Interruption of small, medium-voltage transformer current with a vacuum circuit breaker

Abstract

Vacuum circuit breakers are known to potentially cause voltage escalation when interrupting small currents. Consequently, their installation in electrical systems may require the use of specific means aiming at reducing overvoltages. In this paper, the subject is explored in a configuration of an industrial plant. A medium-voltage transformer is connected to the electrical feeding system using a cable equipped with a breaker on the opposite terminal. The risk of voltage escalation is studied when the transformer loaded with a small inductive load is switched off. The study is conducted with an EMTP-like software program; a detailed high-frequency model of the transformer is used as well as a vacuum circuit breaker model able to represent current chopping and restriking. The protection provided by surge arresters and a filter is also studied.