Study On The Technology Of High-Voltage Long-Lifetime Vacuum Surface Flashover Switch

A vacuum surface flashover switch has obvious advantages such as natural vacuum,simple structure,obviously-decreased weight and volume when applied in space environment.Therefore,researching the working mechanism and characteristics,enhancing the life of the vacuum surface flashover switches are of great importance to accelerating the pulse power technology to be applied in the space environment.The main research content and results of this thesis are as follows:A 1-D model on the desorption layer pressure distribution is established.The quasi-Townsend discharge process and the discharge channel resistance collapse process are researched.The dependences of the pressure and the Townsend-ionization factor on time are obtained.The breakdown time delay and its relation on the breakdown field are interpreted.The electron ionization impact frequency and the increasing tendencies of the the ionization degree of the discharge channel during the breakdown process are deduced.It is obtained that the time for the discharge channel resistance to collapse is 1-10 ns,the channel resistivity after collapse is of an order of 10-5 ?·m,and the resistance per unit length is 0.1?1?/cm.A model on the gas dissipation in the switch recovery stage is established.The influences of the quantity of the release gas and the energy of the desorption molecular on the insulation recovery time is analyzed.It is concluded that the time for the secondary desorption gas to dissipate is about several hundreds of microseconds,the time for the vaporized gas to dissipate is on the order of millisecond,and the repetition rate of the switch can reach hundreds to thousands of hertz.A repetitive high-voltage pulsed experimental setup is established.The switch characteristics such as the closure time,the switch-on resistance,the repetition ability and the operating electrical field are researched experimentally.The expression for the time part of the switch resistance is that ?R=13.28?T/E0,in which,KT is 10-20 ns kV/cm for different insulation materials.With the analysis on the time part of the switch inductance,the method to calculate the switch closure time is put forward.The relationships between the switch-on resistance and the switch discharge length as well as the conduction current are researched,and the expression for the switch-on resistance that Rs = KRlI-? is obtained,in which KR is 1.2?2.7 and ? is 0.9?1.3 for different types of insulation materials.The insulation recovery time for the ceramic surface flashover switch is measured to be 200?300 ?s with the multi-pulse method,and the insulation recovery time for the organic material surface flashover switch is milliseconds to tens of millisecond.The influences of the dielectric material,shape,thickness on the switch operating voltage are researched.A switch operating electric field larger than 190kV/cm is obtained with the circular truncated cone shaped fused silica as the insulation material.The dielectric damage mechanism caused by the surface flashover is experimentally researched,and three types of damage pattern are obtained.The ceramic materials with high thermal shock resistance and without metal elements have better flashover resistance.The lifetime of fused silica is over 104 pulses.The damage mechanisms due to flashover mainly include:the thermal erosion,the intense radiation caused decomposition and the structural crack.The thermal erosion results in the organic materials to be decomposed and to form grooves.The carbon deposited in the grooves leads the insulation ability to decrease.The ceramic material containing the metal elements can be decomposed under intense ultraviolet radiation and can cause the elementary-substance metals to form on the dielectric surface,which leads the flashover voltage to decrease.As to the ceramic material without the metal elements,the structural destruction by thermal stress is the main reason for insulation failures.A high-voltage long-lifetime flashover switch is developed.The operating voltage is close to 800 kV;the closure time is 2.2 ns.The lifetime is 22,000 pulses under a conductive current of 10 kA.The double-layer parallel-plate structure is adopted for this switch.The dielectric material is fused silica,with a conical angle of-20°.