scope:

This part of IEC 60255 specifies minimum requirements for over/under current relays. This standard includes a specification of the protection function, measurement characteristics and time delay characteristics. This part of IEC 60255 defines the influencing factors that affect the accuracy under steady state conditions and performance characteristics during dynamic conditions. The test methodologies for verifying performance characteristics and accuracy are also included in this standard. The over/under current functions covered by this standard are the following: IEEE/ANSI C37.2 IEC 61850-7-4 Function Numbers Logical nodes Instantaneous phase overcurrent protection 50 PIOC Time delayed phase overcurrent protection 51 PTOC Instantaneous earth fault protection 50N/50G PIOC Time delayed earth fault protection 51N/51G PTOC Negative sequence overcurrent or current unbalance protection 46 PTOC Phase undercurrent protection 37 PTUC Voltage-dependent overcurrent protection 51V PVOC This standard excludes thermal electrical relays as specified in IEC 60255-8. General requirements for measuring relays and protection equipment are specified in IEC 60255-1.