B90 Bus Differential Relay and Breaker Failure Protection

1. B90 Bus Differential Relay and Breaker Failure Protection • Cost-efficient • Good performance • Modern communications capability • Member of the Universal Relay (UR) family • Easy integration with other URs • Common configuration tool for all B90 IEDs • Proven algorithms (B30) and hardware (UR) • Expandable • Two levels of scalability (modules and IEDs)

2. Busbar Protection Schemes GE offer Approach • High-impedance / linear couplers • non-configurable busbars • cheap relay, expensive primary equipment • Blocking schemes for simple busbars • Analog low / medium - impedance schemes • Digital relays for small busbars • Digital relays for large busbars • Phase-segregated cost-efficient digital relays for large busbars PVD SPD Any BUS B30 B90 NEW!

3. Why Digital Bus Relay? • Re-configurable busbars require dynamic assignment of currents to multiple zones • expensive and dangerous when done externally on secondary currents (analog way) • natural and safe when done “in software” • Breaker Fail for re-configurable busbars is naturally integrated with the bus protection • No need for special CTs (cost) • Relaxed requirements for the CTs (cost) • Advantages of digital technology

4. Design Challenges for Digital Busbar Relays • Reliability • Security: • Immunity to CT saturation • Immunity to wrong input information • Large number of inputs and outputs required: • AC inputs (tens or hundreds) • Trip rated output contacts (tens or hundreds) • Other output contacts (tens) • Digital Inputs (hundreds) • Large processing power required to handle al the data

5. Traditionally Two Distinctive Architectures are Offered Distributed Bus Protection Centralized Bus Protection • Fits better new installations • Perceived less reliable • Slower • Fits better retrofit installations • Perceived more reliable • Potentially faster

6. Phase B Protection iB, vB TRIPB Phase C Protection iC, vC TRIPC New Architecture – Digital Phase-Segregated Busbar Scheme • Foundation: • Single-phase IEDs for primary differential protection • Separate IEDs for Breaker Failure and extra I/Os • Inter-IED communications for sharing digital states • Scalability and flexibility Phase A Protection iA, vA TRIPA Breaker Failure

7. B90 Capacity • Up to 24 circuits in a single zone without voltage supervision • Multi-IED architecture with each IED built on modular hardware • Up to 24 AC inputs per B90 IED freely selectable between currents and voltages (24+0, 23+1, 22+2, ..) • Up to 96 digital inputs per B90 IED • Up to 48 output contacts per B90 IED • Flexible allocation of AC inputs, digital inputs and output contacts between the B90 IEDs

8. B90 Features and Benefits • Maximum number of circuits in one zone: 24 • Number of zones : 4 • Busbar configuration: No limits • Sub-cycle tripping time • Security (only 2msec of clean waveforms required for stability) • Differential algorithm supervised by CT saturation detection and directional principle • Dynamic bus replica, logic and signal processing • No need for interposing CTs (ratio matching up to 32:1) • CT trouble per each zone of protection • Breaker failure per circuit • End fault protection (EFP) per circuit • Undervoltage supervision per each voltage input • Overcurrent protection (IOC and TOC) per circuit • Communication, metering and recording

9. B90 Applications • Busbars: • Single • Breaker-and-a-half • Double • Triple • With and without transfer bus • Networks: • Solidly grounded • Lightly grounded (via resistor) • Ungrounded

10. B90 Architecture Overview • Phase-segregated multi-IED system built on Universal Relay (UR) platform • Each IED can be configured to include up to six modules: • AC inputs (up to 3 x 24 single phase inputs) • Contact outputs (up to 6 x 8) • Digital Inputs (up to 6 X 16) • Variety of combinations of digital inputs and output contacts • Fast digital communications between the IEDs for sharing digital states

11. B90 Architecture • No A/C data traffic • No need for sampling synchronization, straightforward relay configuration - all A/C signals “local” to a chassis • Data traffic reduced to I/Os • Direct I/Os (similar to existing UR Remote I/Os) used for exchange of binary data • Oscillography capabilities multiplied (available in each IED separately) • Programmable logic (FlexLogic) capabilities multiplied • SOE capabilities multiplied • Extra URs in a loop for more I/Os

12. 8 AC single-phase inputs 8 AC single-phase inputs 8 AC single-phase inputs Other UR-based IEDs B90 Components: Protection IEDs • Modular architecture (from 2 to 9 modules) • All modules but CPU and PS optional • Up to 24 AC inputs total (24 currents and no voltages, through 12 currents and 12 voltages) • Three I/O modules for trip contacts or extra digital inputs • Features oriented towards AC signal processing (differential, IOC, TOC, UV, BF current supervision) Power Supply DSP 1 I/O I/O Comms CPU I/O DSP 2 DSP 3 B90 is built on UR hardware (4 years of field experience)

