Determining optimum TMS and PS of overcurrent relays using big-M method

The time of operation of overcurrent relays (OCRs) can be reduced, and at the same time coordination can be maintained, by selecting the optimum values of time multiplier setting (TMS) and plug setting (PS) of OCRs. This paper presents formulation of the problem of determining optimum values of TMS and PS of OCRs as a constrained nonlinear optimization problem, and solution of the same using big-M (penalty) method, which is a method used to find optimum solution of linear programming problem (LPP). The method introduces artificial variables in the objective function to get an initial basic feasible solution (IBFS). Artificial variables are removed using iterative process which also leads to an optimum solution.