In various fields as electricity, petroleum, chemical, metallurgy, papermaking, water treatment, pharmaceuticals, etc., electric motors have been used widely. The traditional motor control circuit is protected by a low-voltage motor composed of thermal relay, fuse or electromagnetic current relay. Due to onefold function, large maintenance and repair, and low degree of informationization, it is unable to meet the growing needs of the modern automation level. In order to make the motor run normally and work reliably, it is necessary to control, protect and manage the motors.