Generator Protection

GENERATOR PROTECTIONGENERATOR PROTECTION

ByBy

Subhash ThakurSubhash Thakur

[email protected]@ntpceoc.co.in

Gen Stator Thermal ProtectionGen Stator Thermal Protection Field Thermal ProtectionField Thermal Protection Gen stator fault ProtectionGen stator fault Protection Gen rotor field ProtectionGen rotor field Protection Gen abnormal operating conditionsGen abnormal operating conditions System backup ProtectionSystem backup Protection Power transformer ProtectionPower transformer Protection

Generator ProtectionGenerator Protection


Stator Thermal protectionStator Thermal protection

Thermal protection for the generator stator core and windings Thermal protection for the generator stator core and windings Generator overloadGenerator overload

Winding Temperature Winding Temperature Over currentOver current

Failure of cooling systemsFailure of cooling systems RTDs ThermocoupleRTDs Thermocouple Flow and pressure sensorFlow and pressure sensor

Localized hot spots caused by core lamination Localized hot spots caused by core lamination insulation failures or by localized or rapidly developing insulation failures or by localized or rapidly developing winding failureswinding failures Generator Core monitorGenerator Core monitor


Turbine-generator short time thermal capability for balanced three-phase loading


Generator Field Thermal protectionGenerator Field Thermal protection

Thermal ProtectionThermal Protection Direct rotor Body temperature measurement Direct rotor Body temperature measurement

not possible not possible Core Monitor may detect overheatingCore Monitor may detect overheating

Protection for field over excitationProtection for field over excitation IDMT/ Definite Time IDMT/ Definite Time Excitation limitersExcitation limiters

Generator Protection Generator Protection

Generator field short time thermal capability

Generator Protection Requirement Generator Protection Requirement

Generator faults are considered to be serious since they Generator faults are considered to be serious since they may cause severe and costly damage to insulation, may cause severe and costly damage to insulation, windings, and the core may also produce severe windings, and the core may also produce severe mechanical torsional shock to shafts and couplings.mechanical torsional shock to shafts and couplings.

Fault current may continue to flow for many seconds even Fault current may continue to flow for many seconds even after the generator is tripped, because of trapped flux after the generator is tripped, because of trapped flux within the machine, thereby increasing the amount of fault within the machine, thereby increasing the amount of fault damage.damage.

As a consequence, for faults in or near the generator that As a consequence, for faults in or near the generator that produce high magnitudes of short-circuit currents, some produce high magnitudes of short-circuit currents, some form of high-speed protection is normally used to trip and form of high-speed protection is normally used to trip and shut down the machine as quickly as possible in order to shut down the machine as quickly as possible in order to minimize damage. minimize damage.

Stator fault ProtectionStator fault Protection

High Speed Differential protectionHigh Speed Differential protection– Will detect Phase to Phase Faults, Double phase Will detect Phase to Phase Faults, Double phase

faults involving earthfaults involving earth– Single phase to Earth will not be detected due to Single phase to Earth will not be detected due to

limited earth fault current available.limited earth fault current available.

Two types of high-speed differential relays Two types of high-speed differential relays are commonly used for stator phase fault are commonly used for stator phase fault detection:detection:– High-impedance differentialHigh-impedance differential– Biased differentialBiased differential

High Impedance Differential RelayHigh Impedance Differential Relay

Use two sets of identical dedicated CTs.Use two sets of identical dedicated CTs. PS class CT with stringent parameters to be usedPS class CT with stringent parameters to be used This scheme has higher sensitivity than the This scheme has higher sensitivity than the

percentage differential relay.percentage differential relay. Through fault stability achieved by using Through fault stability achieved by using

stabilising resistors in the relay circuitstabilising resistors in the relay circuit..

High Impedance Differential RelayHigh Impedance Differential Relay

Stabilizing resistor calculation :Stabilizing resistor calculation : Vs = If (Rct+2Rl)Vs = If (Rct+2Rl) If - Maximum through fault current in the If - Maximum through fault current in the

systemsystem (converted to sec side)(converted to sec side)

Rct- Secondary resistance of the CTRct- Secondary resistance of the CT Rl – lead resistance of the sec connection Rl – lead resistance of the sec connection (typ 8.73 ohms per km for 2.5 sq mm cu (typ 8.73 ohms per km for 2.5 sq mm cu

cable)cable) Rs = Vs/Is – (VA/Is*Is)Rs = Vs/Is – (VA/Is*Is)

Typical setting 5- 10% of rated current.Typical setting 5- 10% of rated current.

