Preliminary Investigation Of Hydrogen Spark Gap Switch

High power switch is one of the major parts in pulse power system. For the advantage of simple structure, widely using voltage and current, high dI/dt, the gas spark switch is widely used and researched. With the development of pulse power modulator, high power microwave and cold plasma, high repetition rate spark gap is requested. To improve the repetition rate of the switch, the insulation recovery time of the switch must be decreased. In this paper, the recovery characteristics of different gases are researched by the way of theory analysis, software simulation and experiment research. The result provides a theoretic and experimental basis to research the multi-pulse or repetitive pulse operation with high power spark switch.At first, the breakdown mechanism of gas spark gap is analyzed. The influences of different parameters on the recovery characteristic are researched, such as pressure, gap distance and gas type. Radius and temperature of arc channel of different gas type used in spark gap have been calculated using the PSpice software, energy conservation equation and experimental equation.The electric field of spark gap switch has been researched using the COSMOL MULTIPHYSICS software. A 3-D model is established for simulation of gas temperature decay. According to the continuity equation, momentum equation, energy conservation equation and the ideal gas state equation, the influence of heat transfer coefficient, specific capacity at constant pressure, dynamic viscosity on temperature decay have been given using ANYSYS-CFX, a software for fluid mechanics. The adaptive equations of heat transfer coefficient, specific capacity at constant pressure, dynamic viscosity varying with temperature are listed. Using these equations, temperature decay simulations for nitrogen and hydrogen have been done. The result helps to estimate the recovery time of different gases with high power.A high pressure gas spark switch is designed, according to the theoretical analysis and software simulation. Under a certain safety factor, 60 atmospheric pressures in the switch can be obtained. A single coaxial pulse power forming line using the de-ionned water as transmission dielectric has been build up which can work steadily with peak voltage of 1MV.Finally, the recovery characteristics of self breakdown switch of hydrogen, nitrogen, and SF6 have been tested. A series of two-pulse experiments are performed at breakdown voltage up to 450kV (520kV for hydrogen), peak current up to 30kA, pulse width 60ns. With an interval of 7ms also, the hydrogen spark gap switch could obtain good insulation recovery, while under the same condition 25ms is needed for SF6 and 50ms is needed for nitrogen.The rise times of the pulse voltage for different gases at different conditions are also measured. The results show that hydrogen has the rapidest rise time, and with the pressure increasing and gap distance decreasing the rise time decrease.