A plasma-injection-triggered long-spacing air gap switch for fast protection of series compensation device

The series capacitor compensation technology can improve the transmission capacity of long-distance transmission lines and the stability of the power grid. However, it faces limitations due to quick failure of the mainstream capacitor protection device, the metal oxide varistor, after multiple actions. To improve the conduction performance and service life of the fast protection device for series compensation capacitors, this paper proposes a long-spacing air gap switch (LAGS) based on double capillary discharge triggered plasma jet and focuses on the influence of microcavity structure parameters on trigger characteristics of the LAGS. The results show that the conduction performance of LAGS is optimal under the structure of a 20-25 mm long secondary cavity, a 4 or 5 mm long primary cavity, and a 10 mm thick ground electrode. Under the optimized parameters, the switch can be conducted stably for about 110 times at a 1.4 kV trigger voltage. Due to the recoil effect of the secondary cavity on the primary cavity, the primary cavity is severely eroded, which lowers the density and velocity of initial plasma, making it hard to penetrate the gap. By transforming the middle electrode into a 2-0.6 mm contracted shape, the recoil effect can be mitigated without reducing trigger energy. Therefore, at a 1.4 kV trigger voltage, the service life of the gap switch can be extended to 220 times with a less than 500 μs conduction delay. The research results indicate that a 10 cm long LAGS is expected to meet the sub-millisecond and reusable conduction requirements of the series compensation protection system.