Partial discharges and breakdown voltage diagnostics during thermal aging of insulating materials

This paper is focused on thermal aging and accompanied partial discharge diagnostics of two mainly used resin rich mica tapes, which are utilized as a part of insulation system of large rotating machines like turbo or hydro generators. The first tested specimen was mica composite material based on glass fibre and epoxy resin and the second one was composite based on PET and epoxy resin as well. The specimens were tested under laboratory conditions. The materials were thermally aged and the changes of its physical and chemical properties were measured and evaluated. For accelerating the aging process different temperature values (170 – 186 °C) were chosen. The aging time was determined for each temperature value. Specimens of tested material were performed and cured as flat plate 100×100 mm. The measuring of these specimens was carrying out by test voltage at special electrode test setup. For comparing the aging process of the investigated material the trends of measured partial discharge (pd) parameters (inception voltage, extinguish voltage, peak charge level) were studied and described in dependence on exposure time, temperature and applied voltage during measurement