Enerator Rotections: Asic Nformation & Ecommendations Part-i

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Generator Protections Basic Information & Recommendations Part-I Kamin Dave Senior Application Engineer

DOBLE ENGINEERING COMPANY

Generator Protections ¾ ¾ ¾ ¾

Stator Protections Rotor Protections Exciter Protections Backup Protections

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Generator Protections ¾ Stator Protections:1. 2. 3. 4.

Generator differential Protection (87G) Generator Split Phase differential Prot(50D) Over Voltage Protection (59) Over all Generator-Transformer differential Protection (87GT) 5. 0 – 95% Stator E/F & 100% Stator E/F Protection (59N/27TN) 6. Protection against Stator winding over Heating & over loading (51O/L) Knowledge Is Power

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Generator Protections ¾ Rotor Protections:1. 1st & 2nd Rotor E/F Protection (64F1/64F2) 2. Stator Unbalanced current Protection (NPS-46) 3. Loss of Excitation Protection (LOF-40G)

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Generator Protections ¾ Abnormal Operating Conditions:1. 2. 3. 4. 5. 6.

Reverse Power Protection (32R) Low forward Power Protection (37L/32L)) Under Frequency Protection (81U/F) Over Frequency Protection (81O/F) Out of Step or Pole-Slip Protection (78) Generator Over Speeding Protection

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Generator Protections ¾ Other Miscellaneous Protections:1. Generator – Transformer Over fluxing Protection (24) 2. Restricted E/F Protection if it required 3. Back up Impedance Protection or Back up Protection using Voltage Dependent (Voltage restrain / Voltage controlled) over current unit (21/51V) 4. Breaker Flash over Protection 5. Voltage Balance Scheme (LOP-60) Knowledge Is Power

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Protection schemes are recommended for Generator Prot based on Size:PROTECTION

ANSI CODE

SMALL (Up to 10MW)

MEDIUM (Up to 10MW)

LARGE (Above 10MW)

Stator Over heat

51 O/L

Yes

Yes

Yes

Voltage dependent O/C

51V

Yes

Yes

Yes

Under Impedance or Back up Impedance

21

-

Optional either 21 or 51V

Yes

Over voltage or Over fluxing

59 or 24 (99)

-

Yes

Yes

Under Voltage

27

-

Yes

Yes

Over frequency

81O

-

Yes

Yes

Under frequency

81U

Yes

Yes

Yes

Generator differential

87G

Yes

Yes

Yes

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REMARKS

Only for alarm

Required above 50MW & GT unit

Only for alarm

Less than 1MW optional

Protection schemes are recommended for Generator Prot based on Size:GeneratorTransformer combined differential

87GT

-

Yes

Yes

Negative Phase sequence

46

-

Yes

Yes

Restricted earth fault

64R

Optional either 87G or 64R

-

-

Stator E/F 0-95% & 100%

51N & 27N & 59GN

Yes

Yes

Yes

Rotor E/F-1st & 2nd

64F1 & 64F2

-

Yes

Yes

Reverse Power

32

Yes

Yes

Yes

Low forward Power

37

-

Yes

Yes

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Stage-1 for alarm & Stage-2 for Trip

Protection schemes are recommended for Generator Prot based on Size:Field failure

40

-

Yes

Yes

Pole slipping

78

-

-

Yes

Over speed

12

Yes

Yes

Yes

Turn to Turn fault in stator

50/51

-

-

Yes

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Above 50MW single unit

Above 250MW single unit

Protection schemes are recommended for Generator Prot based on Size:ROTOR AND BEARING PROTECTION: PROTECTION

Vibration Indicator

ANSI CODE

SMALL (UP TO 1MW)

MEDIUM (UP TO 10MW)

LARGE (ABOVE 10MW)

-

Yes

Yes

Yes

Bearing temperature & alarm trip

26 or 38

Yes

Yes

Yes

Bearing Insulation

26 or 38

Yes

Yes

Yes

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REMARKS

Protection schemes are recommended for Generator Prot based on Size:REQUIRED ALARMS: ABNORMAL CONDITION

AIR COOLED

HYDROGEN COOLED

REMARKS

Bearing Oil pressure low

Yes

Yes

Bearing temperature high

Yes

Yes

Stator winding temperature high

Yes

Yes

Lubricating oil temperature low

Yes

Yes

Sp. For diesel generator

Governor oil pressure low

Yes

Yes

Sp. For STG

Cooling water inlet pressure low

Yes

Yes

Battery voltage low

Yes

Yes

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Sp. For battery starting engine

Tripping Criteria: ¾ Class-A Tripping: ƒ Turbine Trip + GCB Trip + Field Breaker Trip ¾ Class-B Tripping: ƒ Turbine & Boiler Trip ¾ Class-C Tripping: ƒ GCB Trip only or GCB & FB Trip ¾ ¾

GCB = Generator Circuit Breaker FB = Field Breaker

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Tripping Criteria TRIP TYPE:

TT

¾ DIFFRENTIAL ¾ STATOR EARTH ¾ ROTOR EARTH ¾ OVERVOLTAGE ¾ OVERCURRENT ¾ UNBALANCE ¾ UNDERFREQUENCY

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ACA - PROT - 2 / 45

Apparatus Maintenance and Power Management for Energy Delivery

GCB

FB

Tripping Criteria TRIP TYPE

TT GCB FB

¾ UNDEREXCITATION W / O LOSS OF FIELD WITH LOSS OF FIELD ¾ REVERSE POWER LONG TIME (STAGE-1) SHORT TIME (STAGE-2)

(OPERATES ONLY AT TT) Knowledge Is Power

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Technical Specification: Generator ¾ ¾ ¾ ¾ ¾ ¾ ¾ ¾ ¾

588 MVA, 16.2 kA, 21 kV, 0.85 PF Hydrogen gas pressure : 3.5 bar Excitation : 340 V, 4040 A Critical speeds : 864, 1806 (exciter), 2388 rpm Short circuit ratio : 0.52 Sub-transient reactance Xd” : 7.2 % Negative Sequence reactance(XG2) : 8% Transient reactance Xd’ : 24.1 % Synchronous reactance Xd : 231 % (1/0.52) Knowledge Is Power

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Technical Specification: Generator ¾ ¾ ¾ ¾ ¾ ¾ ¾

Zero Sequence Reactance (X0) Time (Td”) short circuit Time (Td’) short circuit Short Circuit Ratio (SCR) Capacitance between Stator Winding & Ground Surge Capacitance betn Step-up Tr & GCB Capacitance bewn TR winding & Ground

: 13% : 0.032s : 0.75s : 0.52 : 0.385 microF : 0.25 microF/Phase : 0.2 microF/Phase

