1. Universal Relay Family
B30 Bus Differential Relay

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

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

4. Protection: Low-impedance biased differential protection
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. During an external fault
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
DIF – differential
RES – restraining
t0 – fault inception
t2 – fault conditions
External fault: ideal CTs t0 t2

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

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

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

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

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

13. Adaptively switched between
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
DIF1
AND OR
TRIP
DIR OR
AND
SAT
DIF2

20. Logic

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

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

30. Sample External Fault on Feeder 1 (Case 1)
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. dI/dt principle enables the B30 to detect CT saturation (Case 2)
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. The status signal is a FlexLogicTM operand
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 U7a F1 BUS SECTION 1 BUS SECTION 2 BUS Z1
SOURCES
SRC 1
FLEXLOGIC TM
Cont Ip 1 On
BUS Z1
BUS ZONE 1A STATUS
BUS ZONE 1A SOURCE
BUS SECTION 1

41. Dynamic Bus Replica: Example

42. Dynamic Bus Replica: Example

43. Dynamic Bus Replica: Example

44. Dynamic Bus Replica: Zoning

45. Sensitive settings are possible Very good through-fault stability
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.)