Morphological characteristics of streamer region for long air gap positive discharge

Abstract

Knowledge of leader corona is the basis for long spark discharge modelling, which is critical to understand the underlying physics of lightning flashes and dielectric breakdown of long air gap widely utilized in power systems. This paper presents an accurate observation of the leader corona. The morphology of the leader corona region during the discharge was obtained using a high-speed camera and an image-enhanced charge-coupled device camera. Statistical results showed that the morphology of the streamer region varied at different discharge sub-phases. The first corona was a conical region with the average apex angle of 118.91°; the leader corona region behaved as a cone with an average vertex angle of 75.87° during the leader propagation process; the streamer area in the final jump was a combination of a cylinder and a cone with the average vertex angle of 82.61°. Noting that the obtained cone apex angle of the leader corona during the leader propagation phase was significantly smaller than that in photographical reports, and the observation results were related to the selected temporal resolution of the optical image apparatus. The discussion on the effect of the single-frame exposure time on observation results found that the average vertex angle of the conical streamer region gradually decreased with the decrease of the single-frame exposure time, and eventually tended to a stable value of about 75.96°. For comparison purposes, discharge experiments under two gap-distances demonstrated that on the premise of stable leader, the statistical distribution characteristics of the leader corona vertex angle were consistent, indicating the universal applicability to the simulation researches. Finally, it is found that the distortion of the electric field caused by the space charge explained the variation of the streamer area during the discharge process.

A machine learning‐based approach for dielectric strength prediction of long air gaps with engineering configurations

“…The physical descriptions about long air gap discharge revealed by experimental observations are helpful to guide the EF feature extraction. According to the photographical reports in literatures about the morphological characteristics of positive long air gap discharge, and the experience of physical models about streamer propagation, the streamer region is usually assumed to be a conical region that initiates from the sharp electrode, and then splits into many branches [6, 11, 33]. Inspired by this idea, we defined a conical zone between the energized conductor and the grounded crossarm or window.…”

“…Insulation design of high voltage transmission line relies on the determination of air gap discharge voltage. With the development of extra-high voltage (EHV) and ultra-high voltage (UHV) transmission and transformation technologies [1,2] in the past few decades, numerous studies have been conducted on long air gap discharge characteristics [3][4][5], experimental observations of discharge phenomena [6][7][8], and theoretical modelling of air discharge process under switching or lightning impulse voltages [9][10][11]. These studies reveal the propagation and transition mechanisms of streamer, leader and final jump during long air gap discharge process, and also develop various physical and engineering models aiming at simulation of different discharge stages and prediction of 50% discharge voltage (U 50 ).…”

Numerical simulation of the effect of atmospheric condition on the lightning strike for wind turbine

“…Meanwhile, the lightning development and attachment mechanism considering space charge density distribution were carried out by some researchers. Gu discovered the electric field distortion produced by the space charge and discussed the variation of the streamer during the discharge process [Gu et al, 2020]. To determine the mechanisms of corona and leader initiation for rotating wind turbines, Yu established a three-dimensional drift and diffusion model.…”

Multiple discharges before leader inception in long air gaps under positive switching impulses

“…In related studies, the experimental investigation is one of the most important tools. Many long air gap discharges have been observed under different conditions, for example, with the length ranging from tens of centimetres to more than 10 m [4][5][6][7][8], under the lightning impulse [9][10][11][12] or the switching impulse [5,[13][14][15][16], with the rod-plate [13,17,18], the rod-rod [19][20][21] or the plate-rod [22].…”