Study on the Influence of the DC Voltage on the Upward Leader Emerging From a Transmission Line

The evaluation of the lightning shielding failure of a transmission line is very important in power transmission system design, and the operation voltage has rarely been considered before. However, when the operation voltage reaches 800 kV and the tower height is near 100 m, the influence of operation voltage may not be ignored. In this paper, an experimental system consisting of an air gap between a plate/rod and a conductor was established, where the dc voltage could be applied to the conductor and was accompanied by a negative impulse voltage on the plate/rod electrode. An upward leader up to 1.54 m in length was observed, and the leader velocity and charge density were obtained in a 11-m-long air gap, whereas the voltage on the conductor was 800-kV dc. The influence of dc operation voltages on the upward leader was studied. The experimental results showed that the upward leader will emerge much earlier and may progress longer with dc operation voltages. That is, the lightning attachment to the conductor may occur more easily when the voltage of the conductor is opposite in polarity to that of the downward lightning than when the conductor has no operation voltage.