The line differential protection relay is a combined distance and line differential protection and control IED. The relay provides complex protection, control and monitoring functions for transmission overhead lines and cables.
The protection relays provide a variety of versatile protection functions along with the main line differential protection (87L) such as distance protection (21), teleprotection schemes (POTT, PUTT etc.), current protection (50/51, 50/51N, 67/67N, 46/46BC), voltage protection (27, 59, 47), frequency protection (81U/81O/81R), power protection (32/37), power swing/out of step detection (68/78), switch on to fault protection (SOTF), breaker failure protection (50BF). The scope of functions is supplemented with the automatic reclosing function (79) with synchro-check/synchro-switch feature (25). CT errors, CT saturation, voltage transformer supervision and dead line detection function optional charging current compensation are implemented in the configuration for increased stability and sensitivity. Because of the implemented control, measuring and monitoring function, the IED can also be used as a bay control unit.