Traditional automatic switchover methods can hardly correctly distinguish between two cases: the cause of bus voltage loss is the incoming line fault or the cut of incoming line by the security and stability control system. It may cause the incorrect operation or refusing action of the automatic switchover device

which affects the stable operation of power system and the reliability of power supply. According to different variation characteristics of bus voltage and incoming line current when the security and stability control system cuts the incoming line and the incoming line is removed because of the fault. This paper proposes an opening criterion for automatic switchover to adapt to the actions of the security and stability control system. The criterion can lock the automatic switchover function when the security and stability control system cuts the incoming line

and it can also reliably open the automatic switchover function when the incoming line is removed due to fault. Finally

the correctness of the criterion is verified by a simulation test. This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2015AA050201).