Condition assessment of generator stator insulation by DC ramp and IR tests

This paper proposes a method of condition assessment of generator stator winding insulation by simultaneously fitting time variation of Insulation Resistance (IR) and DC Ramped voltage plots. The insulation conductivity (σ), permittivity (ε) and response function (f(t)) was used for the assessment. A novel model which derived starting from the frequency domain dielectric response is proposed to model DC Ramp and IR test results. DC ramp, IR and FDS tests were conducted on a non-aged epoxy mica insulated winding sample to verify the proposed model. In a separate laboratory investigation, FDS measurements were conducted on Asphalt-mica and Epoxy-mica insulated winding samples to analyse the parameter variation during artificially ageing and drying. In parallel, DC ramp and IR tests were conducted on field aged windings and their conditions were assessed by the test results and the estimated parameters.