fundamentalsofgeneratorprotection

8/16/2019 fundamentalsofgeneratorprotection

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Abdul Wahab Memon 1

g GE EnergyServices

11/11/2001

Fundamentals of Generator Protection

by

Abdul Wahab Memon


2/43

Abdul Wahab Memon 2

g GE EnergyServices

11/11/2001

• Single line and three diagrams are schematics used by Poer Systems

!ngineers to indicate the interconnections of the different "oer

systems com"onents# $hey ill be used through the "resentation to

illustrate the basic com"onents of the Generator Protection System#• Single line diagrams are draings that sho in a %single "hase format&

the interconnection of different "oer systems com"onents# $hey are

intended to "ro'ide a %general "icture& of the "oer system#

• $hree lines diagrams sho a detailed interconnection of all of the

three "hases of the different "oer system com"onents#

Single (ine and $hree (ine )iagrams


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Abdul Wahab Memon *

g GE EnergyServices

11/11/2001

Single (ine )iagram


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Abdul Wahab Memon +

g GE EnergyServices

11/11/2001

$hree (ine )iagram


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Abdul Wahab Memon ,

g GE EnergyServices

11/11/2001

$hree (ine )iagram


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Abdul Wahab Memon -

g GE EnergyServices

11/11/2001

Protecti'e .elaying om"onents

• $he basic com"onents of a "rotecti'e relaying systems are

nstrument $ransformers

• urrent $ransformers $s3

• Potential $ransformers P$s3 .elays

• )igital Generator Protection )GP3

• !lectromechanical .elays

4ther om"onents

• ircuit 5rea6ers

• ontrol and $ri" ircuits

• $erminal bloc6s and control ires

!7ui"ment to be Protected


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Abdul Wahab Memon 8

g GE EnergyServices

11/11/2001

nstrument $ransformers

nstrument transformers9 in general9 are electromagnetic de'ices

designed to electrically isolate the high 'oltage "oer system from thelo 'oltage control circuits# $hey are designed to reduce the

magnitude of the "oer system currents and 'oltages to le'els that the

"rotecti'e relaying de'ices can safely manage#


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Abdul Wahab Memon :

g GE EnergyServices

11/11/2001

urrent $ransformers


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Abdul Wahab Memon ;

g GE EnergyServices

11/11/2001

urrent $ransformers

!7ui'alent ircuit

<l

?e @ $urns

" /@ "

s

e

" Primary urrent

s Secondary urrent

e MagnetiBing

urrent

?e !MF

@ @ominal current

ratio


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Abdul Wahab Memon 10

g GE EnergyServices

11/11/2001

urrent $ransformers

• $he rated secondary current9 in most a""lications9 is either ,A or 1A#

n the CS9 the great maDority of the installations use ,A rated $s#

• As a rule of thumb9 the rated "rimary current of the current

transformer is normally chosen as 1#, times the maEimum antici"atedsteady state load current#

• $y"ically a 10 ire 1 ohm "er 1000 ft3 is used to connect the

secondary side of the $s to the load#

• $he burden im"edance is the total im"edance connected to the $

terminals eEcluding the im"edance of the ire# $he im"edance of the)GP is 0#022 ohms H ,I for ,A relays#


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g GE EnergyServices

11/11/2001

urrent $ransformers

Polarity mar6s are used to indicate the direction of the flo of current in

the secondary side of the current transformer critical for some relaying

a""lications such as differential and re'erse "oer relays3# $he

nomenclature used is such that if the "rimary current lea'e enter3 the

current transformer through the "olarity mar69 it ill enter lea'e3 thecurrent transformer through the "olarity mar6 in the secondary circuit#

$he flo of current in the secondary side is such that the magnetic fluE

that they "roduce ill o""ose the one "roduced by the "rimary current#

• • •• •

•

•

•


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g GE EnergyServices

11/11/2001

urrent $ransformers

Saturation ur'es

?s

e

• From the e7ui'alent circuit of the $J

s "/@ > e

• Ade7uate selection of current transformers

ill arrant that

s "/@ e 03

but if the ?s eEceeds the 6nee "oint 'oltage

of the current transformer9 saturation ill

occur# Cnder saturation9 e could no longer

be neglected#

?6nee


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Abdul Wahab Memon 1*

g GE EnergyServices

11/11/2001

urrent $ransformers

• $he accuracy class of current transformers for "rotecti'e relaying is defined in

