A typical industrial power network may consist up to hundreds of pieces of equipment and requires even more protection relays to protect the system. Each protection relay in the power network needs to be coordinated with the relays protecting the adjacent equipment. The overall protection coordination is thus very complicated. A new concept of protection coordination by time is introduced in this paper to formulate all the system relays and system equipment operation into a set of optimization equations and constraints. Its purpose is to search for an optimal protection setting to minimize the system disturbance time as well as the time of interruption of power supply. An evolutionary algorithm is applied as a constraint satisfaction optimization tool to search for the optimal relay setting. This method can find out the best protection relay coordination that cannot be achieved by traditional methods. This is the most significant achievement.
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