Generator Protection

(1)

GENERATOR PROTECTION

By

Subhash Thakur

PE-Elect



Gen Stator Thermal Protection

_{Gen Stator Thermal Protection}



Field Thermal Protection



Gen stator fault Protection

_{Gen stator fault Protection}



Gen rotor field Protection



Gen abnormal operating conditions

_{Gen abnormal operating conditions}



System backup Protection



Power transformer Protection

Generator Protection

(3)

Generator Protection

Stator Thermal protection

Thermal protection for the generator stator core and windings Thermal protection for the generator stator core and windings

 Generator overload_{Generator overload}

 _{Winding Temperature}_{Winding Temperature}  _{Over current}_{Over current}

 Failure of cooling systems_{Failure of cooling systems}

 _{RTDs Thermocouple}_{RTDs Thermocouple}

 Flow and pressure sensor_{Flow 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 failures

winding failures

(4)

Generator Protection

(5)

Generator Protection

Generator Field Thermal protection



Thermal Protection

_{Thermal Protection}

 Direct rotor Body temperature measurement _{Direct rotor Body temperature measurement} not possible

not possible

 Core Monitor may detect overheating_{Core Monitor may detect overheating}



Protection for field over excitation

_{Protection for field over excitation}

 IDMT/ Definite Time _{IDMT/ Definite Time}  Excitation limiters_{Excitation limiters}

(6)

Generator Protection

(7)

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

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

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

shut down the machine as quickly as possible in order to

minimize damage.

(8)

Stator fault Protection



High Speed Differential protection

_{High Speed Differential protection}

– Will detect Phase to Phase Faults, Double phase Will detect Phase to Phase Faults, Double phase faults involving earth

faults 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

detection:

– High-impedance differentialHigh-impedance differential

– Biased differentialBiased differential

(9)

High 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 used

_{PS 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.



Through fault stability achieved by using

_{Through fault stability achieved by using}

stabilising resistors in the relay circuit

.

(10)

High Impedance Differential Relay

Stabilizing resistor calculation :

Vs = If (Rct+2Rl)

If - Maximum through fault current in the

system

(converted to sec side)

Rct- Secondary resistance of the CT

Rl – lead resistance of the sec connection

(typ 8.73 ohms per km for 2.5 sq mm cu

cable)

Rs = Vs/Is – (VA/Is*Is)

Typical setting 5- 10% of rated current.

(11)

Biased 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.}

(12)

Biased Differential protection

(13)

 Current based system_{Current 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

windings

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

a differential voltage which makes the relay operate.

Typical setting

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

INTERTURN PROTECTION

(14)

Inter turn protection

Split Phase Protection

V o l t g a Voltage Based

(15)

Generator Grounding Practices

It is common practice to ground all types of

generators through some form of external

impedance

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.

Typical Grounding practices

Ungrounded_Ungrounded

Solid Grounding_{Solid Grounding}

High-impedance grounding_{High-impedance grounding} Low-resistance grounding_{Low-resistance grounding} Reactance grounding_{Reactance grounding}

(16)

Generator Grounding Practices



Ungrounded

_Ungrounded

–

Phase to ground fault current limited

–

Generators are not often operated ungrounded

as it may produce high transient over-voltages

during faults and makes the fault location

difficult to determine.



Solid Grounding

_{Solid Grounding}

–

Solid grounding of a generator neutral is not

generally used since this practice may result in

high mechanical stresses and excessive fault

damage in the machine.

(17)

Generator Grounding Practices

 High Impedance Grounding_{High Impedance Grounding} – High resistance groundingHigh resistance grounding

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

A up to 150% of rated full-load current.

(18)

Stator Earth Fault Protection



_{E/F current is typically limited to}

5-10A

to

5-10A

to

minimizes

the

damage to laminations.



First earth fault is less critical

_{First earth fault is less critical}

but needs clearance as

 I_I_{t may develop into a ph to ph fault .}_{t may develop into a ph to ph fault .}  Second fault will result in very high _{Second fault will result in very high}

current. current.



Two types of coverage:

_{Two types of coverage:}

 100 % winding_{100 % winding}  95 % winding_{95 % winding}

(19)



Any fault involving earth results shift of

_{Any fault involving earth results shift of}

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

generator terminal Open Delta voltage.



Typical coverage

_{Typical coverage}

95% Of Stator Winding.

