Arc-extinguishing characteristics of semi-enclosed structures based on theory of positive shock wave reflection

Yuning Chen,Jufeng Wang,Yanlei Wang,Yiyi Zhang,Ping Huang

doi:10.1063/5.0075753

Abstract

Lightning current in the process of discharge can cause the potential differences between insulators to rise, hindering the normal operation of the equipment. To reduce the potential difference between insulators during a lightning strike, this study proposes a semi-enclosed structure to limit the rise of potential between insulators. Lightning-induced overvoltage causes the semi-enclosed structure to discharge, forming an arc channel. Because the arc is compressed by the structure, an overpressure-induced shock wave is generated. Positive reflection occurs when the shock wave hits the wall that damages the development of the arc through superposition. By using the theory of positive reflection of shock waves, the overpressure due to a positively reflected wave, generated by an impulse current of 8/20 µs with a peak value of 10 kA, was as high as 4.8 MPa, 48 times the initial pressure. Moreover, a 3D high-current impulse discharge model was established in COMSOL to simulate the process of shock discharge of the structure in the case of a large current. Finally, current-induced shock tests were carried out in the semi-enclosed structure. The results show that the maximum pressure in the semi-enclosed structure was 4.38 MPa at 10 µs and conductivity dropped to zero at 80 µs. In experiments, the amplitude of the impulse current decreased from 9.54 to 5.72 kA, and the current dropped to zero at about 65 µs. The results show that the semi-enclosed structure can extinguish the arc and limit the rise of potential between insulators.

Highlights

After the breakdown of a lightning flashover, a discharge channel is formed on the surface of the insulator2 that causes the lightning current to flow into a grounding grid along it
● The model of impulse discharge in the case of a large current established by simulations in this study can adequately describe the law of discharge of the arc in the impulse scitation.org/journal/adv discharge channel
Conductive particles in the channel of the arc column were blown out of the semi-enclosed structure by the airflow, and external air flowed into it to replace conductive particles and stop the development of the arc. ● By using the theory of regular reflection of the shock wave, the authors determined that the overpressure value generated in the semi-enclosed structure reached a maximum of 4.8 MPa under a 10 kA 8/20 μs impulse current, and the overpressure obtained in the simulation was 4.38 MPa

Summary

INTRODUCTION

Most overhead lines in areas that are prone to lightning strikes, with highly resistive soil and complex topography, such as mountainous areas, are vulnerable to damage due to lightning. After the breakdown of a lightning flashover, a discharge channel is formed on the surface of the insulator that causes the lightning current to flow into a grounding grid along it. After the breakdown of a lightning flashover, a discharge channel is formed on the surface of the insulator that causes the lightning current to flow into a grounding grid along it. This causes the potential of the ground grid to rise, resulting in a large potential difference in it that can cause serious damage to the equipment and even personnel.. Under the action of the difference in pressure inside and outside of the semi-enclosed structure, the reflected wave pushes airflow to the open end, destroying the arc.. This paper analyzes the process of regular reflection of the shock wave in the case of the discharge of high-impulse current in a semi-enclosed structure. COMSOL simulations and experiments are used to verify that the semi-enclosed structure reduces the current flowing into the ground by changing pressure and conductivity

BACKGROUND—SHOCK WAVE ORTHOREFLECTION THEORY

Simulation results and analysis

Test circuit

Analysis of results

CONCLUSIONS