A@S standard ,8#1* by to symbolsJ a letter designation and a 'oltage

rating#

• We ill focus on letter designation %& hich

J indicates that the transformer ratio can be calculated# $his classification co'ers

bushing current transformers and any others hose core lea6age fluE has no effect in

the ratio#

• $he secondary terminal 'oltage rating is the 'oltage the transformer ill deli'er

to a standard burden at 20 times secondary current ithout eEceeding a 10K

ratio error#

• A transformer ith accuracy class >100 ill not eEceed a 10K ratio errorhen the secondary current is in beteen 1 to 20 times rated if the secondary

im"edance does not eEceeds 1 ohm#

• >:009 >+009 and >200 are also eEam"les#


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Abdul Wahab Memon 1+

g GE EnergyServices

11/11/2001

urrent $ransformers

Saturation cur'es are also used to estimate the current transformer

"erformance# $hey sho in a log>log scale9 the eEcitation current for a

gi'en a""lied .MS secondary 'oltage as it is 'aried from 1K of theaccuracy class secondary 'oltage to a 'oltage not to eEceed 1-00

'olts3 that ill cause an eEcitation current of , times normal secondary

current hile 6ee"ing the "rimary o"en circuited#


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Abdul Wahab Memon 1,

g GE EnergyServices

11/11/2001

urrent $ransformers

This testreportis in

accordance with

ANSI/IEEE C57.13 1993

ABOET!IS "INET!E O"TA#E

$O%A#IEN E&CITIN#C'%%ENT

$O%AN( 'NIT)I"" NOTBE "ESS

T!AN 95* O$ T!E C'%E A"'E

BE"O) T!IS"INE T!E

E&CITIN#C'%%ENT$O% A

#IEN O"TA#E $O%AN(

'NIT)I"" NOTE&CEE+

T!EC'%EA"'EB(

,O%ET!AN -5*

C'%%ENT%ATIO %ATIO

T'%NS SEC%ES.

O!,S AT 75 C.

+%A)IN#NO.

+ATE ENTE%E+B( C!EC0E+ B(

.5.-.1

1

1

1

1

SECON+A%(E&CITIN# %,SA,2S34 I

.1 .- .5 .1 .- .5 1. -

,O+E"1

rn

B

%

2 . O .

I

7&O 51

s t 6r e n t

eC 8 ra w

nT ar 9s o c

ea t r $ .8

se r nI

:3 ; 51

.

51-1A3-;

E&CITATION C'%E

:5

B0!1//1

e

1-1B5:74:9/1-1A-5794:


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Abdul Wahab Memon 1-

g GE EnergyServices

11/11/2001

urrent $ransformers

Wye connection

.

.

.

.

• • • •• •

• .elay currents in

"hase ith system

currents

•.es"ond to all systemloads or fault

geometries

• Fa6e residual currents

due to $ beha'ior


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g GE EnergyServices

11/11/2001

urrent $ransformers

)elta connection.

.

. • • • • • •


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Abdul Wahab Memon 1:

g GE EnergyServices

11/11/2001

urrent $ransformers

• urrent transformers sometimes are connected delta to meet the re7uirements

of the relays connected to them#

• For balance three "hase loads or faultsJ

s "/@3 L S.$ * S.$ S7uare .oot

• For "hase to "hase loads or faults

s "/@3 L S.$ *3/2 in to "hases3

s "/@3 L S.$ * in one "hase3

• $he secondary currents are shifted *0Irelati'e to the "rimary for three "hase

faults or loads

)elta onnected


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Abdul Wahab Memon 1;

g GE EnergyServices

11/11/2001

Potential $ransformers


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g GE EnergyServices

11/11/2001


• Potential transformers P$s39 also 6non as 'oltage transformers9 are

normal transformers hose "rimary indings are connected directly to

the high 'oltage "oer system and its secondary indings are rated at

-;#* ? for "hase to neutral 'oltages or 120 ? for "hase to "hase

'oltages# $he "erformance and e7ui'alent circuit are similar to those of

a "oer transformer#

• Since the burden im"edance of the relays connected to the secondary

side of the P$s is normally high9 they beha'e li6e ideal transformersJ

?"/?s @"/@s

here ?" Primary ?oltage N ?s Secondary ?oltageN @" turns of

the "rimary indings and @s turns of the secondary inding#


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g GE EnergyServices

11/11/2001


!7ui'alent ircuit

<m

<l

• •=

>

? "

=

>

@ "

@s

"

@

@ "

s ?

