Fluctuation of partial discharge inception voltage and discharge location of twisted pair sample under repetitive impulse voltage

Partial discharge inception voltage (PDIV) of twisted pair under repetitive bipolar impulse voltage was found to fluctuate as PDIV measurements repeat. In this paper the discharge location is observed to each PDIV measurement using high-sensitive CCD camera just after PD inception. The result shows the PD location changes as measurements repeats; discharge occurs in a whole air gap between two wires in the early stage, then it tends to concentrate at local sites in the final stage. In the middle stage discharge location behaves complicatedly. The PD behavior was discussed in relation with surface conductivity of enameled wire and discharge product in air.