Research on the Liquid Metal Bridge Formation Process at Contact Separation Moment of DC Air Circuit Breaker

The liquid metal bridge generated at the microspot of the contact has a crucial role in the formation of the arc, which provides the initial energy distribution for the ignition of the arc when the dc air circuit breaker is interrupted. A transient model of microspot thermal process which includes solid, liquid, and gas phase transition of liquid metal bridge during dc air circuit breaker contact separation was established in this article. The key parameters such as temperature, electric potential, and melting voltage of the material during liquid metal bridge formation process were analyzed, and the effects of different microspot surface topographies and contact materials on the liquid metal bridge formation process were also considered. The results show that the microscopic contact surface topography affects the contact microspot thermal process. The liquid metal bridge is formed fastest in pin-pin microspot surface topography and slowest in sphere-sphere microspot surface topography. The formation of the liquid metal bridge of the pure silver contact is the fastest and that of the pure tungsten contact is the slowest at the pin-pin microspot surface topography. A reasonable choice of contact materials can slow down the formation of liquid metal bridge and reduce contact ablation, which can improve the reliability of the circuit breaker and extend contact service life. This article can provide a reference for further research on the mechanism of arc formation process and exploring of ablation resistance contact materials. It can also provide a complement to the traditional arc magneto-hydro-dynamic (MHD) modeling.