Investigation of the Dielectric Strength of Epoxy Insulators for Compressed Gas Systems. Final Report

摘要

This investigation was initiated to improve the detectability of faulty cast epoxy insulators for spacing in high voltage compressed gas transmission lines and substations. It was thought that more sensitive and discriminating partial discharges could detect smaller cavities where partial discharges would occur and cause delayed breakdown in service. The original objective to detect cavities which might cause failure was shown to be practically unattainable, since cavities which might cause failure could be of so small an area that they were practically indetectable. The project then took a new course - to establish the stress-failure time cure for cast epoxy systems and to correlate the level of the stress-time curve with the magnitude of defects, notably tiny cavities, which reduced both the short time and long time dielectric strength. The results strongly support the hypothesis that for a given dielectric resin system that the stress-time curve is shifted up or down depending in an inverse fashion with the defect cavity size and directly with the partial discharge threshold stress. This has led to the conclusion that sufficiently high short time a-c proof test is capable of eliminating specimens which might fail eventually by internal discharges. It has also been shown that when the level of our overvoltage proof test is selected properly, it does not significantly reduce the voltage endurance at lower strsses. Such an overvoltage test would supplement a partial discharge test which it was shown can be improved. (ERA citation 09:010451)