New directional protection for distribution networks

Directional elements need to be able to differentiate between load current and fault current when two sources are present in the distribution network (closed-loop). When the fault current is about two- or three-times the load current, this is easy to accomplish. But when the directional element is used in a relay that is protecting a distributed generator (DG) the fault and load current may be within the same range, and the direction to the fault still need to be identified. A new directional element for the phase overcurrent relay is proposed to achieve this using individual phase torques and the negative sequence torque. Yet a bigger contribution of this paper is deriving the minimum pickup thresholds for correct operation of the proposed directional element.