Asynchronous modular contactor for intelligent motor control applications

R&D activities have been carried out for decades by many researchers in order to improve electromechanical contactor performance employing electronic control. This includes electronic controlled contactor opening to minimize contact erosion, and closing to reduce contact bounce. But the improvement is limited with significant increase of cost and size due to the inherent design structure of contactors: simultaneously switching of all three poles. Meanwhile, solid-state motor starters have shown great benefit with point-on-wave (POW) switch-on to minimize transient current and torque stress of induction machines during motor starting process. However, cost and size is a premium. A novel technology that employs asynchronous modular concept and POW switching has been developed. This improves motor starting and contactor switching performances in respect to switching transients and contact erosion while utilizing small size and low cost electromechanical contactors. These contactors are assembled into a flexible modular contactor assembly that allows each pole to be switched independently with precise POW switching control. This paper focuses on motor starting applications to achieve significant reduction of motor starting transients and contactor switching capability improvement. Asynchronous modular contactor prototypes with newly developed 24VDC controlled contactors have been developed. The evaluation tests of the prototype proved significant transient current and torque stress reduction during motor starting.