On the Leader Inception and Propagation of DC Conductor Under Equivalent Near-Ground Electric Field of Downward Lightning

Lightning shielding failure is the major threat to safe operation of UHVDC transmission lines. The spatial charge generated from corona discharge of conductors under DC operation voltage affects lightning shielding failure, with the exact impact unclear. The voltage waveform from a Marx impulse voltage generator can't accurately simulate the electric field changes around conductors during lightning downward leader propagation towards the ground. In this paper, a novel impulse voltage generator with a controllable capacitive charging unit was applied a negative impulse voltage to the plane, simulating the electric field of lightning downward leader approaching the ground, while a positive DC voltage with amplitude of 50 kV was applied to the conductor. This setup aimed to study the leader inception and development under the combined effect of DC operation voltage and equivalent near-ground electric field of downward lightning. The effect of varying DC operation voltage amplitude on leader inception and propagation was explored. Results showed that as the DC voltage increased, the time of leader inception was delayed, and the time of gap breakdown shortened. The current during the stable leader development phase decreased from 8 A at 10 kV DC voltage to 4 A at 30 kV DC voltage. Also, the initial leader development speed slowed with increasing DC voltage. This indicated that the space charge from conductor corona discharge under DC voltage suppressed leader inception and propagation. The findings offered experimental evidence for analyzing lightning shielding failure in UHVDC lines.