_{95% Of Stator Winding.}



Typical Setting:

_{Typical Setting:}

–

5% with 1 Sec TD

95 % Stator Earth Fault

(20)

100 % Stator E/F Protection

• Third Harmonic Principle

Third Harmonic Principle

• Relay responds to the reduction of the 3

Relay responds to the reduction of the 3

rdrd

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 increase in third Harmonic Voltage at

The Generator Terminals, which Will Cause

Relay Operation.

(21)

100% SEF based on third harmonics

measurements

(22)

100% SEF based on third harmonics

measurements

Disadvantages

Due to design variations, certain generating

units may not produce sufficient third

harmonic voltages.

This method does not protect the machine

during stand still conditions.

(23)

100% stator earth fault protection

(Low freq. injection principle)

20 Hz RE max. 200 V I 20 Hz RE max. 200 V I



Detects the ground faults

by injecting a low frequency

signal (say 20 hz) at the

neutral earthing transformer

and monitor the earth

current in the winding.

(24)

SEF USING INJECTION PRINCIPLE

TYPICAL CONNECTION

Typical settings for 500 MW unit

Trip : 1 KOhm / 1 sec Trip : 1 KOhm / 1 sec Alarm : 10 Kohm /10 sec Alarm : 10 Kohm /10 sec

DC or AC Blocking R_L Bandpass (8Ω at 20 Hz) 20-Hz-Generator (appr. 25 V) U I Relay a b a b 400A 5A Low ohmic Earthing transformer Neutral transformer

(25)

Rotor Earth Fault Protection

Effects

 First rotor E/F does not cause immediate damage_{First 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 forces_{Causes 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

(26)

Rotor E/F Using Low frequency injection method

(27)

Rotor E/F Using Low frequency injection method

(28)

Negative sequence protection

 _{Causes of negative squence current}_{Causes 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 by withstand 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 i

permissive i₂₂22x t = 5 – 10_{x t = 5 – 10}

settings adopted for ntpc settings adopted for ntpc

ii_{2 =}_{2 =} = 7.5 % = 7.5 % i

(29)

Negative sequence protection

(30)

Loss of field protection

(31)

Loss of field protection

 Acts as an induction generator_{Acts 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 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}

plane

 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.

(32)

Trip characteristics of loss of field protection

(33)

Trip characteristics of loss of field

protection

(34)

Trip characteristics of loss of field protection

(35)

Generator Capability Curve

(36)

Out of step protection

 Machine runs out of synchronism with the network_{Machine 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 stress_{Results 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 swing

irrecoverable 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 swings

(37)

Out of step protection settings

(38)

Typical Over Fluxing Withstand

Capability

(39)

Accidental back energisation

 Cause_Cause

– Flash over of the generator breakerFlash over of the generator breaker

– Incorrect closing of the generator breakerIncorrect closing of the generator breaker  Effects_Effects

– 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 The rapid heating iron paths near the rotor surface due to stator induced current.

due to stator induced current.

 Over current + CB auxiliary contacts_{Over current + CB auxiliary contacts}

– checks for the current when the gen breaker checks for the current when the gen breaker contacts are open

contacts are open

– set below the rated current(90%)set below the rated current(90%)

– o/c and u/v measurementso/c and u/v measurements

(40)

Accidental Back Energisation

(41)

(42)

Low forward and reverse power

inter lock



To allow entrapped steam in the turbine to

_{To allow entrapped steam in the turbine to}

be utilized to avoid damage of the turbine

blade.



To protect the machine from motoring action

_{To 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

2 sec)



Trip under class A, after a

_{Trip under class A, after a}

long time delay

_{long time delay}

if

_if

turbine is not tripped (typically set at 10 -30

sec)

(43)

O/V & U/F protection

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

Typical 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 protection

Typical setting:

U/FU/F O/FO/F Alarm - 48.5hz 5 sec 51 hz 1 sec

Alarm - 48.5hz 5 sec 51 hz 1 sec

Trip - 47.4 hz 2 sec

(44)

 For uncleared system fault_{For 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 by_{Detected by}

– over current over current

– impedanceimpedance

– Impedance type preferred as the line is Impedance type preferred as the line is provided with distance relays

provided 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 sec_{Time setting 1.5 –2 sec}

(45)

Over view of type of fault Vs protection

FAULT/

ABNML

EFFECT

EFFECT PROTECTIONPROTECTION

Thermal over Thermal over loading

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

insulation failure Thermo couples/ Thermo couples/

Over current relays Over current relays External fault

External fault Unbalanced loading stressUnbalanced loading stress Over load/negative phase Over load/negative phase sequence relay, Backup sequence relay, Backup Impedance/ Earth Fault Impedance/ Earth Fault Stator faults