"

<

@

@ "

s

"

s

=

>

?s b

• ?"9 "9 @"

Primary 'oltage9

current and turns

• ?s9 s9 @s

Secondary

'oltage9 current

and turns

•


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g GE EnergyServices

11/11/2001


Wye onnected P$

• $he secondary 'oltages

are a true re"resentation

of all three "hase to

ground 'oltages#• $hree sets of P$s are

re7uired#

a

b

c

•

•

•

•

•

•

)

GP


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Abdul Wahab Memon 2*

g GE EnergyServices

11/11/2001


4"en )elta onnected P$

•(ine to neutral 'oltages

are not a'ailable#

• 4nly to sets of P$s are

re7uired#

a

b

c

•

• •

•

)

GP


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Abdul Wahab Memon 2+

g GE EnergyServices

11/11/2001

)igital Generator Protection


25/43

Abdul Wahab Memon 2,

g GE EnergyServices

11/11/2001

Single (ine )iagram


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Abdul Wahab Memon 2-

g GE EnergyServices

11/11/2001

)GP onnection )iagram


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g GE EnergyServices

11/11/2001

)ifferential Protection :83

•

•

•

•

4

. .

" O "

Os s

O > s s

• )uring normal o"eration or faults outside of the $s differential Bone3 no

current flos through the 4"erating oil# 4nly for internal faults ill s be

different than Os#

• $o identical $s are re7uired

. .estrain oil

4 4"erating oil


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Abdul Wahab Memon 2:

g GE EnergyServices

11/11/2001

Ground Fault Protection -+G3

• Most generators are grounded 'ia a

distribution transformer# $he load resistor

.3 connected on the transformer secondary

is designed to limit the fault current

beteen ,> 10 A# Fault currents greater

than 10 A do significant burning damage#

• ,; is a sensiti'e 'oltage relay ty"ically ,

'olts "ic6 u"3 tuned to res"ond only to the

fundamental fre7uency 'oltage ith a time

delay of *>, sec# $he ,; relay "rotects ;,K

of the stator inding#. ,;


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Abdul Wahab Memon 2;

g GE EnergyServices

11/11/2001

4'er eEcitation Protection 2+3

2

1#1:

+,

1#10ALARM

$ime

sec3

?/B PC3• $he magnetic fluE in the generator is

"ro"ortional to the ratio of the

generator terminal 'oltage to the

generator fre7uency#

• !Ecessi'e o'er eEcitation abo'e1#10 "u3 increases core losses and

could result in a brea6don of the

inter>laminar insulation hich could

lead to a core melt don#

• 4'er eEcitation could be the result ofa regulator failure9 a sudden load

reDection9 or a decrease in the

o"erating s"eed

1#0, ontinuos 4"eration

Trip


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Abdul Wahab Memon *0

g GE EnergyServices

11/11/2001

4'er ?oltage Protection ,;3

•

•

•

•

,; .elay

• $he o'er 'oltage relay is used

as a bac6 u" for the o'er

eEcitation "rotection#

• Generally s"ea6ing9 it is set as

follos

> AlarmJ 1#0, Q ? Q 1#10

> n'erse $ri"J 1#10 Q ? Q 1#1:

> nst# $ri"J ? R 1#1:


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g GE EnergyServices

11/11/2001

Motoring / .e'erse Poer Protection *23

• Motoring can occur as a result of the loss of the "rime mo'er

f the field is energiBed the generator ill beha'e as a synchronous motor#

$he generator ill not eE"erience damage but the turbine#

f the field is o"en the generator ill beha'e as a induction motor# naddition to the "ossible damage to the turbine steam39 the induced !ddy

currents ill "roduced o'erheating that could result in rotor damage#

• Sensiti'ity

Prime Mover Motoring Power (%)

