Section 6 Current protection6.1 Instantaneous phase overcurrent protection 3-phaseoutput PHPIOC (50)6.1.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberInstantaneous phase overcurrentprotection 3-phase outputPHPIOC3I>>SYMBOL-Z V1 EN506.1.2 ApplicationLong transmission lines often transfer great quantities of electric power from productionto consumption areas. The unbalance of the produced and consumed electric power ateach end of the transmission line is very large. This means that a fault on the line can easilyendanger the stability of a complete system.The transient stability of a power system depends mostly on three parameters (at constantamount of transmitted electric power):• The type of the fault. Three-phase faults are the most dangerous, because no powercan be transmitted through the fault point during fault conditions.• The magnitude of the fault current. A high fault current indicates that the decrease oftransmitted power is high.• The total fault clearing time. The phase angles between the EMFs of the generatorson both sides of the transmission line increase over the permitted stability limits if thetotal fault clearing time, which consists of the protection operating time and thebreaker opening time, is too long.The fault current on long transmission lines depends mostly on the fault position anddecreases with the distance from the generation point. For this reason the protection must1MRK 511 286-UUS A Section 6Current protection87Application manual
