K-factor value of SF6 gas gap under non-homogeneous electric field for UHV-class gas-insulated switchgear

The lightning impulse voltage test waveform of power equipment is prescribed in the IEC 60060-1 "High-voltage test techniques" revised in 2010. This revision introduced an evaluation method by k-factor function (test voltage function), which converts an overshoot waveform to a test voltage waveform. At present, the test standard for UHV-class equipment is being studied and the authors have experimentally acquired k-factor values for gas-insulated switchgears, oil-immersed transformers and air insulation using the largest possible model assuming an actual UHV-class equipment to date. This paper reports the experimental result on the breakdown characteristics of lightning impulse voltage test waveforms for the SF6 gas insulation model under a nonhomogeneous electric field. The k-factor value was calculated by measuring the breakdown voltage and time using the superimposed oscillation frequency and the overshoot rate as parameters. The change with respect to the superimposed frequency of this experiment was similar to that of the existing k-factor function, and the effectiveness of evaluation by the k-factor function was confirmed.