NB: ¾ Sub-transient reactance Xd” is used for Breaker rating calculations. ¾ Transient reactance Xd’ is used for O/C & E/F relay co-ordination & motor starting studies. ¾ Higher SCR, lower the reactance, higher the machine size & higher the cost. Lower the SCR, higher the reactance, low the machine size & lower the cost

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Technical Specification: Generator ¾ Unity PF lag capability: ¾ Unity PF lead capability:

433 MVA 250 MVA

¾ Total losses 6920 kW;

ƒ Break up: • Iron: 600kW; • Short circuit: 2800kW • Excitation: 1390kW; Windage: 1680kW • Bearing and shaft seals: 450 kW

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Technical Specification: PMG-Pilot Exciter ¾ Low excitation power-400 HZ permanent magnet generator is provided as pilot exciter with brushless exciters. ¾ The PMG ELP 50/42-30/16 is rated : 65 KVA, 220 V, 3 Ph, 91 A and 158 A for field forcing. ¾ Frame has laminated core with 3ph wdg. Rotor has mounted poles. Permanent magnets are screwed to poles.

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Technical Specification: Brushless Exciter for 500MW-BE70/90-30/6-20 ¾ Rating: 3840 kW, 6300 A, 600 V ¾ 10 seconds output: 7050 kW ƒ Current & voltage: 8600 A, 820 V. ¾ Nominal current : 4030 Amp. ¾ Response ratio: >2 ¾ 60 diodes per wheel (20 per arm) ¾ Current per diode: 67 A, and with 6 out of 20 diodes failed: 96 A ¾ Armature dia: 70 cm; Length 90 cm Knowledge Is Power

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Technical Specification: Generator Capability Curve 450

400

0.4

0.7 MAX

RATED

0.85 0.9

LAG 300

0.95

200 100

MVAR

0

100 200 300

400 500 588

MW

1.0

100 LEAD A. C. ARON 99 07 31

0.95

200 250

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0.85 P.F

Technical Specification: 500MW Generator Efficiency 99

η

% 98.5 98 97.5 97

0

25%

50%

75%

100%

LOAD IN MW : % FULL LOAD Knowledge Is Power

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Technical Specification: Generator ¾Flux density stator & rotor : 2 - 2.5 Tesla ¾H2 coolers heat load : 4424 kW ¾Continuous unbalanced load :8% ¾Short time negative sequence I2t : 10s

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Unbalanced Load – Time Curve 10 6

2

1

I2 t = 10 sec I2 PU

0.1 0.08 0.03 0.3

t in Seconds

1

10

100

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1000

Stator Over Current Limit: 3-Phase Balanced Load

2.2 I PU

Stator O/C Curve of 500MW Machine

2.0 1.8 1.6 1.4 1.2 10

20

40 60

t in Seconds

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100

200

Stator Over Current Limit: 3-Phase Balanced Load

Stator O/C Curve Limit as per ANSI C50.13-1989

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PERMISSIBLE LOADING RATED MVA min: 1 SHORT TIME RATED MVA -10%

2

2 5 10

+5%

+5% -5% 0 VOLTS FREQ. DEVIATION

CONTINUOUS RATED MVA 3 %MVA 90 95 97 100 -5% SPEED +3% PF=RATED

1

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- 5%

Basic Generator Data for Relay Setup ¾IRating = 16200 Ampere ¾CTR = 20000/5A ¾IRating on secondary = (IRating)/ (CTR) = (16200) / (4000) = 4.05A

¾VRated = 21000V ¾PTR = 21/0.110kV

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Basic Generator Data for Relay Setup ¾VRating on secondary = (VRating)/ (PTR) = (21000) / (190.90) = 110V (L-L)

¾VRating on secondary = (VRating)/ (PTR*1.7325) = (21000) / (190.90*1.7325) = 63.5V (L-N)

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Basic Connection: PT Input “Line to Line Voltage” VL-L = 21000V

VNOMINAL = 110VL-L VAB VBC

Relay

VCA Knowledge Is Power

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Basic Connection: PT Input “Line to Line Voltage”

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Basic Connection: PT Input “Line to Ground Volatge-3 wire” VL-L = 21000V

VNOMINAL = 110VL-L VAB VBC VCA

Relay Knowledge Is Power

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Basic Connection: PT Input “Line to Ground Voltage” VL-L = 21000V

VL-N = 21000V/1.7325

VNOMINAL = 63.5VL-N VAN VBN

Relay

VCN Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Basic Connection: PT Input “Line to Ground Voltage”

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Stator Overheating Protection (51O/L)

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Stator Overheating Protection (51O/L) ¾ Causes: ƒ ƒ ƒ ƒ ƒ ƒ

Over Loading of Generator Stator Over Current Short-circuited laminations Failure of core bolt insulation Failure of Ventilation Coolant circuit failure

¾ Setting Criteria: Based on Generator O/L Curve (Say: 115% for 30s) ¾ RTD or PT100 is required to sense over temp. Knowledge Is Power

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Stator Overheating Protection (51O/L) ¾What is the difference between Stator Over Load & Over Current??? ¾Stator Over Load: ƒ Power Output of Machine (KVA or KW) exceeds it’s maximum continuous over load power limit ƒ PMAX(KW) = 1.7325*VL-L*ILOAD*COS (Ang) ƒ Machine voltage is not much reduce during over load condition (i.e. 85-95% of VRated) ƒ Phenomenon is much harmful for Prime over (i.e. Turbine/Engine) Knowledge Is Power

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Stator Overheating Protection (51O/L) ¾What is the difference between Stator Over Load & Over Current??? ¾Stator Over Current: ƒ Stator current exceeds it’s maximum limit during faults ƒ Machine voltage collapse & reduced below 30% (Depends on Faults & Location) ƒ PMAX(KW) = 1.7325*VL-L*ILOAD*COS (Ang) ƒ Phenomenon is much harmful for Stator winding (Slide22 shows; ANSI limit) Knowledge Is Power

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Stator Overheating Protection (51O/L) +VE

2.5s – 25s 51O/L-Timer

51O/L-1

R R

51O/L 75-200%

51O/L-Timer-1

3

Annunciation ckt.

