Electrical Breakdown in Composite Insulating Systems: Liquid-Solid Interface Parallel to the Field

The location of electrical breakdown in a composite insulating system has been measured. In these experiments, a paper sample was mounted so that it connected the two electrodes. Electrode structures ranging from plane-plane to sphere sphere were used. The electrode-paper system was tested in oil to determine the properties of an oil paper interface. The data indicated that, in a carefully prepared system, the breakdown will not necessarily occur at the interface. In addition, it was found that breakdown voltages were not significantly lower for those breakdowns which occurred at the interface than for those which did not. It was noted that if the paper was not dried or if many gaseous voids were left in or on the paper, the breakdown regularly occurred at the interface and at a lower voltage.