Switching behavior of different contact materials under capacitive switching conditions

Abstract

For vacuum circuit-breakers capacitive current switching means a specific operating condition. Though it differs notably from the short-circuit current interruption situation, the circuit-breaker design needs to be reconsidered and adapted. Capacitive switching combines high inrush-currents at the connection of a capacitive load and considerable low breaking currents at its disconnection. A reliable dielectric performance of the breaker is required since the occurrence of a restrike under recovery voltage stress can cause voltage escalation. In terms of a reliable performance of the circuit-breaker the choice of contact design and material takes centre stage. The behavior of various contact materials and designs are studied during a series of tests, representing complete switching cycles for a 24 kilovolt (kV) system voltage. The test series is comprised of making operations and current interruptions followed by a subsequent capacitive recovery voltage. Under these conditions diverse variants of copper-chrome composite materials are analyzed and contrasted. Thereby the effect of additive materials is observed. The pre-arcing behavior and the occurrence of restrikes are observed as an indication of the alteration of the contact systems dielectric condition during the test series. In this regard the tested CuCr contact types show a distinctly differing behavior in their pre-arcing and restrike performance. Furthermore a serious erosion of the contact surfaces can be observed occasionally. This can affect the dielectric condition of the contact system significantly. In addition optical investigation of arcing periods by high-speed movies show the localization of an arc being established on the contacts and particles escaping the contact gap can be noticed.