DC Circuit

G Power Circuit Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

-VE

Stator Overvoltage Protection (59)

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Stator Over Voltage Protection (59) ¾Causes: ƒ Transient Over Voltages • Surge Voltages mainly originate in Transmission System because of Lightning Strokes ƒ Power Frequency Over Voltages • Defective operation of AVR • Sudden Load thrown off

¾Protection is normally offered by other relays like over fluxing relay Knowledge Is Power

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Stator Over Voltage Protection (59) ¾ Setting Criteria: Based on Generator Open circuit voltage characteristic Curve. ¾ Normally, Inverse Characteristic element is used for Stage-1 for Alarm/Trip (Say: 105% to 110% of Un for 45s to 50s) ¾ Definite Time element is used for Stage-2 for Tripping (115% to 125% for 500ms to 3000ms). Stage-2 must e set below the maximum stator voltage possible, taking in to account magnetic core saturation. Knowledge Is Power

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Stator Over Voltage Protection (59) ¾Advisable to provide surge diverters for TG also - to be connected between phases & earth. Design value (1.2 - 1.4)*Un allows 50 Hz over voltage on load rejections. ¾Surge diverters to be explosion proof or other constructional measures be taken to avoid danger to persons or near by components in case of over voltages. Knowledge Is Power

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Generator-Transformer Overfluxing Protection (24)

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Generator-Transformer Over Fluxing Protection (24) ¾Causes: ƒ Generator Regulator Problem • AVR or Voltage Regulator Fails • Operating Error during off line manual regulator operation • Loss of VT supply of AVR ƒ System Problem • Unit Load Rejection: Full Load or – Partial Load • Power System Islanding during Major disturbances in Grid Knowledge Is Power

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Generator-Transformer Over Fluxing Protection (24) ¾Fundamental Voltage & Flux relation: EAVE

=

N*Flux*Frequency

But, Foam Factor (ERMS/EAVE) is 1.11; ERMS

=

1.11*N*Flux*Frequency

Flux

=

(ERMS) / (1.11*N*Frequency)

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Generator-Transformer Over Fluxing Protection (24) ¾ Flux = (VN / FN)---Æ (Volts/Hz) ƒ Flux increases when System voltage rises at Rated Frequency ƒ Flux increases when System Frequency fall at Rated Voltage ¾ Saturation of Magnetic Core of the GT due to exceeded the V/Hz ratios ¾ Serious Over heating will occur in bolts & support structure of machine which destroys their own insulation as well as coil insulation if the phenomenon persist for longer duration Knowledge Is Power

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Generator-Transformer Over Fluxing Protection (24) ¾Specific Over Fluxing Protection is not Mandatory & It is generally offered as an optional by other Protection like Over Voltage. Protection should be in circuit whenever field CB is closed ¾IEEE C50.13 Generator should continuous withstand 105% of rated excitation at full load ¾Normally Inverse & DMT type relays are used for application Knowledge Is Power

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Generator-Transformer Over Fluxing Protection (24) ¾Setting Criteria: Based on Generator V/Hz with stand capability Curve (Say: 1.05 V/Hz or 1.1 V/Hz of Un/Fn) ¾Normally, Inverse Characteristic element is used for Stage-1 (1.05 to 1.1 V/Hz for Alarm/Trip for 45-50s) ¾Definite Time element is used for Stage-2 for Tripping (1.15 to 1.25 V/Hz for 2s - 6s) Knowledge Is Power

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Generator-Transformer Over Fluxing Protection (24)

Setting Criteria for Inverse Time Over Fluxing relay

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Generator Under Frequency Protection (81)

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Generator Under Frequency Protection (81) ¾ Causes: ƒ Demand of Active Power suddenly Increases in Power Grid ƒ Islanded system, inadequate input quantity and quality of fuel (i.e. Problem occur in Steam valve in Steam Turbine or Fuel Pump in Diesel Engine/Gas Engine etc.) ƒ Islanded system, Two or more Machines are running in parallel on more than 70% load & outage of machine due to machine fault, increases load on another machine to create under freq. on running machine Knowledge Is Power

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Generator Under Frequency Protection (81)

¾It’s a Prime-mover Protection. Each turbine is having critical speed. Operation of machine at a speed which is close to critical speed would causes excessive vibration in Primemover & also it produces mechanical stress in turbine blades ¾Prolonged operation at under frequency would result in to damage of Primemover Knowledge Is Power

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Generator Under Frequency Protection (81)

¾As per IEC, BS and ANSI standards, limits of voltage & frequency variation within which the generator can operate at full load without exceeding specified temperature by more than 10 degree ¾A typical example of Under freq withstanding capability of ABB generator as shown below slide;

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Generator Under Frequency Protection (81) Frequenc y in %

Rated Voltage 100%

P.F.=1.0, P = PN Cont.

P.F.=0.8, P = PN Cont.

No Load P=0 Cont.

100% 96%

100%

Cont.

Cont.

Cont.

95%

100%

Cont.

30Min.

Cont.

92.5%

100%

30Min.

2 Min.

Cont.

90%

100%

2 Min.

-

Cont.

87.5%

100%

-

-

30Min.

85%

100%

-

-

2 Min.

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Generator Under Frequency Protection (81) ¾ Setting Criteria: Based on Generator Permissible Loading Curve (Say: 48.5Hz for 50Hz) ¾ Normally, Stage-1 is the delayed tripping (Say: 48.5Hz for 3s-10s) ¾ Stage-2 element is also delayed but operating is lesser than Stage-1 element (Say: 48Hz for 0.5s - 5s) ¾ Operation at Frequency below 47.5Hz allowed only for 2-hours in entire life of set (Turbine) Knowledge Is Power

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Generator Over Frequency Protection (81)

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Generator Over Frequency Protection (81) ¾ Causes: ƒ Full or Partial Load Rejection (Load thrown off) ƒ Overshedding of Load during a major system disturbance ¾ Condition is not a serious problem since control system or operator action can be used to quickly restore generator speed but, if it is not then Machine may pull out of step condition & it is required to trip on over freq. protection Knowledge Is Power

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Generator Over Frequency Protection (81)

¾Setting Criteria: Based on Transient Stability (Say: 50.5Hz for 50Hz) ¾Normally, Stage-1 is the delayed tripping (Say: 50.5Hz for 3s-10s) ¾Stage-2 element is also delayed but operating is lesser than Stage-1 element (Say: 51Hz for 0.5s - 5s) ¾Operation at Frequency above 51.5Hz allowed only for 2-hours in entire life of set (Turbine) Knowledge Is Power

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Generator Under/Over Frequency Protection (81) +VE

-VE

0.5s – 5s 2/81-Timer 52

81G-1

T 0.5s – 5s 2/81-Timer 81G-2

T 86F-2

81G-2

Reverse active clutch & Time Motor

TM

DC Circuit Knowledge Is Power

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Generator Under/Over Frequency Protection (81) +VE

-VE 86F TM-1

2/81-1

86F-2

R 86F-3 Annunciation ckt. 86F-1 Trip ckt.

