Experimental Investigation Of Triggered Spark Gap Switches

The spark gap switch, as a high-energy and high-current switching facility, has been widely used in many kinds of high-power systems which always demand their switches to run in a high operating voltage, high repetition rate, low jitter and short breakdown time. When the switch operates in different condition, the variation of timing features of spark gap switches is taken into the main consideration of this paper.As to theory, two mechanisms, Townsend and streamer, are believed to function in the discharging process of spark gap switches and turn out to be the foundation of the theoretical analysis about the discharging mechanism of spark gap switches. Thereby, a conclusion is obtained that the breakdown of triggering gap is unnecessary while the breakdown of main gap is quite important to the breakdown of the whole switch, but the sequence of these two breakdown process will influent the velocity of the breakdown of the whole switch. Following that, a mathematical model is built up to calculate the breakdown time of spark gap switches. The simulation result demonstrates that with operating voltage increasing, the switch works in two different discharging modes: a slow one with timing parameters sharply decreasing, and a fast one with timing parameters falling a little when operating voltage increases. Comparison is made between simulation and experimental result, which indicates a difference of breakdown time and operating voltage range between them. However, due to the proper prediction for the trend of breakdown time vs. operating voltage, the mathematical model would be helpful for the design of spark gap switches.To attest the result of theoretical analysis, it is considerate to design a spark gap switch with an adjustable main gap distance, the ability to support the gas pressure from 1×105Pa to 4×105Pa, and an airflow system with adjustable velocity of airflow, as well as the testing system.After the preparations mentioned above, experiments are carried about systematically to investigate the influence from main gap distance, gas pressure, the velocity of airflow and operating voltage on the performance of the spark gap switch. First of all, when increasing the operating voltage, the switch works in two different discharging modes as the theoretical result: a slow one with timing parameters sharply decreasing, and a fast one with timing parameters fluctuating around minimum values. Secondly, when changing the distance of main gaps from 6mm to 10mm, the minimum value of breakdown time increased and operating voltage range expanded. Thirdly, when increasing the gas pressure in the spark gap, the operating voltage range expanded and in high operating voltage a breakdown time of 20ns was observed, but jitter increased slightly. Finally, transverse gas flow was utilized in order to inhibit pre-fire. Testing result demonstrates that gas flow would restrain pre-fire effectively and therefore expand operating voltage range with a little increased jitter.