Abstract
Electric machines with high specific power are crucial for the more electric aircraft propulsion. However, the harsh operating environment such as low air pressure and high temperature will challenge the motor’s insulation system and cause partial discharge (PD), which threatens the reliability of the machine. This article proposes a PD-free stator winding design regarding an air-core high-frequency permanent magnet synchronous machine for aircraft propulsion. The experiment and simulation are performed under sinusoidal voltage due to the power quality requirement by the standard for aircraft. PD inception voltage (PDIV) with respect to air pressure and temperature was obtained experimentally for form-wound windings and was analyzed to derive the PD-free criteria. A 3-D stator model was built and used to simulate the electric field and temperature distributions with a finite-element method. In addition, the effect of voids and delamination on electric field distortion was also taken into consideration to allow for a safety margin and meet the PD-free requirement. To achieve high-specific-power requirement and PD-free requirement simultaneously, a multiobjective genetic algorithm was adopted to perform the optimization and obtain the Pareto fronts at various air pressures. Finally, the PDIV value of the designed winding was measured to verify the PD-free design. The main purpose is to combine the experimental results and the simulation tool to obtain an acceptable PD-free design in the meantime achieving high power density, which may provide helpful guidance on motor insulation design for the more electric aircraft propulsion.
Highlights
E LECTRIC aircraft attracts increasing attention because the conventional nonelectrical system will be replaced by the more electrical system to improve efficiency, and to reduce weight, fuel cost, and carbon emission [1]–[3]
According to IEC 60270, PD inception voltage (PDIV) is defined as the applied voltage at which repetitive partial discharge (PD) are first observed in the test object when the voltage applied to the object is gradually increased from a lower value at which no PD is observed
The results indicate that the introduction of defects to the form-wound winding decreases the PDIV to some extent, which is reasonable and agrees with general understanding
Summary
E LECTRIC aircraft attracts increasing attention because the conventional nonelectrical system will be replaced by the more electrical system to improve efficiency, and to reduce weight, fuel cost, and carbon emission [1]–[3]. The most challenging part of electric propulsion lies in the high specific-power requirement and long-time reliability of the electric machine, especially when it operates at high-voltage and low-pressure conditions. The electric machine on an aircraft may experience 0.2-atm air pressure at a cruising altitude of 11.9 km [5], which will pose huge threats to the stator winding insulation. Since the electric machine for aircraft propulsion will inevitably operate under high altitude conditions, the effect of low air pressure on PD magnitude, phase distribution, and insulation degradation needs profound exploration. This article presents the possible PD challenges to the insulation of these form-wound windings when they are used for electric aircraft propulsion. The form-wound windings and those with four typical insulation defects, which represent the general causes of stator insulation failure, are electrically pressed under various pressures. This article may provide insight and useful suggestions to reliable stator insulation design for electric aircraft propulsion
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