DC Circuit Knowledge Is Power

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Reverse Power Protection (32R)

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Reverse Power Protection (32R) MVAR

MW

FMachine < FSystem

G

D

Y

MVAR

-MW

MW

Relay setting Threshold -MVAR

Machine Act as a Synchronous Motor Knowledge Is Power

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Reverse Power Protection (32R) MVAR

MW

VMachine < VSystem FMachine < FSystem

G

D

Y

MVAR

-MW

MW

Relay setting Threshold -MVAR

Machine Act as a Induction Motor Knowledge Is Power

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Reverse Power Protection (32R) ¾ Causes: ƒ Two or more machines are running in parallel & Prime-mover of one of the machine fails. Turbine has Problems; exhaust hood temperature on steam turbines ƒ Sometimes the condition appear during synchronization of machine, if incoming machine frequency is lesser than bus frequency

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Reverse Power Protection (32R) ¾ Protection against the motoring action of the generator while the generator looses it’s Prime-mover input ¾ Protection is applied for Prime-mover ¾ Normally, Protection is applied only when machines are operating in parallel with each other as well as Power Grid ¾ Generator unaffected by reverse power, but act as a Synchronous Motor (Exporting Reactive Power & Importing Active Power) Knowledge Is Power

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Reverse Power Protection (32R) ¾ Effect: ƒ Steam Turbine:• Steam turbine tends to overheat, when steam supply is cut off and the turbine still rotates as the generator runs as motor. Steam turbine, act as a pump and the steam is trapped. The turbulence losses in the trapped steam may then built up a high temperature in lowpressure stage. Hence, the turbine blades are overheated due to windage or air friction. However, the heat caused by turbulence of the trapped steam can de-temper turbine runner. Knowledge Is Power

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Reverse Power Protection (32R) ¾ Effect: ƒ Hydro Turbine:• In case of hydro turbine, the flow of water starts reducing or complete cut off and hence bubbles are formed causing cavitations in the turbine resulting to damage turbine runner. ƒ Diesel Engine:• In case of diesel driven set, loss of motive power is likely to be cause by some mechanical failure, such as bearing over heating leading to closure of fuel valves, and continued running is likely to cause several damages in engine. Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Reverse Power Protection (32R): Allowable limit Prime Mover Diesel (Two cycle-2 stroke) stroke) Diesel (Four cycle-4 Gas turbine (Single shaft)

Allowable limit of %P of Reverse Power 25% of rated power 15% of rated power 100% of rated power

Gas turbine (Double shaft) 10% to 15% of rated power Steam turbine

0.5% to 7.5% of rated power

Hydro turbine

1% to 3% of rated power Knowledge Is Power

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Reverse Power Protection (32R) ¾ Sequential Tripping: ƒ Used on Steam Turbine Generator to Prevent Overspeed ƒ This trip mode only used for boiler/reactor or turbine mechanical problems

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Reverse Power Protection (32R) ¾ Sequential Tripping: ƒ Step 1: • Abnormal Turbine/Boiler/Reactor condition is detected

ƒ Step 2: • Turbine Valves closed; Generator allowed to briefly “Motor” (i.e. Importing Active Power from Grid)

ƒ Step 3: • A Reverse Power relay in Series with Turbine Valves position switches confirms all Valves have closed Knowledge Is Power

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Reverse Power Protection (32R) ¾ Sequential Tripping: ƒ Step 4: • Generator is required to Isolate from Power System G

D

Y

MW MVARs

GCB

ƒ Consider • Export High MVARs • Import Low MW Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Reverse Power Protection (32R) Sequential Tripping Logic:

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Reverse Power Protection (32R) ¾ Setting Criteria: As the overheating of the turbine blade does not occur instantaneously while the generator starts motoring, so it is not required to trip instantaneously. ƒ Set Point 1: • -P<0.5% for Steam Turbine Generator • Operating Time 10s

ƒ Set Point 2: • -P<0.5% for Steam Turbine Generator • Operating Time 2s Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Low Forward Power Protection (37L)

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Low Forward Power Protection (37L) MVAR

MW G

D

Y

MVAR

-MW

MW Relay setting Threshold

-MVAR Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G)

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ Protection Against Internal Faults in Machine ¾ Operating Criteria: Differential protection relay operate when the current at two ends of feeder differ or mismatch by more than threshold value of relay (Idiff>Idiffset) NGR

CT1

CT2 Y

G

D GCB

E

F1

I1

I2

R

Idiff = (I1 – I2)

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ Protection Against Internal Faults I1

I2

CT1

CT2

3

G1

D

3

NGR

Y GCB

F1

E I1

I1

R

I2

I2

Idiff = I1+I2

NGR D

G2

Y GCB

E Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ Protection Against Internal Faults I1

CT1

CT2

3

G1

Y

3

NGR

D GCB

F1

E I1

I1

R Idiff = I1

Note: I2 is very less compared to I1 so it will be neglected

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Apparatus Maintenance and Power Management for Energy Delivery

L O A D

Generator Phase Differential Protection (87G) ¾ Stable for External Faults I1

NGR

I2

CT1

CT2 D

3

3

G1

Y GCB

I2

E

F2

I2 I1

R Idiff = I1+I2 = 0

I1

NGR D

G2

Y GCB

E Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ Mainly Two Types of Differential Schemes; ƒ High Impedance Differential Protection Schemes ƒ Low Impedance Differential Protection Schemes

Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

3 3 3

3 3 3

Generator Phase Differential Protection (87G): High Impedance Scheme

G

R

Y

Pickup Setting: 5%-25% of IFLC

B

Metrosil & Stabilizing Resistor

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G): High Impedance Scheme

Distorted CT output & Low resistance Path

Stabilizing resistor provide stability: Negligible Current flows through relay coil External fault & one of the CT Saturated Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ High Impedance Differential Scheme; ƒ Simple & Low cost Scheme ƒ Only Pickup setting & Easy to set it ƒ Stabilizing resister Increases stability of relay against high through fault current ƒ Operating on current balance principal ƒ Non-linear resistor or Metrosil is required for surge voltage absorb during internal & through fault condition ƒ Special PS class CTs (With low turn ratio errors) of identical ratio & ratings required for scheme ƒ CAG34, MFAC34, MCAG34, etc. relays are used as high impedance differential relays. ƒ Much suitable for Generator/Motor Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ Essential Requirement for High Impedance Differential Scheme are; ƒ ƒ ƒ ƒ

Equal CT Ratio Low CT secondary winding resistance Adequate knee-point voltage output from CTs Low lead burdens

¾ Harmonic Settings are not available, so scheme is difficult to applied for Transformer ¾ Three Winding differential protection scheme become a more complex than low impedance scheme Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G): High Impedance Scheme

¾Setting Criteria: Typical Recommended setting is 10% or 20% ¾Relay Operating Time should be less than 50ms. ¾Ensure through fault stability by adjusting proper value of stabilizing resistor

