Surface Flashover of Fiberglass Reinforced Epoxy Composite Insulation in Vacuum at Liquid Nitrogen and Room Temperatures using Power Frequency AC and Lightning Impulse Waveforms

The dielectric strength of vacuum insulation is reduced considerably when high voltage electrodes are bridged by solid insulation. Further reduction of strength can occur when the solid material outgases as in the case of fiber reinforced plastics (FRP). Even when the overall vacuum is acceptable, the higher gas pressures near the insulator surface can result in unacceptably low hold- off strengths. For superconductor applications in high voltage power equipment the problem of outgassing may be reduced or eliminated by the low temperatures employed. We will report on ac and impulse surface flashover studies of two types of fiberglass reinforced epoxy composite insulators, G-10 and G-11, at ambient temperature and at low temperature, using liquid nitrogen cooled electrodes, at vacuum pressures below l.0x10−6 Torr (1.3x10−4Pa). Also, AC and impulse breakdown voltages for a pure vacuum gap are compared to the gap breakdown voltages obtained for the electrode-insulator-electrode arrangement. In addition, preliminary results on the effect of orientation of the layers in G-10 and G-11 on breakdown, surface flashover, and puncture are also presented.