13. Other UR-based IEDs B90 Components: Logic IEDs • Modular architecture (from 2 to 9 modules) • All modules but CPU and PS optional • Up to 96 digital inputs or • 48 output contacts or • Virtually any mix of the above • Features oriented towards logic functions (BF logic and timers, isolator monitoring and alarming) I/O I/O I/O Comms CPU I/O I/O I/O Power Supply B90 is built on UR hardware (4 years of field experience)

14. Phase A AC signals and trip contacts Phase B AC signals and trip contacts Phase C AC signals and trip contacts Digital Inputs for isolator monitoring and BF B90 Scheme for Large Busbars Dual (redundant) fiber with 3msec delivery time between neighbouring IEDs. Up to 8 B90s/URs in the ring

15. Security of the B90 Communications • Dual (redundant) ring – each message send simultaneously in both directions • No switching equipment (direct TX-RX connection) • Self-monitoring incorporated • Information re-sent (repeated) automatically • 32-bit CRC • Default states of exchanged flags upon loss of communications (allows developing secure applications)

16. B90 Communications • The communications feature (Direct I/Os) requires digital communications card (dual-port 820nmm LED) • Up to 96 inputs / outputs could be sent / received • Up to 8 UR IEDs could be interfaced • When interfacing with other URs, 32 inputs / outputs are available • The Direct I/O feature is modeled on UCA GOOSE but is sent over dedicated fiber (not LAN) and is optimized for speed • User-friendly configuration mechanism is available • Simple applications do not require communications

17. Typical B90 Applications for Large Busbars 7 to 24 feeders Basic: 87 & BF for less than 16 feeders Extended: BF for more than 16 feeders Full version: 24 Feeders with BF.

18. Typical B90 Applications for Large Busbars 7 to 24 feeders 7 to 24 feeders

19. B90 and Small Single Busbars – 8-circuit busbar 8 phase-C currents 8 phase-B currents 8 phase-A currents One B90 IED with 3 zones could protect a single 8-circuit busbar! Power Supply DSP 1 I/O I/O Spare CPU I/O DSP 2 DSP 3 Diff Zone 2 Diff Zone 1 Diff Zone 3 Two levels of scalability allow flexible applications

20. B90 and Small Single Busbars – 12-circuit busbar Two B90 IEDs with 2 zones could protect a single 12-circuit busbar! 4 phase-B currents 4 phase-C currents 8 phase-C currents 8 phase-B currents 4 phase-A currents 8 phase-A currents Power Supply Power Supply DSP 1 I/O I/O Spare CPU I/O DSP 2 Spare CPU I/O DSP 2 DSP 3 DSP 1 I/O Spare Spare Two levels of scalability allow flexible applications

21. B90 and Small Single Busbars – 16-circuit busbar Three B90 single-zone IEDs could protect a single 16..24-circuit busbar! 8 phase-C currents 8 phase-C currents 8 phase-B currents 8 phase-A currents 8 phase-B currents 8 phase-A currents Power Supply Power Supply Power Supply DSP 1 I/O Spare Spare DSP 1 I/O Spare Spare DSP 1 I/O Spare Spare CPU I/O DSP 2 Spare CPU I/O DSP 2 Spare CPU I/O DSP 2 Spare Two levels of scalability allow flexible applications

22. Applicability to Ungrounded and Lightly Grounded Systems • Three phase protection units for phase-to-phase faults and saturation detection • Fourth unit with AC inputs for zero-sequence differential protection (fed from split-core or regular CTs) Phase B Phase C Phase A IA IB IC Block on external faults 3I0 Ground B90 can be applied to solidly and lightly grounded as well as ungrounded systems

23. B90 Configuration Program (1) B90 Protection system is a “site” … • URPC program used for configuration • Common setting file for all B90 IEDs • All B90 can be accessed simultaneously • Off-line setting files can easily be produced (2) That includes the required IEDs (3) Functions available for dealing with all IEDs simultaneously

24. B90 Algorithms • Bus differential protection • Dynamic bus replica • Isolator monitoring and alarming • End Fault Protection • Breaker Failure

25. t2 t0 CT Saturation Problem t0 – fault inception t2 – fault conditions External fault: ideal CTs

26. t2 t0 CT Saturation Problem t0 – fault inception t2 – fault conditions External fault: CT ratio mismatch

27. t2 t1 t0 CT Saturation Problem t0 – fault inception t1 – CT saturation time t2 – CT saturated External fault: CT saturation

