Study on the Influence of Space Charge on the Upward Leader Emerging From the Conductors of UHVDC Transmission Lines

The space charge produced by the glow corona from tall objects is known to inhibit the initiation of upward leaders. However, in contrast to consideration of the glow corona at the surface of conductors caused by thunderclouds, the inhibitive effect of ion flow on the initiation of upward leaders from conductors due to dc operation voltage has been relatively neglected in previous studies of the leader progression model. In this paper, the glow corona at the surface of a conductor due to the thundercloud and the operation voltage have been analyzed quantitatively and compared with each other. It is found that the influence of the operation voltage on the distribution of ion flow is the largest in the area near the conductor. Since the operation voltage has a greater influence on the inception of the upward leader than the thundercloud, it should therefore also be considered in the leader progression model. A new simplified model is hence proposed to account for the distribution of ion flow under thundercloud conditions. In addition, a simulation experiment is designed to study the influence of ion flow on the initiation of the upward leader from a 6-bundled conductor, and the results are used to verify the validity of the simplified model. Finally, the model is applied to assess the influence of ion flow on the inception of upward leaders under different lightning currents. The calculation results show that the ion flow causes the upward leader to incept later, and reveal that the influence of the thundercloud on the inception of the upward leader is small, although it influences the distribution of the ion flow significantly.

I. Introduction

Lightning shielding failure is the major cause of outages for transmission lines operating at 500 kV and above [1], [2]. For UHVDC transmission lines, the glow corona at the surface of a conductor caused by the interaction of a thundercloud with the operation voltage is significant before the approach of the downward leader. The existence of the space charge caused by this glow corona may influence the inception of the upward leader and, thus, change the exposed area of the conductor.