The KH-1 relay is used to supervise breaker closing to insure that power flows from the source to the load bus after closing.
KH-2 Instantaneous Directional Overcurrent Relay
The type KH-2 instantaneous directional overcurrent relay is used whenever a directional unit with an adjustable pickup is desired. A typical application is for directional lockout for current balance paralleling when two or more load tap changing transformers are connected in parallel.
KH-21 Direction Overcurrent Relay
The KH-21 relay is an under power relay using two high speed single phase directional elements in an FT-21 case. This is equivalent to two single phase elements for measuring power using these elements’ contacts in series. The relay utilities break contacts for an under power application. The contacts will be closed to trip in the absence of power flow.