Gen Protn Philosophy&Settings

8/12/2019 Gen Protn Philosophy&Settings

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GENERATOR PROTECTION Combiflex R

ABB India

Utilities - Automation


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CLASSIFICATION OF TRIPPING

CLASSIFICATION OF TRIPPING

Objective is to trip only the absolutely essential so that

- Damage is minimum

- Overspeeding of the TG due to sudden load throw off is avoided

- Impact of tripping of large set on the grid is minimum

- Auxiliaries if possible are kept energised and time to restart the unit is

minimum


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CLASS-A TRIPPING

CLASS-A TRIPPING

This is adopted for those electrical faults of Generator and Generator

transformer and unit auxiliary transformer for which tripping can not

be delayed.

This leads to simultaneous tripping of

- Generator Transformer HV side CB

- Field Circuit Breaker

- LV side incomer breakers of UAT

- Auto changeover from unit to station for unit auxiliaries and

tripping of turbine


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CLASS-B TRIPPING

CLASS-B TRIPPING

This is adopted for all turbine faults (Mechanical) and for some

electrical faults of Generator, Generator transformer and unit auxiliary

transformer for which it is safe to trip the turbine.

Subsequently the Generator is tripped through low forward power

interlock

Ensures that unit does not overspeed due to trapped steam in the

turbine during the shutdown and also the loss of power to the grid from

the Generator is not sudden.


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CLASS-C TRIPPING

CLASS-C TRIPPING

This is adopted for all faults beyond the Generator system which can be

cleared by tripping of Generator transformer HV side CB alone.

In this case the TG set runs with HP-LP bypass system in operation and

the Generator continues to feed the unit auxiliary load through unit

auxiliary transformers.


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Class CGenerator Pole slipping Relay

Without Under voltageClass BGenerator Field Failure Relay

I stage alarmClass B II stageGenerator Rotor Earth Fault Relay

I stage alarmClass C After some

time (say 30mins) II stage

Generator Under frequency Relay

I stage alarmClass BGenerator Transformer Overfluxing Relay

Class AGenerator Stator E/F Relay (95%)

Class AGenerator Stator E/F Relay (100%)

Class AUnit Overall Differential Relay

Class AGenerator Transformer Differential Relay

For interlock in Class B

tripping

Generator Low Forward Power Relay

Class AGenerator Differential Relay

REMARKSTRIPPING MODEPROTECTIVE RELAY

TYPICAL CLASSIFICATION OF TRIPPING

TYPICAL CLASSIFICATION OF TRIPPING


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I-stage alarmClass C II-stageGenerator Transformer Winding Temperature Device

Class AUnit Auxiliary Transformer H.V. side O/C Relays (Backuup)

I-stage alarmClass A II-stageGenerator Transformer Buchholz Relay

For alarmGenerator Definite time O/C Relay

I-stage alarmClass CGenerator Negative Sequence Current Relay

Class AUnit Auxiliary Transformer Differential Relay

Class BGenerator Transformer H.V. side Backup E/F relay

Class CGenerator Transformer H.V. side Backup O/C relay

Class AGenerator Voltage Restrained Relay

Class CGenerator Distance Backup Impedance Relay

I-stage alarmClass C II-stageGenerator Transformer Oil Temperature Device

Class AGenerator Reverse Power Relay


TYPICAL CLASSIFICATION OF TRIPPINGTYPICAL CLASSIFICATION OF TRIPPING


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TYPICAL CLASSIFICATION OF TRIPPINGTYPICAL CLASSIFICATION OF TRIPPING

AlarmUnit Auxiliary Transformer(s) Oil Level Device

I-stage alarm

II-stage-trip unit switch

gear incomer breaker(s)

and Auto change-over.

