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Nowadays the phase controlled switching is a preferred method for capacitive switching. Thus the prestrike characteristic is an important issue for the control strategy. The objective of this paper is to understand the prestrike characteristics of vacuum interrupters (VIs) in the capacitive making operations of 40.5 kV vacuum circuit breakers (VCBs). In the experiment, three VIs with CuCr50 (50 wt% of Cr) contact material and three VIs with CuCr40 (40 wt% of Cr) contact material with contact diameter of 50 millimeters were prepared. The CuCr50 and CuCr40 contact materials are made by using infiltration and arc-melted technology, respectively. An L-C oscillating circuit generated an inrush current with a frequency of 207 Hz and with a peak of 6.48 kA, while the applied voltage was 46.3 kV which is equivalent to the peak voltage for a 35 kV three-phase network whose capacitive voltage factor is 1.4. The experimental results show that the complementary cumulative distribution function (CCDF) of the prestrike gaps dpre follows a 3-parameter Weibull distribution. The prestrike gap below which prestrike would always occur is similar for all six test VIs which is 2.4–3.1 mm. However, the average values of d\0, ?50 and ?90 for infiltration CuCr50 contact material are 57.5%, 45.3% and 28.9% higher than the ones in arc-melted CuCr40 contact material, respectively. During the inrush current flowing, at each zero-crossing of the inrush current the prestrike arc tries to extinguish with the occurrence of three types of contact gap breakdowns. Furthermore, if the contact gap breakdowns are withstood at the inrush current zero-crossing, inrush current interruption phenomenon happens, which proves a common phenomenon in capacitive making operation. The inrush current interruption phenomenon is mainly determined by the prestrike distance and not by the material quality. The experimental results imply that the field emission dominated breakdown and the micro-particle induced breakdown both take effect in the prestriking and contact gap breakdown process.

Nowadays the phase controlled switching is a preferred method for capacitive switching. Thus the distribution of prestrike gaps is an important issue for the control strategy. The objective of this paper is to understand the distribution of prestrike gaps for the contact materials manufactured by arc-melted and infiltration preparing technology in the capacitive service condition of 40.5kV vacuum circuit breakers (VCBs). In the experiment, CuCr50 contacts with a diameter of 50 millimeters were prepared by arc-melted and infiltration technology respectively. The test vacuum interrupters are equipped with cupped axial magnetic field type electrodes. 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. The experimental results show that the complementary cumulative probability of the prestrike gap d pre follows the 3-parameter Weibull distribution. The prestrike gap below which prestrike would always occur is different for all four test VIs, and the scattering of the prestrike gaps is different, too. It means the distribution of prestrike gaps for all four VIs significantly varies with closing operations as the preparing technologies are different. Thus the distribution of prestrike gaps is important when employing phase controlled switching in VCBs for the capacitive switching.

Nowadays the phase control closing technology is a preferred method for capacitive switching. Thus the distribution of prestrike gaps is important for the control strategy. The objective of this paper is to understand the distribution of prestrike gaps for the contact materials manufactured by infiltration and arc-melted preparing technology in the capacitive service condition of 40.5kV vacuum circuit breakers (VCBs). In the experiment, CuCr50 and CuCr40 contacts with a diameter of 50 millimeters were prepared by infiltration and arc-melted technology respectively. 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. The experimental results show that the complementary cumulative probability of the prestrike gap d pre follows the 3-parameter Weibull distribution. The d 100 below which prestrike would always occur is similar for all six test VIs, while the scattering of the prestrike gap is different. It means the distributions of prestrike gaps for all six VIs significantly varies with closing operations as the contact materials and preparing technologies are different. Thus the distribution of prestrike gaps is important when employing phase control closing technology in VCBs for the capacitive switching.