Biased Type Diff RelayBiased Type Diff Relay

Less stringent CT parameters. CTs can be shared with other Less stringent CT parameters. CTs can be shared with other protections.protections.

Through fault stability achieved through biasing.Through fault stability achieved through biasing. CT mismatch (typ of the order of 1:5 ) can be accommodated.CT mismatch (typ of the order of 1:5 ) can be accommodated. More suitable for numerical integrated protection systems as the More suitable for numerical integrated protection systems as the

CTs can be shared for many functions.CTs can be shared for many functions. Modern numerical relays have flexible settings for Modern numerical relays have flexible settings for Id, b (point of slope change) and the slopes. Id, b (point of slope change) and the slopes.

Biased Differential protectionBiased Differential protection

Typical bias setting: 10% of rated current.

Current based systemCurrent based system– For generators with split neutrals with all six terminals For generators with split neutrals with all six terminals

brought out on neutral side.brought out on neutral side.– Delayed low-set o/c relay which senses the current in Delayed low-set o/c relay which senses the current in

the connection between the neutrals of the stator the connection between the neutrals of the stator windingswindings

Voltage based system Voltage based system – Relay compares the neutral NGT sec voltage and Relay compares the neutral NGT sec voltage and

Genertaor terminal open delta voltage. Genertaor terminal open delta voltage. – Balance during external E/F or normal conditionBalance during external E/F or normal condition– During inter turn fault open delta voltage will be During inter turn fault open delta voltage will be

developed and NGT sec voltage will be zero, resulting in developed and NGT sec voltage will be zero, resulting in a differential voltage which makes the relay operate.a differential voltage which makes the relay operate.

Typical settingTypical setting

Definite time type relays: minimum setting with 1 sec delay.Definite time type relays: minimum setting with 1 sec delay.

INTERTURN PROTECTIONINTERTURN PROTECTION

Inter turn protectionInter turn protection

Split Phase Protection

Voltga

Voltage Based

Generator Grounding PracticesGenerator Grounding PracticesIt is common practice to ground all types of It is common practice to ground all types of

generators through some form of external generators through some form of external impedanceimpedance

limit the mechanical stresses and fault damage limit the mechanical stresses and fault damage in the machine, in the machine,

to limit transient voltages during faults, and to limit transient voltages during faults, and to provide a means for detecting ground faults to provide a means for detecting ground faults

within the machine.within the machine.

Typical Grounding practicesTypical Grounding practicesUngroundedUngroundedSolid GroundingSolid GroundingHigh-impedance groundingHigh-impedance groundingLow-resistance groundingLow-resistance groundingReactance groundingReactance groundingGrounding-transformer groundingGrounding-transformer grounding

Generator Grounding PracticesGenerator Grounding Practices UngroundedUngrounded

– Phase to ground fault current limitedPhase to ground fault current limited– Generators are not often operated ungrounded Generators are not often operated ungrounded

as it may produce high transient over-voltages as it may produce high transient over-voltages during faults and makes the fault location during faults and makes the fault location difficult to determine.difficult to determine.

Solid GroundingSolid Grounding– Solid grounding of a generator neutral is not Solid grounding of a generator neutral is not

generally used since this practice may result in generally used since this practice may result in high mechanical stresses and excessive fault high mechanical stresses and excessive fault damage in the machine.damage in the machine.

Generator Grounding PracticesGenerator Grounding Practices High Impedance GroundingHigh Impedance Grounding

– High resistance groundingHigh resistance groundingThe high-resistance grounding method utilizes a resistor The high-resistance grounding method utilizes a resistor connected across the secondary of the distribution transformer connected across the secondary of the distribution transformer to limit the maximum ground fault current. to limit the maximum ground fault current. For a single-phase-to-ground fault at the machine terminals, the For a single-phase-to-ground fault at the machine terminals, the primary fault current will be limited to a value in the range of primary fault current will be limited to a value in the range of about 3 A to 25 A.about 3 A to 25 A.

– Ground fault neutralizer groundingGround fault neutralizer grounding The ground fault neutralizer grounding method utilizes a The ground fault neutralizer grounding method utilizes a

secondary tunable reactor to limit the maximum ground fault secondary tunable reactor to limit the maximum ground fault current.current.

Low –resistance groundingLow –resistance grounding In this method, a resistor is connected directly between the In this method, a resistor is connected directly between the

generator neutral and ground. generator neutral and ground. For a single-phase-to-ground fault at its terminals the primary For a single-phase-to-ground fault at its terminals the primary

fault current will be limited to a value in the range of about 200 A fault current will be limited to a value in the range of about 200 A up to 150% of rated full-load current. up to 150% of rated full-load current.

