MS student Brian Wolhaupter with Advisor K. Haran

Last semester, we concluded an initial investigation into the long-term insulative properties of plasma sprayed ceramic coatings (PSCC) for usage as electric machine slot insulation.  To evaluate the insulative properties over time, an isothermal aging test was employed to accelerate the thermally induced degradation of the insulation materials.  The test was run for 216 hours of aging at 315°C which simulates roughly 20,000 hours of continuous use at 220°C according to the Arrhenius equation.  Figure 21 shows the partial discharge inception voltage (PDIV) of the Kapton, Nomex, aluminum oxide (alumina), and the plasma sprayed aluminum oxide. Although the plasma sprayed ceramic coating does not have the initial insulative properties of the Nomex, the Nomex degrades rapidly towards the end of its life, whereas the PSCC sees a small improvement.  We do not believe there was an improvement in the PSCC, but rather a change in environmental conditions.  During testing, we observed a sudden decrease in the PDIV of the PSCC, but this was attributed to the samples sitting on a lab bench over a humid weekend, rather than immediately testing them after they came out of the oven.  Baking the samples for approximately 30 minutes at 125°C returned the PDIV to the original levels.  This humidity dependance must be considered when designing a machine with this insulation, since an increasing humidity could result in insulation failure.  However, the lack of degradation over the expected life of a machine warrants further investigation since the improved thermal conductivity and acceptable insulative properties enable higher power densities by reducing the hot spot temperature inside the motor slot, ensuring the longevity of the more fragile turn insulation on the conductors.

Figure 21. Final comparison of the partial discharge inception voltage over the course of the experiment for the materials included in the study.