MS student Brian Wolhuapter with Advisor K. Haran

Current insulation materials for electric machines are limiting our ability to improve machine power densities. Polymers have been used as machine insulation for decades, but they are not the perfect material class for machine insulation. While they have good dielectric properties, they have low thermal conductivity, low temperature rating, and are susceptible to partial-discharge-induced damage. The low thermal conductivity traps heat in the machine, raising the temperature and accelerating the degradation of the polymer insulation. Ideally, insulation would have similar dielectric properties to polymers, but with better thermal properties to maintain its insulative properties for longer and at higher temperatures. Technical ceramics meet these requirements, but they are difficult to use as machine insulation, especially for machine groundwall insulation.

My research, funded by the Grainger CEME, addresses these challenges by investigating plasma-sprayed ceramic coatings as a potential solution. These coatings allow for layers of ceramics to be applied directly to stator cores without the need for an intermediate bonding material. Currently, I am running an experiment investigating the electrical properties of plasma-sprayed aluminum oxide (Figure 1) over time in an isothermal aging test. It is being compared to polyimide (A), aramid (B), and sintered aluminum oxide (C), materials well investigated as electrical insulation. This is necessary because the long-term electrical properties of these coatings are unknown. To be used in electric machines, it is necessary that the insulation maintain its properties throughout the machine lifetime.

Figure 1. Plasma sprayed coatings: A: polyimide, B: arimide,
C: sintered aluminum, D: aluminum oxide.