Thermal Characteristics of Positive Leaders under Different Electrode Terminals in a Long Air Gap

Du Du,Li Li,Zeng Zeng,Zou Zou,Liu Liu,Sun Sun,Ma Ma,Tang Tang

doi:10.3390/en12214024

Abstract

The thermal characteristics of the positive leader discharges occurring under the different electrode terminals in a 1 m rod-plate air gap were studied quantitatively using Mach–Zehnder interferometry and a high-speed video camera. When disturbed by the discharge channel, the interference fringes are distorted because of the change in the refractive index of air, which is related to the gas density. Therefore, the gas temperature and gas density distribution in the leader channel can be retrieved from the offset of the interference fringes. Based on these results, the thermal characteristics of the leader channel were studied under different electrode terminals with a radius of curvature of 2.5 mm and 5 mm for cone electrodes and a diameter of 40 mm for a spherical electrode. The results show that the gas temperature in the leader channel increased while the gas density decreased as the radius of curvature of the electrode terminal decreased. Additionally, a smaller radius of curvature leads to a larger thermal diameter, but the difference in the thermal diameter is not obvious; for the terminals used in this paper, the difference is within 2 mm.

Highlights

Overhead power transmission lines, which are used for long-distance transmission in power systems, are insulated by the air [1]
The results show that for the cone terminals, the thermal diameter ranged from 1.2 mm to 2.6 mm under the electrode with a radius of curvature of 2.5 mm and ranged from 0.8 mm to 2.6 mm under the electrode with a radius of curvature of 5 mm; for the spherical terminal with a diameter of 40 mm, the maximum thermal diameter was 0.6 mm
The temperature and density characteristics of the leader channel were obtained from the offsets of the interference fringes

Summary

Introduction

Overhead power transmission lines, which are used for long-distance transmission in power systems, are insulated by the air [1]. It is very important to study the mechanism of gas discharges in long air gaps via both simulations and experiments [3,4,5,6]. The leader discharge is the essential breakdown mechanism in long air gaps and leader discharges exist widely in natural phenomena such as lightning [7,8,9,10,11,12,13]. The study of the characteristics of leader discharges can provide a basis for optimization of the external insulation in power systems, and provides a theoretical basis for the design of insulation, which has great theoretical and practical application value. The Renardières Laboratory established the first comprehensive system for the observation of long air gap discharges and divided the long air discharge process into three main stages: the streamer, Energies 2019, 12, 4024; doi:10.3390/en12214024 www.mdpi.com/journal/energies

Methods

Results

Conclusion