02-2 excitation course (1)

8/20/2019 02-2 Excitation Course (1)

1/311539pk

EXCITATION SYSTEMSEXCITATION SYSTEMS

Copyright © P. Kundur

This material should not be used without the author's consent


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Excitation SystemsExcitation Systems

1. Functions and Performancee!uirements

". E#ements of an Excitation System

$. Ty%es of Excitation Systems

&. Contro# and Protection Functions

'. Mode#in( of Excitation Systems

Out#ine


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Functions and PerformanceFunctions and Performance

e!uirements of Excitation Systemse!uirements of Excitation Systems

T)e functions of an excitation system are

to %ro*ide direct current to t)e sync)ronous

(enerator fie#d +indin(, and

to %erform contro# and %rotecti*e functions

essentia# to t)e satisfactory o%eration of t)e

%o+er system

T)e %erformance re!uirements of t)e excitation

system are determined -y

a /enerator considerations0

supply and ad!ust "ield current as the generatoroutput #aries within its continuous capability

respond to transient disturbances with "ield "orcing

consistent with the generator short term capabilities$

- rotor insulation "ailure due to high "ield #oltage

- rotor heating due to high "ield current

- stator heating due to high %& loading

- heating due to e(cess "lu( )#olts*+,

- Po+er system considerations0

contribute to e""ecti#e control o" system #oltage and

impro#ement o" system stability


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E#ements of an Excitation SystemE#ements of an Excitation System

Exciter 0 %ro*ides dc %o+er to t)e (enerator fie#d +indin(

Regulator 0 %rocesses and am%#ifies in%ut contro# si(na#sto a #e*e# and form a%%ro%riate for contro# of t)e exciter

Terminal voltage transducer and load compensator 0

senses (enerator termina# *o#ta(e, rectifies and fi#ters it

to dc !uantity and com%ares +it) a reference #oad com%

may -e %ro*ided if desired to )o#d *o#ta(e at a remote

%oint

Power system stabilizer: %ro*ides additiona# in%ut si(na#

to t)e re(u#ator to dam% %o+er system osci##ations

Limiters and protective circuits0 ensure t)at t)e

ca%a-i#ity #imits of exciter and (enerator are not

exceeded


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Ty%es of Excitation SystemsTy%es of Excitation Systems

C#assified into t)ree -road cate(ories -ased on t)e

excitation %o+er source0

0 2C excitation systems

0 AC excitation systems

0 Static excitation systems

1. 2C Excitation Systems0

0 uti#i3e dc (enerators as source of %o+er

dri*en -y a motor or t)e s)aft of main (enerator

se#f or se%arate#y excited

0 re%resent ear#y systems 415"6s to 1576s

#ost fa*or in t)e mid81576s -ecause of #ar(e si3e

su%erseded -y ac exciters

0 *o#ta(e re(u#ators ran(e from t)e ear#y non8

continuous r)eostatic ty%e to t)e #ater system

usin( ma(netic rotatin( am%#ifiers


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Fi(ure 98" s)o+s a sim%#ified sc)ematic of a ty%ica# dc

excitation system +it) an am%#idyne *o#ta(e re(u#ator 0 se#f8excited dc exciter su%%#ies current to t)e main

(enerator fie#d t)rou() s#i% rin(s

0 exciter fie#d contro##ed -y an am%#idyne +)ic)

%ro*ides incrementa# c)an(es to t)e fie#d in a -uc:8

-oost sc)eme

0 t)e exciter out%ut %ro*ides rest of its o+n fie#d -yse#f8excitation

". AC Excitation Systems0

0 use ac mac)ines 4a#ternators as source of %o+er

0 usua##y, t)e exciter is on t)e same s)aft as t)e

tur-ine8(enerator

0 t)e ac out%ut of exciter is rectified -y eit)er

contro##ed or non8contro##ed rectifiers

0 rectifiers may -e stationary or rotatin(

0 ear#y systems used a com-ination of ma(netic and

rotatin( am%#ifiers as re(u#ators most ne+ systems

use e#ectronic am%#ifier re(u#ators


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Fi(ure 9."0 3C e(citation system with amplidyne #oltage

regulators


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".1 Stationary rectifier systems0

0 dc out%ut to t)e main (enerator fie#d su%%#iedt)rou() s#i% rin(s

0 +)en non8contro##ed rectifiers are used, t)ere(u#ator contro#s t)e fie#d of t)e ac exciter Fi(.9.$ s)o+s suc) a system +)ic) is re%resentati*eof /E8A;TEEX system

0


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Fi(ure 9.$$ 6ield controlled alternator recti"ier e(citation

system

Fi(ure 9.&$ &lternator supplied controlled-recti"ier

e(citation system


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Fi(ure 9.'$ 9rushless e(citation system


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$. Static Excitation Systems0

