Improving the protective coordination of overcurrent relays in subtransmission networks with a practical and effective approach

Based on the IEC and IEEE standard characteristic curve equations of digital overcurrent relays as well as the customized curve equation for electromechanical overcurrent relays, a practical and effective approach is proposed to improve the protective coordination of overcurrent relays in radial or single-ring subtransmission networks for enhancing the reliability of the power system. The improvements include the reduction of the operating time of upstream overcurrent relays and the elimination of coordination curve intersections if detected. An actual case of a single-ring subtransmission network with six buses in Taiwan Power Company is simulated to validate the feasibility of the method proposed and to demonstrate its practical value suitable for application in the power industry.