Stator faults

Winding burn out Winding burn out

Shorting of of core lamination Shorting of of core lamination

Differential protection Differential protection

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

Inter turn protection Inter turn protection Rotor fault

Rotor fault Damage to shaft/bearingDamage to shaft/bearing Two stage rotor E/F protectionTwo stage rotor E/F protection Motoring

Motoring Damage to turbine bladesDamage to turbine blades LFPR/Rev power Inter lockLFPR/Rev power Inter lock O/V,O/F,U.F

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

core failure of blades O/V relay Volt/Hz relay O/V relay Volt/Hz relay

U/F relay U/F relay Loss of field

Loss of field Induction gen operationInduction gen operation Absorb MVAR from

Absorb MVAR from

system/damage to rotor wdg system/damage to rotor wdg

Loss of field Loss of field

(46)

COMMONLY USED GEN/GEN TRFR RELAYS

PROTECTION

PROTECTIONALSTOM/AREVAALSTOM/AREVA ABBABB SIEMENSSIEMENS REMARKREMARK HIGH IMP HIGH IMP DIFF DIFF CAG 34 CAG 34 MICOM P343 MICOM P343 RADHA RADHA REG 216

REG 216 7UM SERIES7UM SERIES

In case of duplicated diff,

one low imp & one high

imp preferred

For trfr biased relay

preferred preferred BIASED DIFF BIASED DIFFMBCHMBCH MICOM MICOM P 633 P 633 RADSB RADSB RET 316 RET 316 7 UT 7 UT POWER POWER RELAYS RELAYS RXPE

RXPE PPXPPX 7 UM SERIES7 UM SERIES Directional power relays Directional power relays LOSS OF

LOSS OF

FIELD

FIELD YCGFYCGF RAGPC(DIR _O/C+U/V)RAGPC(DIR _O/C+U/V) 7UM SERIES7UM SERIES Impedance_admittanceImpedance_admittance / /

100% E/F 100% E/F PVMMPVMM MICOM P343 MICOM P343 PG871 PG871 GIX GIX REG 216 REG 216 7UE22 7UE22 7UM SERIES 7UM SERIES

Low frequency injection

type

type preferred over 3 rd preferred over 3 rd harmonic principle

harmonic principle

95% E/F

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

BACK UP

IMP

(47)

PROTECTIO

N

N ALSTOM

ALSTOM ABBABB SIEMENSSIEMENS RemarksRemarks OVER OVER FLUXING FLUXING GTTM GTTM RATUBRATUB RALK RALK 7RW 7RW IDMTIDMT POLE POLE SLIPPING SLIPPING ZTO+YTGM1 ZTO+YTGM1 5 5 RXZF+RXPE

RXZF+RXPE 7UM 5167UM 516 IMPEDANCEIMPEDANCE IMP+ DIR O/C

IMP+ DIR O/C

IMP+NO OF POWER IMP+NO OF POWER SWINGS SWINGS ACC. BACK ACC. BACK ENERG ENERG CTIG

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

CURRENT CURRENT ELEMENT+U/V ELEMENT+U/V INTER INTER TURN TURN VDG VDG MICOM MICOM REG

REG 7UM SERIES7UM SERIES comp of open delta 0n comp of open delta 0n gen term+ngt sec

gen term+ngt sec

voltage voltage NEG PH NEG PH SEQ SEQ CTN

CTN RARIBRARIB 7UM SERIES7UM SERIES MEASUREMENT OF I2MEASUREMENT OF I2 REF

REF CAG/FAGCAG/FAG RADHDRADHD 7UM SERIES7UM SERIES HIGH IMP PREFFEREDHIGH IMP PREFFERED ROTOR E/F ROTOR E/F VDGVDG MICOM MICOM SERIES SERIES REG SERIES

REG SERIES 7UR 227UR 22

7 UM SERIES

(48)

Type of fault

Type of fault ProtectionProtection ChannelChannel RecommendatioRecommendatio n n Short circuit Short circuit 87 G187 G1 87G2 87G2 87 GT 87 GT 1 1 2 2 1 OR 2 1 OR 2

Stator Earth Fault

Stator Earth Fault 64G164G1 64G2 64G2 1 1 2 2 Inter turn Inter turn 95G95G 1 OR 21 OR 2 unbalance unbalance 46G46G 1 OR 21 OR 2 Over load

