Voltage Escalation in the Switching of the Motor Control Circuit by the Vacuum Contactor

A turn-to-turn fault of a high-voltage motor which was controlled by a vacuum contactor prompted this study. The study revealed that a voltage escalation can certainly occur by the repetition of re-ignitions as indicated by recent several papers,1,2, but the cause of the escalation is different from that reported. This paper presents a new theory for the voltage escalation, makes clear the conditions for the occurrence of the escalation, and leads to the conclusion that protectors are indispensable in the application of the contactors to the motor control circuit.