Laboratory and Field Investigations of Generator Stator Insulation

This Paper presents the condition assessment of synchronous generator stator insulation used in Sri Lankan power stations. The work has three parts i.e. theoretical, laboratory and field investigations. In the first part, theory behind dielectric insulations have been broadly discussed with the aid of different non – destructive test methods used to assess the conditions of the generator insulation. In the laboratory investigations, two naturally wetted asphalt mica, one dry polyester mica and one dry epoxy mica spare stator windings were tested under drying and wetting conditions. The used test methods were DC ramp, time variation resistance (IR), polarization and depolarization current (PDC), frequency dielectric spectroscopy (FDS) and partial discharge (PD) tests and the relationships have been est5ablished among them. In the field investigations, different generators belonging to Ceylon Electricity Board were tested by using DC ramp test. It was found that the DC ramp test, as an easy and simple field test, can be effectively used to investigate the moisture effect on generator insulation.