Scheme of Gas Gap Switch Used in Fast Bypass Protection for Series Compensation Device and Its Trigger Discharge Ablation Characteristics

The low-voltage problem at the receiving end of long-distance and heavy-loading distribution lines becomes outstanding year by year. It is urgent for flexible control and very fast operation of bypass protection switches for series compensation devices. Therefore, the protection action of the series compensator is analyzed, and an operation scheme of the plasma-jet-triggered gas gap switch (PTGS) is innovatively proposed. The trigger lifetime of PTGS is the key factor of bypass protection equipment’s operation lifetime. The prototype of high-performance PTGS was designed, and its trigger cavity’s deterioration caused by discharge ablation was studied. The results show that increasing trigger times, the surface roughness and the nozzle diameter of the trigger cavity gradually increase. The ablation pores and bulges appear on the inner wall of the trigger cavity and deteriorate continuously, thus leading to cracks and even penetrating discharge trench, weakening the plasma jet characteristic parameters (jet velocity, jet height, and jet diameter), and the trigger delay increases obviously. The degradation process of trigger performance of PTGS caused by discharge ablation is divided into stable period, dispersion period, and decline period. Considering strong insulated and electronegative trigger environment in SF6, and the electronegativity effect of decomposition products caused by arc ablation, the development process of plasma jet is significantly inhibited, and the trigger lifetime of PTGS is reduced. Increasing SF6 pressure, the trigger lifetime decreases significantly, the trigger delay increases sharply with the accumulation of the trigger times, and it disperses notably in dispersion period. The induced breakdown of main gap initially occurs in saturation period initially. Increasing the trigger times, it gradually transits to dissipation period and reburning period. The results can provide theoretical reference for the design and optimization of the fast bypass protection switches used in the controllable series compensation device.