7.2.2 FunctionalityThe underimpedance protection for generators and transformers ZGCPDIS, has theoffset mho characteristic as a three zone back-up protection for detection of phase-to-phase short circuits in transformers and generators. The full scheme three zones haveindependent measuring phase-to-phase loops and settings that gives high flexibilityfor all types of applications.All three zones can be individually definite time delayed.A load encroachment characteristic is available for the third zone as shown in figure65.IEC07000117-2-en.vsdjXOperation area Operation areaROperation areaNo operation area No operation areaIEC07000117 V2 ENFigure 65: Load encroachment influence on the offset mho Z3 characteristic7.2.3 Function blockIEC10000122-2-en.vsdZGCPDISI3P*U3P*BLOCKBLKZLDCNDTRIPTRZ1TRZ2TRZ3STARTSTZ1STZ2STZ3IEC10000122 V2 ENFigure 66: ZGCPDIS function block1MRK 502 048-UEN A Section 7Impedance protection147Technical manual
