 5 or 6 criteria:

> Magnitude criteria; confirmation of two simultaneous

thresholds per zone:

Exceeding the bias slope characteristic (k)

Exceeding differential operating current threshold

(ID>2).

> Exceeding the supervision threshold (ID>1).

> Signal quality criteria:

No CT saturation detected

Current variation detected on at least two

Peripheral Units

> Time or angular criterion.

The measurement elements on 2 samples taken at

1200 Hz. A first sample for the initial measurement

and a second sample for tr ip confirmation.

> Check zone supervision.

The zone element(s) are only permitted to trip if the

order is confirmed by the check zone element.

> Local criteria (optional)

The Peripheral Units can be set to only authorise

tripping if there is confirmation by local overcurrent

criteria.

DEAD ZONE OR BLIND SPOTPROTECTION

The current transformers surrounding the busbars

define the limits of the main zones. When the circuit

breaker is opened a dead zone or blind spot is created

between the CB and the associated CT. The P740

detects this condition automatically and provides

protection for this zone also.

CONTINUOUS SUPERVISION

OF CURRENT CIRCUITS

The P740 detects any abnormality in the current circuit

by continuously monitoring it. Under normal operating

conditions the differential current will be negligible. An

anomaly is detected by a threshold, ID>1, which can

be set to alarm from 1% of the primary basis current

(Ibp).

DIFFERENTIAL CURRENT SETTING

When switching operations are carried out in the

substation, incorrect topology replicas may occur. In

this case, a differential current appears. The

differential elements of the MiCOM P740 are allowed

to operate only if the differential current reaches a

threshold ID>2which is set above the highest load

current.

ADDITIONAL ULTRA HIGH SPEEDEXTERNAL FAULT BLOCKING

The ultra high-speed saturation detection is carried out

in each PU and can generate a control signal from the

moment of the first sample (0.4 ms).

Dual characteristics

PU1connectedto BB1

PU2 not connected to BB1= Activation

of Dead Zone protection

CB OpenCB Closed

Dead Zone

BB1

Intertrip contact

to other end

ID>2

Trip

ISID>1

idiff

Perce

ntage

bias-

k

IDN>2Restrain

Trip

IIDN>1

ibias

ibias

idiff

Percentage

bias- kN

SEF Block threshold

kNmin =0.2

BlockEnable

Restrain

SN

Dead zone protection

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6>7

Programmable scheme

logic editor (MiCOM S1)

PHASE OVERCURRENT ANDEARTH FAULT PROTECTION

Two independent stages each of phase overcurrent and

earth fault protection is provided in the Peripheral Units.

These elements provide backup protection for the

individual circuits.

The two stages can be programmed as:

> First stage can be programmed as definite time (DT)

delay or one of the nine inverse time (IDMT) curves

(IEC/UK and IEEE/US).

> Second stage can only be programmed as definite

time.

CIRCUIT BREAKER FAILUREPROTECTION (LBB)

The MiCOM P740 busbar protection scheme can work

in co-ordination with external breaker failure

protection relays. In this configuration, the receipt of an

external breaker failure information results in tripping of

all the adjacent circuit breakers, via the topological

recognition system knowing which breaker is connected

to which zone.

The P740 also offers an in-built integrated solution

for breaker failure protection. This requires all

Peripheral Units to receive a duplication of the trip

commands generated in their associated bay.

In general the Breaker Failure protection must be

executed on a per phase basis which involves the

possibility of receiving tripping orders on a per pole

basis.

CURRENT TRANSFORMERMISMATCH CORRECTION

The MiCOM P740 can correct mismatch between

current transformer ratios over a very wide range up

to 40. Its associated user interface provides a range

between 1 A and 30,000 A primary.

Since the current transformer ratings in a substation

may be of mixed ratios, the MiCOM P740 enables a

common base current to be defined, irrespective of

the feeder section concerned.

The settings on the Central Unit are all adjusted to this

common current, known as the primary base current (Ibp).

ISOLATION AND MAINTENANCEOPERATING MODE

For ease of operation or maintenance of the busbar

protection system, the Central Unit and the Peripheral

Units can receive specific commands designed to

allow system testing or other intervention without any

danger of unwanted tripping.

In the Central Unit, a centralized command to isolate

the busbars at two levels can be applied selectively

zone wise:

> Differential protection (87 BB) in monitoring mode

(measurements active and tripping deactivated).The

Breaker Failure protection remains operational.

> Differential protection (87 BB) and Circuit Breaker

Failure protection (50 BF) in monitoring mode.The

additional local protection functions (51, 51N, etc...)

remain operational.

