The numerical feeder protection relay SPAA 120 C is used for selective short-circuit and earth-fault protection of radial distribution networks. The feeder protection relay is an integrated device incorporating a two-phase phase overcurrent unit and a directional neutral overcurrent unit in one relay. Further, the feeder protection relay incorporates circuit-breaker failure protection.
When sensitive earth-fault protection is required, the feeder protection relay type SPAA 121 C is recommended. The feeder protection relays SPAA 120 C and SPAA 121 C have identical functions. The only difference between the two relays is the rated current of the earth-fault relay units, i.e. 1 A and 5 A for the relay SPAA 120 C and 0.2 A and 1 A for the relay SPAA 121 C.