Generator Protection

Generator Protection

GENERATOR CONTROL AND PROTECTION

Generator Protection • • • • • • •

Introduction Device Numbers Symmetrical Components Fault Current Behavior Generator Grounding Stator Phase Fault (87G) Field Ground Fault (64F)

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Stator Ground Fault ult (87N, 51N, 59N, 27-3N)

GENERATOR CONTROL AND PROTECTION

Generator Protection • • • • • • •

Introduction Device Numbers Symmetrical Components Fault Current Behavior Generator Grounding Stator Phase Fault (87G) Field Ground Fault (64F)

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Stator Ground Fault ult (87N, 51N, 59N, 27-3N)

GENERATOR CONTROL AND PROTECTION

Generator Protection • • • • • • • • •

Loss of Field (40Q, 40Z) Over/Under Frequency (81O/81U) Overexcitation an and O Ov vervoltage ((2 24, 59 59) Out of Step (78) Negative tive Sequence (Curre rrent Unbalance) (46 (46) Ina In advert verte ent Energiz rgiza atio tion (27 (27, 50, 60, 81 81,, 62, 86 86)) Loss of Voltage Transformer (60) System Backup (51V, 21) Conclusion

GENERATOR CONTROL AND PROTECTION

Generator Protection 63

49

25 G 51N

64F

51 60

87G

REG

62

32-1

59N

87T

24

47

27

81U

59

81O

32-2

40

51V

51

50 IE

46

273N

51GN

GENERATOR CONTROL AND PROTECTION

Steam Generator Stator Windings

GENERATOR CONTROL AND PROTECTION

Hydraulic Generator Stator / Rotor

GENERATOR CONTROL AND PROTECTION

Hydraulic Generator Stator Core

GENERATOR CONTROL AND PROTECTION

Generator Protection

GENERATOR CONTROL AND PROTECTION

Split Phase Relaying CT

GENERATOR CONTROL AND PROTECTION

Cylindrical Rotor in Need of Repair

GENERATOR CONTROL AND PROTECTION

Generator Protection

GENERATOR CONTROL AND PROTECTION

Generator Protection

GENERATOR CONTROL AND PROTECTION

Symmetrical Components •

Positive Sequence –

•

Negative Sequence –

•

A set of three phasors that have the same magnitude, are equally displaced from each other by 120º, and have the same phase sequence as the system under study (ex ABC) A set of three phasors that have the same magnitude, are equally displaced from each other by 120º, and have the opposite phase sequence as the system under study (ex ACB)

Zero Sequence –

A set of three phasors of equal magnitude that are all in phase or have zero displacement from each other

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Symmetrical Components Example Problem •

One conductor of a three phase line is open. The current flowing to the delta connected load thru line a is 10A. With the current in line a as reference and assuming that line c is open, find the symmetrical components of the line currents.

GENERATOR CONTROL AND PROTECTION

Symmetrical Components Example Problem • Ia = 10/0° A, Ib = 10/180° A, Ic = 0 A • Ia0 = (1/3)(Ia + Ib + Ic ) • Ia0 = (1/3)(10/0° + 10/180° + 0) = 0 • Ia1 = (1/3)(Ia + αIb + α2 Ic ) • Ia1 = (1/3)(10/0° + 10/180+120° + 0) • Ia1 = 5.78 /-30° • Ia2 = (1/3)(Ia + α2 Ib + αIc ) • Ia2 = (1/3)(10/0° + 10/180+240° + 0) • Ia2 = 5.78 /30°

GENERATOR CONTROL AND PROTECTION

Symmetrical Components Example Problem •

Ib0 = 0

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Ib1 = 5.78 /-150°

•

Ib2 = 5.78 /150°

•

Ic0 = 0

•

Ic1 = 5.78 /90°

•

Ic2 = 5.78 /-90°

GENERATOR CONTROL AND PROTECTION

Symmetrical Components Example Problem •

Ia0 = 0, Ib0 = 0, Ic0 = 0

•

Ia1 = 5.78 /-30° , Ib1 = 5.78 /-150° , Ic1 = 5.78 /90°

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Ia2 = 5.78 /30° , Ib2 = 5.78 /150° , Ic2 = 5.78 /-90°

GENERATOR CONTROL AND PROTECTION

Symmetrical Components Example Problem •

Note: the components Ic1 and Ic2 have definite values although line c is open and can carry no net current. As expected, the sum of these currents is zero.

