Study and testing of the directional phase overcurrent protection relay and the RCA's impact on its performance and directional decision making

Abstract

This thesis presents a background on power system protection devices, relay principles, modern relay technology and relay testing. It focuses on the study of the directional phase overcurrent relaying concept that can be briefly explained by the relay tripping whenever the faulted current exceeds a pre-determined pick up value in a specific predefined direction, in order to isolate only the faulted part of the network. This reliable and selective protection is generally used in multisource networks, parallel transmission lines and mesh distribution networks. It is mainly characterized by its Maximum Torque Angle and Relay Characteristic Angle (RCA) also known as the directional angle as it decides the direction of the tripping zone. The variation of the RCA setting has a direct impact on the sensitivity operation of the relay (45 degrees' maximum sensitivity operation for any type of fault). Tests have been performed on The Four Step Directional Phase Overcurrent Protection Function of the Line Distance Protection REL670 ABB IED numerical relay. In one hand, the 51/67 ANSI protection has been tested and results were discussed in order to make a simplified testing guide for this protection. In the other hand, different cases of RCA settings were evaluated under symmetrical and asymmetrical fault types to showcase that the 45 degrees' angle is the best applicable value for a maximum sensitivity.