Overcurrent Relay Coordination Optimization with Partial Differentiation Approach for the Validation of Coordination Violation

Conventional optimization methods for approaching overcurrent relay settings focus on minimizing the operating time of total relays at maximum fault current to accelerate the fault clearance time. However, to judge whether the entire relay curve of each relay pair always meets the constraints of 0.2 or 0.3 sec to the object curve is rather difficult as the curves may have different slopes. Additionally, the coordination time at the closest position for the curves of a relay pair should be checked for coordination validation. Therefore, this work presents a novel partial differentiation approach method to ensure that the curves of overcurrent relay coordination do not intersect with each other and violate the coordination time interval. Relay setting values are normally plotted on the time-current plane to verify the closing or intersection between relay pairs. Thus, a computer program based on the partial differentiation approach is also developed to calculate the current value of the intersection or closest position. Furthermore, a case study involving an industrial power system demonstrates the effectiveness of the proposed method by validating the results of optimization relay coordination.