28. Differential Protection • B90 algorithms aimed at: • Improving the main differential function by providing better filtering, faster response, better restraining technique, robust switch-off transient blocking, etc. • Incorporating a saturation detection mechanism that would recognize CT saturation on external faults in a fast and reliable manner • Applying a second protection principle namely phase directional (phase comparison) for better security

29. Bus Differential Function – Block Diagram

30. B90 Differential Function – Theory of Operation • Definition of the Restraining Current • Operating Characteristic • CT Saturation Detector • Default Tripping Logic • Customizing the Tripping Logic

31. Various Definitions of the Restraining Signal “sum of” “scaled sum of” “geometrical average” “maximum of”

32. Restraining Current • The amount of restraint provided by various definitions is different; sometimes significantly different particularly for multi-circuit differential elements such as busbar protection • When selecting the slope (slopes) one must take into account the applied definition of the restraining signal • The B90 uses the “maximum of” definition of the restraining current

33. “Sum of” vs. “Max of” definitions of restraint • “Sum of” approach: • more restraint on external faults; less sensitivity on internal faults • “scaled sum of” may take into account the actual number of connected circuits increasing sensitivity • characteristic breakpoints difficult to set • “Max of” approach (B30, B90 and UR in general): • less restraint on external faults • more sensitivity on internal faults • breakpoints easier to set • better handles situations when one CT may saturate completely (99% slope settings possible)

34. Differential Function – Characteristic

35. Differential Function – Adaptive Approach • large currents • quick saturation possible due to large magnitude • saturation easier to detect • security required only if saturation detected • low currents • saturation possible due to dc offset • saturation very difficult to detect • more security required

36. AND OR OR TRIP AND Adaptive Logic DIF1 DIR SAT DIF2

37. Adaptive Approach Dynamic 2-out-of-2, 1-out-of-2 operating mode 2-out-of-2 operating mode

38. AND OR OR TRIP AND Directional Principle DIF1 DIR SAT DIF2

39. Directional Principle • Voltage signal is not required • Internal faults: • all fault (“large”) currents approximately in phase • External faults: • one current approximately out of phase Secondary current ofthe faulted circuit(deep CT saturation)

40. Directional Principle • Implementation: • step 1: select fault “contributors” • A “contributor”is a circuit carrying significant amount of current • A circuit is a contributor if its current is above higher break point • A circuit is a contributor if its current is above a certain portion of the restraining current • step 2: check angle between each contributor and the sum of all the other currents • Sum of all the other currents is the inverted contributor if the fault is external; on external faults one obtains an angle of 180 degrees • step 3: compare the maximum angle to the threshold • A threshold is a factory constant of 90 degrees • An angle shift of more than 90 degrees due to CT saturation is physically impossible

41. External Fault

42. Internal Fault

43. AND OR OR TRIP AND Saturation Detector DIF1 DIR SAT DIF2

44. t2 t1 t0 t0 fault inception t1 CT starts to saturate t2 external fault under heavy CT saturation conditions Saturation Detector

45. NORMAL SAT := 0 The differential saturation current below the condition first slope for certain period of time EXTERNAL FAULT SAT := 1 The differential- The differential restraining trajectory characteristic out of the differential entered characteristic for certain period of time EXTERNAL FAULT & CT SATURATION SAT := 1 Saturation Detector – The State Machine

46. Saturation Detector • Operation: • The SAT flag WILL NOT be set during internal faults whether or not any CTs saturate • The SAT flag WILL be SET during external faults whether or not any CTs saturate • By design the SAT flag is NOT used to block the relay but to switch to 2-out-of-2 operating principle

47. Examples – External Fault

48. Examples – Internal Fault

49. User-Modified Tripping Logic • All the key logic flags (DIFferential, SATuration, DIRectional) are available as FlexLogicTM operands with the following meanings: • BUS BIASED PKP - differential characteristic entered • BUS SAT - saturation (external fault) detected • BUS DIR - directionality confirmed (internal fault) • FlexLogicTM can be used to override the default 87B logic • Example: 2-out-of-2 operating principle with extra security applied to the differential principle:

50. Dynamic Bus Replica • Dynamic bus replica mechanism is provided by associating a status signal with each current of a given differential zone • Each current can be inverted prior to configuring into a zone (tie-breaker with a single CT) • The status signal is a FlexLogicTM operand (totally user programmable) • The status signals are formed in FlexLogicTM – including any filtering or extra security checks – from the positions of switches and/or breakers as required • Bus replica applications: • Isolators • Tie-Breakers • Breakers