Resistor cost and size usually preclude the use of resistors. Resistor cost and size usually preclude the use of resistors.

Stator Earth Fault ProtectionStator Earth Fault Protection

E/F current is typically limited to 5-10A toE/F current is typically limited to 5-10A to minimizes the damage to laminations. minimizes the damage to laminations. First earth fault is less critical but needs clearance asFirst earth fault is less critical but needs clearance as IIt may develop into a ph to ph fault .t may develop into a ph to ph fault . Second fault will result in very high current.Second fault will result in very high current.

Two types of coverage:Two types of coverage: 100 % winding100 % winding 95 % winding95 % winding

Any fault involving earth results shift of Any fault involving earth results shift of Neutral voltage.Neutral voltage.

This shift can be detected by measuring the This shift can be detected by measuring the Voltage across Grounding Resistor Or from the Voltage across Grounding Resistor Or from the generator terminal Open Delta voltage.generator terminal Open Delta voltage.

Typical coverageTypical coverage 95% Of Stator Winding. 95% Of Stator Winding.

Typical Setting:Typical Setting:– 5% with 1 Sec TD5% with 1 Sec TD

95 % Stator Earth Fault95 % Stator Earth Fault

100 % Stator E/F Protection100 % Stator E/F Protection

• Third Harmonic PrincipleThird Harmonic Principle• Relay responds to the reduction of the 3Relay responds to the reduction of the 3rdrd

Harmonic Component Harmonic Component • For a Stator Phase-to-ground fault at or For a Stator Phase-to-ground fault at or

near the Generator Neutral, there will be an near the Generator Neutral, there will be an increase in third Harmonic Voltage at The increase in third Harmonic Voltage at The Generator Terminals, which Will Cause Relay Generator Terminals, which Will Cause Relay Operation.Operation.

100% SEF based on third harmonics 100% SEF based on third harmonics measurementsmeasurements

100% SEF based on third harmonics 100% SEF based on third harmonics measurementsmeasurements

DisadvantagesDisadvantages

Due to design variations, certain Due to design variations, certain generating units may not produce generating units may not produce sufficient third harmonic voltages. sufficient third harmonic voltages.

This method does not protect the This method does not protect the machine during stand still conditions.machine during stand still conditions.

100% stator earth fault protection 100% stator earth fault protection (Low freq. injection principle)(Low freq. injection principle)

20 Hz

RE

max.200 V

I

20 Hz

RE

max.200 V

I

Detects the ground Detects the ground faultsfaults by injecting a low by injecting a low frequency frequency signal (say 20 hz) at the signal (say 20 hz) at the neutral earthing neutral earthing transformer transformer and monitor the earth and monitor the earth current in the winding.current in the winding.

SEF USING INJECTION PRINCIPLE SEF USING INJECTION PRINCIPLE TYPICAL CONNECTION TYPICAL CONNECTION

Typical settings for 500 MW unitTypical settings for 500 MW unitTrip : 1 KOhm / 1 secTrip : 1 KOhm / 1 sec

Alarm : 10 Kohm /10 secAlarm : 10 Kohm /10 sec

DC or AC

Blocking

RL

Bandpass(8 at 20 Hz)

20-Hz-Generator(appr. 25 V)

U

I

Relay

a

b

a

b

400A5A

Low ohmicEarthing transformer

Neutraltransformer

Rotor Earth Fault ProtectionRotor Earth Fault Protection

EffectsEffects First rotor E/F does not cause immediate damageFirst rotor E/F does not cause immediate damage Second E/F results in short circuit of rotor winding.Second E/F results in short circuit of rotor winding. Causes magnetic unbalance/mechanical forcesCauses magnetic unbalance/mechanical forces

Measure Low frequency injection method

– Modern rotor earth fault protection relay operates on the principle of low frequency injection into the field winding via capacitors.

– Corresponding current or resistance during E/F is sensed

Typical setting for a 500 mw Generator Alarm 25 k ohm time = 10 sec Trip 5 k ohm time = 1 sec

Rotor E/F Using Low frequency injection methodRotor E/F Using Low frequency injection method

Rotor E/F Using Low frequency injection methodRotor E/F Using Low frequency injection method

Negative sequence protectionNegative sequence protection

Causes of negative squence currentCauses of negative squence current– one pole open in lineone pole open in line– Unbalanced loadsUnbalanced loads– Unbalanced system faultsUnbalanced system faults

Induces double frequency rotor current in the rotor surface Induces double frequency rotor current in the rotor surface thereby leading to high and dangerous temperatures in a short thereby leading to high and dangerous temperatures in a short span of time.span of time.