0 a## com%onents are static or stationary

0 su%%#y dc direct#y to t)e fie#d of t)e main

(enerator t)rou() s#i% rin(s0 t)e %o+er su%%#y to t)e rectifiers is from t)e main

(enerator or t)e station auxi#iary -us

$.1 Potentia#8source contro##ed rectifier system0

0 excitation %o+er is su%%#ied t)rou() a

transformer from t)e main (enerator termina#s

0 re(u#ated -y a contro##ed rectifier

0 common#y :no+n as -us8fed or transformer8fed

static excitation system

0 *ery sma## in)erent time constant

0 maximum exciter out%ut *o#ta(e is de%endent on

in%ut ac *o#ta(e durin( system fau#ts t)e

a*ai#a-#e cei#in( *o#ta(e is reduced

Fi(ure 9.7$ Potential-source controlled-recti"ier e(citation system


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$." Com%ound8source rectifier system0

0 %o+er to t)e exciter is formed -y uti#i3in( currentas +e## as *o#ta(e of t)e main (enerator

0 ac)ie*ed t)rou() a %o+er %otentia# transformer

4PPT and a satura-#e current transformer 4SCT

0 t)e re(u#ator contro#s t)e exciter out%ut t)rou()

contro##ed saturation of excitation transformer

0 durin( a system fau#t, +it) de%ressed (enerator

*o#ta(e, t)e current in%ut ena-#es t)e exciter to

%ro*ide )i() fie#d forcin( ca%a-i#ity

An exam%#e is t)e /E SCT8PPT.

$.$ Com%ound8contro##ed rectifier system0

0 uti#i3es contro##ed rectifiers in t)e exciter out%ut

circuits and t)e com%oundin( of *o#ta(e and

current +it)in t)e (enerator stator

0 resu#t is a )i() initia# res%onse static system +it)

fu## >fau#t8on> forcin( ca%a-i#ity

An exam%#e is t)e /E /ENEEX system.


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Fi(. 9.?$ Compound-source recti"ier e(citation system

Fi(ure 9.9$ :E;EE< compound-controlled recti"ier

e(citation system ©=EEE751 >71?


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Contro# and Protecti*e FunctionsContro# and Protecti*e Functions

A modern excitation contro# system is muc) more

t)an a sim%#e *o#ta(e re(u#ator

It inc#udes a num-er of contro#, #imitin( and

%rotecti*e functions +)ic) assist in fu#fi##in( t)e

%erformance re!uirements identified ear#ier

Fi(ure 9.1& i##ustrates t)e nature of t)ese functions

and t)e manner in +)ic) t)ey interface +it) eac)

ot)er

any (i*en system may inc#ude on#y some or a## of

t)ese functions de%endin( on t)e s%ecific

a%%#ication and t)e ty%e of exciter

contro# functions re(u#ate s%ecific !uantities at

t)e desired #e*e#

#imitin( functions %re*ent certain !uantities from

exceedin( set #imits

if any of t)e #imiters fai#, t)en %rotecti*e functionsremo*e a%%ro%riate com%onents or t)e unit from

ser*ice


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Fi(ure 9.1&0 E(citation system control and protecti#e

circuits


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AC e(u#ator0

-asic function is to maintain (enerator stator *o#ta(e

in addition, ot)er auxi#iaries act t)rou() t)e ac

re(u#ator 2C e(u#ator0

)o#ds constant (enerator fie#d *o#ta(e 4manua#contro#

used for testin( and startu%, and +)en ac re(u#ator isfau#ty

Excitation System Sta-i#i3in( Circuits0 excitation systems +it) si(nificant time de#ays )a*e

%oor in)erent dynamic %erformance

un#ess *ery #o+ steady8state re(u#ator (ain is used,t)e contro# action is unsta-#e +)en (enerator is ono%en8circuit

series or feed-ac: com%ensation is used to im%ro*et)e dynamic res%onse

most common#y used form of com%ensation is aderi*ati*e feed-ac: 4Fi(ure 9.1'

Fi(ure 9.1'$ 3eri#ati#e "eedbac@ e(citation control system

stabili,ation


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Po+er System Sta-i#i3er 4PSS0

uses auxi#iary sta-i#i3in( si(na#s 4suc) as s)aft

s%eed, fre!uency, %o+er to modu#ate t)e

(enerator fie#d *o#ta(e so as to dam% system

osci##ations

;oad Com%ensator0

used to re(u#ate a *o#ta(e at a %oint eit)er +it)in

or externa# to t)e (enerator

ac)ie*ed -y -ui#din( additiona# circuitry into t)e

A@ #oo% 4see Fi(. 9.17

+it) C and XC %ositi*e, t)e com%ensator re(u#ates

a *o#ta(e at a %oint +it)in t)e (enerator

used to ensure proper sharing %&s between generatorsbussed together at their terminals

commonly used with hydro units and cross-compound

thermal units

+it) C and XC ne(ati*e, t)e com%ensator

re(u#ates *o#ta(e at a %oint -eyond t)e (enerator

termina#s

commonly used to compensate "or #oltage drop across

step-up trans"ormer when generators are connected

through indi#idual trans"ormers


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Fi(ure 9.17$ Schematic diagram o" a load compensator

T)e ma(nitude of t)e resu#tin( com%ensated *o#ta(e 4V c , +)ic) is

fed to t)e A@, is (i*en -y

( ) tcctc = !


