Influence of temperature on developing processes of surface discharges in oil-paper insulation

In order to study the influence of temperature on the developing processes of surface discharges in oil-paper insulation, a discharge test assembly was established to simulate the surface discharges in transformers, which consisted of a surface discharge model, a test rig and a PD detect complex. Long-term laboratory tests under 60°C, 90°C and 100°C were conducted to observe the entire evaluation process of surface partial discharges from its inception to the eventual occurrence of flashover, using boosting voltage application. PD was detected by conventional impulse current (CIC) signals. Phenomena and features of surface discharges at different developing stages were observed and captured by a camera. The experimental results show that, (a) as the oil temperature increases, the PD inception voltage and flashover voltage gradually descend; (b) the destruction to pressboard is much serious under high temperature. These features could be used as criteria to infer different evolutionary stages of surface discharges under different temperatures.