GE L90 Instruction Manual

Also see for L90: Communications manual Communications guide Instruction manual Instruction manual Instruction manual

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GE Multilin L90 Line Differential Relay 5-1355 SETTINGS 5.5 GROUPED ELEMENTS5When the scheme is initiated, it immediately sends a trip signal to the breaker initially signaled to trip (this feature is usuallydescribed as Re-Trip). This reduces the possibility of widespread tripping that results from a declaration of a failed breaker.DETERMINATION OF A BREAKER FAILURE CONDITION:The schemes determine a breaker failure condition via three ëpathsí. Each of these paths is equipped with a time delay,after which a failed breaker is declared and trip signals are sent to all breakers required to clear the zone. The delayedpaths are associated with Breaker Failure Timers 1, 2, and 3, which are intended to have delays increasing with increasingtimer numbers. These delayed paths are individually enabled to allow for maximum flexibility.Timer 1 logic (Early Path) is supervised by a fast-operating breaker auxiliary contact. If the breaker is still closed (as indi-cated by the auxiliary contact) and fault current is detected after the delay interval, an output is issued. Operation of thebreaker auxiliary switch indicates that the breaker has mechanically operated. The continued presence of current indicatesthat the breaker has failed to interrupt the circuit.Timer 2 logic (Main Path) is not supervised by a breaker auxiliary contact. If fault current is detected after the delay interval,an output is issued. This path is intended to detect a breaker that opens mechanically but fails to interrupt fault current; thelogic therefore does not use a breaker auxiliary contact.The Timer 1 and 2 paths provide two levels of current supervision, Hi-set and Lo-set, that allow the supervision level tochange from a current which flows before a breaker inserts an opening resistor into the faulted circuit to a lower level afterresistor insertion. The Hi-set detector is enabled after timeout of Timer 1 or 2, along with a timer that will enable the Lo-setdetector after its delay interval. The delay interval between Hi-set and Lo-set is the expected breaker opening time. Bothcurrent detectors provide a fast operating time for currents at small multiples of the pickup value. The overcurrent detectorsare required to operate after the breaker failure delay interval to eliminate the need for very fast resetting overcurrent detec-tors.Timer 3 logic (Slow Path) is supervised by a breaker auxiliary contact and a control switch contact used to indicate that thebreaker is in/out of service, disabling this path when the breaker is out of service for maintenance. There is no current levelcheck in this logic as it is intended to detect low magnitude faults and it is therefore the slowest to operate.OUTPUT:The outputs from the schemes are:ï FlexLogicô operands that report on the operation of portions of the schemeï FlexLogicô operand used to re-trip the protected breakerï FlexLogicô operands that initiate tripping required to clear the faulted zone. The trip output can be sealed-in for anadjustable period.ï Target message indicating a failed breaker has been declaredï Illumination of the faceplate Trip LED (and the Phase A, B or C LED, if applicable)MAIN PATH SEQUENCE:Figure 5ñ80: BREAKER FAILURE MAIN PATH SEQUENCEPROTECTION OPERATION BREAKER INTERRUPTING TIMECALCULATED CURRENT MAGNITUDEACTUAL CURRENT MAGNITUDE FAILED INTERRUPTIONCORRECT INTERRUPTIONRampdown(ASSUMED 1.5 cycles)INITIATE (1/8 cycle) BREAKER FAILURE TIMER No. 2 (±1/8 cycle)BREAKER FAILURE CURRENT DETECTOR PICKUP (1/8 cycle)BREAKER FAILURE OUTPUT RELAY PICKUP (1/4 cycle)FAULTOCCURS1 2 3 4 5 6 7 8 9 10 11000AMP(ASSUMED 3 cycles)cycles827083A6.CDRMARGIN(Assumed 2 Cycles)BACKUP BREAKER OPERATING TIME(Assumed 3 Cycles)