Abstract: The device of automatic transfer to standby power supply (ATS) is widely used in electric power system. There are three operation modes for ATS, one is two power supply sources backingup for each other, another is automatic transfer to standby transformer, and the third one is automatic transfer by bus tie breaker. Here, taking a fault treatment of automatic transfer circuit for the standby power supply of auxiliary power system in one thermal power plant’s No.1 and No.2 units of Guangdong, 6kV and 380V respectively, for the example, the important points and the problems needed to pay attention in maintenance and checking of ATS were investigated.

Key words: device of automatic transfer to stand-by power supply (ATS), abnormalities analysis, fault treatment