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Emerging power electronic drives and converters, especially wide bandgap (WBG) technology-based devices, are expected to operate at high voltages and switching frequencies, potentially reaching up to several hundred kHz. These operating conditions pose significant challenges to the reliability of insulation systems in motor windings, which are critical to the longevity and safe operation of electrical machines. This study investigates the impact of high-frequency square wave voltage pulses on the lifetime of motor winding insulation by conducting lifetime tests on twisted pair magnet wire commonly used in electrical machines. The experiments were conducted in the frequency range of 100 kHz to 300 kHz, with rise times of 50 ns and 400 ns (slew rate ranging from 2.4kV/μ s to 19.2kV/μs), to simulate the conditions typical in modern power electronics and inverter-driven systems. The results show that fast rise times and high switching frequencies influence turn-to-turn insulation's aging and breakdown characteristics. The findings highlight the importance of switching frequency and rise time in determining the reliability of insulation systems, offering critical data to enhance the design and performance of electrical machines in the context of high-frequency operation.
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This content will become publicly available on September 14, 2026
Impact of Frequency on the Breakdown Voltage in Litz Wire Under Square Wave Excitation
Wide bandgap (WBG) and ultra-wide bandgap (UWBG)-based inverters are increasingly being adopted in More Electric Aircraft (MEA) and All Electric Aircraft (AEA) due to their ability to operate at higher switching frequencies with improved efficiency and power density. However, these advantages come with drawbacks, including increased electrical stress and exacerbation of AC losses, such as the skin effect and proximity effect. Litz wire, known for its effectiveness in mitigating these losses, is becoming a preferred conductor in highvoltage, high-frequency aerospace applications. This study investigates the breakdown voltage behavior of Litz wire insulation under square wave voltage stress across different frequencies. Twisted-pair Litz wire specimens were tested using a state-of-the-art high-voltage pulse generator with fixed rise times to emulate inverter-fed conditions. The resulting breakdown voltages were statistically analyzed using the Weibull distribution to evaluate insulation strength and failure predictability. The findings offer new insights into the insulation characteristics of Litz wire under realistic high-frequency converter stress and support the development of converter-resistant insulation systems for next-generation aerospace electrical power systems (EPS).
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- Award ID(s):
- 2306093
- PAR ID:
- 10652890
- Publisher / Repository:
- IEEE
- Date Published:
- Page Range / eLocation ID:
- 133 to 136
- Format(s):
- Medium: X
- Location:
- Manchester, United Kingdom
- Sponsoring Org:
- National Science Foundation
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