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Bnderexcitation ;imiter 4BE;0

intended to %re*ent reduction of (eneratorexcitation to a #e*e# +)ere steady8state 4sma##8si(na# sta-i#ity #imit or stator core end8re(ion)eatin( #imit is exceeded

contro# si(na# deri*ed from a com-ination ofeit)er *o#ta(e and current or acti*e and reacti*e%o+er of t)e (enerator

a +ide *ariety of forms used for im%#ementation

s)ou#d -e coordinated +it) t)e #oss8of8excitation

%rotection 4see Fi(ure 9.1?

O*erexcitation ;imiter 4OX;

%ur%ose is to %rotect t)e (enerator fromo*er)eatin( due to %ro#on(ed fie#d o*ercurrent

Fi(. 9.19 s)o+s t)erma# o*er#oad ca%a-i#ity oft)e fie#d +indin(

OX; detects t)e )i() fie#d current condition and,after a time de#ay, acts t)rou() t)e ac re(u#atorto ram% do+n t)e excitation to a-out 116 ofrated fie#d current if unsuccessfu#, tri%s t)e acre(u#ator, transfers to dc re(u#ator, andre%ositions t)e set %oint corres%ondin( to rated*a#ue

t+o ty%es of time de#ays used0 4a fixed time, and4- in*erse time

+it) in*erse time, t)e de#ay matc)es t)e t)erma#ca%a-i#ity as s)o+n in Fi(ure 9.19


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Fi(ure 9.1?$ Coordination between AEB BDE relay and

stability limit

Fi(ure 9.19$ Coordination o" o#er-e(citation limiting with

"ield thermal capability


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@o#ts %er =ert3 ;imiter and Protection0

used to %rotect (enerator and ste%8u% transformer

from dama(e due to excessi*e ma(netic f#ux

resu#tin( from #o+ fre!uency andDor o*er*o#ta(e

excessi*e ma(netic f#ux, if sustained, can cause

o*er)eatin( and dama(e t)e unit transformer and

t)e (enerator core

Ty%ica# @D=3 #imitations0

@D=3 #imiter 4or re(u#ator contro#s t)e fie#d

*o#ta(e so as to #imit t)e (enerator *o#ta(e +)en

@D=3 exceeds a %reset *a#ue

@D=3 %rotection tri%s t)e (enerator +)en @D=3

exceeds t)e %reset *a#ue for a s%ecified time

Note0 T)e unit ste%8u% transformer #o+ *o#ta(e

ratin( is fre!uent#y ' -e#o+ t)e (enerator

*o#ta(e ratin(

%*+, )p.u. 7.2/ 7.2 7.7/ 7.78 7.8/

3amage Time ininutes

:E; 8.2 7.8 1.8 28.8 ∞


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Mode#in( of Excitation SystemsMode#in( of Excitation Systems

2etai# of t)e mode# re!uired de%ends on t)e

%ur%ose of study0

t)e contro# and %rotecti*e features t)at im%act

on transient and sma##8si(na# sta-i#ity studies are

t)e *o#ta(e re(u#ator, PSS and excitation contro#sta-i#i3ation

t)e #imiter and %rotecti*e circuits norma##y need

to -e considered on#y for #on(8term and *o#ta(e

sta-i#ity studies

Per Bnit System0

Se*era# c)oices a*ai#a-#e0

a %er unit system used for t)e main (enerator fie#d

circuit

chosen to simpli"y machine eFuations but not

considered suitable "or e(citer FuantitiesG under

normal operating conditions "ield #oltage in the order

o" 8.887 )too small

- %er unit system used for excitation system

s%ecifications

rated load "iled #oltage as one per unit

not con#enient "or system studies


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9.7." Mode#in( of Excitation System Com%onents

T)e -asic e#ements +)ic) form different ty%es of excitation

systems are t)e dc exciters 4se#f or se%arate#y excited acexciters rectifiers 4contro##ed or non8contro##ed

ma(netic, rotatin(, or e#ectronic am%#ifiers excitation

system sta-i#i3in( feed-ac: circuits si(na# sensin( and

%rocessin( circuits

Separately excited dc exciter

Fi(ure 9."7$ 9loc@ diagram o" a dc e(citer

Sel!excited dc exciter

T)e -#oc: dia(ram of Fi(. 9."7 a#so a%%#ies to t)e se#f8

excited dc exciter. T)e *a#ue of " E # )o+e*er, is no+ e!ua#

to R e $R g !% as com%ared to R e $R g for t)e se%arate#y excited

case.

