Electrical Protection

Transcription

1 Electrical Protection

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3 Electrical Faults Phase to phase Phase to ground Phase to phase to phase Phase to phase to phase to ground

4 Purpose of Protection System Minimize damage Leave unaffected equipment in-service Maintain equipment operating limits Maintain electrical system stability

5 Requirements of a Protection System Speed Reliability Security Sensitivity

6 Some terms Over-current Overload Inverse time

7 Protection Zones

8 Simple Zone

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10 Double Protection Bus Zone Circuit Breaker X Circuit Breaker Y CT 1 CT 2 CT 3 CT 4 Bus CT 4 CT 3 CT 2 CT 1 "B" Bus Protection "A" Bus Protection

11 Bus Zone H2 Bus Zone H3 Bus H2 x Bus Zone H1 Bus H1 Y Bus H3 Zone SST1 Zone T1 Transformer T1 Protection SST1 LV Bus Transformer SST1 Bus L1 Bus Zone L1 Zones G1 Zone G1

12 Breaker Failure Minimizes the amount of equipment removed from service in event of a failure Failure Determination Not started opening in a certain time Not open in a certain time Current not broken in a certain time

13 Duplicate Protection Schemes CT 1 CT 2 PT Electrical bus Electrical System System Input A Protection B Protection Protection Logic Initiate Trip Close Initiate Trip Close Protection Output Action Q Breaker X Breaker Y Device Z Electrical Devices

14 Bus Protection

15 Bus Protection Over-current Differential Back-up Under voltage

16 Over-current Relay CT 2000/5 A I 1P I 1S

17 Differential Protection I = I 1P = I 2P CT1 2000/5 A X Bus H1 Y CT2 2000/5 A I 1P I = I 1S = I 2S I 2P I 1S I 2S I 1S I 2S I = I 1S = I 2S

18 Fault Conditions Fault CT1 2000/5 A X Bus H1 Y CT2 2000/5 A I 1P I 2P I 1S I 2S I 1S I 2S

19 X CT 2000/5 A Bus H1 Y CT 2000/5 A I 1P I 2P I 3P I 1S I 3S CT 2000/5 A I 2S T1 I 3S I 1S I 2S

20 Bus Protection Scheme Bus Differential Backup T1 S Bus X Zone L1 Load L1 Y Zone L2 Load L2

21 Back-up relay Over Current Backup Relay Differential Relay X T1 S Bus Load L1 Y Load L2

22 Bus Under Voltage Protection Armature shown in the non-energized (trip) position Normally Open Contacts To Potential Transformer

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25 Bus Protection Over-current Differential Back-up Under voltage

26 Transformer Protection

27 Transformer Protection Instantaneous Differential Gas Thermal Overload Ground

28 Transformer Characteristics High magnetizing inrush currents Ratio mismatch with CTs aggravated by tap-changers Phase shifts Transformers are affected by over-fluxing Affected by over-temperature

29 Transformer Zone T1 Zone T1 CT 1 CT 2 CT 3 CT 4 CT 4 CT 3 CT 2 CT 1 "B" Transformer Protection "A" Transformer Protection

30 Differential T1 CT1 CT2 I 1P I 2P I 1S Restraint Coil Restraint Coil I 2S I 1S Operate Coil I 2S I = I 1S = I 2S

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35 Gas Relay

36 Winding Temperature

37 Ground Fault Protection CT1 T1 CT2 I N CT3 Differential Relay I F Transformer Star Point Ground CT Ground Backup I N

38 Transformer Protection Instantaneous Differential Gas Thermal Overload Ground

39 Motor Protection

40 Service Factor Continuous allowable overload Many motors some with a power rating and a service factor A 10 HP motor with a service factor of 1.15 has a maximum continuous output of 11.5 HP

41 Motor Protection Summary Instantaneous Over-current Stall Thermal Overload Phase Unbalance Ground

42 Inverse Time Relay

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44 Overload

45 Ground Fault Protection

46 Single Phase to Ground Protection

47 Stalls

48 Thermal Overload & Phase Unbalance

49 Diagram of the Unit He a ter (electrical connectio ns no t shown) Rotation as Elements Heat/Cool Phase Unbalance Contacts Load Indicating Pointer Adjus table Ove rload Contac t Overload Setting Pointer Actuating Bimetal Ambie nt Co mpensating Bime tal Shaft Heat Shield

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57 Motor Protection Summary Instantaneous Over-current Stall Thermal Overload Phase Unbalance Ground

58 Generator Protection

59 Classes of TG trips Class A Trip generator breaker, field breaker and turbine Electrical trips before the output breakers Class B Trip generator output but leave it supplying station service Electrical faults in the switchyard

60 Classes of TG trips Class C Over excitation high V/Hz Only used when generator is isolated from grid Class D Trip turbine Trip Generator after motoring is detected Mechanical type turbine trips high condenser pressure

61 Generator Protection Over-current Overload Differential Split phase differential Ground Rotor ground Phase Unbalance Low field Under frequency Out of Step Reverse power

62 R Ge ne rator Terminals W Diffe re ntial Relay B Protection Zo ne s Neutral Co nnection to Gro und a) He althy Phas e b) Faulted Phas e c ) Ope n Circ uit in the Phas e

63 Differential Generator Star Point I P = I 1P = I 2P I 1P CT1 G1 CT2 To Main Transformer I 2P I 1S Restraint Coil Restraint Coil I 2S I 1S Operate Coil I 2S I s = I 1S = I 2S

64 Ground Fault Protection T1 G1 GT1 I F Stator Ground Relay

65 Rotor Ground Fault

66 Other Protections Phase Unbalance Loss of field Under frequency Out of Step

67 Reverse Power G Reverse Power Re aly V. T.

68 Generator Protection Over-current Overload Differential Split phase differential Ground Rotor ground Phase Unbalance Low field Under frequency Out of Step Reverse power

69 For You To Do