Insulation design of low voltage electrical motors fed by PWM inverters

L. Lusuardi, A. Cavallini, M. G. de la Calle, J. M. Martínez-Tarifa and G. Robles, “Insulation design of low voltage electrical motors fed by PWM inverters,” in IEEE Electrical Insulation Magazine, vol. 35, no. 3, pp. 7-15, May-June 2019.

doi: 10.1109/MEI.2019.8689431

Abstract— This paper proposes a model to determine the partial discharge inception voltage of magnet wires, including the effect of elevated temperatures, and shows its applicability to the complete range of wire geometries considered in IEC Standard 60317-13.

For long, the insulation of magnet wires used in low voltage motors was mostly stressed by temperature and vibrations. In addition, moisture sometimes hastened thermo-mechanical stress by hydrolyzing the insulation leading to crack formation. The ultimate breakdown mechanism was an excessive leakage current throughout cracks and pinholes in the insulation. Within this framework, the thickness of the insulation was dictated mostly by mechanical considerations, to prevent crack formation during manufacturing and operation. Electrical stress did not play a key role in the aging process.
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Keywords— inverter-fed machine, partial discharges, insulation design.