Partial discharge inception characteristics by different measuring methods in magnet wire under surge voltage application

We have been investigating the PD activities of magnet wire for inverter-fed motor under surge voltage application. In this paper, we obtained and compared PD inception characteristics by using different measuring methods and discussed PD generation mechanism in consideration of surface charging. PD signals were detected by electrical, optical and electromagnetic methods using high-frequency current transformer (CT) with balance circuit method, photo multiplier tube (PMT) and monopole antenna. Experimental results firstly revealed that PD inception voltage (PDIV) measured by PMT was the lowest, i.e. PMT exhibited the highest sensitivity for PD detection under surge voltage. Secondly, the surface charging on enameled wire caused by PD at the rise time of surge voltage could generate PD at the fall time of the surge voltage. Furthermore, according to the overshoot factor of surge voltage, generation probability of initial electrons and so on, PD could be generated not only at the rise time and fall time of the surge voltage, but also in the plateau duration.