r&i - Generator,Gt,Uat

8/9/2019 r&i - Generator,Gt,Uat

1/46

ElectricalProtection

Schemes at STPS An Overview


2/46

Electrical Protection Schemes takeactions only after sensing theoccurrence of the fault and thuscannot prevent the fault. (Minorexceptionsare there.)

Then why protections are required?

to limit the damage to thecomponents which are under fault.

to save the rest of the PowerSystem.


3/46

Basic components of the ProtectionSchemes:

urrent !ransformer (!) andPotential !ransformer (P!)

Protective " #uxiliary $elays

ircuit %reaker

& Power Source for operation of theircuit %reaker and auxiliary powerfor $elays


4/46

Functioning of Protection Scheme:

'etting nputs from ! andor P!*$elay determines whether there isany fault. f it detects any fault thengives trip command to the circuit+reaker. 'etting command* circuit

+reaker disconnects the faultysections from rest of the powersystem.


5/46

,ithout leaving any portion of the -etwork

unprotected* dierent protection schemes areprovided for dierent areas of the Electrical

-etwork* e.g.

'enerator* 'enerator !ransformer " /nit!ransformers

Motors 001 kv " 230 kv feeder

001 kv %us +ar

4.456 %us and its systems.

7ur current discussion will +e +ased on8

'enerator* 'enerator !ransformer " /nit!ransformers Protections.


6/46

Protection of Generator, GeneratorTransformer & Unit Transformers

6arious protections are classi9ed into three ma:or !rip 'roups8

Class-A Trip: $esults in simultaneous tripping of prime mover and generator.

overs most Electrical faults.

Class Trip:

!ur+ine is tripped 9rst* followed +y the generator* through ;


7/46

Generator !i"erentialProtection #$%G

t is one of the important protections to protect generatorwinding against internal faults such as phase>to>phaseand three phase>to>ground faults. !his type of fault isvery serious +ecause very large current can ?ow and

produce large amounts of damage to the winding if it isallowed to persist. 7ne set current transformers of thegenerator on neutral and phase side* is exclusively usedfor this protection. !he dierential protection cannotdetect turn>to>turn fault and phase to ground within one

winding for high impedance neutral grounding generator. $elay8 '$> and '$> (@ /M 40 of Siemens)

lass # tripping

nstantaneous


8/46


9/46


10/46


11/46

)*+ Stator Earth 'a(ltProtection #*)G

(@ /M 40 of Siemens)

lass # tripping

nstantaneous %y this protection maximum AD from the line

end of the winding can +e protected. $emainingAD from neutral end remains unprotected.


12/46

..+ Stator Earth 'a(ltProtection #/0G

#n external 01 FG signal is fed to the Statorwinding through secondary of the -'!. f anearth fault occurs in the stator winding

including star point* the 01 FG voltage drivesa current through the fault resistance. (@ /M 40 of Siemens) lass # tripping

nstantaneous


13/46

Generator 1otor Earth 'a(ltProtection #/0 1

#ny rotor 9eld winding of the generator is electricallyisolated from the ground. !herefore the existence ofone ground fault in the 9eld winding will usually notdamage the rotor. Fowever the presence of two or

more ground faults in the winding will cause magneticand thermal im+alance plus localiGed heating anddamage to the rotor metallic parts. !he rotor earthfault may +e caused due to insulation failure ofwinding or inter>turn fault followed +y localiGed heat.

.


14/46

# & voltage is applied +etween rotor shaft(Earthed) and neutral of the Exciter

#rmature. #rmature winding of Exciter isconnected to the 'enerator and '$> (@ /M 40 of Siemens)

lass # tripping


15/46

Generator Stator 2nter T(rn'a(lt Protection #$% G2

'enerator Stator nter !urn open delta transformer. n normal condition(%alanced generator terminal voltage) open delta voltage will

+e Gero +ut in case of inter turn fault a voltage will +eappeared there. Sensing this voltage the relay will operate ifthe voltage +e greater than preset value (corresponding tosingle turn inter turn fault).

7pen delta voltage also appears n case of stator earth fault

and thus -'! secondary voltage is used as a correctionfactor for inter turn fault protection.

$elay8 @SH40 of Siemens

lass # tripping


16/46

GEE1ATO1 U!E1 E3C2TAT2OO1 4OSS O' E3C2TAT2O #0.G

!his protection is applied to generators to detectreduction or loss of excitation to the 9eld windings.

!his condition of the generator may lead to heatingin tur+o alternators.

,hen the synchronous machine with excitation* isconnected to the grid* it generates reactive poweralong with active power to the grid and the rotorspeed is same as that of grid freIuency. ;oss of 9eld

or loss of excitation results in loss of synchronism+etween rotor ?ux " stator ?ux. !he synchronousmachine operates as an induction machine at higherspeed and draws reactive power from the grid.


