Directional Over-current relay

• It is used in fault conditions. There is a collapse of system voltage increase in current called fault current. For short circuit protection, relays are so connected that they develop maximum operating torque under fault condition. This relay is preferred for the use of protective relay under short circuit or fault conditions.

Directional Power or Reverse Power relay

• It has to be used under non-fault conditions i.e. used in reverse power condition of a turbo alternator. There is no collapse of system voltage and no fault current. These relays are so connected that they develop maximum torque when direction of power flow reverses. This relay is not suitable for use as a protective relay under short circuit conditions.