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ Low Impedance Differential Scheme; ƒ Complex & Higher cost Scheme compared to High impedance scheme ƒ Settings are more complex & %Slope Characteristics settings are differ from manufacturer’s to manufacturer’s ƒ The scheme is also called as a percentage differential scheme ƒ For External faults-----Æ High restraint current ƒ For internal faults-----Æ Low restraint current ƒ High sensitivity during internal faults ƒ Chance of mal-operation of relay during high through fault current ƒ 7UT62/MICOMP632/DUOBIAS/SPAD346 etc. relays are used as low impedance differential relays ƒ Much suitable for Transformer Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G) ¾ Low Impedance Differential Scheme; ƒ Normally, Single Slope Characteristic is sufficient if the Protection is applied for Generator/Motor because both the CTs are on same voltage level, so we can minimize %CT error during an external fault ƒ Dual Slope Characteristic is required if the Protection is applied for Transformer

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Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G): Low Impedance Differential Protection in MICOM P345 Relay

Slope is not start from origin & depends on “IS2” setting. Turn point for slope is easy to set Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G): Low Impedance Differential Protection in 7UM62 Relay

IBias = I1 + I2 First slope is always starts from origin & 2nd slope is depends on Base Point2 setting. Turn point for 2nd slope is set in following way; For example; Base point2 = 2.5A then 2nd slope starts after 5A Knowledge Is Power SM

Apparatus Maintenance and Power Management for Energy Delivery

Generator Phase Differential Protection (87G): Low Impedance Differential Protection in REG316 Relay

Slope is starts from origin & cut of point is depends on “b” setting Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Phase Sequence Protection (46)

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46) ¾ Unbalance phase currents create Negative Sequence current in Generator Stator

¾ Negative Sequence current interacts with normal positive sequence current to induce a double freq. (120Hz) current in Rotor winding & it causes surface heating Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46) ¾ Generator withstand capacity; I22t = K Where; K = Constant (Large Generator has smaller “K” value) & It’s differ Manufacturer’s to Manufacturer’s I2 = Negative Sequence current Table-I shows unbalance withstand capacity of machine as per ANSI C50.13-1989 Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46) Permissible NPS current (I2) Percentage of stator winding

Type of Generator Salient Pole With connected amortisseur windings

10

Without connected amortisseur windings

5

Cylindrical Rotor Indirectly Cooled

10 8 6 5

Directly Cooled to 960MVA 961 to 1200 MVA 1201 to 1500 MVA Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46) Type of Generator

Permissible I22t

Salient Pole Generator

40

Synchronous Condenser

30

Cylindrical Rotor Generators Indirectly Cooled

30 10 See curve in Slide 82

Directly Cooled up to 800MVA Directly Cooled (801 to 1600 MVA)

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46)

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46)

¾Adjust Definite Time Tmax & Tmin in relay shown in below slides

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46)

Tmin is the Definite Time

Generator Withstand Curve Relay Characteristic Inverse to be set below

Generator Cont. Withstand capacity

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46)

Tmax (Definite Time)

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Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46) ¾Back up Protection: Relay Operation reqd. to co-ordinate for HV fault as well as Auxiliaries

500MVA/21KV

GT

F1 Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Negative Sequence Protection (46) Xd” = 7.2% XG2 = 8% XT = 9.5%

I1 = I2 = 100 / (Xd” + XG2 + 2XT) I1 = I2 = 100 / (7.2 + 8 + 2*9.5) I1 = I2 = 2.92 P.U. Relay operating time is required to co-ordinate on HV faults. Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40)

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G): ¾Loss of Excitation Magnetic Coupling between Stator MMF & Rotor Field Lost ¾Prime Mover still driving unit ¾Large slip frequency current induced in rotor

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G): Basic Diagram

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G): Basic Diagram of Brushless Excitation Auto

R Y B

VT

M

GEN VOLT SET POINT MEASURING CIRCUIT COMPENSATE

CT

G

BALANCING Manual INSTMT. M SET POINT DV GEN VOLT CONTROLLER

CONTROLER

FOLLOW UP CONTROL GATE CONTROL AUTOMANUAL SELECTOR

DE-EXCITN CONTROL

EXC

THYR.

PMG

FB

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Apparatus Maintenance and Power Management for Energy Delivery

GATE CONTROL

Loss of Excitation Protection (40G): Basic Diagram of 210MW Static Exciter RECTIFIER TRANSFORMER 2500 KVA 15.75 KV/575V DYN 5 AVR FCB CEX 3000 1200V 3000A COIL 220V DC

TY1

~ =

TY2

AUTO MANU

TY3

~ =

TY4

G

NO LOAD 917A, 95 V FULL LOAD 2500A, 300 V 5 KVA 415 / 35V 220 V BATTERY

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾How Excitation System Works??? Start Output Terminal Voltage (VG) of Machine Detected Reactive Current (IQ) of Machine Detected Reference Voltage (VGREF) of Output Terminal of Machine is Set according to Reactive Current (IQ), Reference Voltage VHREF Of High Voltage side of Transformer & Transfer function FH of Phase Compensation Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾How Excitation System Works??? Output Terminal Voltage (VG) is subtracted from reference VGREF of output terminal of Machine

A timing signal is produced according to difference signal Output from subtracting unit Field Current is supplied to Field Winding according to Timing signal End Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G): How Excitation Fails???

If it Open!!!

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G): How Excitation Fails???

If it Fails!!! Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G): How Excitation Fails??? If it Fails!!!

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G): How Excitation Fails??? If it Shorts or Open!!!

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ Causes: ƒ ƒ ƒ ƒ

Field Open Circuit (Field current is zero) Field Short Circuit (Field current is too high) AVR Control Failure Accidental Tripping of field breaker

¾ Momentary; It will Import Reactive & Real Power (Motoring Action) ¾ After Motoring Action; Importing Reactive Power & Exporting Real Power ¾ Synchronous Generator Becomes Induction Generator Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G) MVAR

MVAR G

D

Y

MW

-MW

MW

-MVAR

Machine Act an Induction Generator Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Loss of Excitation Protection (40G) MVAR

MVAR G

D

Y

MW

-MW

MW

-MVAR

Machine Act an Induction Motor Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ Slip Induced Eddy Currents Heat Rotor Surface ¾ System Voltage Collapse due to Reactive Power demand Increasing in Power System ¾ Reactive power is drawn from grid proportional to short circuit ratio. Power factor is low, end zone heating increases. ¾ Partial loss of excitation may cause pole slipping-highly detrimental to the machine. ¾ During failure of field, field suppression shall be cut off from circuit and active load decreased to 60% rated within 30 sec and to 40% in next 1.5 minutes. Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ THW -210 can operate at 40% rated load for a total period of 15 minutes. Set to be tripped there after. ¾ Excitation to be removed when speed is 2000 rpm, to prevent rotor overheating. ¾ Problem more severe for Steam Turbine ¾ Problem less severe for hydro turbine (Salient Pole)

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

How to set Relay????

