Directional relays detect the direction of fault current and are combined with sensing elements like overcurrent relays for effective operation. 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. This White Paper describes the sense, the potentials and the use of directional protection and directional zone selectivity functions, hereafter called “D” and “SdZ D” respectively. In these applications, modern directional elements provide an output signal to control the operation of the sensing elements or a restraining. Directional relays are not just overcurrent devices with extra logic. They compare current from CTs with voltage from PTs to determine the fault direction. That single capability is decisive in parallel feeders, ring networks, and multi-infeed grids, where faults may be fed from both sides.
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