Online Assessment of Contact Erosion in High Voltage Gas Circuit Breakers based on different Physical Quantities

In this paper, an effort has been made to evaluate the online condition of arc contacts as a vital component of interruption chamber in high voltage puffer type SF6 circuit breakers. The relationship between eroded mass caused by short-circuit current interruption and different thermal stress indices such as transferred electrical charge, current squared, and arc energy is investigated, by performing many experiments with different current amplitudes and arcing times. It is demonstrated that none of the known indices can solely determine mass erosion caused by the current interruption. Therefore, the equations including two of defined parameters are proposed to evaluate mass erosion. The method using arc energy and transferred electrical charge owns the highest accuracy in evaluating mass loss. However, considering the complexity of arc voltage measurements, a second method using current and arcing time can be also utilized. In addition, the development of erosion during the lifetime of arc contacts is studied. It is shown that arc roots tend to form on new uneroded areas of the contacts during current interruption, resulting in different erosion rates between the first few and subsequent interruptions due to change of morphology of the contacts after the first few switching operations