Partial discharges of thermally and electrically aged insulation

The working life of electrical machines is primary affected by the insulation system quality. Diagnostics methods help to understand the momentary state of insulation and to avoid the possible damage or electrical breakdown of machines through the repair or insulation rewinding. Partial discharges testing belongs to one of the high applicable test method of insulating materials within electrical machines. The described experiment consists of laboratory thermal and electrical aging of main wall insulation and consequently testing of partial discharges. The test material consists of resin rich mica composites based on glass fabric and epoxy resin. The flat specimens of insulation were cured and thermally and electrically aged and the partial discharges were measured accordingly. The thermal aging was performed at four different temperatures (170, 175, 180, 186°C) at different times. The electrical aging was completed at two different voltage levels (10, 12 kV) at different times. The flat specimens were tested at special electrode setup. The conductive rubber electrodes were used to avoid the gliding discharges on the surface of specimen. The trends of partial discharge main parameters (ignition voltage, extinguish voltage, pulse count, average discharge current, peak charge level) are studied and described in dependence on exposure time, temperature and applied voltage.