6.7.7 Operation principleBreaker failure protection, 3-phase activation and output CCRBRF is initiated fromprotection trip command, either from protection functions within the IED or fromexternal protection devices.The start signal is general for all three phases. A re-trip attempt can be made after a settime delay. The re-trip function can be done with or without CB position check basedon current and/or contact evaluation. With the current check the re-trip is onlyperformed if the current through the circuit breaker is larger than the operate currentlevel. With contact check the re-trip is only performed if breaker is indicated as closed.The start signal can be an internal or external protection trip signal. This signal willstart the back-up trip timer. If the opening of the breaker is successful this is detectedby the function, by detection of either low current through RMS evaluation and aspecial adapted current algorithm or by open contact indication. The special algorithmenables a very fast detection of successful breaker opening, that is, fast resetting of thecurrent measurement. If the current and/or contact 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 3where it is sufficient to detect failure to open (high current) in one pole, 1 out of 4where it is sufficient to detect failure to open (high current) in one pole or highresidual current and 2 out of 4 where at least two current (phase current and/orresidual current) shall be high for breaker failure detection.• The current detection level for the residual current can be set different from thesetting of phase current detection.• Back-up trip is always made with current or contact check. It is possible to havethis option activated for small load currents only.SR SR QORANDAND30 mst150 msSTARTSTL1 ORBackupTrip L1BFP Started L1Reset L1BLOCKRetrip Time Out L1IEC09000976-2-en.vsdTime out L1IEC09000976 V2 ENFigure 53: Simplified logic scheme of the CCRBRF starting logic1MRK 511 287-UEN A Section 6Current protection131Technical manual
