US Patent 7741937 Power switching apparatus and method of controlling the same

A power switching apparatus includes a breaker unit, an operating unit, a measuring unit, and a controlling unit. The breaker unit is connected on a three-phase current line, and includes switches each corresponding to one of phases of the three-phase current line. The operating unit simultaneously turns on or off the switches. The measuring unit measures a current flowing in each phase, and determines a time point where current flowing in one of the phases becomes zero as a reference time point. The controlling unit controls, when interrupting load current, the operating unit to turn off the switches in a range from 20 degrees to 40 degrees of an electric angle from the reference time point.