Method for calculating corona inception voltage of ultra-high-voltage direct current transmission lines with frequency-domain characteristics of corona current

Corona inception voltage is of great significance for the design of ultra-high-voltage direct current transmission lines. In this study, based on the change rule of frequency-domain characteristics of corona current, a new method for calculating corona inception voltage is proposed. First, corona current waveforms are collected through experiments and the range of measuring voltages is determined according to the frequency spectrum characteristics of corona current. Then, the curves representing the relationship between the change rate of corona current octave power and the voltage at different centre frequencies (6–20 kHz) are obtained through least-square fitting. The voltage at which the fitted curve reaches the first peak value with the rise of voltage is identified as corona inception voltage. Finally, with the proposed method, the corona inception voltage for a six bundled conductor system in the biggest outdoor corona cage of the world is obtained. Combined with the experimental results of A-weighted sound level of audible noise, the comparisons between the obtained corona inception voltage and that calculated with I/U − U curve fitting method, I − U curve fitting method and an audible noise-based method prove that the proposed method is reasonable.