Impact of temperature on the PDIV of induction motor turn insulation analogy in dry air

This work investigates the impact of temperature on the partial discharge inception voltage (PDIV) of an induction motor turn insulation analogy in dry air. This analogy consist of a pair of contacting aluminum electrodes coated with a ≈60–80 µm-thick layer of polymer. Based on a previously published breakdown prediction model and references found in the literature, the PDIV variance due to temperature is assumed to be mainly affected by the coating's relative permittivity—a function of temperature and test voltage frequency—and the density of ambient air. To separate and investigate these effects individually, perfluoroalkoxy alkane (PFA) and polyamide (PA) coatings are used. The relative permittivity of PFA is almost invariant to both temperature and frequency within the ranges examined in the work (25 ∘C–105 ∘C and 10–50 000 Hz, respectively), whereas PA's shows a substantial dependence on both. PDIV and PD extinction voltage (PDEV) values obtained from measurements over the temperature and frequency ranges are compared to predictions obtained from the breakdown model and good agreement with a maximum deviation of 100 V (peak) is obtained for the PA samples. For PFA samples, measurement challenges and substantial differences between the PDIV and the corresponding PDEV due to PFA's characteristic properties are discussed. In view of these limitations, the agreement between the model and the experiment is also considered satisfactory for PFA. The provided model, which considers only thermally-induced changes in the coating's permittivity and air density, is regarded as suitable for predicting the PDIV in systems similar to the turn insulation of induction motors, under the influence of temperature and assuming negligible ambient air humidity.