Failure analysis of arc ablated tungsten-copper electrical contacts

Tungsten-copper (WCu) contact materials are the core components of high-voltage electrical switches. However, significant arc ablation effect at high voltage and high current often leads to connection interruption and mechanical loss, which seriously affects the safe operation of appliances. In this paper, the failure mechanisms of tungsten-copper contact materials caused by significant arc ablation in the sulfur hexafluoride (SF6) atmosphere were investigated. Results showed that the arc ablation of contact materials is mainly caused by the evaporation and splashing of copper component which has a low melting point, followed by the ablation and spallation of the tungsten (W) skeleton structure. All of these have roughened the surface of contact materials and then further accelerated the volatilization of copper (Cu) component and the reactions between the contact materials and arc extinguishing medium of SF6. Finally, the contact materials lost their functions of arc extinguishing and current switching. Simulated experimental work has also been performed and it verified the above observed failure mechanisms of contact materials. Due to the instantaneously high temperature and high voltage generated during the arcing, both the Cu and W phases in the WCu alloy have suffered significant evaporation and mass losses.