Discharge characteristic in ELF — ULF bands under non-uniform AC field gap in synthetic air

The frequency characteristics of AC discharge under non-uniform field gap were investigated in synthetic air. In the experiment, the frequency of AC high-voltage (ACHV) f was changed from 1 to 3,000 Hz. The gap distance of a needle to plane electrode was fixed at 1.0, 2.0 and 3.0 cm. As a result, in the case of positive corona observation, the corona mode at the corona onset voltage changed from streamer to burst due to the increase of f. Furthermore, the positive corona onset voltage decreased sharply when the corona mode changed to burst. That the frequency of which the positive corona mode changed to burst f_b was varied according to the gap distance. On the other hand, in the case of the negative corona observation, the corona mode at the corona onset voltage was constantly trichel pulse in spite of an increase of f. However, the negative corona onset voltage also decreased sharply when f was increased to f_b. Moreover, the negative corona onset voltage was slightly higher than the positive corona onset voltage in case of all gap distance. With regard to sparkover, the sparkover voltage gradually increased until f was increased to f_b. In contrast, after f was exceeded f_b, the spakover voltage decreased with increasing the frequency.