X-ray triggered PD measurements in small sized spherical voids at the detection limit

Pulsed X-ray triggered PD measurements were introduced in electrical testing in order to eliminate the statistical time lag. Moreover it was shown recently that the PD mechanism in air filled voids in epoxy insulation does not change with respect to natural inception of PD. In this paper we address the question of the detection limit of this method concerning the void size. In the case of bisphenol A based epoxy, as used in real GIS spacer insulators, we find clear indication that air-filled voids can be reliably triggered to diameters down to 0.3mm. Below this limit, the deposited charge becomes small and approaches the detection limit of the PD system. Therefore we conclude that our method is not limited by the size of the void.