A selective two-level command may be applied

selectively for each Peripheral Units:

> Maintenance of bay(s) for human intervention.

In this state, all I/O are deactivated.The busbarprotection is still in service, but the CB of the feeder

in service can not be tripped.

> Intervention on the equipment for maintenance and

testing.

PROGRAMMABLE SCHEME LOGIC

Powerful programmable scheme logic (PSL) allows the

user to customize the protection and control functions.

It is also used to programme the functionality of the

optically isolated inputs, relay outputs and LED

indications.The programmable scheme logic

comprises of gate logic and general purpose timers.

The gate logic includes OR, AND and majority gate

functions, with the ability to invert the inputs and

outputs, and provide feedback.The programmable

scheme logic is configured using the graphical MiCOM

S1 PC based support software.

PLANT STATUS

Checks and monitoring of the plant status can be

made, and an alarm raised for any discrepancy

conditions between the open and closed auxiliary

contacts of the isolators and circuit breakers.

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MEASUREMENTAND RECORDING FACILITIES

The P740 series relays are capable of measuring and

storing the values associated with a fault. All the

events, faults records and disturbance records are time

tagged to 1 ms using an internal real time clock. An

optional IRIG-B port is also provided for accurate time

synchronization. A lithium battery provides a back up

for the real time clock and all records in the event of

supply failure.

MEASUREMENTS

The measurements provided, which may be viewed in

primary or secondary values, can be accessed via

the back lit liquid crystal display. They are also

accessible via the communication ports. The following

instantaneous parameters can be viewed:

> Central unit (P741

Differential current Idiff / phase / zone

Bias current Ibias / phase / zone

Check zone Idiff / phase> Peripheral units (P742 & P743)

Phase currents IA IB IC

Neutral current IN

Sequence currents

Frequency

EVENT RECORDER

Up to 250 time tagged event records are stored in

battery backed memory, and can be extracted via the

communication port or be viewed on the front panel

display.

FAULT RECORDER

Records of the last 5 faults are stored in the

battery-backed memory of both the Central and

Peripheral Units.

Each fault record includes:

> Indication of the faulty zone (CU + PU)

> Protection element operated

> Active setting group

> Fault duration

> Currents and frequency (PU)

> Faulty zone differential and bias current (CU)

DISTURBANCE RECORDER

The Central and Peripheral units of the P740 have

independent disturbance recording facility. The

Peripheral Units can record 4 analogue and 32 digital

channels, whereas the Central unit stores 8 analogue

and 32 digital channels in addition to 1 time channel.

> Specific analogue channels Ibias / Idiff (CU)

IA, IB, IC, IN (PU)

> Maximum duration of one record and number of

records

1.2s per record and 8 records (CU)

up to 10.5s per record and minimum of

20 records (PU)

Disturbance records can be extracted from the relay

via the remote communications and saved in the

COMTRADE format. These records may be examined

using MiCOM S1 or any other standard COMTRADE

viewer.

Disturbance record viewed in MiCOM S1

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LOCAL AND REMOTECOMMUNICATIONS

Two communication ports are available as standard; a rear

port providing remote communications and a front port

providing local communications.

The front RS232 port has been designed for use with MiCOM

S1, which fully supports functions within the relay by providing

the ability to programme the settings off-line, configure the

programmable scheme logic, extract and view event,

disturbance and fault records, view the measurement

information dynamically and perform control functions (using

Courier protocol).

The default remote communications is Courier / K-bus and can

be converted to IEC60870-5-103.

DIAGNOSTICS

Automatic tests performed including power-on diagnostics andcontinuous self-monitoring ensures a high degree of reliability.

The results of the self-test functions are stored in battery

backed memory. Test features available on the user interface

provide examination of input quantities, states of the digital

inputs and relay outputs. A local monitor port provides digital

outputs, selected from a prescribed list of signals, including the

status of protection elements.

HARDWARE

All models within the MiCOM P740 series relays include:

> A back-lit liquid crystal display

> 12 LEDs

> Optional IRIG-B port (CU),

> RS232 (front port) & RS485 (rear port),

> Fibre optic connection from the CU to the PUs,

> Download/monitor port,> Battery (supervised),

> N/O and C/O watchdog contacts

> Supervised +48 V field voltage

> Dual rated CT inputs 1A/5A

> Universal opto inputs with progammable voltage threshold

The optically isolated inputs are independent and may be

powered from the +48V field voltage.

