Determination of the best switching phase is one of the core problem of synchronous switching technology.During the switching process

the vacuum gap will pre-strike

making the breaker can’t close at the scheduled phase

then affect the accuracy of closing phase.In this paper

experiments using the PMA vacuum breaker and respectively under different voltages were done to get the relation between pre-strike gap and voltage

also researched how closing speed affects the pre-strike.Considered the mechanical dispersion

the impact to the closing phase was proposed.It is proposed that using BP network select the best switching phase

which provides the theoretical basis for the breaker realizing the synchronous switching.