40 100 40 40 220t ms ms ms ms msD ³ + + + =EQUATION1266 V1 EN (Equation 32)where it is considered that:the operate time of overcurrent protection B1 is 40 msthe breaker open time is 100 msthe resetting time of protection A1 is 40 ms andthe additional margin is 40 ms7.2 Four step single phase overcurrent protectionPH4SPTOC (51)7.2.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberFour step single phase overcurrentprotectionPH4SPTOC44 altI>OC V1 EN517.2.2 ApplicationThe Four step single phase overcurrent protection(PH4SPTOC, 51) function is used inseveral applications in the power system. Some applications are:• Short circuit protection of feeders in distribution and subtransmission systems.Normally these feeders have radial structure.• Back-up short circuit protection of transmission lines.• Back-up short circuit protection of power transformers• Short circuit protection of different kinds of equipment connected to the powersystem such as; shunt capacitor banks, shunt reactors, motors and others.• Back-up short circuit protection of power generators.The single phase overcurrent protection is used in IEDs having only input from one phase,for example busbar protection for large busbars (with many bays).Section 7 1MRK 505 337-UUS -Current protection174Application manual