Unit Auxiliary Transformer(s) Oil Temperature

Devices

I-stage alarm

II-stage-trip unit switch

gear incomer breaker(s)

and Auto change-over to

station service

Unit Auxiliary Transformer(s) Oil Temperature

Device(s)

I-stage alarmClass CUnit Auxiliary Transformer Buchholz Relay(s)

AlarmGenerator Transformer Oil Level Device



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TYPICAL GROUPING OF RELAYSTYPICAL GROUPING OF RELAYS

GROUP-I

- Generator Differential Relay

- Generator Transformer Differential Relay

- Generator Stator Earth Fault Relay for protection of 100% stator winding

- Generator Over-voltage Relay

- Generator Underfrequency Relay

- Generator Rotor Earth Fault Relay

- Generator Field Failure Relay

- Generator Low Forward Power Relay

- Generator Reverse Power Relay

- Generator voltage restrained O/C Relay

- Generator Transformer HV side O/C Relay (for backup protection)

- Unit Auxiliary Transformer(s) Differential Relay(s)

- Generator Negative Phase Sequence Current Relay


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TYPICAL GROUPING OF RELAYSTYPICAL GROUPING OF RELAYS

GROUP-II

- Unit overall Differential Relay

- Generator Stator Earth Fault Relay for protection of 95% startor winding.

- Generator Transformer Overfluxing Relay

- Generator Overvoltage Relay.

- Generator Rotor Earth Fault Relay.

- Generator Field Failure Relay.

- Generator Pole Slipping Relay.

- Generator Low Forward Power Relay.

- Generator Reverse Power Relay.

- Generator Distance Backup Relay.

- Generator HV standby Earth Fault Relay.

- Unit Aux Transformer(s) H.V. side overcurrent Relay (for back up protection)

- Generator Negative Phase Sequence Current Relay.

- Generator definite time over-current Relay.


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GeneratorData :

Rated MVA : 247 MVA

Rated kV : 15.75kV

Full load current : 9065A

Sub-transient Reactance Xd : 21.4%

Neutral Grounding Transformer :

25 kVA, 15.75 kV/240 V, Resistor: 0.5 ohms, 280A.

Field Circuit Voltage : 600V

Negative Sequence Particulars :

1) A symmetrical short circuit performance is given by 12t 2) Continuous negative sequence withstand current of generator-5%

which implies that maximum difference between the line current

is about 10%.

SYSTEM DETAILSSYSTEM DETAILS


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b) 400 kV side CT : 500/ 1 A, RCT= 3 , Vk=1000 V

class PS, star connection

c) Neutral side CT : 500/1 A, PS, Vk=1000 V,RCT=3

3) RLLead resistance : One way lead resistance of 15 m, 2.5 mm2

single cable is 0.1 (looping done in CT

Marshalling box)

SYSTEM DETAILSSYSTEM DETAILS


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Relay particulars:

Type : RAGEA

RXIG 95% Relay : 5-15V; 50 Hz.

RXIG 100% Relay : 0.4-1.2V, 150 Hz.

RXEG Supervision Relay : 40-120 V

RXKE1 for 95% Element : 20ms-99s

RXKE1 for 100% Element : 20ms- 99s

Auxiliary Voltage : 220 V DC

GENERATOR 100% EARTH FAULT RELAYGENERATOR 100% EARTH FAULT RELAY


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Calculations:

95% Element:

When a fault occurs on the high voltage side of a / Y step-up transformer,There is no voltage

displacement of the generator neutral due to Zero Sequence currents. But still a small generatorneutral voltage exists for an External ground fault due to a small capacitive coupling between

primary and secondary of the generator step-up transformer. If the data to Calculate this small

neutral voltage is not available, then relay sensitivity Is restricted to about 4-5%.

Also, the 95% relay of RAGEA is suitable for operation at lower frequency and thus can act as a

reliable earth fault protection during start-up. It Operates with increased sensitivity down to about

25 Hz, the operating value being about 0.6x set voltage. At still lower frequency of 10Hz, the relay

operates at 0.8 x set voltage.

Secondary side voltage of grounding transformer for a fault on generator terminal is 240/ 3 = 138V.

From experience it is found that, a setting of 5.4 V of the voltage gives adequate discrimination

against such faults.



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Time delay setting need to be selected considering PT fuse operating time in case of a fault ongenerator PT. This delay also gives stability against relay picking up from stray voltages.

Delay of about 1-2 secs is recommened.

100% Element:

Setting of this relay is approx. 50% of 3rdharmonic voltage measured across the Generator

grounding transformer.