T)e station o%erators usua##y trac: t)e *o#ta(e re(u#ator -y

%eriodica##y adustin( t)e r)eostat set%oint so as to ma:e

t)e *o#ta(e re(u#ator out%ut 3ero. T)is is accounted for -y

se#ectin( t)e *a#ue of " E so t)at t)e initia# *a#ue of V R is

e!ua# to 3ero. The parameter " E is thereore not ixed# but

varies with the operating condition&


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Fi(ure 9."9$ 9loc@ diagram o" an ac e(citer

Fi(ure 9.$6$ ecti"ier regulation model

'( Exciter and Rectiier


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Fi(ure 9.$&$ )a =ntegrator with windup limits

Fi(ure 9.$&$ )b =ntegrator with non-windup limits

e%resentation0

System e!uation0

;imitin( action0

e%resentation0

System e!uation0

;imitin( action0

)indup and *on!)indup Limits


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9.7.$ Mode#in( of Com%#ete Excitation Systems

Fi(ure 9.$5 de%icts t)e (enera# structure of a detai#ed

excitation system mode# )a*in( a one8to8one

corres%ondence +it) t)e %)ysica# e!ui%ment.


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Standard IEEE Mode#sStandard IEEE Mode#s

IEEE )as standardi3ed 1" mode# structures for

re%resentin( t)e +ide *ariety of excitation systems

current#y in use 4see IEEE Standard &"1.'8155"0

t)ese mode#s are intended for use in transient

and sma##8si(na# sta-i#ity studies

Fi(ures 9.&6 to 9.&$ s)o+ four exam%#es


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%& Type +(%' Exciter model

,& Type '(%' Exciter model

Fi(ure 9.&6$ =EEE type 3C7& e(citation system model. ©=EEE 7557>4?

Fi(ure 9.&1$ =EEE type &C7& e(citation system model. ©=EEE 7557>4?

T)e ty%e 2C1A exciter mode# re%resents fie#d contro##ed dc

communtator exciters, +it) continuous#y actin( *o#ta(e re(u#ators.T)e exciter may -e se%arate#y excited or se#f excited, t)e #atter ty%e

-ein( more common.


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/& Type '(0' exciter model

0& Type ST%' exciter model

T)e ty%e AC&A exciter mode# re%resents an a#ternator su%%#ied contro##ed

rectifier excitation system 8 a )i() initia# res%onse excitation systemuti#i3in( fu## +a*e t)yristor -rid(e circuit. Excitation system sta-i#i3ation is

usua##y %ro*ided in t)e form of a series #a(8#ead net+or: 4transient (ain

reduction. T)e time constant associated +it) t)e re(u#ator and firin( of

t)yristors is re%resented -y T '. T)e o*era## (ain is re%resented -y " '& T)e

rectifier o%eration is confined to mode 1 re(ion. ectifier re(u#ation effects

on exciter out%ut #imits are accounted for -y constant " ( .

T)e ty%e ST1A exciter mode# re%resents %otentia#8source contro##ed8rectifier

systems. T)e excitation %o+er is su%%#ied t)rou() a transformer from

(enerator termina#s t)erefore, t)e exciter cei#in( *o#ta(e is direct#y

%ro%ortiona# to (enerator termina# *o#ta(e. T)e effect of rectifier re(u#ation

on cei#in( *o#ta(e is re%resented -y " ( . T)e mode# %ro*ides f#exi-i#ity to

re%resent series #a(8#ead or rate feed-ac: sta-i#i3ation. ecause of *ery

)i() fie#d forcin( ca%a-i#ity of t)e system, a fie#d current #imiter is

sometimes em%#oyed t)e #imit is defined -y l LR and t)e (ain -y " LR .

Fi(ure 9.&"$ =EEE type &C& e(citation system model © =EEE 7557 >4?

Fi(ure 9.&$$ =EEE type ST7& e(citation system model © =EEE 7557 >4?


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Mode#in( of ;imitersMode#in( of ;imiters

Standard mode#s do not inc#ude #imitin( circuits

t)ese do not come into %#ay under norma#

conditions

T)ese are, )o+e*er, im%ortant for #on(8term and*o#ta(e sta-i#ity studies

Im%#ementation of t)ese circuits *aries +ide#y

mode#s )a*e to -e esta-#is)ed on a case -y case

-asis

Fi(ure 9.&? s)o+s as an exam%#e t)e mode# of a

fie#d current #imiter


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4a #oc: dia(ram re%resentation

4- ;imitin( c)aracteristics

Fi(ure 9.&?$ 6ield-current limiter model

02-2 excitation course (1)

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