All-Inorganic Electrical Insulation Systems for High-Power Density Electrical Machines

This paper introduces the concept of ‘All-Inorganic Electrical Insulation (EI) System’ to enable the next generation of high-power-density electrical machines (EMs) that can operate at extreme conditions, namely high voltages (V) up to 1 kV DC and high temperatures (T) up to 500°C. The feasibility was explored for this concept using experiments and simulations by investigating the inorganic materials adapted to design high-T and high-V EMs. Candidate materials are (i) developed for magnet wire insulation and (ii) selected for a slot filler. In particular, employing physical vapor deposition (PVD), aluminum nitride (AlN) ceramic thin-film coatings were developed on Cu conductors. The experimental results demonstrate very high dielectric breakdown field strength (1 kV/micron for > 90 nm coatings) and thermal conductivity (290 W/m·K at room T (RT), 160 W/m·K at $\mathrm{T} = 300\ ^\circ \mathrm{C}$), surpassing existing thin-film insulating materials. Thermal simulations using MotorCAD software compare conventional organic insulation of magnet wires with the AlN coatings. The AlN insulation alone potentially reduces operating T by 6 °C, enhancing EM efficiency. Combining AlN coatings with a selected high thermal conductivity slot filler at 500 °C enables fivefold heat dissipation, boosting potential power density by 50%. These findings demonstrate the potential of all-inorganic EI systems to deliver a step change in high-T EM design for aerospace, traction, and nuclear applications.