Typical value of this 3rdharmonic voltage = 1-2V

Setting should be adjusted at site depending on actual measured value.

Time delay of 2 secs. Can be set.

Supervision Relay:

This is usually set about 80% of rated voltage, approx. 90 V.



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Recommended Settings :

95% Relay : 5.4 V,1 sec.

100% Relay : 0.5 V, 2 sec.

Supervision Relay : 90 V



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Rated MVA = 247 MVA

Rated kV = 15.75 kV

Rated Load Impedance = 15.75/ 247 = 1.0043 prim.

CTR / PTR = ( 10000 / 5 ) / ( 15.75 x 10/ 110 ) = 13.97

Setting of RAKZB = 70 % of Rated Load Impedance

= 0.7 x 1.0043 x 13.97 = 9.82sec.

Forward Reach = Reverse Reach

ZF= ZR= 9.82 sec.

ZF= ZR= ( 0.2 f / la 3 ) x ( A / B ) f = 50 Hz. Ia= ln= 5 A

( A / B ) = 8.5

Choose A = 80, then B = 9.4

GENERATOR BACK-UP IMPEDANCE PROTECTION-RAKZBGENERATOR BACK-UP IMPEDANCE PROTECTION-RAKZB


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Type : RXNB

Operating Value : Approx. 5 Kat Ux = 0 V and

: Approx. 245 Kat Ux = 600 V

The relay operates for an insulation resistance Rxdependent upon Uxwhen

( ( Ux+ 48 ) / 2.5 ) 14 K= Rx

U1 : supply Voltage

Um : Super imposed voltage between the negative pole of the field

winding and the earth

Ux : Field voltage between the fault location & negative pole of the field wdg.

Rx : Insulation Resistance between the field windind & the earth at the fault

location.

Ij : Current in the measuring circuit.

ROTOR EARTH FAULT RELAY- RXNBROTOR EARTH FAULT RELAY- RXNB


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Delay on pick-up : Approx. 11sec.

Maximum permissible

Field circuit voltage : 600V continuous, 1500v for 9 sec Bias circuit voltage : 240VK10%, 50Hz.

Auxiliary voltage : 240V DC

Recommended settings :

The relay has fixed settings as described.



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GENERATOR NEGATIVE SEQUENCE PROTECTION (RARIB)GENERATOR NEGATIVE SEQUENCE PROTECTION (RARIB)

Relay particulars:

Type : RARIB

Operating according to t : (In / I2) K where In = rated primary current of Auxiliary CT

K = 1-63secs.

Operating value start : 4-16%

Alarm element : 3-9%

Time delay of alarm : 6secs.

Cooling down time : (K x 170)/2 where a is a constant which is internally

reconnectible in complete steps between 0 and 6


CT details : 10000/5A


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GENERATOR NEGATIVE SEQUENCE PROTECTION (RARIB)GENERATOR NEGATIVE SEQUENCE PROTECTION (RARIB)

Calculations:

Secondary current corresponding to full load = 4.53A

Setting IM= (4.53/5) x In= 0.906 Inwhere Inis set to 5A.

Recommended settings:

IM = 0.906 x 5AK = 8 on relay (System Details)

Alarm relay = 4% of IM

Trip relay = 8% of IM

Time lag relay for delayed alarm : 6secs.

Cooling down time constant : 2.6 x K

In the absence of valid data of the machine, this has been set at the lowest value.

This is not field adjustable.


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GENERATOR DIFFERENTIAL RELAYGENERATOR DIFFERENTIAL RELAY

Relay Particulars :

Type : RADHA

Rating : 5A

Operating Voltage : 40/50V

Operating Current : 20mAAuxiliary Voltage : 220V DC

System Details :

CT Details : 10000/5A, RCT=1.5

Vk=600V

CT lead resistance RL : Pilot wire loop resistance from CT to interconnection point

of CT leads at Bus duct=0.2 (One way length is 15m,

2.5mmcs)


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Calculations:

1) Maximum through fault current = 1/Xd = 1/0.214=4.67 pu

Base Current = 9.065KA If= 4.67 x 9.065KA = 42.33KA

CT sec. Current Ik= 21.2A

Maximum rms voltage that will develop across the relay for this through fault

current = Ik(RCT+RL)

= 36.04V

Normally a setting of 110% of this voltage will provide full stability against external

fault.