Negative sequence protection relays shall be set to the NPS Negative sequence protection relays shall be set to the NPS withstand capability of the machine which is given bywithstand capability of the machine which is given by

k = k = ii2222x t x t

Typical for 500 mw Typical for 500 mw Permissible neg seq current = 5 – 8 % of stator currentPermissible neg seq current = 5 – 8 % of stator current

permissive ipermissive i2222x t = 5 – 10x t = 5 – 10

settings adopted for ntpcsettings adopted for ntpc ii2 =2 = = 7.5 % = 7.5 % ii22

22xtxt = 8 = 8

Negative sequence protectionNegative sequence protection

Loss of field protectionLoss of field protection

Loss of field protectionLoss of field protection

Acts as an induction generatorActs as an induction generator Induced eddy currents in the field winding, rotor body, Induced eddy currents in the field winding, rotor body,

wedges and retaining ringswedges and retaining rings MW flow in to the system/ MVAR flows in to the machine.MW flow in to the system/ MVAR flows in to the machine. The apparent imp moves in to the forth quadrant of x-y The apparent imp moves in to the forth quadrant of x-y

planeplane

Method of detection:Method of detection: Impedance measurement with Under VoltageImpedance measurement with Under Voltage

Some relays are set in the admittance plane matching Some relays are set in the admittance plane matching with the capability curve of the machine.with the capability curve of the machine.

Trip characteristics of loss of field protectionTrip characteristics of loss of field protection

Trip characteristics of loss of field Trip characteristics of loss of field protectionprotection

Trip characteristics of loss of field protectionTrip characteristics of loss of field protection

Generator Capability CurveGenerator Capability Curve

RELAY LINE

Out of step protectionOut of step protection

Machine runs out of synchronism with the networkMachine runs out of synchronism with the network Cyclic variation of rotor angle Cyclic variation of rotor angle Current increases.Current increases. Results in the winding stressResults in the winding stress It may also damage the auxiliaries of the affected unit It may also damage the auxiliaries of the affected unit

Method of detection Method of detection – Variations in impedance measured at Gen TerminalVariations in impedance measured at Gen Terminal– Distinguish between the recoverable swing and the Distinguish between the recoverable swing and the

irrecoverable swingirrecoverable swing– blinders and a supervisory mho element, blinders and a supervisory mho element, – Trips the machine when imp is inside the mho and Trips the machine when imp is inside the mho and

cross the blinders with the specified time.cross the blinders with the specified time.– Minimum impedance (multiple zone) + counting no Minimum impedance (multiple zone) + counting no

of swingsof swings

Out of step protection settingsOut of step protection settings

Typical Over Fluxing Withstand Typical Over Fluxing Withstand CapabilityCapability

Accidental back energisationAccidental back energisation CauseCause

– Flash over of the generator breakerFlash over of the generator breaker– Incorrect closing of the generator breakerIncorrect closing of the generator breaker

EffectsEffects

– Cause operation as an induction motorCause operation as an induction motor– Damage machine and turbineDamage machine and turbine– The rapid heating iron paths near the rotor surface due to The rapid heating iron paths near the rotor surface due to

stator induced current. stator induced current.

Over current + CB auxiliary contactsOver current + CB auxiliary contacts– checks for the current when the gen breaker contacts checks for the current when the gen breaker contacts

are openare open– set below the rated current(90%)set below the rated current(90%)– o/c and u/v measurementso/c and u/v measurements

Setting - Setting - o/c 1.2 times & o/c 1.2 times & u/v 70% u/v 70%

Accidental Back EnergisationAccidental Back Energisation

Reverse /Low forward power ProtectionReverse /Low forward power Protection

Low forward and reverse powerLow forward and reverse power inter lock inter lock

To allow entrapped steam in the turbine to be To allow entrapped steam in the turbine to be utilized to avoid damage of the turbine blade.utilized to avoid damage of the turbine blade.

