GRD differential protection systems provide fast, sensitive protection against phase-to-phase, and three phase faults internal to AC machines. The system consists of three torodial current sensors and one three phase differential relay.
These self-balancing differential relays are used to supplement overcurrent relays which provide overload and locked rotor protection. The GRD relay can be set to detect faults as low as 2 amps primary, preventing the burning of iron laminations, thereby greatly reducing the time and cost of repair since restacking the core would not be necessary.