Distribution of Dynamic Prestrike Electric Field Strength when Switching on Inrush Current in 40.5kV Vis

Because of the relatively high probability of restrike, vacuum circuit breakers (VCBs) with the merits of environmental friendly and maintenance-free could not be used in the reactive power compensation of Extra High Voltage (EHV) substation. This disadvantage is attributed to the erosion of the contacts caused by prestrike arc. The objective of this paper is to determine the distributions of dynamic prestrike electric field strength for the contact materials manufactured by vacuum infiltration, vacuum casting and arc-melted preparing technology in the capacitive switching of 40.5kV vacuum circuit breakers (VCBs). In the experiment, CuCr50 and CuCr40 contacts with a diameter of 50 millimeters were prepared. L-C oscillating circuit generated inrush current with a frequency of 207Hz and with a peak of 6.48kA, while the applied voltage was 46.3kV which is equivalent to the peak voltage for a 35kV three-phase network whose capacitive voltage factor is 1.4. As the previous studies on the vacuum breakdown process was limited to a fixed contact gap, the experimental results showed that the dynamic prestrike electric field strength for VCBs in capacitive current making follow the power function distribution, and it was less than the static breakdown electric field strength of the same gap distance. The differential values between them reveal the influences of protrusions and micro particles during capacitive current making in VCBs.