1.1 x 36.04 = 39.65V

A relay version of 40-50V to be selected & to be set at 40 V

Minimum knee point voltage requirement : Vk= 2 x 40 = 80V

Minimum Primary operating current : Ip= n1(IR+ Im+ Ires)


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Where IR = Relay operating current = 0.02A

Im = Magnetising current of CT at set value

= 0.005 A (assumed)

Ires = 5mA for MXA 983-B at 70V

Ip = 10000/5 (0.02 + 0.05 + 0.005) = 150A


40 V


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LOSS OF EXCITATION RELAY (RAGPC)LOSS OF EXCITATION RELAY (RAGPC)

Relay particulars:

Type : RAGPC

Rating : 5A

Scale Ranges : RXPE40 Directional Relay : 1-4A

: RXIG Overcurrentl Relay : 2.5-7.5A

: RXEG2 Under Voltage Relay : 40-120V

System Particulars:

The generator is capable of delivering 247 MVA continuously at 15.75kV terminal

voltage, 9065 A stator current and 3 kg/cmhydrogen pressure with cold gastemperature not exceeding 40C and distillate termperature at inlet of stator wdg notexceeding 40C. The generator capability curve is as per enclosed diagram.

CT Details : 10000/5A, RCT=1.5 , Vk=600V, Class : PS


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PT Details : 15.75kV /110V, 200VA, 3P / 0.5M

Calculations:

The characteristic of RXPE40 unit super- imposed on generator capability curve is

shown in the diagram. The setting of RXPE should correspond to about 70 MVA

as can be seen from the diagram.This corresponds to a secondary current of 1.28A.

The undervoltage and overcurrent relays are usually set at about 85% of Unand 115%

if Inrespectively.


For under voltage relay RXEG2

Setting Range : 85-90% of Un(=110 V)

Recommended Setting : 95V (86% of Un)


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2) For Overcurrent relay RXIG2

Setting Range : 110-115% of In(=5A)

Recommended Setting : 5.75A (115% of In)

3) For Directional relay RXPE40

Recommended Setting : 1.28A


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GENERATOR CAPABILITY CURVE & LOSS OF EXCITATION RELAY CH.GENERATOR CAPABILITY CURVE & LOSS OF EXCITATION RELAY CH.


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GENERATOR TRANSFORMER OVER-ALL DIFFERENTIAL RELAYGENERATOR TRANSFORMER OVER-ALL DIFFERENTIAL RELAY

Relay particulars:

Type : RADSB

Rating : 5A


Restraint Operating value : Settable at 20, 25, 32, 40 or 50% of In

Unrestraint Operating value : Reconnectible to 8, 13 0r 20 times In

Calculations:

For determining auxiliary Ct requirement

In1on 15,75 kV side = (250 x 10) / (3 x 15.75)KA

= 9164.56A

In2on 420 kV side = (250 x 10) / (3 x 420)KA

= 343.67A


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In1= (5/10000) x 9164 = 4.58A

In2= (1/500) x343.7 = 0.687

Ratio of auxiliary CT = 0.687 / (4.58/ 3 )

= 0.687 / 2.64

Vk=30 x In (RICTS) = 30 x (5/ 3) x RICTS

= 30 x RICTS

Setting Calculations:

a) Operating current setting :

Maximum tap changing position : 5%

According to the designers recommendation a minimum current sensitivity of

about 15% greater than the worst turns ratio mismatch at the tap changer should

normally be selected.


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Therefore, for 5% variation of taps operating current setting of 20% gives enough

margin for CT unbalance and other errors.

b) Unrestricted operating current setting:

This feature is to provide instantaneous tripping in the event of severe internal

faults.

Recommended unrestrained relay setting to take care of inrush currents on

switching, from experience based on full load current equal to normal relay rating.

In pratice such a situation arises in case of this transformer when an external

close-in fault is cleared.

