Universal Relay Family

1. Universal Relay Family B30Bus Differential Relay

2. Contents... Features CT Saturation Problem Theory of Operation Dynamic Bus Replica Operation Examples (link) Q&As (link) Benefits

3. Features • Configuration: • up to 5 feeders with bus voltage • up to 6 feeders without bus voltage

4. Features • Protection: • Low-impedance biased differential protection • CT saturation immunity • sub-cycle tripping time • dynamic 1-out-of-2 or 2-out-of-2 operation • Unbiased differential protection • Dynamic bus replica • CT trouble monitoring • Undervoltage (2 elements) • Phase Overcurrent (2 elements)

5. Features • Metering: • Oscillography • Event Recorder • Phasors / true RMS

6. CT saturation problem • During an external fault • fault current may be supplied by a number of sources • the CTs on the faulted circuit may saturate • saturation of the CTs creates a current unbalance and violates the differential principle • a conventional restraining current may not be sufficient to prevent maloperation • CT saturation detection and a directional principle enhance through-fault stability

7. DIFFERENTIAL – RESTRAINT Point t2 t0 DIF – differential RES – restraining t0 – fault inception t2 – fault conditions External fault: ideal CTs

8. DIFFERENTIAL – RESTRAINT Point t2 t0 DIF – differential RES – restraining t0 – fault inception t2 – fault conditions External fault: ratio mismatch

9. DIFFERENTIAL – RESTRAINT Point t2 t1 t0 DIF – differential RES – restraining t0 – fault inception t1 – CT starts to saturate t2 – fault conditions External fault: CT saturation

10. DIFFERENTIAL – RESTRAINT Point t2 t0 DIF – differential RES – restraining t0 – fault inception t2 – fault conditions Internal fault: high current

11. DIFFERENTIAL – RESTRAINT Point t2 t0 DIF – differential RES – restraining t0 – fault inception t2 – fault conditions Internal fault: low current

12. DIFFERENTIAL – RESTRAINT Point t2 t1 t0 DIF – differential RES – restraining t0 – fault inception t1 – CT starts to saturate t2 – fault conditions External fault: extreme CT saturation

13. Operating principles • Combination of • low-impedance biased differential • directional (phase comparison) • Adaptively switched between • 1-out-of-2 operating mode • 2-out-of-2 operating mode • by • Saturation Detector

14. Biased Characteristic: Restraining Current • Restraining Current is a “maximum of” the bus zone currents : • better stability on external faults (as compared to the “average of” definition) • better sensitivity on internal faults (as compared to the “sum of” definition)

15. Biased Characteristic: Shape • Two breakpoints • Two slopes • both slopes provide TRUE percentage restraint, i.e. they are represented by straight lines crossing the origin of the differential-restraining plane • if the slopes are different, discontinuity of the characteristic occurs • the discontinuity issue is solved by a smooth “gluing” function

16. Biased Characteristic: Shape HIGH SLOPE LOW SLOPE PICKUP LOW BPNT HIGH BPNT

17. Biased Characteristic: Two distinctive regions • low currents • saturation possible due to dc offset • saturation very difficult to detect • more security required

18. Biased Characteristic: Two distinctive regions • large currents • quick saturation possible due to large magnitude • saturation easier to detect • security required only if saturation detected

19. Logic AND OR OR TRIP AND DIF1 DIR SAT DIF2

20. Logic

21. Logic AND OR OR TRIP AND DIF1 DIR SAT DIF2

22. Directional principle • Internal faults - all currents approximately in phase

23. Directional principle • External faults - one current approximately out of phase

24. Directional principle • Check all the angles • Select the maximum current contributor and check its position against the sum of all the remaining currents • Select major current contributors and check their positions against the sum of all the remaining currents

25. Directional principle

26. Directional principle

27. Directional principle

28. Logic AND OR OR TRIP AND DIF1 DIR SAT DIF2

29. Saturation Detector t2 t1 t0 • differential-restraining trajectory • dI/dt t0 – fault inception t1 – CT starts to saturate t2 – fault conditions External fault: CT saturation

30. Saturation Detector Sample External Fault on Feeder 1 (Case 1)

31. Saturation Detector Analysis of the DIF-RES trajectory enables the B30 to detect CT saturation (Case 1)

32. Saturation Detector Sample External Fault on Feeder 4 - severe CT saturation after 1.5msec (Case 2)

33. Saturation Detector dI/dt principle enables the B30 to detect CT saturation (Case 2)

34. Saturation Detector: State Machine

35. Saturation Detector • Operation: • The SAT flag WILL NOT set during internal faults whether or not the CT saturates • The SAT flag WILL SET during external faults whether or not the CT saturates • The SAT flag is NOT used to block the relay but to switch to 2-out-of-2 operating principle

36. Examples • The oscillograms on the next two slides were captured from a B30 relay under test on a real-time digital power system simulator

37. B30 Bus Differential Relay: External Fault Example

38. B30 Bus Differential Relay: Internal Fault Example

39. Dynamic Bus Replica • The dynamic bus replica mechanism is provided by associating a status signal with each current of the differential zone • The status signal is a FlexLogicTM operand • The status signals are formed in FlexLogicTM – including any filtering or extra security checks – from the positions of switches and/or breakers

40. Dynamic Bus Replica BUS SECTION 1 BUS SECTION 2 BUS ZONE 1A STATUS Cont Ip 1 On BUS BUS ZONE 1A SOURCE U7a Z1 TM FLEXLOGIC SOURCES F1 SRC 1

41. Dynamic Bus Replica: Example

42. Dynamic Bus Replica: Example B30 #1

43. Dynamic Bus Replica: Example B30 #2

44. Dynamic Bus Replica: Zoning B30 #1 D60 #1 B30 #2

45. Benefits • Sensitive settings are possible • Very good through-fault stability • Fast operation: • fast form-C contacts and FlexLogicTM operands: typically 10-12ms • form-A trip rated contacts: typically 13-15ms • Benefits of the UR platform (metering and oscillography, event recorder, FlexLogicTM, fast peer-to-peer communication, etc.)