Study On Self-breakdown Characteristics Of The Triple-electrode Switch System

In recent years,pulsed power technology has been widely used in scientific research and industrial engineering,the compact Marx generator with low inductance and high energy density has been widely used in engineering because of its advantages such as small size,light weight,high energy efficiency and repeatable operation.As a key component of the Marx generator,the gas switch directly determines the output characteristics and operating characteristics of the generator.It not only needs to pass through the strong current and the large charge pulse,but also can trigger accurately,so the triple-electrode switch has the advantages of good controllability,short closing time,low jitter and low delay,compared with the two-electrode switch.The self-breakdown process of triple-electrode switch in Marx generator is very important for the design and the safe operation.In this thesis,the design scheme of triple-electrode switch system is presented from the aspects of structure design for electrode body,the selection of insulation support,the spacing between poles and the selection of insulating medium.In order to realize the adjustment of electrode spacing of the system and ensure the uniformity of electric field inside the main discharge electrode,the insulation support design of umbrella skirt with Teflon is selected,to improve insulation strength and ensure the safety,reliability and stability of switch system.Build triple-electrode gas switch system experimental platform,which are static breakdown experiments on different electrode gap and pressure,the results of study show that,using SF₆ gas as the research object,with main electrode gap and SF₆ pressure increases,the self-breakdown voltage increases;with the increase of pressure,the breakdown voltage dispersion and static stability reduce switch.According to the design of electrode system,the static breakdown characteristics of the switch are the most stable when the electrode gap is 4.3mm in 100 kPa.In order to study self-breakdown micro-process of the system,a fluid-chemical hybrid model is established.The complete initial discharge process of triple-electrode switching system is simulated by using the data obtained from self-breakdown experiment.And the physical mechanism and influencing factors of the process are analyzed quantitatively.The results show that the initial process of discharge to the plasma channel,the initial electrons of cathode are generated due to field emission;the plasma channels between electrodes are initially formed with the electrons move to the anode and interact with other particles;when the discharge time is increased to 10 ns,a relatively stable plasma channel is formed at the near-pole edge.The maximum electron density in plasma channel is outside the cathode sheath,and the electron density in cathode sheath is approximately 0;the electron temperature mainly concentrates the near-cathode region with the largest space electric field intensity;compares the plasma channel characteristics in vacuum medium,N₂ and SF₆: The electron density in vacuum medium is the largest and the electron temperature is the highest in N₂.Compare with horizontal distribution of the plasma electron density in different spacing and different plate area,the following conclusions are getting: With the increase of the electrode spacing,the uniformity of electron density increases when the plasma channel is formed,and the arc area spread outwards.When the radius of upper plate is 45 mm,the plasma channel is formed with the smallest electron density and the most uniform horizontal distribution.