Excitation System

ByBySusobhan Patra

5/8/2014

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• General Conception• Different Types of Excitation systems• Operational characteristics• Case studies- sharing ideas

Excitation System

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Ia

j XsI t

Xs IacosØ

Ø

Phasor diagram

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Basic dynamo principleΦ = B cos Ø A

= BA cos ωt

Change of magnetic flux = dΦ/ dt

Rate of change of magnetic flux dΦ/ dt = -BAω sin ωti.e. e = NBAω sin ωt

e0 = NBAωe = e0 sin ωt

GeneratorWhen a closed coil is rotated rapidly in a strong magnetic field, the number of magnetic flux lines passing through the coil changes continuously. Hence, an emf is induced in the coil and a current flows in it in a direction given by FRH Rule

MotorWhen a current is passed through a coil placed in a magnetic field, the coil experiences a torque in a direction given by FLH Rule. The torque gives a continuous rotary motion to the coil in the magnetic field.

If UgSynchronous

Machine

AVR- Automatic voltage control system

Controller

Excitation System

Specification (TGS)

• Apparent power in air 70.59 MVA• Active power 60 MW• Phase Current 3881 amps• No of phases 3• No of poles 2• Terminal Voltage 10.5 ± 5 KV• Speed 3000 rpm• Frequency 50 Hz• Frequency 50 Hz• Power factor 0.85 (lagging)• Field current for rated output 833 amps• Field voltage 202 V

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PILOT EXCITER

MAIN EXCITER FIELD

ALTERNATORFIELD

ALTERNATOR OUTPUT

CONNVENTIONAL EXCITATION SYSTEM FOR ALTERNATOR

PILOT EXCITER MAIN EXCITER 3-Ph ALTERNATOR

R FIELD

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MANUAL Channel Thyristor

bridge

Pulse from Manual channel control

Pulse from Auto channel control

Field Breaker

AUTI Channel Thyristor

bridge

From PMG

Gen

Gen. Rotor Rotating Diode Bridge Main Exciter

Schematic Diagram for Brush Less excitation System

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Main Exciter

PMG

Rotating Diode Bridge

Brush Less excitation System5/8/2014

Case studies:• Failure of PMG• Failure of fuse• Failure of Magnet• Rise in PMG Temp

- +

..

. ...

.

...

.

...

.

.. . .

5/1 AC.T.

GENERATOR

AUXILIARY SLIPRINGS

ROTATING RECTIFIER UNIT

EXCITER

P.M.G. SINGLE PHASE PILOT EXCITER

500/5AC.T.

R

Y

B

BRUSHLESS EXCITATION SUSTEM

EXCITER TERMINAL BOARD

X 1 2 5 6 7 8 9 10 113 4XXJ2

A.V.R. CUBICLE

+ -

FOR TEST ONLY

12A

V31

AXCITER/ GEN. FIELDCURRENT AMMETER

J1

EXCITER TERMINAL BOARD

+

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PMGMain

Exciter Armature

Rotating Rectifier

Slip Ring for rotor voltage FB &

protection

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Excitation System: SpecificationMain Exciter

• Maxm continuous rating 207 KW• Rated terminal voltage (at 225 VDC

Rectifier DC terminals)• Rated current (at rectifier 920 ADC

DC terminal• Frequency 150 Hz• Rated speed 3000 rpm• No of phases 3• No of poles 6• Rotating Rectifier• Diodes (Positive) type IR GB 490 / U• Diodes (Negative) type IR GB 491 / UR• Diodes (Negative) type IR GB 491 / UR• No of rings 2• No. of + ve diodes per ring 9• No. of - ve diodes per ring 9• Peak inverse voltage of diodes 2200 V repetitive peak volts• Connections Full wave, 3 arm bridge with 3 parallel paths per arm• Fuse type EE GSA 250• No of fuses 18• Fuse current rating 250 A rms• Fuse voltage rating 240 A rms• Neon indicators 18 (one per parallel path)

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PERMANENT MAGNET FIELD ON ROTOR, ARMATURE ON STATOR

ARMATURE ON ROTOR, FIELD WINDING ON STATOR

SILICON DIODE BRIDGE ON SHAFT

PILOT EXCITER MAIN EXCITER ROTATING RECIFIER

HOLLOW SHAFT

SOLID SHAFT

REGULATOR

THYRISTOR CONTORLLED BRIDGE

Controlled dc to field on stator

Alternator terminal

3-ph power(1-Ph 200Hz at TGS)

3-Ph (3-ph 150 Hz at TGS)

Alternator field

C.T

P.T

AVR

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Rotating Rectifier Ring

+VE

Rotating Rectifier Ring

-VE

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Carbon Brush on slip rings for measurement of Rotor Voltage & protection Terminal block

POSITIVE DIODE CARRING RING

NEON LAMP

AUX. SLIP RING

RO

TO

R W

IND

ING

1P 2P 3P 4P 5P 6P 7P 8P 9P

ROTATING RECTIFIER ASSEMBLY OF BRUSHLESS EXCITATION SYSTEM

A2 B2 C2 A2 B2 C2 A2 B2 C21 2 3 4 5 6 7 8 9

FUSEDIODE

NEGATIVE DIODE CARRING RING AUX. SLIP RING

RO

TO

R W

IND

ING

1N 2N 3N 4N 5N 6N 7N 8N 9N

TO ROTOR VOLT METERAND ROTOR E/F RELAY

1P, 2P, 3P, 4P………….9P : DIODE & FUSE ASSEMBLY ON POSITIVE RING1N, 2N, 3N, 4N………..9P : DIODE & FUSE ASSEMBLY ON NEGATIVE RING

