Conference Agenda

The transition toward sustainable aviation requires the electrification of propulsion systems, encompassing hybrid-electric, fully electric, and hydrogen fuel cell technologies. While high-voltage systems offer enhanced power density, they also introduce significant electrical insulation challenges under high-altitude conditions, where pressure, temperature, and humidity vary considerably. This study investigates partial discharge (PD) characteristics of motor winding insulation under low-pressure conditions (from atmospheric pressure down to 4 kPa) using both sinusoidal and repetitive pulse waveforms. An arrow-pair model with insulated conductors was tested in a controlled-pressure environment. The results indicate that reduced pressure increases PD current amplitude and expands the luminescence region, while also extending the PD current pulse width and shifting the frequency spectrum toward lower frequencies. Additionally, under repetitive pulse conditions, the PD extinction voltage (PDEV) decreases significantly relative to the PD inception voltage (PDIV) due to a reduced availability of initial electrons. These findings emphasize the necessity of considering the PD characteristics specific to low-pressure environments in insulation design to enhance the reliability of electric aircraft propulsion motors.

　Inverter-fed motors are increasingly utilized due to their energy-saving and high efficiency. However, electrical insulation systems are susceptible to premature failure when exposed to inverter surge voltages. These surges arise from impedance mismatches among the inverter, motor, and cables. Notably, inverter surge voltages with short rise times tend to be concentrated in the first coil, leading to increased voltage stress on turn insulation, potentially causing layer short circuits.

　In stator windings powered by a commercial power supply, voltage is evenly distributed. However, with an inverter power supply, the voltage distribution becomes uneven, resulting in higher turn-to-turn voltage in the first coil. To account for this, turn insulation is designed with a higher margin, increasing copper losses, and necessitating a larger motor frame size.

　To establish an optimal electrical insulation system, understanding voltage distribution across each coil is essential. Direct measurement is challenging, so simulation is a valuable alternative. This paper presents measurement and simulation results using impulse voltages with varying rise times.

　The charging voltage of the power supply’s capacitor was set to 1.0 kV, with an output impulse width of 20 µs, and rise times of 150 ns, 400 ns, and 850 ns. The impulse voltage was applied to the first coil of phase U, with both the neutral point and frame grounded. The waveform was recorded using an oscilloscope with a high voltage probe.

　An equivalent circuit was developed using LTspice. The motor’s circuit constants were determined through theoretical calculations. The circuit parameters of the impulse power supply were set according to design specifications. To ensure consistency, the rise times in the simulation were set to 150 ns, 400 ns, and 850 ns.

　Using measurement results, impulse voltage rise times were applied to simulate coil-to-coil voltage and turn-to-turn voltage of the first coil. A comparison revealed general agreement in voltage distribution and turn-to-turn voltage. However, a discrepancy of up to 20% was observed in the coil-to-coil voltage, likely due to the rising portion of the impulse voltage and mutual inductance between coils. These results suggest simulations are valuable for understanding voltage distribution, with accuracy improving by adjusting equivalent circuit constants. Model simplification is crucial for enhancing simulation efficiency.

　Future research will explore multi-level inverters, pulse width, winding temperature variations, and rotor influences on voltage distribution. Additionally, investigating insulation material properties and their aging degradation over time could provide valuable insights.

The flight control system is critical for ensuring aircraft safety and precise maneuverability, and the Electro-Hydrostatic Actuator (EHA) system represents a key technology for future more-electric and all-electric aircraft. This study takes a 270 V random-wound motor as the research object and establishes three-dimensional electrostatic field models of turn-to-turn, phase-to-phase, and main insulation using physical field simulation software. Electric field distributions and Partial Discharge Inception Voltage (PDIV) under various insulation gap sizes are analyzed by applying Paschen's law. The results indicate that the errors between measured and predicted PDIV values are within 15%, providing valuable guidance for insulation design, optimization, and reliability evaluation of EHA motors.