Our policy is one of continuous development. Accordinglythe design of our products may change at any time. Whilstevery effort is made to produce up to date literature, thisbrochure should only be regarded as a guide and isintended for information purposes only. Its contents do notconstitute an offer for sale or advise on the application ofany product referred to in it. We cannot be held responsiblefor any reliance on any decisions taken on its contentswithout specific advice.

AUTOMATION-L3-P740-BR-05.05-1021-GB

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Tel.: +44 (0) 1785 250 070

www.areva-td.com

www.areva-td.com/protectionrelays

Device Track Record

>> Low impedance biased differential busbar protection, MBCZ,

launched in 1988 and over 800 cubicles sold

>> Over 200 DIFB, medium impedance biased differential busbar

protection scheme delivered since its launch in 1992.

>> Medium impedance biased differential busbar protection with linear current

combination, DIFB CL, launched in 1996. Over 70 cubicles delivered.

>> Since the launch of the P740, over 50 systems have been delivered.

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Customer benefits This architecture can

accommodate the mostcomplex substation layouts

and different CT classesand manufacturers.

The use of fibre optics forcommunication betweenPeripheral Units and theCentral Unit gives thefollowing advantages:

- High communicationspeed

- Eliminates insulationproblems

Fast fault clearance(Typical tripping time 15 ms).

>

T&DEnergy Automation & Information

MiCOM P740

Numerical Busbar Protection

>> The consequences of a faulton the busbars of a powertransmission or distributionnetwork substation may be veryserious. Poor quality of supply toconsumers and damage to theelectrical equipment are veryreal threats.

ALSTOM has developed a newand fully numerical busbarprotection. The primary

objectives are to provide totalprotection stability under normaloperating conditions and for allexternal faults, whilst reactingquickly to internal faults. Thisprotection scheme is theMiCOM P740.

The MiCOM P740 provideshigh-speed protection ( Distributed architecture (up to 1.000 m

of optical fibre) or in a centralised cubicle.

> Topological configuration can

accommodate up to 8 zones.

> Advanced topological analysis using

operational research algorithms

(registered patent).

> Trip supervision by "check zone"

element for security.

> Low CT requirements allow the core

to be shared with existing protection.> Innovative algorithms for CT

saturation detection

(registered patent).

The minimum permitted saturation

time is 2 ms for stability.

> Bias characteristics to maintain

stability during transient CT responses

in presence of a significant DC

component.

> Security against accidental open

circuit of CTs by the use of delta

algorithms.

> Phase segregation with a separateelement for sensitive earth fault

detection (high impedance earthed

networks).

> Automatic control of the sensitive

earth fault element by phase elements.

> User-friendly interface for operation

and commissioning staff including

two levels of maintenance.

Our products>

> >

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Main protection functions

> Architecture

The architecture of the numerical

differential busbar protection is builtaround a P741 Central Unit (CU) whichgathers and processes all the analoguemeasurements from the P742 and P743Peripheral Units (PU) via direct fibreoptic connections.It is possible to protect:

8 zones.

32 Peripheral Units per Central Unit.

> Protection

> Central Unit (P741)

Busbar bias differential protection. Check Zone protection

Breaker Fail protection

(general 3 poles trip).

> Peripheral Units (P742/3)

Dead zone protection (short zone

between CTs and circuit-breakers).

Non directional Overcurrent

protection.

- Phase fault (2 stages).

- Earth fault (2 stages).

Breaker Fail protection

(single or three pole retrip).

Busbar protection

The operation of the MiCOM P740 isbased on the numerical application ofKirchoff's Law for the selective detectionand ultra high-speed isolation of afaulty section of a busbar.

> Universal topologicalprocessing algorithms

The MiCOM P740 uses new universalalgorithms based on operational

research which create, in real time,architectures of up to 8 zones.

> Stabilisation againstCT saturation

One of the most important objectives ofa differential busbar protection is toensure stability when CTs becomesaturated, particularly under externalfault conditions.In order to avoid this risk ofmaloperation, the MiCOM P740 usesinnovative ultra high-speed algorithmsbased on signal consistence variationmodel (registered patent).

> Bias characteristic

The operation of the MiCOM P740 isbased on an algorithm with acharacteristic (see figure 2) in which the

differential current is compared with abias value.The purpose of this characteristic is toensure the stability of the protection

when there is an external fault, differingCT tolerances and errors whichotherwise would lead to spuriousdetection of an in-zone fault.

> Global supervision by

check zone element

One of the most frequent causes of themaloperation of busbar protectionschemes is an error in actual plantstatus. This leads to the production of adifferential current.