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

Stator Limit PF=0.85

Under Excited

Over Excited

Rotor Limit

Generator Capability Curve Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

Generator Capability Curve Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) Rotor Limit

Over Excited

X

PF=0.85

Under Excited

-R

Stator Limit

R

-X

Z = (KV2/MVA)*(CTR/PTR)

Generator Capability Curve: R-X Plot Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

Generator Capability Curve Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) Stator Limit

Initially it’s a Motoring Action when excitation fails

Xd

Rotor Limit Generator Capability Curve: R-X Plot Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) Stator Limit

After Motoring Action Machine start to work as An Induction Generator

Xd

Rotor Limit Generator Capability Curve: R-X Plot Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ ZPU = (MVABase*ZOhms)/(KVBase2) ¾ ZOhms = ((KVBase2)*(ZPU)/(MVABase) ¾ Xd’Ohms = (21)2*(0.241)/(588) ¾ Xd’Ohms = 0.18075 Ohms-Æ Primary side

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

¾ Xd’Ohms = 0.18075*(CTR/PTR) ¾ Xd’Ohms = 0.18075*(4000/190.90) ¾ Xd’Ohms = 3.7871 Ohms-Æ Secondary side

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ ZPU = (MVABase*ZOhms)/(KVBase2) ¾ ZOhms = ((KVBase2)*(ZPU)/(MVABase) ¾ Xd

Ohms

= (21)2*(2.31)/(588)

¾ Xd

Ohms

= 1.7325 Ohms

Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

¾ Xd

Ohms

= 1.7325*(CTR/PTR)

¾ Xd

Ohms

= 1.7325*(4000/190.90)

¾ Xd

Ohms

= 36.3 Ohms-Æ Secondary side

Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

¾Offset Setting; ¾ (Xd’Ohms )/2= 1.893 Ohms-Æ Secondary side

¾Circle Diameter Setting; ¾ Xd

Ohms

= 36.3 Ohms-Æ Secondary side

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

¾Modern Numerical Relay have Dual Characteristics

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) Machine Operating Limit in Leading PF

Zone 2 setting crosses Steady state Stability Limit

Setting Criteria: 1 for Dual Characteristics Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ OFFSET Setting: ¾ ZPU = (MVABase*ZOhms)/(KVBase2) ¾ ZOhms = ((KVBase2)*(ZPU)/(MVABase) ¾ Xd’Ohms = (21)2*(0.241)/(588) ¾ Xd’Ohms = 0.18075 Ohms-Æ Primary side Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ OFFSET Setting: ¾ Xd’Ohms = 0.18075*(CTR/PTR) ¾ Xd’Ohms = 0.18075*(4000/190.90) ¾ Xd’Ohms = 3.7871 Ohms-Æ Secondary side

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ ZONE 1 Setting: ¾ ZPU = (MVABase*ZOhms)/(KVBase2) ¾ ZOhms = ((KVBase2)*(ZPU)/(MVABase) ¾ Xd

Ohms

= (21)2*(1)/(588)

¾ Xd

Ohms

= 0.75 Ohms Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ ZONE 1 Setting: ¾ Xd

Ohms

= 1.7325*(CTR/PTR)

¾ Xd

Ohms

= 1.7325*(4000/190.90)

¾ Xd

Ohms

= 7.857 Ohms-Æ Secondary side

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ ZONE 2 Setting: ¾ ZPU = (MVABase*ZOhms)/(KVBase2) ¾ ZOhms = ((KVBase2)*(ZPU)/(MVABase) ¾ Xd

Ohms

= (21)2*(2.31)/(588)

¾ Xd

Ohms

= 1.7325 Ohms Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40) ¾ ZONE 2 Setting: ¾ Xd

Ohms

= 1.7325*(CTR/PTR)

¾ Xd

Ohms

= 1.7325*(4000/190.90)

¾ Xd

Ohms

= 36.3 Ohms-Æ Secondary side

Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

¾Offset Setting; ¾ (Xd’Ohms )/2= 1.893 Ohms-Æ Secondary side

¾Circle Diameter Setting; ¾ZONE 1 ¾ Xd

Ohms

= 7.857 Ohms-Æ Secondary side

¾ZONE 2 ¾ Xd

Ohms

= 36.3 Ohms-Æ Secondary side Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40)

Setting Criteria: 2 for Dual Characteristics Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Loss Of Excitation Protection (40): MICOM P345 Relay

Setting Criteria: 2 for Dual Characteristics Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

0-95% Stator Ground Fault Protection (59GN)

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN) ¾ It provides a protection for stator ground faults on generator which are high impedance grounded (NGT through NGR or NGR etc.) ¾ Protection function normally applicable for unit connected generators ¾ Ground current can be limited up to about 3A to 25A on primary side

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground VLN = 21000/1.7325

IF IF

PTR = 21000/240V CTR = 20/1A

100 Ohms, 10s

Maximum Ground Fault Amps = (Line to Neutral Voltage) ----------------------(NGR Resistance)

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground

a

IF

VLN = 21000/1.7325 PTR = 21000/240V CTR = 20/1A

100 Ohms, 10s

Ground Fault Amps at fault location = (Maximum Ground Fault current * %A)/100 Where; %A = (100 – Fault at location of stator winding)

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground VLN = 21000/1.7325 PTR = 21000/240V CTR = 20/1A

100 Ohms, 10s

Maximum Ground Fault Volts = (Line to Neutral Voltage*PT secondary volts) ------------------------------------(PT Primary Volts)

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground VLN = 21000/1.7325 PTR = 21000/240V CTR = 20/1A

100 Ohms, 10s

Ground Fault Volts = (Ground fault Amps*PT secondary volts*NGR Resistance) --------------------------------------------(PT Primary Volts)

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground Appendix: PTR = 21000/240V NGR Value = 100 Ohms 59GN Relay Range = 5.4V to 20V Maximum Ground Fault Amps = (Line to Neutral Voltage) ----------------------(NGR Resistance) IF-Max

IF-Max

= (12121.21) ------------------------100 =

121.21 Amps

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground Appendix: PTR = 21000/240V NGR Value = 100 Ohms 59GN Relay Range = 5.4V to 20V Fault at 90% location of Stator Winding from Phase Terminal %A

= (100 – 90) = 10%

Ground Fault Amps at fault location = (Maximum Ground Fault current * %A)/100 IF at location “A”

= (121.21*10)/100

IF at location “A”

= 12.12 Amps

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground Appendix: PTR = 21000/240V NGR Value = 100 Ohms 59GN Relay Range = 5.4V to 20V Fault at 90% Location of Stator Winding from Phase terminal Ground Fault Volts = (Ground fault Amps*PT secondary volts*NGR Resistance) --------------------------------------------(PT Primary Volts) Ground Fault Volts =

