Parameter Uncertainty in the Optimal Coordination of Overcurrent Relays

Abstract

Generally the relay coordination problem is solved without considering parameter<br><br>uncertainties. While uncertainties in the line parameters and CT ratios make the fault current<br><br>passing through the overcurrent relay inaccurate and could cause the miss-coordination. To<br><br>overcome this drawback, in this paper, a novel method based on interval analysis is introduced to<br><br>model parameter uncertainties in the coordination problem. Considering parameter uncertainties,<br><br>the coordination constraints are formulated as a set of inequalities with interval coefficients.<br><br>Monte-Carlo simulation technique is used to determine the boundary values of these interval<br><br>coefficients. In this case, the optimal coordination problem is formulated as an Interval Linear<br><br>Programming (ILP) problem. Using mathematical theorems, the optimal value of ILP problem<br><br>can be obtained by solving a standard Linear Programming (LP) problem. The proposed method<br><br>is applied to the 8-bus and IEEE 30-bus test systems and the results show the ability of interval method to model the parametric uncertainties