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The sum of the currents in line a is 10/0°

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The sum of the currents in line b is 10/180°

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

Single Phase Line to Ground Fault GENERATOR CONTROL AND PROTECTION

Symmetrical Components

Generator Sequence Networks GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Symmetrical Components

GENERATOR CONTROL AND PROTECTION

Fault Current Behavior of a Synchronous Generator

GENERATOR CONTROL AND PROTECTION

Fault Current Behavior of a Synchronous Generator

GENERATOR CONTROL AND PROTECTION

Fault Current Behavior of a Synchronous Generator

GENERATOR CONTROL AND PROTECTION

Fault Current Behavior of a Synchronous Generator

Max DC Offset

No DC Offset

GENERATOR CONTROL AND PROTECTION

Fault Current Behavior of a Synchronous Generator

GENERATOR CONTROL AND PROTECTION

Fault Current Behavior of a Synchronous Generator

GENERATOR CONTROL AND PROTECTION

Generator Grounding

GENERATOR CONTROL AND PROTECTION

Generator Grounding •Low Impedance Grounding •Single phase to ground fault current between 200A and 150% •High Impedance Grounding •Single phase to ground fault current between 5 and 20A

GENERATOR CONTROL AND PROTECTION

Generator Stator Phase Fault Protection (87G)

GENERATOR CONTROL AND PROTECTION

Generator Stator Phase Fault Protection (87G) •87G used to protect for: •3 phase line to line •1 phase line to line •multi-phase line to ground •May not be able to detect a 1 phase to ground fault on high impedance grounded generators •Restraint or Percentage Differential Trip Characteristic •Used to improve sensitivity for detecting small levels of fault current •Also maintains security against inadvertent tripping due to thru faults GENERATOR CONTROL AND PROTECTION

Generator Stator Phase Fault Protection (87G)

GENERATOR CONTROL AND PROTECTION

Generator Stator Phase Fault Protection (87G)

GENERATOR CONTROL AND PROTECTION

Generator Stator Phase Fault Protection (87G) •Split-phase protection scheme •Able to detect turn-turn faults •Windings for each phase split into equal groups •Individual winding currents are vector summed •Any difference in winding current results in a output from CT •Overcurrent relay (50/51) can be used to monitor difference current •Setting must be above any normal unbalances that may exist

GENERATOR CONTROL AND PROTECTION

Generator Stator Phase Fault Protection (87G)

GENERATOR CONTROL AND PROTECTION

Generator Field Ground Fault Protection (64F)

GENERATOR CONTROL AND PROTECTION

Generator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

For Low Impedance Grounded Generators GENERATOR CONTROL AND PROTECTION

Generator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

For Low Impedance Grounded Generators GENERATOR CONTROL AND PROTECTION

Generator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

External Generator Phase-Ground Fault GENERATOR CONTROL AND PROTECTION

Generator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

External Generator Phase-Ground Fault GENERATOR CONTROL AND PROTECTION

Generator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

Internal Generator Phase-Ground Fault GENERATOR CONTROL AND PROTECTION

Generator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

Internal Generator Phase-Ground Fault GENERATOR CONTROL AND PROTECTION

Generator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

High Impedance Grounded 50MVA, 13.2kV Generator Xc = 10,610Ω for 0.25uf @ 60Hz Rpri = 10,610/3 = 3537 Ω GENERATOR CONTROL AND PROTECTION

Loss of Field Protection (40Q, 40Z)

GENERATOR CONTROL AND PROTECTION

Loss of Field Protection (40Q, 40Z)

GENERATOR CONTROL AND PROTECTION

Loss of Field Protection (40Q, 40Z)

GENERATOR CONTROL AND PROTECTION

Over/Under Frequency Protection (81O/U) •Causes: •Significant load addition •Sudden reduction in mechanical input power •Loss of generation •Loss of load •Underfrequency can cause: •Higher generator load currents •Overexcitation •Turbine blade fatigue •Overfrequency can cause: •Overvoltage on hydro turbines GENERATOR CONTROL AND PROTECTION

Overexcitation and Overvoltage Protection (24, 59) •Modern Excitation Systems include over excitation limiting and protection, but it may take several seconds to limit •Overexcitation occurs when the V/Hz ratio exceeds 105% at FL and 110% at no load •V/Hz relays set at 110% with a 5 – 10 sec delay •Generator overvoltage can occur without exceeding V/Hz relay setting due to large over speed on hydro generator •Generator overvoltage relay, 59 may be used

GENERATOR CONTROL AND PROTECTION

Out of Step Protection (78) •High peak currents and off-frequency operation can occur when a generator losses synchronism •Causes winding stress, high rotor iron currents, pulsating torques and mechanical resonances •Conventional relaying approach – analyzing variations in apparent impedance as viewed at generator terminals •Variation in impedance can be detected by impedance relaying and generator separated before the completion of one slip cycle

GENERATOR CONTROL AND PROTECTION

Out of Step Protection (78) EA

EB ZA

ZT

ZB

A

B

Generator

Transformer 

System

+X EA /EB>1

B

EA /EB=1

ZB

Q EA /EB