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FuseDiodeLamp

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Brushless Excitation

• No use of any brush

• PMG output is fed to the AVR

• AVR output is the field for the main exciter

• Main exciter output is directly coupled with the rotating rectifier

• The output from rectifier is directly connected to the generator • The output from rectifier is directly connected to the generator rotor

• Carbon brushes are used for voltage measurement & rotor protection system- rotor E/F

• There are two channels for operation control

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AUTO Mode• It is built as a voltage regulator and is ON during normal

operation & the reference point is set through manual switch

• Various limiters and corrective control circuits are used for stable operation up to operating limits.

• In case of any malfunction the AVR will change over to manual modemode

MANUAL Mode:

• It is built as a simple field current regulator

• It serves as a back up channel in case of failure of the AUTO channel.

• Operations in this channel require expert adjustment and continuous monitoring of the parameters as there is no automatic limiter action.

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Digital AVR with BL Excitation

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n UNITROL 6080 Hardware Devices (D1..D4)Power INterface

PIN6080

PIN6080

PIN6080

3.2.3 UN6080 Control HW

CCM6080 CCM6080CCM6080

Combined IO

Communication Control

Measuring

n Communication Control Measuring CCM6080 (UC D240)

CCM6080 CCM6080CCM6080

3.2.3 UN6080 Control HW

UG IG

AO

Optical Links Ethernet

CCM 6080 X12 X113 X14

PIN – 6080 X12 X113 X14

DCS800 Box

D1…D4

CCM 6080 X12 X13

X113

GDI X113

PIN – 51 X12 X13

D5

• Providing variable DC current with short time overload capability

• Control terminal voltage on preset value with required accuracy

• Ensure stable operation with network and/ or other machines

• Keep machine within permissible operating range.

• Contribution to transient stability subsequent to a fault.

• Communicate with the power plant control system

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• Display of actual values• Local operation of the excitation system• Parameter settings• Transient recorder• Event/Fault recorder

Excitation Control Terminal

Band pass filter

Rippledetection

Diode failure

Rotating Diode Failure

Rotating rectifier

t

Ie

Diode failure

filter

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UG set point

UG nominalU

UG max setpoint

Setting range V/Hz

Set point V/Hz Limiter

ff nominal

UG min set point

Allowed range of operation

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Static Excitation (Digital Voltage regulator)

• The DVR regulates the voltage of the synchronous machine by direct control of the rotor current using thyristor converter.

• Redundancy in the regulator section is ensured by means of two fully separate channels with independent measuring inputs, control and monitoring

Thyristor Converter for Excitation Control

• 3 Phase fully controlled thyristor bridges, each bridge consisting of 6 thyristors, arm fuses & snubber circuit.

• Cooling fan for keeping the junction temperature rise of every device within safe limits.

• Pulse transformers for electrical isolation between power & control circuits and coupling the firing pulses to the gates.

• Fuse monitoring Unit

• Air Flow Monitoring Unit

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SEE

5/8/2014Regulation Field Flushing

AVR

Thyristor

Usyn

U>70%

Ug

t

Field flashing off

Thyristor bridgestarts to conduct

U>70%

U>10%Field flashing characteristic

Field flashing failedFCB Trip

10sField flashing OFF

5s

100%Softstart

Ug Sequence:

Field Flashing Circuit

Generator

AuxiliarySources

~ +

DiodeBridge

Thyristorbridge

U>70%

Field flashing breaker

• Field breaker CLOSE

• Excitation ON

• Pulses to the thyristors are released

• Field Flashing breaker closes if start up with residual machine voltage is to low

• Stator voltage raises

• Field flashing breaker opens

• The softstart function raises the generator voltage smoothly up to itsnominal value.

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SEE

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One Thyristor panel

Complete Thyristor cubicle- 3 Channels

SEE- Case study

Damaged holder

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Slip Ring & Carbon Brush Holder

CB-32x32x64

Channel 1 (The AUTO):• It is built as a voltage regulator and is ON during normal operation.

• Various limiters and corrective control circuits are used for stable operation up to operating limits.

• In case of any malfunction the DVR will change over to Channel 2.

Channel 2 (The MANUAL):Channel 2 (The MANUAL):• It is built as a simple field current regulator

• It serves as a back up channel in case of failure of the AUTO channel.

• No special limiters.

• Operations in this channel require expert adjustment and continuous monitoring of the operating parameters.

• In case of any malfunction of channel 2 it will lead to excitation failure.

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Pulse Trafo

Pulse Trafo

Pulse TrafoAVR

CT

PT

E.T.

THYRISTORBRIDGE

3 CHANNELS

BACK

GROTOR

Q1

Q2

SCHEMATIC DIAGRAM FOR STATIC EXCITATION SYSTEM FIELD FLASHING SUPPLY

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Q&A

Thank you very much

Save Energy

5/8/2014