2

Models available

Features P741 P742 P743

CentralUnit

PeripheralUnit

Peripheral

Unit87BB/P

87BB/N

87CZ

50/51/P

50/51/N

CTS

50BF

8 Opto Universal Inputs, 8 Output relays(MiCOM 16case, 80 TE)

16 Opto Universal Inputs, 8 Output relays(MiCOM 8case, 40 TE)

24 Opto Universal Inputs, 21 Output relays

(MiCOM 12case, 60 TE)

Phase segregated currentdifferential busbar protection

Sensitive earth fault busbar protectionCheck zone element (Supervision)

Phase Overcurrent protection

Earth Overcurrent protection

Current transformers supervision

Breaker fail protectionLocal single orthree pole re-tripGeneral three poleback-trip

Fibre Optic signalling channels

Figure 1

Double Busbarwith transfer bus

BB1

CentralUnitOptical Fibre Peripheral UnitsPeripheral Units

BB2

BB3

BB4

TransferBus

2 P742or

P743

P742 P743 P741 P742P743

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However, if all currents of the wholesubstation are taken into account, theirsum will remain null if a fault is notpresent, irrespective of the error in plantstatus/position.Consequently, the tripping order for azone element is conditional on theoperation of a check zone element.The main advantage of this element isthe total insensitivity to defectiveauxiliary contacts.

> Dead zone or Blind spot

The current transformers surrounding thebusbars define the limits of the mainzones. When the circuit breaker isopened a dead zone or blind spot isautomatically created between the CBand the associated CT.

> Continuous supervision of thecurrent circuits by

measurement of thedifferential current value

Under normal operating conditions thedifferential current will be negligible. Ananomaly is detected by a threshold,ID>1, which can be set to alarm from1% of the primary basis current (Ibp).

> Differential current setting

When switching operations are carriedout in the substation, incorrect topologyreplicas may occur. In this case, adifferential current appears.The differential elements of the MiCOMP740 are allowed to operate only if thedifferential current reaches a thresholdID>2 which is set above the highest loadcurrent.

> Stabilisation of the protectionin the event of CT saturationfor external fault

One main quality of the MiCOM P740is its ability to detect CT saturation in

less than 2 ms.The signal processing algorithmsimplemented in the MiCOM P740combine a simulation of the flux built upin the core of the CTs with a recursiveconsistence variation control(registered patent).

> Additional ultra high speedexternal fault blocking

The ultra high-speed saturation detectionis carried out in each PU and cangenerate a control signal from themoment of the first sample (0.4 ms).

> Dual characteristics

The MiCOM P740 offers phase-segregated protection and a separateelement for earth fault detection.

> Multiple tripping criteria

The MiCOM P740 maintains the highestlevel of stability, under all conditionsincluding:

> A hardware failure

> Incoherence of signals applied from

external plant or generated by the

power system.

> Any tripping order must therefore be

made conditional on the simultaneous

occurrence of 5 or 6 criteria:

> Magnitude criteria; confirmation of

two simultaneous thresholds per zone:

Exceeding the bias slopecharacteristic (k)

Exceeding differential operating

current threshold (ID>2).

> Exceeding the supervision threshold

(ID>1).

> Signal quality criteria:

No CT saturation detected

Current variation detected on at

least two Peripheral Units

No discrepancy detected.

> Time or angular criterion.

The measurement elements on 2samples taken at 1200 Hz.

A first sample for the initial

measurement and a second sample

for trip confirmation.> Check zone supervision.

The zone element(s) are only

permitted to trip if the order is

confirmed by the check zone element.> Local criteria (optional)

The Peripheral Units can be set to

only authorise tripping if there isconfirmation by local overcurrent

criteria.

Additional protection

The following back-up protectionfunctions are implemented locally in thePeripheral Units (P742/P743).

> Phase and Earth Faultovercurrent protection either

Definite Time (DT) or IDMT(IEC/UK, IEEE/US curves)

Two independent stages are availablefor phase and earth:

> First stage (I>1 or IN>1) can be

programmed as Definite Time (DT)

delay or dependant on one of nine

inverse time (IDMT) curves

(IEC/UK and IEEE/US).

> Second stage (I>2 or IN>2) can only

be programmed as definite time.

> External Breaker Failureprotection from the busbarprotection system

The usual 50 BF relay is totallyindependent of the others and thecontrol connection with the busbarprotection system is hardwired. Receiptof an external 50BF information resultsin tripping of all the adjacent circuitbreakers, via the topological recognitionsystem knowing which breaker isconnected to which zone.