13 % 13%

When energised from

HV side LV side

Y-(LV) Any

Transformer Transformer

Connection Size


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Maximum pick-up current setting = 20% of In

Unrestrained operating current setting = 13 times In


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GENERATOR TRANSFORMER HV WINDING RESTRICTED EARTH

FAULT RELAY


FAULT RELAYRelay particulars:

Type : RADHD

Rating : 1A

Operating Voltage : 10/15V

Operating Voltage : 20mAAuxiliary Voltage : 220V DC

Calculations:

Maximum through fault current = (250 x 1) / (3 x 420 x 0.145)

= 2370A

If = 2370 / 500 = 4.74A

Minimum relay = If (RCT+ 2RL) = 4.74 (3 + 0.2)

Operating Voltage = 15.17V


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FAULT RELAY


FAULT RELAY

Thus, setting can be = 15V

Minimum Knee point voltage of CT = =2 x 15V = 30V


Voltage setting = 15V


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GENERATOR TRANSFORMER OVER-FLUXING RELAYGENERATOR TRANSFORMER OVER-FLUXING RELAY

Relay particulars:

Type : RATUB

Rating : 110V, 50Hz AC

Setting Range : Start, Alarm 1.5 to 3V / Hz

Calculations:

Following are some comments regarding setting of RATUB

1 ) Transformer can withstand 10% of rise in V /Hz continuously

Therefore setting U/ f start can be selected as

1.09 x (Un/fn) = 1.09 x (110/50) = 2.4V/Hz

2) Plot of transformer U/f withstand characteristics on RATUB characteristics gives

K = 2 as the one giving


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Operating times lower than transformer withstand time for rise in U/f up to

1.35 x (Un/fn). Characteristics of transformer super-imposed on relay characteristics

is shown in diagram.

3) Beyond 1.35 x (Un/fn) rise in U/f operating time of RATUB varies from 6 to 2.2 secs at

K=2, whereas transformer requires instantaneous tripping. Usually instantaneous

element of O/V relay set suitably takes care of these conditions.

4) Alarm unit can be set at same value as trip, 2.4V/Hz and time setting can be at

3.5 secs.

However if instantaneous tripping is desired from RATUB itself alarm unit can be

used for this purpose in which case setting of this unit will be 1.35 x (Un/fn)=1.35 x

(110/50) = 3V/Hz with delay set at 0.1 secs.


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(U / f) start = 2.4V / Hz

K = 2

(U / f) alarm = 2.4V / Hz with time delay 3.5 secs.


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THE OPERATING TIME t AS A FUNCTION OF THE RELATIONSHIP BETWEEN THE ACTUAL

EXCITATION ANS THE SET STARTING VALUE, FOR DIFFERENT TIME CONSTANTS K.

THE OPERATING TIME t AS A FUNCTION OF THE RELATIONSHIP BETWEEN THE ACTUAL

EXCITATION ANS THE SET STARTING VALUE, FOR DIFFERENT TIME CONSTANTS K.


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INTERTURN FAULT PROTECTIONINTERTURN FAULT PROTECTION

Relay particulars:

Type : RXIG28

Range : 5-15V

Aux PT details:

PT-1 : 145.5V/200V, 3P, 15VA

PT-2 : 3.25V/65V, 3P, 15VA

Calculations:

Voltage per turn per slot = 131.25V

In case of split windings

Vfor a single turn fault = 131.25/2=65.645V


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INTERTURN FAULT PROTECTIONINTERTURN FAULT PROTECTION

VBA = 65.625 *(110/3) *[3/(15.74*10)]

VCD = 0.46 *65/3.25 = 9.2V

The relay can be set at 50% of the voltage developed across the relay for a single turn

Fault.

Recommended Setting:

RXIG28 setting = 5V


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LIST OF REQUESTED PROTECTIVE FUNCTIONS * DIVIDED

UP INTO TWO SYSTEMS

LIST OF REQUESTED PROTECTIVE FUNCTIONS * DIVIDED

UP INTO TWO SYSTEMS

A B

X

X

X

X

X

X

X

X

X

Generator Differential

Over all Differential

Minimum Impedance

(or alternatively)Overcurrent/Undervoltage

(for thyristor excitation)

(or option)

Overcurrent

Negative sequence

Thermal90% Stator Earth Fault

Neutral Disp.

