Failure mechanisms of dielectric materials for electric motors

Recent trends in electrification have increased demand for advanced sensors and actuators in the transportation and power systems industries. Complex thermomechanical systems used in geothermal energy, industrial gas turbines, aircraft propulsion systems, and spacecraft power systems require high power density devices that generate large amounts of heat in a smaller form factor. The community has looked to high critical flux cooling technology as well as higher-temperature materials development to address these needs. However, the development of high-temperature actuators, like electric motors, has lagged behind the development of high-temperature sensors and circuitry. This study explores the thermal operating limits of electric motor insulation to develop design and downselection criteria for developing high-temperature insulation materials that will meet the demands for high power density in industrial applications. A preceramic resin, polymethylsilsesquioxane, is first used to demonstrate that motor insulation can operate up to 660◦C with a dielectric strength of 162 VRMS, outperforming the stateof-the-art ML240 insulation commonly used in commercial motors. Then, insulation materials spanning a range of chemical structure motifs are used to build electric motor prototypes to determine the excitation current, force, and temperature windows in which each material can operate at the device level. Surprisingly, devices made with ML240 insulation - which has a 663◦C lower intrinsic thermal stability than ceramawire insulation - outperform ceramawire devices by nearly 60◦C. An investigation of the underlying failure mechanisms of the insulation was conducted to explain this result, revealing that thermal expansion-induced mechanical stresses dominate over intrinsic thermal stability in determining the critical failure temperature of a device. To account for these stresses in the development of new, high-temperature insulation materials, a thermal expansion model is developed to downselect materials based on their thermomechanical properties and predict their device-level performance without building experimental device prototypes. This model can be used by both materials scientists and motor engineers to tailor the operating temperature window of film-insulation materials and meet the thermal requirements of a given application.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste