Impulse breakdown characteristics of dielectric materials immersed in insulating oil

Surface discharges along oil-immersed solids chosen to insulate high-voltage, pulsed-power systems are a problem that can lead to catastrophic failure. Knowledge of the electrical fields at which surface flashover, or other types of breakdown event, will occur for different dielectric materials is therefore important for the proper design of insulating components for pulsed-power systems. In the present work, impulse voltages of peak amplitude 350 kV and rise-time 1 ¿s were applied to cylindrical samples of: polypropylene; low-density polyethylene; ultra-high molecular weight polyethylene; Rexolite; and Torlon. Breakdown events were studied under both nonuniform and uniform field conditions, with samples located between a pair of electrodes immersed in insulating oil. Sample lengths were chosen such that breakdown events occurred on the rising edge. Ultra-high molecular weight polyethylene showed the highest average breakdown field 645 kV/cm in uniform fields, and the corresponding field was reduced to ~400 kV/cm in non-uniform fields. The results provide comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage, pulsed-power machines.