Surface flashover in spacer at vacuum/oil interface

The experimental data for surface flashover in polymethyl methacrylate (PMMA) at oil/vacuum interface by ramp input pulses are presented. The spacer is a conical frustum varying in length from 1 mm to 3 mm and in angle from 70/spl deg/ to 70/spl deg/. With the slope dV/dt of the input pulse, flashover field varies from 30kV/mm to 10kV/mm in case of vacuum/solid surface flashover and 60 kV/mm to 30 kV/mm in case of oil/solid case. It is an interesting observation that the dependence of flashover strength on the angle of the oil/solid surface flashover follows similar trend as the vacuum/solid interface. Based upon this observation, the variation of the breakdown data for the surface flashover has been interpreted along the lines of Watson Model. The Watson model has been generalized to take care of the time-varying nature of the input pulse.