Capacitive current switching of Vacuum Interrupters and inrush currents

Abstract

Capacitive current switching has become increasingly necessary for power factor correction in distribution systems. However, Restrikes are potentially dangerous as they could cause overvoltage which can be harmful to the power system. The dielectric strength of the Vacuum Interrupter (VI) in a capacitive current switching is strongly determined by a condition of the contact surfaces modified by an inrush current. But the influence of the inrush current on restrike phenomenon of VIs is still not well understood. The objective of this paper is to understand the restrike characteristics of VI under the inrush currents of different amplitudes. The peak values of inrush currents are set at 0kA, 2kA, 5kA and 10kA. VIs with a rated voltage of 7.2kV are used. For the each testing operation, VI suffers an inrush current during a making operation. Then a DC recovery voltage appeared across the vacuum interrupters after a switching current (lower than 1 A) is interrupted. The experimental results show that a higher inrush current induces more damages to the contact surfaces, which result in more restrikes. The restrike probabilities are 4.6%, 17.9% and 30.4% on average at the inrush current of 0kA, 2kA and 5kA respectively. VIs cannot be opened after several test operations by a welding at the inrush current of 10kA. The inrush currents with higher amplitude induce the restike occurring earlier than that of lower amplitude during the recovery voltage.