Increase in contact resistance of vacuum interrupters after shortcircuit testing

Abstract:
A key source of heat during continuous current operation of vacuum circuit breakers is the vacuum interrupter (VI). Circuit breaker operations, in particular short-circuit current operations, can alter the resistance in the VI and thereby alter the heat produced during subsequent continuous current operation. The paper focuses on the change in the VI resistance before and after short-circuit testing. The arc control structure affects the resistance increase after short-circuit testing. Axial magnetic field (AMF) designs produce the lowest increase, with a larger increase for radial magnetic field (RMF) designs. The two different RMF arc control methods tested here lead to similar resistance increases. Short-circuit arcing can change the resistance through three main mechanisms: increasing the resistivity at the surface, increasing the hardness at the surface, and changing the contact area. Analysis suggests that a reduction in the contact area is the primary source of the resistance increase.