Over load 51G51G AlarmAlarm Loss of excitation Loss of excitation 40G140G1 40G2 40G2 1 1 2 2 Out of step Out of step 98G98G 1 OR 21 OR 2 >100 MW>100 MW Motoring Motoring 32 G1/2 / 37 G1/G232 G1/2 / 37 G1/G2 1 / 21 / 2 O/V,O/F O/V,O/F U/F U/F 59/99 59/99 81G1/81G1 81G1/81G1 1 /2 1 /2 1/2 1/2 System back up

System back up 21G21G 1 & 21 & 2 Accidental energisation

Accidental energisation 50GDM50GDM 1 &21 &2 Rotor E/F

(49)

Generator Transformer Protection

 Differential_Differential

– biased differential biased differential

20 % bias setting (to cover tap range and

ct mismatch if any)

time: instantaneous

Back up earth fault

Definite time or IDMT relay

30 % with 2 sec time delay

To be coordinated with distance prot zone 3

(50)

UT PROTECTION



Differential

_Differential

Biased differential used

biased setting 20%



Back up over current

_{Back up over current}

2-3 times the full load current

Delay of 1 sec to take care of any large motor

starting case



Restricted E/F

_{Restricted E/F}

High impedance

Set to 5%-10% in high impedance earthing

Backup E/F

(51)

Other Protections



Overall Differential Protection (87GT)

_{Overall Differential Protection (87GT)}

- Covers generator, GT & UT



GT overhang differential Protection

(87HV)

- Protects GT HV wdg & overhang

portion between GT bushing

_{portion between GT bushing}

and switchyard.

(52)

Typical Generator

protection

scheme

(53)

GCB SCHEME

NON GCB SCHEME

(54)

TRIP LOGIC OF GENERATOR PROTECTION

 Two independent channels with independent CT/VT inputs/ DC _{Two independent channels with independent CT/VT inputs/ DC}

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

Turbine , Excitation, GCB Turbine , 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 CBs_{In 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 Trip_{Class C Trip}

Trips HV CB only. Trips HV CB only.

(55)

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

(56)

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 Di fferential 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 shall be on two and 40G2 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

(57)

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

(58)

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 trip turbine other breakers are tripped through class B 6. Gen Transformer Buchholtz, PRD /other mechanical Protections A A1 7. Unit Transformer

OTI/WTI trip CB Trip UT LV & 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

(59)

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

(60)

Numerical integrated generator protection

systems

 Many functions in the same relay_{Many 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 functions_{Built in DR(fast scan)/SOE functions}

 Self supervision_{Self supervision}  Communicable_Communicable

 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 ABB

REG series OF ABB 7UM SERIES OF SIEMENS7UM SERIES OF SIEMENS MICOM SERIES OF AREVA.

Generator Protection

GENERATOR PROTECTION

GENERATOR PROTECTION

By

By

Subhash Thakur

Subhash Thakur

PE-Elect

PE-Elect

[email protected]

[email protected]



Gen Stator Thermal Protection

Gen Stator Thermal Protection



Field Thermal Protection

Field Thermal Protection



Gen stator fault Protection

Gen stator fault Protection



Gen rotor field Protection

Gen rotor field Protection



Gen abnormal operating conditions

Gen abnormal operating conditions



System backup Protection

System backup Protection



Power transformer Protection

Power transformer Protection

Generator Protection

Generator Protection

Generator Protection

Generator Protection

Generator Protection

Generator Protection

Generator Protection

Generator Protection

Generator Field Thermal protection

Generator Field Thermal protection



Thermal Protection

Thermal Protection



Protection for field over excitation

Protection for field over excitation

Generator Protection

Generator Protection

Generator Protection Requirement

Generator Protection Requirement

Stator fault Protection

Stator fault Protection



High Speed Differential protection

High Speed Differential protection



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 Differential Relay

High 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 used

PS 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

_{Gen Stator Thermal Protection}

_{Gen stator fault Protection}

_{Gen abnormal operating conditions}

_{Thermal Protection}

_{Protection for field over excitation}

_{High Speed Differential protection}

_{Two types of high-speed differential relays}

_{Use two sets of identical dedicated CTs.}

_{PS class CT with stringent parameters to be used}

_{This scheme has higher sensitivity than the}

_{Through fault stability achieved by using}

_Ungrounded