Optimal coordination of non-directional overcurrent relays for active distribution network using new voltage-current relay characteristic

The variation in short-circuit current levels caused by the distributed generation (DG) installation leads to the coordination failure of the overcurrent relay in the protection system. This paper presents a new voltage-controlled overcurrent characteristic of an overcurrent relay. The relay characteristic proposed in this research is designed to improve the performance of overcurrent relays by using a pickup voltage multiplier. The pickup voltage multiplier consists of three key parameters: pickup voltage, parameter D, and time multiplier setting (TMS). This article presents a method for determining the optimal values for pickup voltage parameters D and TMS using nonlinear programming and the interval linear programming solution to minimize the total tripping times and maintain the coordination of the primary and backup relays under short-circuit conditions in the radial system with and without DG integrations under different sizes and locations. The proposed relay characteristic is verified on the IEEE 13-bus and IEEE 33-bus radial distribution system with synchronous-based DG (SBDG) and wind turbine-based DG (WTDG). In addition, the simulation results of the proposed relay characteristic are compared with the conventional standard relays and the overcurrent relay characteristics in the literature. The simulation results of the proposed relay characteristic demonstrate its capability for fast short-circuit clearance, reduction in the total operation time of the protection scheme, and maintaining coordination between the primary and backup relays under increased short-circuit current conditions in power systems with SBDG and WTDG installation.