> Internal breaker failureprotection in the busbarprotection system

Some operators prefer an integratedsolution, which requires all PeripheralUnits to receive a duplication of the tripcommands generated in their associatedbay.In general the Breaker Failure protectionmust be executed on a per phase basis

which involves the possibility ofreceiving tripping orders on a per pole

basis.

i (t)bias

I > 2Di3 in

i2i1

I > 1DIs

perce

ntage

bias

-k=2

0to9

0%

TrippingArea

Restrainarea

i (t)diff nodeDifferential current : = + + i n1 2 iii 3+ ....... +i (t)diffOperating current : = = i

i (t)diff

i (t)bias i 1 i 2 i 3 i nRestraining current : = + + + ....... + = i

i (t)diff node

3

Figure 2

Biascharacteristic

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4

Matching CT Transformer ratios

> Balancing protection

The MiCOM P740 can correct mismatch

between current transformer ratios overa very wide range up to 40. Itsassociated user interface provides arange between 1 A and 30,000 Aprimary.

> Common base ratio

Since the current transformer ratings ina substation may be of mixed ratios, theMiCOM P740 enables a common basecurrent to be defined, irrespective of thefeeder section concerned. The settingson the CU are all adjusted to this

common current, known as the primarybasis current (Ibp).

Isolation and downgradedoperating mode

For ease of operation or maintenance ofthe busbar protection system, theCentral Unit and the Peripheral Unitscan receive specific commands designedto allow system testing or otherintervention without any danger of

unwanted tripping.

> Central Unit - CU (P741)

A central command to isolate thebusbars at two levels can be appliedselectively zone by zone.

> Differential protection (87 BB) in

monitoring mode (measurements

active and tripping deactivated).

The Breaker Failure protection

remains operational.

> Differential protection (87 BB) and

Circuit Breaker Failure protection

(50 BF) in monitoring mode. The

additional local protection functions

(51, 51N, etc...) remain operational.

> Peripheral Units - PU(P742 and P743)

A selective two-level command may beapplied selectively for each PU.

> Maintenance of bay(s) for human

intervention. In this state,

all I/O are deactivated.

The busbar protection is still in

service, but the CB of the feeder in

service can not be tripped.

> Intervention on the equipment for

maintenance and testing.

Control

> Circuit breaker control

The circuit breaker control is availablefrom the front panel user interface, orthe optically isolated inputs.

> Programmable scheme logic

Powerful Programmable Scheme Logic(PSL) allows the user to customise theprotection and control functions. It isalso used to program the functionality ofthe optically isolated inputs, relayoutputs and LED indications.The PSL uses up to 256 logic gates and8 timers and is configured using thegraphical MiCOM S1 PC basedsoftware as illustrated in Figure 3.

> Independent protection

settings groups

The settings are divided into twocategories: protection settings and

control and configuration settings. Foursettings groups are provided for theprotection settings to allow differentoperating conditions and adaptiverelaying.

Measurement and recording

facilities

The P740 series relays are capable ofmeasuring and storing the valuesassociated with a fault. All the events,faults records and disturbance records

are time tagged to 1 ms using aninternal real time clock. An IRIG-B portis also provided for accurate timesynchronisation.

A lithium battery provides a back up forthe real time clock and all records in theevent of supply failure.

> Measurements

The measurements provided, which maybe viewed in primary or secondary

values, can be accessed via the back litliquid crystal display. They are also

accessible via the communication ports.

> Instantaneous measurements

> Central unit (P741) Differential current

Idiff/phase/zone Bias Current

Ibias/phase/zone Check zone

Idiff/phase

> Peripheral units (P742 & P743) Phase currents IA IB IC

Neutral currentIN

Frequency f

Figure 3

Programmable Scheme Logic

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Post fault analysis

> Event recorder

Up to 250 time tagged event recordsare stored in battery backed memory,and can be extracted via thecommunication port or be viewed on thefront panel display.

> Fault recorder

Records of the last 5 faults are stored inthe battery-backed memory.

Each fault record includes: Indication of the faulted phase Indication of the faulted zone (CU) Protection element operated Active setting group Fault duration Currents and frequency (PU) Faulty zone differential and

bias current (CU)

> Disturbance Recorder

The internal disturbance recorder storeson non-volatile memory: 8 analogue channels

ibias/idiff (CU) iA, iB, iC, iN (PU)

32 digital channels 1 time channel Data is sampled 12 times a cycle 20 (PU) & 8 (CU) disturbance records Max. duration of each record for

PU: 10.5 s & CU: 600 ms All channels and trigger sources user

configured (PU)

Disturbance records can be extractedfrom the relay via the remotecommunications and saved in theCOMTRADE format.

