Time Resolved Measurements of X-ray Induced Partial Discharges

The initial statistical time lag of partial discharge (PD) measurements was eliminated by using short x-ray pulses (duration 50 ns) for triggering. Phase resolved PD (PRPD) patterns at low electric field levels were recorded. No significant difference between the PRPD patterns after x-ray pulse triggering and naturally incepted PDs was observed. These measurements were performed with self-produced spherical void samples and even voids of 0.5 mm were detected after one x-ray pulse application. It is assumed that the x-ray pulses provide necessary start electrons to start an avalanche. However, in order to study the effect of the x-ray pulse on the triggering and on the discharge mechanism, time resolved PD measurements with an ultra-wideband detection circuit are necessary. In this work, the classical wide-band PD detection circuit was modified and time resolved measurements were performed. Particular emphasis is placed on the effect of the x-ray dose on the first PD pulses, here shown for one void size. Moreover, the temporal development of subsequent discharges after the total decay of the x-ray pulse is studied. To increase the accuracy of the detection, optical measurements of the discharge are synchronously made with a photomultiplier tube.