In Guoneng Zhumadian Thermal Power Co.,Ltd.(hereinafter referred to as the Zhumadian Compa-ny),the zero-sequence overcurrent action of the branch A of No.1 unit auxiliary transformer tripped,and the block switching of auxiliary power fast switchover device led to the loss-of-power of 6 kV section-IA bus.This paper analyzes the causes of the unit tripping,and puts forward new methods for checking the mi-crocomputer integrated protection device of 6kV house-service equipment and measuring the actual opening time of the switch,thus providing certain references for analyzing the coordination of protection time limit and the reliability of setting the actual auxiliary power protection setting.
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