TimeThe faultoccursProtectionoperate timeTrip and StartCCRBRFNormal tcbopenMarginRetrip delay t1 tcbopen after re-triptBFPresetMinimum back-up trip delay t2Critical fault clearance time for stabilityIEC05000479_2_en.vsdIEC05000479 V2 EN-USFigure 91: Time sequencet2MPh: Time delay of the back-up trip at multi-phase start. The critical faultclearance time is often shorter in case of multi-phase faults, compared to singlephase-to-earth faults. Therefore there is a possibility to reduce the back-up tripdelay for multi-phase faults. Typical setting is 90 – 150 ms.t3: Additional time delay to t2 for a second back-up trip TRBU2. In someapplications there might be a requirement to have separated back-up trip functions,tripping different back-up circuit breakers.tCBAlarm: Time delay for alarm in case of indication of faulty circuit breaker.There is a binary input CBFLT from the circuit breaker. This signal is activatedwhen internal supervision in the circuit breaker detect that the circuit breaker isunable to clear fault. This could be the case when gas pressure is low in a SF6circuit breaker. After the set time an alarm is given, so that actions can be done torepair the circuit breaker. The time delay for back-up trip is bypassed when theCBFLT is active. Typical setting is 2.0 seconds.tPulse: Trip pulse duration. This setting must be larger than the critical impulsetime of circuit breakers to be tripped from the breaker failure protection. Typicalsetting is 200 ms.8.7 Pole discordance protection CCPDSC IP14516-1 v5Section 8 1MRK 505 393-UEN BCurrent protection186 Line differential protection RED650 2.2 IECApplication manual