100% stator earth fault

87G

87T

21

51/27

51

46

4959

64

Generator stator

Short circuits

Assymetry

Stator overload

Earth fault stator

SYSTEMPROTECTION FUNCTIONSANSITYPE OF FAULT


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A B

X

X

X X

X

X X

X

X

X

X X

Mini reactance

Pole slip

Reverse power (double protection for large

Generators)

Max. frequency

Min. frequencyOvervoltage or overcurrent

Undervoltage

Overfluxing Volt/Hz

Overvoltage

ThermalBridge measuring hardware combined with

Voltage function

40

78/21

32

81

8159

27

24

59

4964R

Generator stator

Loss of excitation

Out of step

Monitoring

Over speed

Blade fatigueInterturn fault

Lower voltages

Mag. Circuit

Higher voltage

Generator Rotor

Rotor OverloadRotor ground



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Example : Definite list must be prepared in accordance with electrical scheme andinstallation requirements.

A B

X

X

X

X

X

X

X

X

X

Transformer Differential

Overcurrent

Earth Fault Overcurrent

Restricted Earth Fault

Transformer Differential

Overcurrent

Overload

Residual Overcurrent (possible option in

acc. With requirements)

Restricted Earth Fault (possible option in

acc. With requirements)

87T

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51N

87N

87T

50/51

49

(51N)

(87N)

Step-up Transformer

Short circuit

Ground Fault

Unit Transformer

Short circuit

Ground Fault



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DATA REQUIRED FOR RELAY SETTING CALCULATIONS FOR

GENERATOR PROTECTIONS



1) Generator differential protection 87G-RADHA:

a) Sub-transient reactance Xd

b) CT secondary resistance RCT

c) Lead resistance from CT to junction point RL

2) Differential protection 87L-RADHA:

a) Sub-transient reactance Xd

b) Transformer reactance XT

c) CT secondary resistance RCT

d) Lead resistance from CT to junction point RL

3) 100% Earth fault relay 64G1-RAGEA:

a) 3rdHarmonic voltage across secondary of grounding transformer.


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4) Generator Overvoltage relay - 59G-RXEG:

a) Overvoltage withstand values of the generator.

5) Generator Inter-turn fault relay 50GI-RXIG:

a) Unbalance in current for 1 turn short circuit.

6) Loss of Excitation relay 40G-RAGPC:

a) The generator capability curve.

b) Impedance locus during loss of excitation

c) Variation in machine voltage & current on loss of excitation

7) Negative sequence protection 46G-RARIB:

a) K- A constant in seconds that is the characteristic for the generator

This constant represents the time during which a negative

sequence current that is equivalent to the rated current of the

generator, can be permitted.


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b) Continuous negative sequence withstand value.

8) Under-frequency protection- 81G-RXFE:

a) Generator manufacturers recommendations regarding under frequency

trip.

9) Over current relay 51-RXIG:

a) Continuous withstand current of the unit.

10) Generator Backup Impedance relay 21G-RAKZB:

a) Philosophy adopted for setting:

- to cover only transformer

- to cover next outgoing line but not beyond, under all

generation conditions

- to set for 70% of maximum load impedance.


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11) Pole slipping relay:

a) Impedance locus during pole slip.

12) Over-all differential relay 87GT-RADSB:

a) RCT, Vkof main CT.

b) RL, Lead Resistance.

13) Restricted Earth fault relay 64GT-RADHD:

a) RCTof the main CT.


14) Over fluxing relay 99GT - RATUB:

a) Over fluxing characteristics of the transformer.15) Transformer Ground fault relay 51NGT-CDG:

a) Plug setting.

b) Time setting.


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16) Station Transf. Differential relay 87UTA & 87UTB-RADSB:

a) RCT, Vkof main CT.


17) Station Transf. Overcurrent relay 51UTA CDG33:

a) Plug setting.

b) Time setting.


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Gen Protn Philosophy&Settings

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