Influence of Corona Space Charge on Subsequent Streamer Inception from Horizontal Conductors during Lightning Attachment Process

the space charge generate by the corona discharge near the UHVDC overhead transmission lines can distort the electric field distribution under thunderstorms. this paper presents a numerical model to estimate the corona space charge produced by horizontal conductors in response the electric field generated by both thundercloud and downward leader. Secondly, the corona space charge development process from ground conductors was obtained. The transition process of corona discharge to subsequent streamer is analyzed. the inhibition effect of the space charge layer on the subsequent streamer initiation was calculated by considering different conductor diameters. It is concluded that there is an optimal diameter for horizontal conductors which can ensure a superior capability to launch subsequent streamers, which should achieve a corona-free condition under the electric field of thundercloud.

I. Introduction

The lightning shield failure of UHVDC overhead transmission lines can cause unexpected interruptions of remote power transmission. According to the observation data, more than 90% lightning trip-outs occurred on the positive pole. It suggests that this polarity effect might be caused by the positive corona space charges generated by the positive pole of UHVDC transmission lines, because most of cloud to ground flashes have negative polarity^{[1] [2]}. When the ambient electric field generated by the thundercloud and downward leader increases, the electric field of positive pole conductor can be enhanced and cause the initiation of positive corona discharges. The positive ions will move along the electric field flux to form a space charge layer above the conductors, which can distort the distribution of electric field. Therefore, the subsequent lightning attachment process can be affected by the appearance of space charge layer. However, the widely adopted lightning shielding performance estimation method EGM (electro-geometric model) of overhead transmission lines does not consider the influence of space charge^{[3] [4]}.