Universal Relay Family B30 Bus Differential Relay

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

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

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)

Features Metering: Oscillography Event Recorder Phasors / true RMS

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

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

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

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

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

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

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

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

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)

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

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

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

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

Logic DIF1 AND OR TRIP DIR OR AND SAT DIF2

Logic

Logic DIF1 AND OR TRIP DIR OR AND SAT DIF2

Directional principle Internal faults - all currents approximately in phase

Directional principle External faults - one current approximately out of phase

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

Directional principle

Directional principle

Directional principle

Logic DIF1 AND OR TRIP DIR OR AND SAT DIF2

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

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

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

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

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)

Saturation Detector: State Machine

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

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

B30 Bus Differential Relay: External Fault Example

B30 Bus Differential Relay: Internal Fault Example

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

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

Dynamic Bus Replica: Example

Dynamic Bus Replica: Example

Dynamic Bus Replica: Example

Dynamic Bus Replica: Zoning

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.)