Action Law and Deterioration Characteristics of Trigger Cavity of Plasma-Jet-Triggered Air-Gap Switch

Abstract

The switch-type controllable metal oxide arrester (CMOA) is a flexible method to depress deeply switching overvoltage of transmission system, and the switching time of the fast bypass switch in CMOA is less than 1 ms with the meet of engineering. The plasma-jet-triggered air-gap switch (PTAS) has obvious advantages for the above switch. However, the cumulative effect of increasing the trigger discharge times is prone to trigger failure of the PTAS. In this article, a platform about trigger lifetime of PTAS is established to study the action law and degradation characteristics. The results show that the plasma jet process is divided into three stages: rapid growth stage, stable development stage, and dissipation and decline stage. The peak plasma jet velocity is up to 1.7 km/s, and the shock pressure can reach 5 MPa. With the increase of trigger discharge times, the surface discharge channel of PTAS trigger cavity gradually degrades due to the arc ablation cumulative effect, the surface roughness and nozzle diameter increase, the plasma jet characteristic parameters decrease, and plasma jet ability is weakened. The ablation degradation of trigger cavity surface is characterized by “pore size increasing, pore connection, and gully penetration.” The plasma jet characteristics are consistent with three types of the trigger cavity insulating materials, namely, Poly tetra fluoroethylen (PTFE), PTFE +0.5% Cu powder, and PTFE +0.2% MoS2. The decay rate of plasma jet parameters for +0.5% Cu powder is the fastest. Adding 0.2% MoS2, the ac ablation ability is strengthened. However, the trigger discharge lifetimes of both +0.5% Cu powder and +0.2% MoS2 are lower than that of PTFE. PTFE has obvious advantages in gas-producing performance and ablation resistance ability. The research results provide theoretical guidance for improving the trigger performance of PTAS.