A directional relay is a protective relay that responds not just to the presence of fault current, but also to its direction relative to the relay location. As an essential. t and secure protection throughout the power system. It is necessary to use it in the following conditions: Directional protection is used for all network components in which the direction of flow of power could change, for example. A protection relay is an automatic device designed to detect abnormal conditions in an electrical power system and initiate the operation of circuit breakers to isolate the faulty section. The relay uses this information, often derived from system voltage, to decide.