Prestrike characteristics when switching on inrush current in 40.5kV VIs with axial magnetic field

摘要

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.