17/46

!his will result in the ?ow of slip

freIuency currents in the rotor+ody as well as severe torIueoscillations in the rotor shaft. #s

the rotor is not designed to sustainsuch currents or to withstand thehigh alternating torIues which

results in rotor overheating*coupling slippage and even rotorfailure.


18/46

# loss of excitation normally indicates

a pro+lem with the excitation system.

Sometimes it may +e due toinadvertent tripping of 9eld +reaker*open or short circuit of 9eld winding

or loss of source to the exciter. f thegenerator is not disconnectedimmediately when it loses excitation

wide spread insta+ility may veryIuickly develop and ma:or systemshutdown may occur.


19/46

Generator (n5alance loa6 protection ore7ative se8(ence C(rrent Protection #0/G

!his is to protect the generator from sustainedun+alanced load. ,hen the machinedelivering the eIual currents in three phases*no un+alance or negative phase seIuencecurrent is produced as the vector sum of thesecurrents is Gero* when the generator issupplying an un+alanced load to a system* anegative phase seIuence current is imposedon the generator. !he system un+alance may+e due to opening of lines* +reaker failures orsystem faults.


20/46

!he negative seIuence current in the statorwinding creates a magnetic ?ux wave in the air

gap which rotates in opposite direction to thatof rotor synchronous speed. !his ?ux inducescurrents in the rotor +ody* wedges* retainingrings at twice the line freIuency. Feating occurs

in these areas and the resulting temperaturesdepend upon the level and duration of theun+alanced currents. !he protective relayextracts the negative seIuence component of

the stator current and the relay characteristic isan inverse current time operation. !he setting ismatched with withstand characteristic of thegenerator (provided +y the manufacturer).


21/46

GEE1ATO1 O9E1 E3C2TAT2OP1OTECT2O #))GT

Per unit voltage divided +y per unitfreIuency commonly called 6oltsFertG(6up transformer cores. Moderate over?uxing (21A>221D) increases core lossresulting in increase of core temperatures

due to hysterics " eddy currents loss. ;ongterm operation at elevated temperaturescan shorten the life of the stator insulation.


22/46

Severe over ?uxing can +reakdowninter>laminar insulation followed +y

rapid local core melting. 7ver ?uxingnormally can +e caused +y overexcitation during 7>line condition*and load re:ection or #6$ mal>functioning during 7n>line condition.

$elay8 '$> and '$> (@ /M 40 ofSiemens)

lass # tripping


23/46

GEE1ATO1 O9E1 9O4TAGEP1OTECT2O #*)G

'enerator voltage is at present valueunder normal operating conditions asselected +y operator in #6$. f it parts

from preset value* may +e due to #6$mal>functioning or a system distur+ance.Severe over voltage can cause over?uxing and winding insulation failure.

!wo stage operation with de9nite timedelay #larm " trip.


24/46

Generator Stand By Earth FaultProtection (51NG)

$elay gets input from 2A12 # ! of-'! secondary circuit.

n case of stator ground fault* voltageinduced in secondary of the -'!drives a current through the -'$(1.33A ohm). Sensing this current*

$elay operates. lass # tripping with normal inverse

characteristics.


25/46


26/46

Generator Backup ImpedanceProtection (21G)

!he %ackup mpedanceProtection is a de9nite time

graded protection* for a shortcircuit phase fault in 'enerator*'enerator !ransformer* %us

duct or as +ack up of unclearedexternal network fault.


27/46

!wo stage operations are there.

Stage covers up to the '! and gives lass

# tripping with 1.2 sec delay. Stage covers up to the longest 001 kv

feeder and gives lass tripping with 1.4sec time delay. !ime delay is allowed to

clear the feeder fault through tripping ofthe feeder +reaker itself.


28/46

4ow 'orwar6 Power Protection#%G an61everse Power Protection #;G

&ue to stoppage of steam supply* motoring ofthe !' can occur. t will not aect the generator+ut the tur+ine +lades. !o avoid such situations

;ow


29/46

GEE1ATO1 2E?P1OTECT2O #*.G!=

Employed for protection againstaccidental energisation of 'eneratorunit under S&.

#ppearance of current +efore normalterminal voltage is esta+lished*within the preset time.

Employed for protection againstaccidental closing of ircuit %reaker.

lass # protection.