To protect the machine from motoring actionTo protect the machine from motoring action

Trip under class B after a short time delay in Trip under class B after a short time delay in case the turbine is already tripped ( typ set at case the turbine is already tripped ( typ set at 2 sec)2 sec)

Trip under class A, after a Trip under class A, after a long time delaylong time delay if if turbine is not tripped (typically set at 10 -30 turbine is not tripped (typically set at 10 -30 sec)sec)

Power setting typ 0.5 % of rated powerPower setting typ 0.5 % of rated power

O/V & U/F protectionO/V & U/F protection

Typical settings of a 3 stage o/v relay is as followsTypical settings of a 3 stage o/v relay is as follows

– Alarm 110 % 2 sec Alarm 110 % 2 sec – Trip 120 % 1 secTrip 120 % 1 sec– 140 % instantaneous140 % instantaneous

Abnormal Frequency protectionAbnormal Frequency protection

Typical setting:Typical setting:

U/FU/F O/FO/F

Alarm - 48.5hz 5 sec 51 hz 1 secAlarm - 48.5hz 5 sec 51 hz 1 sec

Trip - 47.4 hz 2 secTrip - 47.4 hz 2 sec

For uncleared system faultFor uncleared system fault

The backup protection is time delayed to The backup protection is time delayed to coordinate with the zone 3 setting of lines coordinate with the zone 3 setting of lines

Detected byDetected by– over current over current – impedanceimpedance– Impedance type preferred as the line is Impedance type preferred as the line is

provided with distance relaysprovided with distance relays Setting should be made to cover the GT imp and Setting should be made to cover the GT imp and

the longest line impedance.the longest line impedance. Setting should take care of the infeed from other Setting should take care of the infeed from other

generators connected to the same bus also.generators connected to the same bus also. Time setting 1.5 –2 secTime setting 1.5 –2 sec

Backup impedance protection

Over view of type of fault Vs protectionOver view of type of fault Vs protectionFAULT/FAULT/

ABNML ABNML EFFECTEFFECT PROTECTIONPROTECTION

Thermal Thermal over loadingover loading

Over heating of stator wdg / Over heating of stator wdg / insulation failureinsulation failure

Thermo couples/Thermo couples/

Over current relaysOver current relays

External External fault fault

Unbalanced loading stressUnbalanced loading stress Over load/negative phase Over load/negative phase sequence relay, Backup sequence relay, Backup Impedance/ Earth FaultImpedance/ Earth Fault

Stator faultsStator faults

Winding burn outWinding burn out

Shorting of of core Shorting of of core laminationlamination

Differential protectionDifferential protection

100% E/F prot/95% E/F100% E/F prot/95% E/F

Inter turn protectionInter turn protection

Rotor faultRotor fault Damage to shaft/bearingDamage to shaft/bearing Two stage rotor E/F Two stage rotor E/F protectionprotection

MotoringMotoring Damage to turbine bladesDamage to turbine blades LFPR/Rev power Inter lockLFPR/Rev power Inter lock

O/V,O/F,U.FO/V,O/F,U.F Insulation failure,Heating of Insulation failure,Heating of core failure of bladescore failure of blades

O/V relay Volt/Hz relayO/V relay Volt/Hz relay

U/F relayU/F relay

Loss of fieldLoss of field Induction gen operationInduction gen operation

Absorb MVAR from Absorb MVAR from system/damage to rotor wdgsystem/damage to rotor wdg

Loss of fieldLoss of field

COMMONLY USED GEN/GEN TRFR RELAYSCOMMONLY USED GEN/GEN TRFR RELAYSPROTECTIPROTECTIONON

ALSTOM/AREVAALSTOM/AREVA ABBABB SIEMENSSIEMENS REMARKREMARK

HIGH IMP HIGH IMP DIFFDIFF

CAG 34CAG 34

MICOM P343MICOM P343RADHARADHA

REG 216REG 216 7UM SERIES7UM SERIESIn case of duplicated diff, In case of duplicated diff, one low imp & one high one low imp & one high imp preferredimp preferred

For trfr biased relay For trfr biased relay preferredpreferred

BIASED BIASED DIFFDIFF

MBCHMBCH

MICOMMICOM

P 633P 633

RADSBRADSB

RET 316 RET 316 7 UT7 UT

POWER POWER RELAYSRELAYS

RXPERXPE PPXPPX 7 UM SERIES7 UM SERIES Directional power relays Directional power relays

LOSS OF LOSS OF FIELDFIELD

YCGFYCGF RAGPC(DIR RAGPC(DIR O/C+U/V)O/C+U/V)

