high sensitivity and high speed tripping as it protects each winding separately and thusdoes not need inrush stabilization.The low-impedance function is a percentage biased function with an additional zerosequence current directional comparison criterion. This gives excellent sensitivity andstability during through faults. The function allows the use of different CT ratios andmagnetizing characteristics on the phase and neutral CT cores. Unlike high impedancerestricted ground fault it allows for mixing with other functions and protection IEDs on thesame CT cores.6.2.3 Function blockANSI09000275-1-en.vsdREFPDIF (87N)I3P*I3PW1CT1*I3PW2CT1*BLOCKTRIPPICKUPDIR_INTBLK2HIRESINIBIASIDIFFANGLE2NDHARMANSI09000275 V1 ENFigure 43: REFPDIF (87N) function block6.2.4 SignalsTable 31:Input signals for the function block REFPDIF (REF1-)Signal DescriptionI3P Group signal for neutral current inputI3PW1CT1 Group signal for primary CT1 current inputI3PW2CT1 Group signal for secondary CT1 current inputBLOCK Block of functionTable 32:Output signals for the function block REFPDIF (REF1-)Signal DescriptionTRIP General trip signalSTART General start signalDIROK Directional criteria has operated for internal faultBLK2H Block due to 2-nd harmonicIRES Magnitude of fundamental frequency residual currentTable continues on next page1MRK 502 048-UUS A Section 6Differential protection119Technical manual
