Surface flashover characteristics of solid CL-Polystyrene and related materials

Summary form only given, as follows. Insulator vacuum surface flashover continues to be a limiting factor in high voltage, high-energy vacuum-to-oil interfaces. CL-Polystyrene is being used in several applications due to its better flashover voltage hold-off. Insulator stacks, built following J.C. Martin´s criteria, require the material constant to be known as well as the proper time scaling. We have performed a series of vacuum flashover experiments, with sufficient number of CL-Polystyrene samples, to determine the material constant required for the JCM 450 empirical equation. Statistics on shot-to-shot and sample to sample variations are presented, together with precisely measured time-to-breakdown, and number of pulses before breakdown. Scaling is performed using teff @ 89% and teff @ 63%. It is shown that most low voltage flashover events (due to possible conditioning) occur late in time (teff @ 63 % or later), and most non-recoverable flashover events occur mostly during the rise time (teff @ 89% or earlier). Testing was performed with a Marx generator producing up to 400 kV peak voltage with a rise-time of 80 to 90 ns and a typical RC decay of 3 ?sec. Unrecoverable sample flashover was determined by three flashover events in a row. Scaling the JCM constant with teff @89%, and considering only the last three flashover events per sample, an averaged value of 235 is obtained for Polystyrene. When all the flashover events are considered in the scaling, an averaged constant value of 210 is then obtained. We have also performed testing on a similar number of samples of Perspex and Acrylic. Experimentally determined, JCM constants are presented for the three materials as well as Weibull distribution and parameters.