Section 8 Current protection8.1 Instantaneous phase overcurrent protectionPHPIOC IP14506-1 v68.1.1 IdentificationM14880-1 v5Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberInstantaneous phase overcurrentprotectionPHPIOC3I>>SYMBOL-Z V1 EN-US508.1.2 Application M12911-3 v6Long transmission lines often transfer great quantities of electric power fromgeneration to consumption areas. The unbalance of the produced and consumedelectric power at each end of the transmission line is very large. This means that afault on the line can easily endanger the stability of a complete system.The transient stability of a power system depends mostly on three parameters (atconstant amount of transmitted electric power):• The type of the fault. Three-phase faults are the most dangerous, because nopower can be transmitted through the fault point during fault conditions.• The magnitude of the fault current. A high fault current indicates that thedecrease of transmitted power is high.• The total fault clearing time. The phase angles between the EMFs of thegenerators on both sides of the transmission line increase over the permittedstability limits if the total fault clearing time, which consists of the protectionoperating time and the breaker opening time, is too long.The fault current on long transmission lines depends mostly on the fault positionand decreases with the distance from the generation point. For this reason theprotection must operate very quickly for faults very close to the generation (andrelay) point, for which very high fault currents are characteristic.The instantaneous phase overcurrent protection PHPIOC can operate in 10 ms forfaults characterized by very high currents.1MRK 505 393-UEN B Section 8Current protectionLine differential protection RED650 2.2 IEC 147Application manual