Ground Fault Volts =

(12.12*138.52*100) --------------------------12121.21 13.85 Volts

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Resistor Ground Appendix: 59GN Relay Setting = 5.4V & TMS = 0.3

Relay Setting % Location “A” Fault Voltage from Neutral

Magnitude on relay terminals

5.4V

5%

6.92V

5.4V

25%

34.63V

5.4V

50%

69.264V

5.4V

75%

103.89V

Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Operating of Relay

Stator Ground Fault Protection (59GN): Resistor Ground Appendix: 59GN Relay Setting = 5.4V & TMS = 0.3

Relay Setting % Location “A” Fault Voltage

Operating of Relay

from Neutral

Magnitude on relay terminals

5.4V

1%

1.38V

Not Operate

5.4V

2%

2.77V

Not Operate

5.4V

3%

4.15V

Not Operate

5.4V

4%

5.54V

Not Operate

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (50G): Resistor Ground Appendix: PTR = 21000/240V NGR Value = 100 Ohms 50G Relay Range = 0.1A to 0.4A CTR = 20/1A Maximum Ground Fault Amps = (Line to Neutral Voltage) ----------------------(NGR Resistance) IF-Max

IF-Max

= (12121.21) ------------------------100 =

121.21 Amps

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (50G): Resistor Ground Appendix: 50G Relay Setting = 0.1A

Relay Setting % Location “A” Fault Current on Fault Current on from Neutral

Primary side

secondary side

0.1A

5%

6.06A

0.3A

0.1A

25%

34.63A

1.51A

0.1A

50%

69.264A

3.03A

0.1A

75%

103.89A

4.54A

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (50G): Resistor Ground Appendix: 50G Relay Setting = 0.1A

Relay Setting % Location “A” Fault Current on Fault Current on from Neutral

Primary side

secondary side

0.1A

1%

1.21A

0.06A

0.1A

2%

2.42A

0.121A

0.1A

3%

3.63A

0.181A

0.1A

4%

4.84A

0.242A

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Impedance Ground (NGT)

F

V

Grounding Transformer Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Impedance Ground (NGT) IF

VLN = 21000/1.7325 KVPri = 21kV KVSec = 0.240kV KVA = 70KVA R = 0.913 Ohms Full Load current in Primary wdg = 3.33A Ground Fault Impedance = 3640.004 Ohms Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Impedance Ground (NGT)

a

IF

VLN = 21000/1.7325

Assume; Fault is just 10% from Neutral Ground Fault Volts = (Ground fault Amps*NGTX Impedance) = (0.333 * 3640.306) = 1212.12 Volts in Primary

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Impedance Ground (NGT)

a

IF

VLN = 21000/1.7325 Ratio = 21000/240 = 87.5

Assume; Fault is just 10% from Neutral Ground Fault Volts = (1212.12) / (87.5) = 13.85V in Secondary

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59GN): Impedance Ground (NGT) ¾Setting Criteria: Typical Recommended setting for IDMTL 59GN relay is 5.4V & TMS is 0.3 ¾Typical Recommended setting for Definite Time 59GN relay is 5V & 2s for Stage-I and 15V & 1s is for Stage-II. ¾Neutral Grounding Resistor value should not be more than Rn = 106/2*3.14*C to avoid harmful transient over voltage because of the Ferro-resonance Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

100% Stator Ground Fault Protection (27TN)

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN) ¾Two Measuring Methods to Detect 100% SEF Protection Scheme; ƒ (3rd ) Third Harmonic Voltage Method • 3rd Harmonic Under Voltage Method • 3rd Harmonic Over Voltage Method • 3rd Harmonic Ratio Method ƒ Sub-harmonic Injection Method Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN) ¾ 3rd Harmonic Voltage Method; ƒ 1% to 3% 3rd Harmonic (Zero sequence) Line to Neutral Voltage developed by Generator during Normal condition because of the capacitance betn Stator winding & Ground ƒ 3rd Harmonic Voltage generated by machine are present in the two ends of Stator Winding, but the magnitude is different depends on design & loading ƒ Fault very close to neutral; 3rd Harmonic voltage reduced to zero (3V0 = 0V) Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN) 3rd Harmonic Current circulate

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN) ¾ 3rd Harmonic Under Voltage Method; ƒ 27H Under voltage relay detect 3rd harmonic voltage (150Hz for 50Hz & 180Hz for 60Hz). ƒ Fault is close to neutral; 3rd Harmonic voltage of machine drop down at neutral end & initiate tripping

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN): 3RD Harmonic Under Voltage Method 3rd Harmonic Under voltage relay

IF

3rd harmonic voltage drop Because capacitance Is shorted

IF 3rd Harmonic Voltage at Neutral End reduced

3rd Harmonic Voltage at Neutral End reduced

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN): 3rd Harmonic Under Voltage Method 3rd Harmonic Present At normal Load Condition on both end

3rd Harmonic drop to Zero at neutral end if fault is close To neutral

3rd Harmonic drop to Zero at terminal end if fault is close To terminal Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN +59GN)

Numerical Relay 3rd harmonic filter Extract only 3rd Harmonic voltage 59GN Element

27TN Element Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN)

Control circuit

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59TN) ¾ 3rd Harmonic Over Voltage Method; ƒ 59TN Over voltage relay detect 3rd harmonic voltage (150Hz for 50Hz & 180Hz for 60Hz). ƒ Fault is close to neutral; 3rd Harmonic voltage of machine Increases at Terminal end & initiate tripping

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59TN): 3RD Harmonic Over Voltage Method

IF

IF

3rd Harmonic Over voltage relay

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59TN)

Control circuit

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (59TN+27TN) ¾ 3rd Harmonic Ratio Method; ƒ In this method; 3rd Harmonic voltage will be measured at both sides, at the neutral (V3N) & at the terminal (V3T) of generator ƒ Normally, Ratio will be constant for balance load condition ƒ Ratio will be modified when ground fault occurs ƒ Ground fault will not detected at null point (Midpoint of winding) ƒ Overlapping scheme (59TN+27TN+59GN) is reqd. to detect ground fault at null point Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: 3rd Harmonic Ratio Method Method:1

V3N

V3T

Operate: V3T/V3N > Set value Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: 3rd Harmonic Ratio Method Method:2

V3N

V3T

Operate: V3N/(V3N + V3T) < Set value Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: 3rd Harmonic Ratio Method

Control circuit

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection (27TN) ¾ Limitation for Directly Connected Machines; ƒ Third Harmonic can Circulate between two Machines ƒ 3rd Harmonic Voltage varies on Generator (G1) based on Loading of G2 & G3 ƒ Difficult to apply 3rd Harmonic under voltage Protection