Gas Turbine, 1 shaft 60-100Gas Turbine, 2 shaft 10-15

Hydro, run of river 2-10

Hydro, dam 50-100

Steam turbine, conventional 1-4


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g GE EnergyServices

11/11/2001

(oss of !Ecitation +03

• (oss of eEcitation can occur by accidentally tri""ing the field brea6er9

o"en or short circuits in the field inding9 regulator failure9 or loss of

"oer to the field#

• When a synchronous generator losses the field it ill beha'e li6e an

induction generator# $he generator ill run abo'e normal s"eed9 it ill

o"erate at a reduced "oer and it ill absorb reacti'e "oer from the

netor6#

• Since the generator is rotating at sli" fre7uency9 currents ill be

induced in the rotor body and edges# Also an alternating tor7ue ill

a""ear in the generator shaft# $he result of this off fre7uency o"eration

could be rotor o'erheating and e'en rotor failure#


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Abdul Wahab Memon **

g GE EnergyServices

11/11/2001

(oss of !Ecitation +03

R

X @ormal (oad

)iameter d

4ffset 1/2 Od

)elay 0#, sec

)iameter 1#0 "#u

4ffset 1/2 Od

)elay 0#0, sec

• $he loss of

eEcitation relay is a

mho ty"e set to the

folloing 'aluesJ


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Abdul Wahab Memon *+

g GE EnergyServices

11/11/2001

@egati'e Se7uence +-3

• @egati'e se7uence currents could result from

> Cnbalanced loads

> Asymmetrical faults#

> 4"en "hase conditions

• !E"osure to negati'e se7uence currents could cause o'erheating of the rotor

body9 retaining rings and slot edges#


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Abdul Wahab Memon *,

g GE EnergyServices

11/11/2001

@egati'e Se7uence +-3

• $he negati'e se7uence "rotection ill "ermit o"eration u" to the generator

continuous negati'e se7uence limit but tri" the unit if the le'el eEceeds this

'alue long enough to reach the "ermissible 2 3T t limit#

t A@S (imit on2Tt

A@S ontinuous

(imit on 2

2

Alarm

$ri"


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Abdul Wahab Memon *-

g GE EnergyServices

11/11/2001

@egati'e Se7uence Protection +-3

Type of Machine Permissible I2**2t Continous I2

Salient ole !enerator 40 5

"ylindrical rotor, indirectly cooled #0 10

"ylindrical rotor directly cooled $ %00 &'( 10 %

A@S .e7uirements for Cnbalanced Faults on Synchronous Generators


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g GE EnergyServices

11/11/2001

Protecti'e .elaying Actions

• Simultaneous tri" $y"e 3J

$ri"s turbine 'al'es closed

4"ens generator brea6er

4"ens field brea6er

• Generator tri" $y"e 3J 4"ens generator brea6er

4"ens field brea6er

(ea'es turbine running at near to rated s"eed

• 5rea6er $ri" $y"e 3

4"ens the generator brea6er only• Se7uential $ri"

$ri"s the turbine first9 the generator brea6er second and then field brea6er#


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Abdul Wahab Memon *:

g GE EnergyServices

11/11/2001

Protecti'e .elaying Actions

Trip Type Protective !elay "# $%& 2% '( )2 %* %$

Tye ) S,G S,G S S S S

Tye )) G G G G

Tye ))) GSe*uential S

S Steam $urbine Generator Set

G Gas $urbine Generator Set


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Abdul Wahab Memon *;

g GE EnergyServices

11/11/2001

5rea6er $ri" ircuit


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Abdul Wahab Memon +0

g GE EnergyServices

11/11/2001

5rea6er $ri" ircuit


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g GE EnergyServices

11/11/2001

)GP Files


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g GE EnergyServices

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)GP Files

)GP Settings


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g GE EnergyServices

Most ommon Problems

• Generally s"ea6ing9 the most common "roblems found ith the

"rotecti'e relaying systems areJ

ncorrect $ and P$ "olarities

m"ro"er ty"e of $s Wire connections

!Ecessi'e burden load on the secondary of the $s

)amaged )GP cards

(ac6 of )GP settings

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