Study On The Influence Of Arc Before Factors On The Arc Forming Process Of SF₆ Circuit Breaker

With the steady increase of the power demand,the improvement of the transmission grade of the power system puts higher requirements on the breaking capacity of the high voltage circuit breaker.Arc is inevitable during the chamber course of the circuit breaker,and the process before forming a stable arc is called the before-arc process.During the before-arc process,contact material is melted and produced liquid metal bridge by high-current.When the temperature reaches the boiling point of the material,the liquid bridge breaks down and the metal vapor is formed,which makes the cathode and anode electrode are filled with metal vapor.The metal vapor and SF₆ gas are both involved in the development of the before-arc process before the nozzle opened.Therefore,the research on the effect of metal vapor in the arc formation process is necessary.The development,evolution and the physical essence of the charged particle swarm during the process from the fracture of liquid metal bridge to the generation of steady-state arc are researched in this dissertation from the microscopic point of view.The formation mechanism of before-arc process in different arc extinguishing media is analyzed.The influence of macro factors on the formation mechanism of micro structures is also discussed.Specific contents are as follows:?1?According to the arc forming process of SF₆ circuit breaker,drift diffusion equation including electrons,positive and negative ions and Poisson equation coupled electric field are established which based on Boltzmann drift diffusion equation and Maxwell-Stefan transport equation.The collision equation was also established based on the collision between particles in SF₆ arc extinguishing chamber.?2?Two-dimensional ax symmetric SF₆ circuit breaker is established based on the actual structure of the 252 kVSF₆ circuit breaker arc chamber and mathematical model.The boundary conditions of the model are also determined.?3?According to the simulation of the change of dielectric components in SF₆ circuit breaker with small current and high current,the electron density,ion density,average electron energy of arc composed of different media are calculated.Dynamic change of electric field intensity in arc extinguishing chamber and the microcosmic difference between the dynamic arc formation process of small current and high current are analyses.?4?In this paper,the influence of different metal vapor content,cathode structure and electrode material on the arc dynamic formation process in the metal vapor mixed SF₆ gas is investigated.The microcosmic electron parameters such as electron density,ion density,electric field intensity and electron energy are obtained.The influence of macro before-arc factors on the parameters of arc formation is analyzed.