Back-to-back Capacitor Switching Performance of Vacuum Interrupters after High Frequency Sub-microsecond Voltage Impulse Conditioning

The objective of this paper is to investigate back-to-back capacitor switching restrike characteristics of vacuum interrupters (VIs) after conditioning by using a series of high-frequency sub-microsecond voltage impulses. 7.2 kV VIs are conditioned by several hundreds of batches of sub-microsecond high voltage impulses (1000Hz, 0.1s). The peak value of each impulse reaches 100kV. If a breakdown occurs under a voltage impulse, a high frequency conditioning current of several kA (peak value) would flow through the VI. Then the back-to-back capacitor switching tests are carried out at the inrush currents with peak values of 2 kA and 5 kA, respectively. The peak value of the recovery voltage reaches about 15 kV. The experimental results show that the restrike probability can be reduced significantly by using this high frequency voltage impulses conditioning method. By using VIs which are not conditioned as a benchmark, the restrike probability of the conditioned VIs is reduced from 17.9% to 9.6% at the inrush current of 2 kA. With a higher inrush current of 5 kA, the restrike probability reaches higher to 30.4% with the no conditioned VIs. However, the restrike probability reduces significantly to 7.9% after the conditioning. For VIs which are conditioned, the contact surfaces are fully covered by the molten metal layer resulting from the conditioning current. The contact welding areas caused by the inrush current are much broader and the depths are much shallower than that of VIs in benchmark.