6.12.2 FunctionalityNegative sequence based overcurrent function DNSPTOC is typically used assensitive earth-fault protection of power lines, where incorrect zero sequencepolarization may result from mutual induction between two or more parallel lines.Additionally, it is applied in applications on cables, where zero sequence impedancedepends on the fault current return paths, but the cable negative sequence impedanceis practically constant.The directional function is current and voltage polarized. The function can be set toforward, reverse or non-directional independently for each step. Both steps areprovided with a settable definite time delay.DNSPTOC protects against all unbalanced faults including phase-to-phase faults. Theminimum start current of the function must be set to above the normal systemunbalance level in order to avoid unwanted operation.6.12.3 Function blockDNSPTOCI3P*U3P*BLOCKBLKOC1ENMLTOC1BLKOC2ENMLTOC2TRIPTROC1TROC2STARTSTOC1STOC2DIROC1DIROC2CURRENTVOLTAGEUIANGLEIEC09000125-1-en.vsdIEC09000125 V1 ENFigure 67: DNSPTOC function block6.12.4 SignalsTable 105:DNSPTOC Input signalsName Type Default DescriptionI3P GROUPSIGNAL- Three phase group signal for current inputsU3P GROUPSIGNAL- Three phase group signal for voltage inputsBLOCK BOOLEAN 0 Block of functionBLKOC1 BOOLEAN 0 Block of over current function OC1ENMLTOC1 BOOLEAN 0 Enable signal for current multiplier - step1 (OC1)BLKOC2 BOOLEAN 0 Block of over current function OC2ENMLTOC2 BOOLEAN 0 Enable signal for current multiplier - step 2 (OC2)1MRK 511 287-UEN A Section 6Current protection153Technical manual
