Contact Erosion Induced by Free-Burning Arcs in an Experimental Gas Circuit Breaker

The electrical lifetime of the Cu-W arcing contacts of high-voltage circuit breakers determines the service lifetime and the reliability of such circuit breakers. Experimental study of the arc erosion of the Cu-W material has been carried out in CO₂ under free-burning arc conditions with peak current ranges from 5 kA to 40 kA. The mass loss was measured at each current level, which is the basic index to characterize the degree of contact erosion. Splashing droplets and molten pool were observed around current zero. It has been found that the mass loss of the plug contact (anode) in CO₂ arc erosion tests is larger than that in SF₆. In order to find the reason for the inconsistent mass loss of Cu-W in CO₂ and SF₆, the effective voltage drops in electrode fall region were determined carefully and found to have similar values in CO₂ and SF₆. From the energy balance and exchange process on the electrode surface, the energy absorbed by the electrode through radiation from the arc column was found to be greater in CO₂ than that in SF₆.