X-ray induced partial discharge testing of full-size EHV insulators

A new partial discharge (PD) measurement system has been assembled which takes advantage of modern ultrawideband instrumentation techniques and which eliminates the influence of statistical time lags on partial discharge initiation processes. The PD test system is designed to accommodate full size 550 kV insulators used in gas-insulated substations (GIS) at up to 800 kV at high sensitivity. The system is intended to improve the effectiveness of factory PD testing, thereby increasing GIS reliability. The system uses X-ray irradiation of the test object to eliminate the statistical time lag during PD measurement. Under X-ray irradiation the PD pulse repetition rate is increased and the discharge inception voltage (DIV) is sharply reduced. The DIV of some insulators under X-ray irradiation was recorded at values more than an order of magnitude lower than without X-rays. The XIPD technology is generic and can be readily extended to a broad range of insulation systems and equipment. The practical implications of this technology on acceptance testing of insulators is also discussed.