7UM SERIES7UM SERIES ImpedanceImpedance / /

admittanceadmittance

100% E/F100% E/F PVMMPVMM

MICOM P343MICOM P343

PG871PG871

GIX GIX

REG 216REG 2167UE227UE22

7UM SERIES7UM SERIESLow frequency injection Low frequency injection typetype preferred over 3 rd preferred over 3 rd harmonic principleharmonic principle

95% E/F95% E/F VDGVDG 7UM SERIES7UM SERIES Open delta of gen sec VTOpen delta of gen sec VT

BACK UP BACK UP IMPIMP

YCG15YCG15

MICOM SERIESMICOM SERIESRAKZBRAKZB

REG REG 7UM 5167UM 516 Minimum impedance Minimum impedance

PROTECTIPROTECTIONON

ALSTOMALSTOM ABBABB SIEMENSSIEMENS RemarksRemarks

OVER OVER FLUXINGFLUXING

GTTMGTTM RATUBRATUB

RALKRALK7RW7RW IDMTIDMT

POLE POLE SLIPPINGSLIPPING

ZTO+YTGZTO+YTGM15M15

RXZF+RXPERXZF+RXPE 7UM 5167UM 516 IMPEDANCEIMPEDANCE

IMP+ DIR O/CIMP+ DIR O/C

IMP+NO OF POWER IMP+NO OF POWER SWINGSSWINGS

ACC. ACC. BACK BACK ENERGENERG

CTIG CTIG RAGUARAGUA 7UM SERIES7UM SERIES O/C +CB AUX O/C +CB AUX CONTACTCONTACT

CURRENT CURRENT ELEMENT+U/VELEMENT+U/V

INTERINTER

TURNTURNVDGVDG

MICOM MICOM REGREG 7UM SERIES7UM SERIES comp of open delta 0n comp of open delta 0n

gen term+ngt sec gen term+ngt sec voltagevoltage

NEG PH NEG PH SEQSEQ

CTNCTN RARIBRARIB 7UM SERIES7UM SERIES MEASUREMENT OF I2MEASUREMENT OF I2

REFREF CAG/FAGCAG/FAG RADHDRADHD 7UM SERIES7UM SERIES HIGH IMP PREFFEREDHIGH IMP PREFFERED

ROTOR ROTOR E/FE/F

VDGVDG

MICOM MICOM SERIESSERIES

REG SERIESREG SERIES 7UR 227UR 22

7 UM SERIES7 UM SERIES

Type of faultType of fault ProtectionProtection ChannelChannel RecommendaRecommendationtion

Short circuitShort circuit 87 G187 G1

87G287G2

87 GT87 GT

11

22

1 OR 21 OR 2

Stator Earth FaultStator Earth Fault 64G164G1

64G264G211

22

Inter turnInter turn 95G95G 1 OR 21 OR 2

unbalanceunbalance 46G46G 1 OR 21 OR 2

Over loadOver load 51G51G AlarmAlarm

Loss of excitationLoss of excitation 40G140G1

40G240G211

22

Out of stepOut of step 98G98G 1 OR 21 OR 2 >100 MW>100 MW

MotoringMotoring 32 G1/2 / 37 G1/G232 G1/2 / 37 G1/G2 1 / 21 / 2

O/V,O/FO/V,O/F

U/FU/F59/9959/99

81G1/81G181G1/81G11 /21 /2

1/21/2

System back upSystem back up 21G21G 1 & 21 & 2

Accidental energisationAccidental energisation 50GDM50GDM 1 &21 &2

Rotor E/FRotor E/F 64F64F 1 OR 21 OR 2

Generator Transformer ProtectionGenerator Transformer Protection

DifferentialDifferential– biased differential biased differential

20 % bias setting (to cover tap range and20 % bias setting (to cover tap range and ct mismatch if any)ct mismatch if any)time: instantaneoustime: instantaneous

Back up earth faultBack up earth faultDefinite time or IDMT relayDefinite time or IDMT relay30 % with 2 sec time delay30 % with 2 sec time delay

To be coordinated with distance prot zone 3To be coordinated with distance prot zone 3

UT PROTECTIONUT PROTECTION

DifferentialDifferential Biased differential usedBiased differential used biased setting 20%biased setting 20%

Back up over current Back up over current 2-3 times the full load current 2-3 times the full load current Delay of 1 sec to take care of any large motor Delay of 1 sec to take care of any large motor starting casestarting case

Restricted E/FRestricted E/F High impedanceHigh impedance Set to 5%-10% in high impedance earthingSet to 5%-10% in high impedance earthingBackup E/FBackup E/F Set to 30% rated current with delay of 1 secSet to 30% rated current with delay of 1 sec

Other ProtectionsOther ProtectionsOverall Differential Protection (87GT)Overall Differential Protection (87GT)

- Covers generator, GT & UT- Covers generator, GT & UT

GT overhang differential Protection GT overhang differential Protection (87HV)(87HV)

- Protects GT HV wdg & overhang - Protects GT HV wdg & overhang

portion between GT bushing portion between GT bushing and switchyard. and switchyard.

