Investigating the inception mechanism of pulsed x-ray triggered partial discharges by time resolved measurements

In this work, the effect of ultra-short (50 ns) X-ray pulses on the triggering and the discharge mechanism of partial discharges (PD) in voids of solid insulation is investigated by time-resolved PD current measurements with an ultra-wideband detection circuit and a photomultiplier tube. PD current pulses from naturally incepted and X-ray incepted voids at different doses and different field strengths are compared. The PD pulse shapes of each inception are compared for rise-time, pulse-width and peak current amplitude. In addition, the potential effects of X-rays on the solid insulation material itself are discussed. It is shown that no negative effect of the X-ray pulse on the solid insulation is expected and that no significant differences are found between X-ray and naturally incepted PD. However, the first pulse of each PD inception is distinctly different compared to all subsequent pulses, especially with varying applied field strengths at the instant of inception. It is concluded that the method of using ultra-short X-ray pulses to trigger PD is generally applicable and only those voids are triggered that would have incepted naturally with longer waiting times. No particular overvoltage stress is needed to test the insulation system.