The vacuum interrupter, the high reliability component of distribution switches, circuit breakers and contactors

The use of vacuum interrupters as the current interruption component for switches, circuit breakers, reclosers and contactors operating at distribution voltages has escalated since their introduction in the mid-19501s. This electrical product has developed a dominating position for switching and protecting distribution circuits. Vacuum interrupters are even being introduced into switching products operating at transmission voltages. Among the reasons for the vacuum interrupter's popularity are its compactness, its range of application, its low cost, its superb electrical and mechanical life and its ease of application. Its major advantage, however, is its well-established reliability. In this paper we show how this reliability has been achieved by design, by mechanical life testing and by electrical performance testing. We introduce the "sealed for life" concept for the vacuum interrupter's integrity. We discuss this in terms of what is meant by a practical leak rate for vacuum interrupters with a life in excess of 30 years. We show that a simple high voltage withstand test is an easy and effective method for monitoring the long-term vacuum integrity. Finally we evaluate the need for routine inspection of this electrical product when it is used in adverse ambients.