Typical Generator protection scheme

Typical Gen Prot SLDTypical Gen Prot SLD

GCB SCHEMENON GCB SCHEME

TRIP LOGIC OF GENERATOR PROTECTIONTRIP LOGIC OF GENERATOR PROTECTION

Two independent channels with independent CT/VT inputs/ DC Two independent channels with independent CT/VT inputs/ DC supply/ Trip relayssupply/ Trip relays

Class “A” Trip (Urgent Trips)Class “A” Trip (Urgent Trips)– All electrical tripAll electrical trip– Issues instantaneous Trip toIssues instantaneous Trip to

Turbine , Excitation, Generator EHV CBs,UT LV CBsTurbine , Excitation, Generator EHV CBs,UT LV CBs– In GCB Scheme Class A1 and A2In GCB Scheme Class A1 and A2– Class A1 Issues instantaneous Trip toClass A1 Issues instantaneous Trip to

Turbine , Excitation, Generator EHV CBs,GCB, UT LV CBsTurbine , Excitation, Generator EHV CBs,GCB, UT LV CBs– Class A2 Issues instantaneous Trip toClass A2 Issues instantaneous Trip to

Turbine , Excitation, GCBTurbine , Excitation, GCB Class-B Trip (Non-urgent Trips)Class-B Trip (Non-urgent Trips)

– Turbine Trips, GT and UT OTI/WTI tripsTurbine Trips, GT and UT OTI/WTI trips– Issues delayed Trip to (After Low Forward Power timer)Issues delayed Trip to (After Low Forward Power timer)

In Non-GCB scheme-Excitation, Generator CBs,UT LV CBsIn Non-GCB scheme-Excitation, Generator CBs,UT LV CBs In GCB scheme, only GCB and field are tripped, UT remains In GCB scheme, only GCB and field are tripped, UT remains

charged through GT.charged through GT. Class C TripClass C Trip

Trips HV CB only.Trips HV CB only.

CLASS OF TRIP

BREAKERS TO BE TRIPPED UNDER VARIOUS CLASSES OF TRIPPING

GCB SCHEME (additional LV CB between Gen and GT)

NON GCB SCHEME

Class A A1: GCB,HVCB,UT LV CB, FIELD, TURBINE (All the system tripped) A2 : GCB, FIELD, TURBINE (Generator circuit tripped & Auxiliaries charged from the grid through GT&UT)

HVCB,UT LV CB, FIELD, TURBINE (All the system tripped)

Class B

GCB,FIELD BREAKER Initiated by Turbine trip & Low Forward / reverse power, to release the trapped steam. Generator circuit breaker tripped & Auxiliaries charged from the grid through GT&UT)

HVCB,UT LV CB, FIELD BREAKER.

Class C HVCB (Generator under House load )

HVCB (Generator under House load )

CLASS OF TRIP

SL NO

PROTECTION FUNCTION

NON GCB

GCB

Preferred grouping of protection

1. Generator Differential Protection, (87 G) (DUPLICATED IN CASE OF GCB SCHEME)

A A2

2. Overall Differential Protection (87GT).

A A1

87 G and 87 GT shall be on two different channels of protection.

3. Generator Transformer Differential protection (87 T)

A A1 87 T shall be in a different channel than 87 GT

4. Over hang differential protection(87 HV)

A A1 87 HV shall be in a different channel than 87T

5. Stator Earth Fault Protection covering 100% of winding based on low frequency injection principle.(64G1).

A A2

6. Stator Standby Earth Fault Protection covering 95% of winding (64 G2)

A A2

64 G1 and 64 G2 shall be on two different channels of protection.

7. Inter-turn Fault Protection (95G1),

A A2

8. Duplicated Loss of field protection (40G1/2 ).

A A2

40G1 and 40G2 shall be on two different channels of protection.

9. Back up Impedance Protection, 3 pole (21G)

A A1

10. Backup Earth Fault Protection on Generator Transformer HV neutral (51NGT)

A A1

21 G and 51 NGT be in different channels

11. Negative Sequence Current Protection, (46G)

A A2

RELAY GROUPING

1. Duplicated Low-Forward Power / reverse power Interlock for steam turbine generator (37 /32G1 & 37/32 G2), each having two stages,

a) short time delayed interlocked with turbine trip

b) long time delayed independent of turbine trip.

