Ch 11 - Generator Protection

1 Generator CONTROL AND PROTECTIONG enerator ProtectionGENERATOR CONTROL AND PROTECTIONG enerator Protection Introduction Device Numbers Symmetrical Components Fault Current Behavior Generator Grounding Stator Phase Fault (87G) Field Ground Fault (64F) Stator Ground Fault (87N, 51N, 59N, 27-3N) Generator CONTROL AND PROTECTIONG enerator Protection Loss of Field (40Q, 40Z) Over/Under Frequency (81O/81U) Overexcitation and overvoltage (24, 59) Out of Step (78) Negative Sequence (Current Unbalance) (46) Inadvertent Energization (27, 50, 60, 81, 62, 86) Loss of Voltage Transformer (60) System Backup (51V, 21)

2 ConclusionGENERATOR CONTROL AND PROTECTIONG enerator Protection G64F6051N87T2481U47276287G5981O32-159N51 -GN32-227-3N40 51V50EI466349 REG515125 Generator CONTROL AND PROTECTIONS team Generator Stator WindingsGENERATOR CONTROL AND PROTECTIONH ydraulic Generator Stator / RotorGENERATOR CONTROL AND PROTECTIONH ydraulic Generator Stator CoreGENERATOR CONTROL AND PROTECTIONG enerator ProtectionGENERATOR CONTROL AND PROTECTIONS plit Phase Relaying CTGENERATOR CONTROL AND PROTECTIONC ylindrical Rotor in Need of RepairGENERATOR CONTROL AND PROTECTIONG enerator Protection Generator CONTROL AND PROTECTIONG enerator Protection Generator CONTROL AND PROTECTIONS ymmetrical Components Positive Sequence A set of three phasors that have the same magnitude, are equallydisplaced from each other by 120 , and have the same phase sequence as the system under study (ex ABC) Negative Sequence A set of three phasors that have the same magnitude, are equallydisplaced from each other by 120 , and have the opposite phase sequence as the system under study (ex ACB)

3 Zero Sequence A set of three phasors of equal magnitude that are all in phase or have zero displacement from each otherGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsExample Problem One conductor of a three phase line is open. The current flowing to the delta connected load thru line ais 10A.

4 With the current in line aas reference and assuming that line cis open, find the symmetrical components of the line CONTROL AND PROTECTIONS ymmetrical ComponentsExample 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+ Ib+ 2Ic) Ia1= (1/3)(10/0 + 10/180+120 + 0) Ia1= /-30 Ia2= (1/3)(Ia+ 2Ib+ Ic) Ia2= (1/3)(10/0 + 10/180+240 + 0) Ia2= /30 Generator CONTROL AND PROTECTIONS ymmetrical ComponentsExample Problem Ib0= 0 Ib1= /-150 Ib2= /150 Ic0= 0 Ic1= /90 Ic2= /-90 Generator CONTROL AND PROTECTIONS ymmetrical ComponentsExample Problem Ia0= 0, Ib0= 0, Ic0= 0 Ia1= /-30 , Ib1= /-150 , Ic1= /90 Ia2= /30 , Ib2= /150 , Ic2= /-90 Generator CONTROL AND PROTECTIONS ymmetrical ComponentsExample Problem Note: the components Ic1and Ic2have definite values although line cis open and can carry no net current.

5 As expected, the sum of these currents is zero. The sum of the currents in line ais 10/0 The sum of the currents in line bis 10/180 Generator CONTROL AND PROTECTIONS ymmetrical ComponentsSingle Phase Line to Ground FaultGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGenerator Sequence NetworksGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONS ymmetrical ComponentsGENERATOR CONTROL AND PROTECTIONF ault Current Behavior of a Synchronous GeneratorGENERATOR CONTROL AND PROTECTIONF ault

6 Current Behavior of a Synchronous GeneratorGENERATOR CONTROL AND PROTECTIONF ault Current Behavior of a Synchronous GeneratorGENERATOR CONTROL AND PROTECTIONF ault Current Behavior of a Synchronous GeneratorMax DC OffsetNo DC OffsetGENERATOR CONTROL AND PROTECTIONF ault Current Behavior of a Synchronous GeneratorGENERATOR CONTROL AND PROTECTIONF ault Current Behavior of a Synchronous GeneratorGENERATOR CONTROL AND PROTECTIONG enerator GroundingGENERATOR CONTROL AND PROTECTIONG enerator 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 PROTECTIONG enerator Stator Phase Fault Protection (87G) Generator CONTROL AND PROTECTIONG enerator Stator Phase Fault Protection (87G) 87G used to protect for.

7 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 PROTECTIONG enerator Stator Phase Fault Protection (87G) Generator CONTROL AND PROTECTIONG enerator Stator Phase Fault Protection (87G) Generator CONTROL AND PROTECTIONG enerator 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 PROTECTIONG enerator Stator Phase Fault Protection (87G)

8 Generator CONTROL AND PROTECTIONG enerator Field Ground Fault Protection (64F) Generator CONTROL AND PROTECTIONG enerator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)For Low Impedance Grounded GeneratorsGENERATOR CONTROL AND PROTECTIONG enerator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)For Low Impedance Grounded GeneratorsGENERATOR CONTROL AND PROTECTIONG enerator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)External Generator Phase-Ground FaultGENERATOR CONTROL AND PROTECTIONG enerator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)External Generator Phase-Ground FaultGENERATOR CONTROL AND PROTECTIONG enerator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)Internal Generator Phase-Ground FaultGENERATOR CONTROL AND PROTECTIONG enerator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)Internal Generator Phase-Ground FaultGENERATOR CONTROL AND PROTECTIONG enerator Stator Ground Fault Protection (87N, 51N, 59N & 27-3N)

9 High Impedance Grounded50 MVA, GeneratorXc = 10,610 for @ 60 HzRpri = 10,610/3 = 3537 Generator CONTROL AND PROTECTIONLoss of Field Protection (40Q, 40Z) Generator CONTROL AND PROTECTIONLoss of Field Protection (40Q, 40Z) Generator CONTROL AND PROTECTIONLoss of Field Protection (40Q, 40Z) Generator CONTROL AND PROTECTIONOver/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.

10 overvoltage on hydro turbinesGENERATOR CONTROL AND PROTECTIONO verexcitation 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 usedGENERATOR CONTROL AND PROTECTIONOut of Step Protection (78)