Although the increase in frequency improves the transmission efficiency of high-frequency transformer, a higher probability of insulation failure is caused by high-frequency partial discharges. Through a high-frequency experimental platform, emission spectrum tests on two types of insulation faults were carried out under high-frequency square wave voltages. Subsequently, the influence of frequency and voltage amplitude on the light intensity and the number of photons of emission spectrum caused by air corona were studied. Finally, the variation of the spectrum of the partial discharge occurring at the interface of gas-solid insulation with frequency was analyzed. The results show that, the characteristic spectrum of air corona is composed of the near-ultraviolet spectrum, which is caused by the energy level transition of N2 molecules, and the number of photons of air corona is positively correlated with voltage amplitude and frequency. Partial discharges at the gas-solid insulation interface have band spectrums in the visible light region and the near-infrared light region except for the near-ultraviolet spectrum due to the energy level transitions of outer layer electronics and the vibrations of C-H chemical bonds of PET molecules. This paper preliminarily verified the feasibility of applying the emission spectrum diagnostic method to two typical partial faults under high-frequency square wave voltages.

When lightning impulse voltages invade substation equipment via transmission lines, the oil-paper insulation is subjected to bipolar oscillation impulse voltage with variable waveform parameters. As one of the most critical failure modes, the creeping discharge characteristic under bipolar oscillation impulse voltage remains unclear. This paper establishes a platform for generating bipolar oscillation impulse voltage with adjustable waveform parameters and investigates the effects of these parameters on creeping discharge characteristic. The results indicate that, under a single application of bipolar oscillation impulse voltage, the breakdown voltage increases with the damping factor following a power-law relationship and increases linearly with the oscillation frequency. The cumulative effect was analyzed through the V-N characteristic, and it is proposed to use the negative reciprocal of the exponential term in the V-N equation as the cumulative coefficient to quantify the strength of the cumulative effect. Within the experimental conditions, as the damping factor and oscillation frequency increased, the cumulative coefficient rose by 40.5 % and 6.7 %, respectively, suggesting that the cumulative effect of creeping discharge weakened. The growth of white marks and changes in characteristic peaks in spectra of Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) on the pressboard surface indicate that impulse voltages trigger the cracking of cellulose chains and the formation of gas channels. Under the cumulative application of the impulse voltage, each creeping discharge progresses along gas channels formed by previous discharges, expanding the damage and degrading the insulation step by step. This study provides insights for optimizing transformer insulation design and mitigating the risk of insulation failure.