Initial impact measurement during opening of vacuum circuit breakers

Welding of the contacts in Vacuum Interrupters (VI´s) applied in Vacuum Circuit Breakers (VCB´s) is inherent to this switching technology. The welds are usually formed between the VI contacts during a closing operation but could also occur during current carrying in a stationary closed position when the contacts are pushed together with insufficient contact force. Especially with high inrush-currents or fault currents, in combination with a long pre-ignition time and/or contact bounce duration, during a closing operation the weld could be of substantial strength. In a worst-case, when the weld strength exceeds the VCB´s weld breaking capability the breaker will fail to open during the next opening command. When the weld breaking capability of the breaker is just sufficient to break a weld the opening characteristic of the breaker could be substantially changed which could impact the interruption capability of the breaker. It is therefore essential that a breaker has good weld breaking capability as this is necessary for proper operation. The objective of the study conducted was to investigate the initial impact phenomena during the opening operation of a VCB. The results could provide valuable guidance for a proper VCB mechanism design.