Novel Voltage Sag Protection Topology of Contactors for Uninterrupted Switching Capability

Voltage sags triggered by a thunder-strike and a short-circuit fault could result in false tripping of ac contactor, a type of highly sensitive electrical equipment applied extensively. Serious consequences, such as unintended shutdown in consecutive industrial manufacturing, would be caused subsequently. Thus, an uninterrupted switching topology for ac contactor from mains supply to backup power supply is proposed in this paper, based on the reverse external voltage turn-off characteristic of the silicon-controlled rectifier. Accordingly, the exciting current is continuous, which ensures the engagement of the contactor under voltage sag and even short interruption. Simulations and experiments are conducted simultaneously. Selected emulational and experimental results are reported to validate the correctness and feasibility of the proposed topology and its control strategy.