B

A

B

A2

37/32 G1 and 37/32 G2 shall be in two different channels of protection

2. Two Stage Rotor Earth Fault Protection based on injection principle.(64F).

A A2

3. Definite Time Delayed Over-Voltage Protection (59G)

A A2

4. Generator Under Frequency Protection (81G) with df/dt elements.

C C

5. i) Over Fluxing Protection (99 T) for Generator Transformer

ii) Over fluxing protection for Generator (99 G)( only incase of GCB scheme)

A

-----

A1

A2

Over Flux function (99) shall be in a different channel than O/V and U/F functions

6. Accidental Back Energisation protection (50GDM) on two principles a) based on U/V and O/C b) based on CB status and O/C

A

A1 50 GDM based on the two principle shall be on two different channels.

7. Instantaneous and time delayed Over Current protection to be used on HV side of excitation transformer.

A A2

8. Generator Pole slipping protection(98G)

A A2

1. Unit Transformer Differential Protection, 3 pole (87UT)

A A1

2. Unit Transformer LV back-up earth fault protection . ( 51NUT).

A A1

3. Unit Transformer LV REF (64 UT LV)

A A1

4. Unit transformer back-up over current protection (51UT).

A A1

87 UT & 51 NUT can be in one channel and 64 UT LV & 51UT shall be in another channel.

5. Gen Transformer OTI/WTI trip

Turbine Trip

Turbine Trip

After turbine trip other breakers are tripped through class B

6. Gen Transformer Buchholtz, PRD /other mechanical Protections

A A1

7. Unit Transformer OTI /WTI trip

UT LV CB Trip

& signal

for change over of

unit board.

UT LV CB Trip &

signal for change over of

unit board.

8. Unit Transformer Buchholtz, PRD /other mechanical Protections

A A1

9. 64 GT (For GT LV wdg & UT HV wdg)

A1

10. EHV CB/GCB LBB A A1 11. EHV BB PROTN A A1

SL.NO INITIATION ACTION

1 GT FIRE PROTECTION

TRIP CLASS A AND DISCONNECT POWER SUPPLY TO GT MB

2 UT FIRE PROTECTION

TRIP CLASS A AND DISCONNECT POWER SUPPLY TO UT MB

3 GT TAP CHANGER OPERATED & HVCB CLOSED

TRIP CLASS A

4 HV CB /FCB CLOSED START GT COOLER

5 GT COOLER SUPPLY TOTAL FAILURE

TRIP CLASS A AFTER TIME DELAY

6 AVR SERIOUS TROUBLE

TRIP CLASS A

ADDITIONAL control/protection interlocks realized through GRP

Numerical integrated generator protection Numerical integrated generator protection systemssystems

Many functions in the same relayMany functions in the same relay Takes multiple CT/VT inputs.Takes multiple CT/VT inputs. Minimum of 2 nos to be used.Minimum of 2 nos to be used. All the prot functions are to be divided in to 2 groups .All the prot functions are to be divided in to 2 groups . Built in DR(fast scan)/SOE functionsBuilt in DR(fast scan)/SOE functions Self supervisionSelf supervision CommunicableCommunicable Has programmable logic gates which simplifies the auxiliary Has programmable logic gates which simplifies the auxiliary

circuits.circuits.COMMON RELAYS ARE COMMON RELAYS ARE REG series OF ABBREG series OF ABB 7UM SERIES OF SIEMENS7UM SERIES OF SIEMENSMICOM SERIES OF AREVA.MICOM SERIES OF AREVA.

GENERATOR DISTURBANCE RECORDERGENERATOR DISTURBANCE RECORDER

Record the graphic form of instantaneous Record the graphic form of instantaneous values of power system variablesvalues of power system variables

Fast scan (1-5 khz) and slow scan (5/10 hz) Fast scan (1-5 khz) and slow scan (5/10 hz) featuresfeatures

Sufficient analogue/digital inputs.Sufficient analogue/digital inputs. Triggering from digital inputs and Triggering from digital inputs and

threshold/rate of change of analogue values.threshold/rate of change of analogue values. Adequate memoryAdequate memory Good frequency responseGood frequency response Individual acquisition units and commom Individual acquisition units and commom

evaluation unit for a stationevaluation unit for a station

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Generator Protection