Application of pulsed x-ray induced partial discharge measurements

The use of short x-ray pulses (duration 50 ns) has shown to eliminate the statistical time lag by providing start electrons for the partial discharge (PD) development in a void, making it possible to detect very small voids at low electric field levels. A single x-ray pulse of a given dose produces a certain number of electron-ion pairs in a given gas volume, depending on the gas parameters. A minimum x-ray dose is thus needed to provide at least one start electron in the void for successful pulsed x-ray induced partial discharge (PXIPD) inception. In the application of x-rays to a conventional PD measurement, it is necessary to consider that photons emitted by the x-ray source are attenuated by every barrier material which is located between the source and the void of the insulator. This paper presents guidelines on how to design a successful PXIPD measurement with any given pulsed x-ray source. To do so, the theoretical background of PDs and the attenuation phenomena of x-ray are shown. The minimum x-ray dose for PD inception in artificially produced spherical voids is determined experimentally and evaluated theoretically.