30/46

Un6er 're8(enc@ #$ UG an6Over 're8(enc@ #$OG Protection

/nder freIuency may occur due to sudden outage ofhuge amount of Power nput to the -etwork and 7ver +elow [email protected] FG 1.A sec delay lass trip 7ver freIuency a+ove A2.1 FG 2sec delay #larm

>a+ove A3.1 FG 1.A sec delay lass trip


31/46

Generator O(t Of StepProtection #%$G

!o protect the 'enerator going out ofsynchronism or sta+ility due to heavyexternal faults* insuKcient excitation

etc. !he relay measures the rate of

change of impedance seen +y the

'enerator. !he relay has a polygon impedance

characteristics de9ned +y the

impedance of the 'enerator* '! and


32/46

7ut 7f Step is detected if

the no. of swing of the measuredimpedance through the impedancecharacteristics in a predetermined

period exceeds the preset value. positive seIuence current is greater

than preset value.

negative seIuence current is lessthan preset value. (as it is asymmetrical fault)


33/46

Overall !i"erential Protection#$% OA

nputs to the $elay are from secondary of four!s8

'enerator neutral side !

'! 001 56 side ! /#!> # 24.A 56 side !

/#!> % 24.A 56 side !

Protect the 'enerator* '!* 24.A 56 %us &uctfrom phase to phase fault* three phase>ground fault etc.


34/46


35/46

!he $elay is of %iased &ierentialcharacteristics.

$elay settings are as follows8 Pick up8 1.0 n

Slope 8 1.0A %ase point 8 1.1 n

Slope 8 1.A %ase point 8 0.A n 0ndFarmonic $estraining8 2AD

AthFarmonic $estraining8 31D

Figh Set8 @.A n $elay8@/!43A of Siemens

lass # tripping


36/46

GT >9 si6e 1estricte6 Earth'a(lt #/0 >GT


37/46


38/46

alculation for Sta+ilising $esistance8

'! full load current 32A1112.@30001L J04.4J #

Max fault current L J04.4J1.2CA L A@12 #(Dmpedance 2C.A)

Secy.


39/46

GT Over c(rrentProtection #* GT $elay type8 @SH42 of Siemens

Pick up 8 1. # (!$ 21112)

!ime setting 1.0A sec

-ormal nverse characteristics

Figh set 8 J # (nst)

lass # tripping.


40/46

UAT !i"erential protection#$%UAT an6 // Bv si6e 1E' #/01

%iased &ierential Protection

Pick up8 1.0 n

Slope 8 1.0A %ase point 8 1.1 n

Slope 8 1.A %ase point 8 0.A n

0ndFarmonic $estraining8 2AD

AthFarmonic $estraining8 31D

Figh Set8 20.1 n

>$E< 8 1.0 #

Sta+ilising resistance 8 2111 ohm.

$elay8@/!423 of Siemens

lass # tripping


41/46

UAT Over c(rrent Protection#*.* UAT

$elay type8 @SH42 of Siemens

Pick up 8 A # (!$ J11A)

!ime setting 1.4 sec

-ormal nverse characteristics

Figh set 8 41 # (nst)

lass # tripping.


42/46

GT UAT

P1OTECT2OS#=echanical

'as operated (chholtD rela@ protection


43/46

'as operated (chholtD rela@ protection

7perates when gases produced +y Electricaldischargearcing inside the transformer travel from

!ank to onservator.Alarm element operates 5@ the slowcollection of 7as in the 7as trap of the rela@while the 7ases are escapin7 from thetransformer tanB to the conservator Thecollecte6 7ases 6isplaces oil 6ownwar6 an6the oat switch operates

Sudden or rapid rush of gases and oil to theconservator* for rapid arcing or a severe fault

pushes a ?ap in the ?ow path* to operate the tripelement

#lso trips for ver@ low oil level in Transformer,in case of tanB leaBa7e, which is sense6 5@

fall in Oil level in conservator


44/46

Press(re 1elief !evice #!iaphra7m:

7perates for excessive pressure rise and or

rate of rise of pressure.

ts purpose is to #voids rupture of tank* in

case of an internal fault?ashover leading to7il spillage and spread of 9re.

Oil s(r7e protection:

-ormally provided for O7;! ham+er

t is similar to %uchholtG relay* +ut with onlyoil surge element (no gas collection cham+erand ?oat)


45/46

O24 TE=PE1ATU1E #A4A1= & T12P:

Set as per manufacturers recommendation

7perates for condition like s(staine6 over loa6 or loss of coolin7

which ca(se a5normal Oil temperat(re rise which can re6(cethe life of the transformer ins(lation

F2!2G TE=PE1ATU1E #A4A1= & T12P:

!op oil temperature corrected for 0$ heating +y proportional currentin replica resistance* otherwise functionally identical to 7! system

a+ove.


46/46

T>AH IOU

Documents

r&i - Generator,Gt,Uat