Breakdown Characteristics and Mechanisms of Short Needle–Plate Air Gap in High-Speed Airflow

To understand the flashover of roof insulators in high-speed airflows, the breakdown characteristics and mechanisms of a short needle-plate air gap are investigated. An interesting and important phenomenon is found based on an artificial wind tunnel: the breakdown voltage first increases and then decreases. An experiential formula is established to describe the relationship among the airflow velocity, gap distance, and breakdown voltage. A good consistency with the experimental results is obtained. Furthermore, the breakdown mechanisms of the air gap in high-speed airflows are proposed, and the phenomenon is explained and verified according to the theories of gas discharge and fluid dynamics. The airflow blowing effect, which includes the deflection effect and blown away effect, and the airflow density effect are proposed as two dominant factors that affect the breakdown process of the air gap in high-speed airflows. The variation trend of the breakdown voltage with the airflow velocity is predicted. Two extreme points are expected during the variation process; i.e., the breakdown voltage has a maximum and a minimum, to which more attention should be paid. This paper is helpful for the safety operation of roof insulators on the high-speed train.