8.7 Mho impedance supervision logic ZSMGAPC SEMOD153841-1 v38.7.1 IdentificationGUID-030C086A-8301-481E-BA0A-6550A9C1482E v2Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberMho Impedance supervision logic ZSMGAPC - -8.7.2 Application SEMOD154555-4 v3The Mho impedance supervision logic (ZSMGAPC) includes features for faultinception detection and high SIR detection. It also includes the functionality forloss of potential logic as well as for the pilot channel blocking scheme.One part of ZSMGAPC function identifies a loss of phase potential that is theresult of a long term (steady state) condition such as a blown fuse or an openvoltage transformer winding or connection. This will block all trips by the distanceprotection since they are based on voltage measurement.In the pilot channel blocking scheme a fault inception detected by a fast actingchange detector is used to send a block signal to the remote end in order to blockan overreaching zone. If the fault is later detected as a forward fault the earlier sentblocking signal is stopped.The blocking scheme is very dependable because it will operate for faultsanywhere on the protected line if the communication channel is out of service.Conversely, it is less secure than permissive schemes because it will trip forexternal faults within the reach of the tripping function if the communicationchannel is out of service. Inadequate speed or dependability can cause spurioustripping for external faults. Inadequate security can cause delayed tripping forinternal faults.ZSMGAPC function also includes functionality for blocking the sample baseddistance protection due to high SIR. SIR directly influences the fault voltage levelfor a given voltage level, and this is the major factor that affects the severity ofCVT transients. Therefore, in cases where the SIR value is too high, furtherfiltering of the measured signals will be needed.8.7.3 Setting guidelines SEMOD174968-1 v1SEMOD154558-7 v4GlobalBaseSel: Selects the global base value group used by the function to defineIBase, UBase and SBase as applicable.PilotMode: Set PilotMode to On when pilot scheme is to be used. In this modefault inception function will send a block signal to remote end to block theoverreaching zones, when operated.1MRK 506 369-UEN B Section 8Impedance protectionLine distance protection REL670 2.2 IEC 285Application manual
