Directional relays are protective devices that isolate faults in power systems by detecting the direction of fault currents. com IEEE Southern Alberta Section PES/IAS Joint Chapter Technical Seminar - November 2016 Protective Relays - Technical Seminar Nov 2016 - Copyright: IEEE 2 Abstract: Protective relays and devices. Directional relays are incorporated in the power systems sector in the field of electrical engineering to enhance the stability and reliability of electricity grids. This post is meant to focus on the condition of operation of the aforementioned handling device, breaking down all its operational. 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. The PR123/P and the PR333/P units carry out excludable directional protection (“D”) against short-circuit with.