en05000278.vsdTRIPRESL1TRIPRESL2TRIPRESL3 OR TRIPRESTRIPUNREL1TRIPUNREL2TRIPUNREL3 OR TRIPUNREOR TRIPTRNSUNRTRNSSENSIEC05000278 V1 ENFigure 41: Transformer differential protection internal grouping of trippingsignalsIEC05000279-TIFF V1 ENFigure 42: Transformer differential protection internal grouping of logical signalsLogic in figures 39, 40, 41 and 42 can be summarized as follows:1. The three fundamental frequency differential currents are applied in a phasesegregated manner to two limits. The first limit is the operate-restraincharacteristic, while the other is the high-set unrestrained limit. If the first limit isexceeded, a start signal START is set. If the unrestrained limit is exceeded, animmediate unrestrained trip TRIPUNRE and common trip TRIP are issued.2. If a start signal is issued in a phase the harmonic and the waveform block signalsare checked. Only a start signal, which is free of all of its blocking signals canresult in a trip command. If the cross-block logic scheme is applied, then only ifSection 6 1MRK 504 135-UEN ADifferential protection108Technical manual
