Understanding the Role of Asynchronous Contact Breaking in Three-Phase AC Contactors Failure

For three-phase alternating current (ac) contactors, the degradation of switching performance is affected by the accumulated arc erosion on contacts seriously. The direct consequence is the asynchronous contact breaking behavior and further disconnection failure. In this article, we explicitly recorded the typical contact voltage, contact current, and coil current waveforms of the contactor during ac-1 electrical endurance tests. Through the analysis of the waveforms, the asynchronous bridge breaking phenomenon within the three-phase ac contactor is discovered. Furthermore, by examining variations in bridge breaking time difference and opening time difference among phases with operation cycles, the correlation between asynchronous bridge breaking behavior and associated unbalanced arc erosion is analyzed explicitly. Finally, the failure mechanisms for the three-phase ac contactor are proposed based on the asynchronous break phenomenon of the contact bridge and the asynchronous separation phenomenon of the three phases.