Design study for decreasing impact forces of an axial type vacuum interrupter in vacuum circuit breaker considering the dynamic characteristics

Vacuum interrupters are now widely used for medium voltage switching up to 38kV in such applications as metal-clad switchgears, circuit breakers, etc. Vacuum interrupter minimizes the damage and loss of the contact points at the optimum zero point of current wave after separation of the contact points, due to its quick vacuum insulation recovery characteristics. The fixed and moving electrodes of vacuum interrupter are mated by a driving mechanism within several milliseconds. Therefore, considerable impact forces occur between the electrodes. These impact forces could cause structural damages to vacuum interrupters and shorten fatigue-life of the products. Also, rebound phenomena could occur between the contacts due to the impact forces. It could not only affect mechanical characteristics but also have a strong influence on electrical conditions. Therefore, it is very important for impact analysis to reflect the dynamic characteristics of materials that consists electrodes as well as the static characteristics. As the dynamic behavior of materials is different from the static(or quasi-static) one due to the inertia effect and the stress wave propagation, an adequate experimental technique has to be developed to obtain the dynamic responses for the corresponding level of the strain rate. In this paper, to determine the dynamic characteristics of materials, the Hopkinson bar experiment is carried out, and for decreasing impact forces of a axial type vacuum interrupter, design study is applied in impact analysis with explicit finite element method. The rebound phenomena between the electrodes during impact periods are compared with the one of modified model which is suggested for the improvements in specific parameters.