Short Time Ac V-t Characteristics of Oil Gaps

The High Voltage Test Committee of the Institute of Electrical Engineers of Japan has investigated the ac V-t characteristics of insulating oil with the participation of seven Japanese transformer manufacturers. The breakdown time ranges from a few seconds to 20 minutes after the voltage application when Rogowsky type electrodes of 7.5 mm gap length were used. If the breakdown voltage V of the above results is represented by V ∝ t
^-1/n
, then n takes an average value of 15.5, and it scatters between 11.6 and 23.7 at the 95% confidence limits. From the results of these data, the time conversion factor of the 10-minute withstand voltage was investigated to obtain a more reasonable value for on-site testing of 500 kV transmission equipment ent in Japan.