Reliability of GIS EHV epoxy insulators: the need and prospects for more stringent acceptance criteria

Partial discharge (PD) scaling relationships, based on a recently developed theory, that allow prediction of PD magnitude in equivalent defects in different insulators for gas switchgear are presented. To maintain high levels of reliability, PD acceptance criteria of 0.5 to 1.0 pC are proposed for 550 kV insulators to obtain a standard of severity equivalent to that in existence at 138 kV. To achieve this level of testing, a number of techniques, including ultrawideband measurements, are proposed to improve present PD detection technology by at least two orders of magnitude. Sensitivities of better than 0.01 pC at up to 400 kV were routinely achieved in a factory-like environment