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Sub-Harmonic Injection Method; ƒ Sub-Harmonic voltage is injected through an injection transformer between the grounding element of the generator & ground ƒ Usually sub-harmonic frequency is 1/4th of Fundamental frequency. i.e. 12.5 Hz for 50Hz & 15 Hz for 60Hz relay ƒ This scheme provides ground fault protection with generator energized or standstill Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method Fn = 50Hz Xco = 1 - --------2*3.14*Fn*C IC = (Vn / Xco)

Frequency highÆ Xco value less-Æ High “Ic” current flows Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method

Finj = 12.5Hz XCo = 1/(2*pi*F*C) 12.5Hz

XL = 2*pi*F*L

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Sub-Harmonic Injection Method; ƒ During Ground Fault condition; 12.5Hz current flows through Ground ckt. The fault resistance appears in parallel with shunt capacitances to ground. Thus, the impedance that limits the sub-harmonic current & this also make the current change ƒ Capacitive Reactance Increases ƒ Inductive Reactance Decreases ƒ Relay Operates if 12.5Hz Ground fault current is more than threshold value Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method G

Equivalent Circuit Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Sub-Harmonic Injection Method; ƒ Iinj = (Einj)/ (Zinj + Rn + ZC Total) Where; Einj = Injection Voltage Zinj = Injection TR Leakage Impedance Zinj = (Rinj + j*Xinj) Rn = Grounding resistor ZC = Capacitive impedance of total ckt.

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Appendix; ƒ Iinj = (Einj)/ (Zinj + Rn + ZC Total) Where; Einj = 56V Zinj = (36 + j*125) Finj = 12.5 Hz Rn = 1212 Ohms CTotal = 2.035 microF ZC = (106) / (2*pi*12.5*2.05)= -j*6214 Ohms Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Appendix; Zinj = (36 + j*125) Where; Rinj = 36 Ohms Xinj = 125 Ohms Now; Xinj = (2*pi*50*L) 125 = (2*3.14*50*L) L = 0.331H Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Appendix; Xinj at Low frequency = (2*pi*12.5*L) = (2*3.14*12.5*0.331) = 25.98 Ohms Now; Zinj = (36 + j*25.98) Ohms

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Appendix; ¾ Relay setting is 20mA ¾ Iinj during Normal load condition is; ƒ Iinj = (Einj)/ (Zinj + Rn + ZC Total) = (56) / (36+j*25.98)+1212-(j*6214) = 0.0088A @ 78.67o

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Appendix; ¾ Iinj during Fault condition is; ƒ Iinj = (Einj)/ (Zinj + Rn + Z’C Total)

Where; Z’C = (ZC * RF) / (ZC + RF) RF = Fault resistance

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Method ¾ Appendix; ¾ Iinj during Fault condition is; ƒ Iinj = (Einj)/ (Zinj + Rn + Z’C Total) = 0.0258A @ 6.67o ƒ Relay will issue trip command

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Transformer & Grounding Resistor Method:1

Grounding Resistor Injection Transformer

IF

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Injection Transformer & Grounding Transformer Method:2

Grounding Transformer Separate Injection Transformer

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Stator Ground Fault Protection: Sub-Harmonic Voltage injection through Grounding Resistor Method:3

Sub-Harmonic Voltage Injection Through Grounding Transformer

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Stator Ground Fault Protection: Sub-Harmonic Voltage injection Method in 7UM62 Relay

25VAC

Relay Measures; Rm = (V@20Hz) --------(I@20Hz) Operates; If Rm < Rset

IF

IF

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Voltage injection Method in MICOMP345 Relay Band pass Filter range Is 15 to 25Hz Or Low Pass Filter (Cut of Freq. 45Hz

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Voltage injection Method in MICOMP345 Relay

Transfer Function of Low Pass Fourier Filter Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Voltage injection Method in MICOMP345 Relay Operating time of relay Is faster than Low pass filter

Filter Response of Band Pass Filter Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Stator Ground Fault Protection: Sub-Harmonic Voltage injection Method in MICOMP345 Relay

NGR

100% SEF scheme with Primary Earthing resistor arrangement Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Earth Fault Protection (64R)

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F)

First Ground Fault will not: •Affect the operation of generator •Produce any damaging effects Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F)

First Ground Fault will: • No current Flow • Establish Ground reference making a Second ground fault more likely • Increase stress to ground at other points in Field winding Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F)

Second Ground Fault will: • Flow of Large Current • Unsymmetrical Flux distribution • Air gap flux badly distorted Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F) Second Ground Fault will: • Short out part of field winding causing unit vibration can damage to bearing • Cause Rotor Heating from Unbalance current • Cause arc damage at point of fault

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F) ¾DC Voltage Injection Method ¾Potentiometer Method ¾AC Voltage Injection Method

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): DC Injection Method

Brush is used to ground Rotor Shaft

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): DC Injection Method Slip Rings

Negative Potential Biasing

F

IF

IF Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): Potentiometer Method •Scheme adopted in Older Machine •Earth fault on Field Wdg Produce voltage across Relay

•Blind spot would exist at the centre of field Wdg & fault would not be detected •Tapping on Potentiometer could be varied By using “Push button” to detect fault on Mid point Knowledge Is Power

•Maximum voltage produce If fault occurs at end of Wdg •Overvoltage relay operates when voltage across the resistor exceeds 64F’s Threshold limit

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): Potentiometer Method FCB

FCB

R1 64R R2

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): Low Frequency Injection Method LC-filter is the low-pass Filter to removed high Frequency Rotor current Low Frequency injection Source to inject low freq. Voltage (20Hz/12.5Hz)

IF

Measuring circuit: Relay operates when actual voltage exceeds Threshold value (U>)

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): Low Frequency Injection Method Low Frequency voltage output is the Square wave output Capacitive coupling blocks normal DC Field voltage, preventing discharge of Large current

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): AC Voltage Injection Method in 7UM62 Fundamental Frequency Injection

Rm = UE ---------IEE Relay Operates; If Rm < Rset 36V/45V

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Apparatus Maintenance and Power Management for Energy Delivery

Rotor Ground Fault Protection (64F): AC Voltage Injection Method in 7UM62 Generating square wave voltage

Rm = Ug ------Ig

Low Frequency AC Voltage Measurement Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Generator: Front & Side view

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Apparatus Maintenance and Power Management for Energy Delivery

Generator: Front view

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Apparatus Maintenance and Power Management for Energy Delivery

DOBLE ENGINEERING PVT. LTD 305-SAKAR, OLD PADRA ROAD, VADODARA. PH: (+91)(265) 655 77 15 & Fax: (+91)(265) 235 62 85 Cell: (+91) 94267 47545 / 98980 55956 E-MAIL: [email protected] [email protected] Website: www.doble.com

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Apparatus Maintenance and Power Management for Energy Delivery