These records may be examined usingMiCOM S1 or COMTRADE viewer.

Plant status

Checks and monitoring of the plantstatus can be made, and an alarmraised for any discrepancy conditionsbetween the open and closed auxiliarycontacts of the isolators and circuitbreakers.

Local communications port

All the relays are equipped with a localcommunications port on the front face.The PUs are also accessible from onecentral point via the protectioncommunication channel, i.e. via theP741 Central Unit.

The local communication port is

designed to be used with MiCOM S1. Itdeals with the local functions and allowsthe user to program bay settings and toconfigure the PSL. Extraction and

viewing of events, disturbance recordingand the fault records is also possible.

Supervision & diagnostics

Continuous self monitoring Continuous local supervision of

current transformers by zero-sequence current control

Continuous central supervision ofcurrent circuits by measurement of thedifferential current(circuitry fault detection)

Trip circuit supervision(using specific PSL)

Power-up diagnostics Test facilities

Diagnostics

Continous self-checking gives a high

degree of reliability. The results of theself-test functions are saved in thebattery-backed memory.The test features available on the userinterface provide the status of the inputquantities, the digital inputs, the relayoutputs and selected internal logic.

A local monitor port providing digitaloutputs, selected from a prescribed listof signals, including the status ofprotection elements may be used inconjunction with test equipment.

Hardware description

All models within the MiCOM P740series relays include: A back-lit liquid crystal display 12 LEDs Optional IRIG-B port (CU), RS232 Port, Fibre optic connection from

the CU to the PUs, Download/monitor port, Battery (supervised), N/O and C/O watchdog contacts Supervised +48 V field voltage

Dual rated CT inputs 1A/5A

The hardware variation between theMiCOM P740 series relay models are:

(1) Universal voltage range opto-inputs(2) N/O: Normally Open

C/O: Change Over

The opto inputs are independent, andmay be energised from any substationbattery voltage, or from the 48V-field

voltage.

User interface

The front panel user interface comprises:

(1) A 2 x 16 characters backlitLCD display(2) Four fixed LEDs(3) Eight user programmable LEDs(4) Menu navigation and data

entry keys(5) READ and CLEAR keys

to view alarms(6) An upper cover identifying

the product name.(7) A lower cover concealing the front

RS232 port & parallel port -download/monitoring port andbattery compartment.

(8) Facility for fitting a security

lead seal

5

P741 P742 P743

Relay

Outputs (2)

Opto

-inputs (1)8 16 24

6 N/O 6 N/O 15 N/O

2 C/O 2 C/O 6 C/O

12

3

4

5

6

78

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The user interface and menu text areavailable in English, French, German

and Spanish as standard. Labelssupplied with the device allow tocustomise the LEDs descriptions.

A user selectable default displayprovides measurement information,time/date, protection functions andplant reference information. The abilityto customise the menu text and alarmtext is also supported.

> Password Protection

Password protection may beindependently applied to the front userinterface, to the front communicationsport and to the rear communicationport. Two levels of password protectionare available providing access to thecontrols and settings respectively.

Software support

WindowsTM 98/ME/2000/NT compatible.MiCOM S1 software which comprises:

Settings editor Programmable Scheme Logic editor Menu text editor Display of fault diagnostics and

measurements Disturbance recorder viewer

Technical data

> Nominal Operating time

Typic 15 ms to energisation of CB tripcoil (including relay contact closure).

> Ratings

> Inputs

AC Current (In)

1 A / 5 A Dual rated

Frequency 50/60 Hz 5Hz

Auxiliary Voltage (Vx)

> Outputs

Field Voltage 48 Vdc

(current limit: 112 mA)> Optocoupled digital inputs

Maximum voltage input

(any setting): 300V dc

> Burdens

> P741

With 8 comms. boards

37 to 41 W

With 5 comms. boards

25 to 29 W

> P742: 16 to 23 W

> P743: 22 to 32 W

> Optical fibre connection

850nm, ST connectors Multi-mode fibre 62.5/125

Data rate: 2.5 Mbits

Maximum lenght: 1000 m

> Front communication port

Multi core Cable 15 m maxi.

Connector RS232 DTE

9 pins D-type Female

Protocol Courier

Isolation ELV for local access

> IRIG-B Port

Carrier signal

Amplitude modulated

Connection BNC

50 coaxial cable

> Download/monitor port

This is a 25 pin D-type female connector

located on the front user interface and is

specially designed for test purposes and

software download.

