Dielectric response of rotating machine stator insulation system

In order to assess the state of the rotating machine insulation winding system, time-domain dielectric measurements are frequently conducted. Time-domain measurements are commonly used in the field in the form of polarization/depolarization test (PDC), high voltage ramped test or other type DC tests. Such measurements, which are related to the low-frequency dielectric response of the insulation system, depend on the insulating materials, the way the components of the insulation system are laid out, the aging of the materials and on external factors such as temperature, moisture absorption or contamination. In the paper, measurements conducted in the time domain are presented for modern epoxy mica winding insulation technology. The influence of the temperature is investigated for epoxy-mica insulation systems for stator bars and a correction procedure for insulation resistance (IR) for epoxy mica insulation is suggested.