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This study quantifies the frequency-dependent dielectric breakdown of Litz wire insulation under repetitive bipolar square-wave voltages, simulating wide-bandgap power converter stress. By testing 14 and 16 AWG conductors at frequencies from 1 kHz to 30 kHz and analyzing results with Weibull statistics, it reveals a significant decrease in mean breakdown voltage with increasing frequency, particularly for smaller conductors. These findings offer critical, construction-specific data for assessing Litz wire reliability in high-frequency power electronics.
Litz wire insulation breaks down 20% lower at 30 kHz than at 1 kHz, revealing a critical frequency-dependent degradation mechanism for high-power converters.
This paper investigates the dielectric breakdown behavior of Litz wire insulation subjected to repetitive fast-edge bipolar square-wave voltages representative of wide-bandgap (WBG) power converter stress. Two conductor sizes, 14 AWG and 16 AWG, were tested in a twisted-pair configuration over frequencies ranging from 1 kHz to 30 kHz using a controlled high-voltage pulse generator with 200 ns rise time. The breakdown voltages obtained at each frequency were statistically analyzed using the weighted two-parameter Weibull method in accordance with IEEE Std 930-2004. Between 1 and 30 kHz, the mean breakdown voltage decreases by approximately 10.7% for the 14 AWG construction and 20.0% for the 16 AWG construction. The 14 AWG specimens exhibit a modest increase between 1 and 5 kHz followed by a decline, whereas the 16 AWG mean decreases across the tested frequencies. The Weibull shape parameter varies nonmonotonically with frequency, characterizing differences in the dispersion of the measured breakdown voltages. These findings provide construction-specific breakdown data relevant to Litz-wire insulation assessment in high-frequency power electronic applications. Possible contributions from charge accumulation, localized discharge activity, and dielectric heating are discussed, but were not directly verified in this study.