Abstract: The automatic reclosing technology is an effective measure to guarantee the safety power supply and stable operation of power system, and has been widely used in electric power system domestic and abroad. A reclosing incorrect operation accident occurred in a 500kV line of Central China Power Grid was introduced, in which the reclosing device of one side of the line had reclosed successfully, but the reclosing device of other side of the line had operated incorrectly and the breaker tripped three times. Through the investigation and analysis of this accident, it is shown that for trying transmission of new line or the line in which the protection system was reformed, in order to inspect the correctness of unit functions and circuit coordination, the prior complete set test of protection devices must follow the mode of simulating same step action of two sets of protection devices, so as to avoid the emergence of such accident or other faults.

Key words: reclosing, complete set test, protection calibration