Investigation on erosion of Cu/W contacts in high-voltage circuit breakers

The prediction and understanding of the erosion process of the Cu/W arcing contacts in high-voltage circuit breakers is important for the improvement of the breaker lifetime. The change of the contact geometry due to erosion is a main factor, which influences the lifetime. It is known that the ablation of contact material depends at least on parameters like the arcing current-amplitude, arcing time, total charge, and contact material properties. Based on experimental results, a method for an improved prediction of the erosion was derived. The experiments have been carried out in a SF6 self-blast circuit breaker test device with commercial high-voltage circuit breaker contacts at a current amplitude up to 45 kA RMS and arcing time up to 17 ms.. From the power balance at the electrodes, the material erosion due to evaporation is calculated. The resulting erosion rates are in good agreement to the experimental results and explain that the specific erosion scales with current, polarity, and the arcing time. This indicates that erosion in this range of arcing stress occurs mainly due to evaporation of contact material and less to emission of droplets.