> Internal Battery

Battery type: AA, 3.6V

6

A = Clearance holesB = Mounting holes

23.25

159.00

10.30

168.0

0

177.00

Front view

Side view30.00

240.00Incl. wiring

Secondary cover (when fitted)

116.55 142.45

155.40 129.50305.50

A B A B B A

A B B AB A

12 off holes Dia. 3.4

303.50

309.60

157.5 max

177.0(4U)

483 (19 rack)

Sealingstrip

All dimensions in mm

CC CA

Operating range (V)

24 - 48 19 - 65 -

48 - 110 37 - 150 24 - 110

110 - 250 87 - 300 80 - 265

Nominal

(V) DC

>

Figure 4 Case size MiCOM P741 (80TE)

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7

7

Central Unit (CU)

Vx aux rating

Communication boards

Hardware options

1

24 - 48Vdc

48 - 125Vdc (30 - 100Vac)

110 - 250Vdc (100 - 240Vac)

1 communication board (up to 4 peripheral units)2 communication boards (up to 8 peripheral units)

Standard version 1IRIG-B input 2

3 communication boards (up to 12 peripheral units)4 communication boards (up to 16 peripheral units)

5 communication boards (up to 20 peripheral units)6 communication boards (up to 24 peripheral units)7 communication boards (up to 28 peripheral units)8 communication boards (up to 32 peripheral units)

1

2

3

1

MiCOM P 4

P741:

23

4

5678

A 1A 0 0* **

Central Unit,8 opto inputs, 8 outputs,Size 16" case (80 TE)

Information required with order

Peripheral Units (PU)

Vx aux rating

In rating

2

24 - 48Vdc

48 - 125V dc (30 - 100V ac)

110 - 250Vdc (100 - 240Vac)

1

2

3

Peripheral Unit,16 opto inputs, 8 outputs,Size 8" case (40 TE)

Peripheral Unit,24 opto inputs, 21 outputs,Size 12" case (60 TE)

3

P742:

P743:

1 & 5 A - 1 1 0 V 1

Without analogue inputs 0

7MiCOM P 4 A 1 * *0A1

23.30 155.40

181.30202.00

10.35

159.00 168.00


A B B A

A B B A

Flush mounting panel

Note: If mounting plateis required use flushmounting cut out dimensions

200.00


Front view

177.00

206.00 30.00Side view

240.00Incl. wiring


157.5 max

177.0(4U)

483 (19"rack)

Sealing strip

Panel cut-out detailA = Clearance holesB = Mounting holes

A = Clearance holesB = Mounting holes

23.25

159.00

10.30

168.0

0

177.00

Front view

Side view30.00

240.00Incl. wiring


116.55 142.45

155.40 129.50305.50

A B A B B A

A B B AB A


303.50

309.60

157.5 max

177.0(4U)

483 (19 rack)

Sealingstrip


> Case

The MiCOM relays are housed in aspecially designed case providing ahigh density of functionality within theproduct, a customisable user interface,and additional functions/informationconcealed by upper an lower covers.

Physical protection of the front paneluser interface and prevention of casualaccess is provided by an optionaltransparent front cover, which can befitted or omitted according to choicesince the front panel has been designed

to IP52 protection against dust andwater.

The case is suitable for either rack orpanel mounting as shown in figures4,5 and 6.

> P741 MiCOM 80TE

> P742 MiCOM 40TE

> P743 MiCOM 60TE

> Weight

P741(with 8 comms. boards):

7.6 kg

P741

(with 1 comms. board):

6.2 kg

P742

7.5 kg

P743

9.2 kg

>

Figure 5 Case size MiCOM P742 (40TE) Figure 6 Case size MiCOM P743 (60TE)

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ALSTOM Track Record -

Busbar protection

>> Low impedance biased differentialbusbar protection (MBCZ)launched in 1988.Over 6.522 units delivered.

>> Over 211 medium impedancebiased differential busbarprotection (DIFB) delivered sincelaunching in 1992.

>> Medium impedance biaseddifferential busbar protection withlinear current combination

(DIFB CL). Over 73 cubiclesdelivered since 1996.

Our policy is one of continuous development. Accordingly the design of our products may change at any time.Whilst every effort is made to produce up to date literature, this brochure should only be regarded as a guide and is intended for

information purposes only. Its contents do not constitute an offer for sale or advise on the application of any product referred to in it.We cannot be held responsible for any reliance on any decisions taken on its contents without specific advise.

