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

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