7.11.7 Operation principleThe Breaker failure protection, phase segregated activation and output (CSPRBRF 50BF)is initiated from protection trip command, either from protection functions within the IEDor from external protection devices.The initiate signal can be phase selective or general (for all three phases). Phase selectiveinitiate signals enable single pole re-trip function. This means that a second attempt toopen the breaker is done. The re-trip attempt can be made after a set time delay. Fortransmission lines single pole trip and autoreclosing is often used. The re-trip function canbe phase selective if it is initiated from phase selective line protection. The re-trip functioncan be done with or without current or contact check. With the current check the re-trip isonly performed if the current through the circuit breaker is larger than the operate currentlevel. With contact check the retrip is only performed if breaker is indicated as closed.The initiate signal can be an internal or external protection trip signal. This signal will startthe back-up trip timer. If the opening of the breaker is successful this is detected by thefunction, both by detection of low RMS current and by a special adapted algorithm. Thespecial algorithm enables a very fast detection of successful breaker opening that is, fastresetting of the current measurement. If the current detection has not detected breakeropening before the back-up timer has run its time a back-up trip is initiated.Further, the following possibilities are available:• In the current detection it is possible to use three different options: 1 out of 3 whereit is sufficient to detect failure to open (high current) in one pole, 1 out of 4 where itis sufficient to detect failure to open (high current) in one pole or high residual currentand 2 out of 4 where at least two current (phase current and/or residual current) shallbe high for breaker failure detection.• The current detection level for the residual current can be set different from the settingof phase current detection.• Back-up trip is always made with current or contact check. It is possible to have thisoption activated for small load currents only.SR SR QORANDAND30 msORBackupTrip ABFP Started AReset ABLOCKRetrip Time Out AANSI09000976-3-en.vsdTime out ABFI_3PBFI_A0150msANSI09000976 V3 ENFigure 121: Simplified logic scheme of the CSPRBRF (50BF) starting logic1MRK 506 335-UUS A Section 7Current protection265Technical manual