South East Asia

Tel.: +65 67 49 07 77 - Fax: +65 68 41 95 55

Pacific

Tel.: +65 67 49 07 77 - Fax: +65 68 46 17 95China

Tel.: +86 10 64 10 62 88 - Fax: +86 10 64 10 62 64

India

Tel.: +91 11 26 44 99 07 - Fax: +91 11 26 44 94 47

North America

Tel.: +1 (484) 766-8100 - Fax: +1 (484) 766-8150

Central America

Tel.: +52 55 11 01 07 00 - Fax: +52 55 26 24 04 93

South America

Tel.: +55 11 30 69 08 01 - Fax: +55 11 30 69 07 93

France

Tel.: +33 1 40 89 66 00 - Fax: +33 1 40 89 67 19

British Isles

Tel.: +44 (0) 1785 27 41 08 - Fax: +44 (0) 1785 27 45 74

Northern Europe

Tel.: +49 69 66 32 11 51 - Fax: +49 69 66 32 21 54

Central Europe & Western Asia

Tel.: +48 22 850 96 00 - Fax: +48 22 654 55 90

Near & Middle East

Tel.: +971 6 556 3971 - Fax: +971 6 556 5133

Mediterranean, North & West Africa

Tel.: +33 1 41 49 20 00 - Fax: +33 1 41 49 24 23

Southern & Eastern Africa

Tel.: +27 11 82 05 111 - Fax: +27 11 82 05 220

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

PAPERRTS

CTS

0V

RX

TX

SERIALPORT

8

9

7

4

6

5

3

2

CONNECTED

DATA READY

TO-T7

DO-D7

0V

RESETEXTERNAL

ACKNOWLEDGE

DOWNLOADCOMMAND

DATA

DOWNLOADTEST/

17

20,21,23,2411,12,15,13,

19,18,22,25

NOT

1 SK1

14

2-9

16

10

1

E16SCN

E18

SK2

E17

C9

OPTO 5 C10

OPTO 3

OPTO 4

OPTO 1

OPTO 2

C8

C7

C6

C5

C4

C3

C1

C2

A18

A16

A17

A15

A14

A12

A13

A10

A11

A7

A8

A9

A6

A5

C14

A4

A3

A2

A1

C17

C18

C16

C15

C12

C13

C11

CONNECTION

OPTO 16

COMMON

OPTO 15

OPTO 14

OPTO 13

OPTO 12

OPTO 11

OPTO 7

OPTO 10

OPTO 9

CONNECTIONCOMMON

OPTO 8

OPTO 6D8

D7

D10

D9

D12

D11

D13

D16

D18

D17

D14

D15

WATCHDOG

WATCHDOG

D2

D5

D6

D4

D3

E13

E14

D1

E12

E11

48V DC FIELDVOLTAGE OUT

-

-

+

+

+

-

E10

E9

E8

E2

E7

E1

COMMUNICATIONFIBRE OPTIC

CURR DIFF

RX2

RX1

TX2

TX1

CASEEARTH

DIRECTION OF FORWARD CURRENT FLOW

NOTE 2.

C

B

AS2 S1

P2 P1

NI

B12

B11

B10

B9

1A

5A

1A

B5

CI

B8

B6

B7

BI

B4

B3

B2

5A

1A

5A

1A

PHASE ROTATION

A

C B

I A

B1 5A

AUX SUPPLYAC OR DC Vx

MiCOM P742 (PART)

MiCOM P742 (PART)

POWER SUPPLY VERSION 24-48V (NOMINAL) D .C. ONLY*

CONTACT

CONTACT

RELAY 8

RELAY 7

RELAY 6

RELAY 5

RELAY 4

TRIP A

TRIP B

TRIP C

EIA485/KBUS

PORT

Busbar protectionPeripheral UnitP742

C.T. SHORTING LINKS

50 OHM BNC CONNECTOR

PIN TERMINAL (P.C.B. TYPE)

9-WAY & 25-WAY FEMALE D-TYPE SOCKET ANSI31_7

(b)

1.

NOTES

(a)

2.C.T. CONNECTION S ARE SHOWN 1ACONNECTED AND ARE TYPICAL ONLY.

3. THIS RELAY SHOULD BE ASSIGNED TOANY TRIP TO ENSURE CORRECT

OPERATION OF THE PROTECTIVE RELAY.

4. OPTO INPUTS 1 & 2 MUST BE USED FORSETTING GROUP CHANGES IF THIS OPTION

IS SELECTED IN THE RELAY MENU.

Figure 7 System overview of the P742 relay

Micom P740

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