Optimal Coordination with Considering the Best TCCC

This chapter discusses the technical issues associated with the multi‐time‐current characteristic curve (TCCCs) approach. For one TCCC approach, most of the papers presented in the literature use the International Electrotechnical Commission (IEC) standard inverse TCCC. The root problem comes from using incompatible TCCCs. One of the possible ways to solve the issue is by smartly using correct TCCCs where the selectivity constraint is always satisfied. The simpler way is to stick with the conventional approach where only one unified TCCC is used for all relays. The IEC extremely inverse TCCC always scores the best position as compared with the others, except the first scenario with the linear programming stage where the IEEE extremely inverse TCCC is the winner. The solutions obtained by different TCCCs are feasible, but they could violate some selectivity constraints for some fault locations. The problem dimension and complexity will dramatically increase if multiple TCCCs are involved.