With the expanding frequency range of power equipment, understanding the frequency-dependent insulation performance of air becomes crucial. To address this, this paper establishes an integrated electrical–optical measurement platform for air breakdown to study the variation patterns of electrical and spectral characteristics of air breakdown at different frequencies. The effects and underlying mechanisms of different frequencies (20 Hz, 50 Hz, and 1 kHz) on the breakdown voltage are explored. Experimental results indicate that the air breakdown voltage increases with frequency as follows: from 17.7 kV at 20 Hz to 18.0 kV at 50 Hz (1.7% increase) and further to 18.9 kV at 1 kHz (5.0% increase from 50 Hz), representing a total increase of 6.8% across the 20 Hz to 1 kHz range. Regarding spectral characteristics, the spectral line intensity enhances with an increase in frequency. Compared to 20 Hz and 50 Hz, the spectral lines of nitrogen ions and oxygen ions become distinctly visible at 1 kHz, the Stark broadening phenomenon intensifies, and transitions from higher vibrational energy levels are enhanced relative to those from lower levels. Analysis via the Boltzmann plot method reveals a negative correlation between electron temperature (Te) and frequency, while the ionization degree (η) shows a positive correlation. Concurrently, the electron drift velocity (vd) increases with frequency, whereas the mean free path decreases (λ). Based on the parallel-plate capacitor model, the air breakdown under the experimental conditions of this study is dominated by collision ionization. As frequency increases, dielectric recovery slows down, and the memory effect strengthens. The interplay between these two competing factors leads to an increase in breakdown voltage with an increase in frequency within the 20 Hz to 1 kHz range. The findings of this study demonstrate that air breakdown exhibits significant frequency dependence, and its breakdown voltage shows statistical distribution characteristics (Weibull parameters) that vary with frequency. This article provides a reference basis for the design of sinusoidal air insulation in the 20 Hz to 1 kHz frequency range.
Wang et al. (Sun,) studied this question.