Tau: The thermal time constant of the protected circuit given in minutes. Pleaserefer to manufacturers manuals for details.TripTemp: Temperature value for trip of the protected circuit. For cables, amaximum allowed conductor temperature is often stated to be 90°C (194°F). Foroverhead lines, the critical temperature for aluminium conductor is about 90 -100°C (194-212°F). For a copper conductor a normal figure is 70°C (158°F).AlarmTemp: Temperature level for alarm of the protected circuit. ALARM signalcan be used as a warning before the circuit is tripped. Therefore the setting shall belower than the trip level. It shall at the same time be higher than the maximumconductor temperature at normal operation. For cables this level is often given to65°C (149°F). Similar values are stated for overhead lines. A suitable setting canbe about 15°C (59°F) below the trip value.ReclTemp: Temperature where lockout signal LOCKOUT from the protection isreleased. When the thermal overload protection trips, a lock-out signal is activated.This signal is intended to block switch in of the protected circuit as long as theconductor temperature is high. The signal is released when the estimatedtemperature is below the set value. This temperature value should be chosen belowthe alarm temperature.8.6 Breaker failure protection CCRBRF IP14514-1 v68.6.1 IdentificationM14878-1 v5Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberBreaker failure protection, 3-phaseactivation and outputCCRBRF3I>BFSYMBOL-U V1 EN-US50BF8.6.2 Application M13916-3 v7In the design of the fault clearance system the N-1 criterion is often used. Thismeans that a fault needs to be cleared even if any component in the fault clearancesystem is faulty. One necessary component in the fault clearance system is thecircuit breaker. It is from practical and economical reason not feasible to duplicatethe circuit breaker for the protected object. Instead a breaker failure protection isused.Breaker failure protection, 3-phase activation and output (CCRBRF) will issue aback-up trip command to adjacent circuit breakers in case of failure to trip of theSection 8 1MRK 505 393-UEN BCurrent protection182 Line differential protection RED650 2.2 IECApplication manual
