In case of interrupting inductive load by vacuum switch

re-ignition of arc is the root cause of generating serious switching over-voltage. Phase selection operation of vacuum switch can effectively eliminate the re-ignition of arc and avoid the serious switching over-voltage. The mechanical reliability of phase selection of vacuum switch is the key in assuring the reliable phase selection operation. On-line detection of mechanical stability of the phase selection of vacuum switch can find timely and avoid invalid phase selection. In this paper

two kinds of on-line detection methods of phase selection characteristic are proposed. One auxiliary contact with stable and simultaneous operation with the main contact is set on the operating mechanism of the phase selection vacuum switch for the signal sensing at the instant opening of the contact

which can achieve the on-line detection of phase selection characteristic and adaptive control of phase selection operation

find timely deterioration of phase selection characteristic and avoid invalid phase selection. The electromagnetic pulse due to re-ignition of arc is identified through detecting space electromagnetic wave of vacuum switch during the interruption period so to achieve on-line detection of re-ignition of arc and find timely invalid phase selection.