Degradation Law of Trigger Characteristics of SF6 and SF6/N2 Gap Switches Triggered by Plasma Jet

In the Jiangsu-Baihetan ±800 kV ultra-high voltage (UHV) hybrid DC transmission project, used to bypass the controllable arresters, the gas gap switches triggered by the plasma jet bear the advantages in fast response, strong insulation recovery ability, and large flow capacity, having a broad application prospect. However, there are still a lack in their optimal selection of gas atmosphere for the trigger gap and a further study needed for the enhancement of trigger characteristics and trigger life. In this paper, by building an experimental platform of plasma jet triggering, the degradation law of the trigger characteristics of plasma jet triggering gas gap is studied. The critical circuit parameters of the gap triggering are respectively obtained in the SF6 and the SF6/N2 mixture, and the trigger life experiment and the law of the performance degradation are carried out under the determined circuit parameters. The results show that, under the same insulation strength and with 10kV gap voltage is 10 kV, the minimum trigger voltage in 0.2 MPa SF6 is 3.5 kV, while it is reduced to 2.6 kV in the condition of 0.266 MPa SF6/N2. Under the optimal trigger circuit parameters and the same insulation strength, at the beginning of the experiment, the gap conduction delay in SF6 is~270 μs, the maximum plasma injection height is 4.8 cm, and the maximum injection velocity is 1296 m/s, while in SF6/N2, the gap conduction delay decreases to~100 μs, the maximum plasma injection height increases to 7.2 cm, and the maximum injection velocity increases to 1525 m/s. With the increase of discharge times, the gap conduction delay increases, the maximum plasma injection height decreases, and the maximum injection velocity decreases until the first trigger failure occurs and the trigger life is over. The trigger life of the gap in SF6 is only 695 times, while that of the gap in SF6/N2 reaches 1540 times. This paper provides a theoretical guidance for the performance and life improvement of the gas gap trigger switches for the controllable arrester, and contributes to its popularization and application in engineering fields. © 2024 Power System Technology Press. All rights reserved.