Research On The Microscopic Before-arc Mechanism Of High Voltage Circuit Breaker

The further study on the process of arc production, development and extinction is theprecondition for arc effective control. The further study on the arcing cause and the effectfactors show that suppressing and controlling before arc generating process is the effectivemethod to improve the breaking ability. The before-arc process is the base of arc existingand the space distributions of microscopic particles, energy distribution, dynamic electicfield strength distrbuiton and sheathe distribution have the key effects on the energy ofsteady-state arc. The before-arc process is a non-linear, time variation and non-equilibriumprocess in tiny time domain and space domain. So the formation, development andevolution of charged particles swarms and the physical essence of arc after liquid metalbridge disrupting and before stable arc generation and origination are researched in thisdissertation based on microscopic angle to explore the formation mechanism of thebefore-arc process of different arc extinguishing dielectric and the different factors thataffect their formation mechanism and parameters are also discussed. The specific contentsare as followings:(1) A dynamic model consisiting of electron development, charged ion movement,microscopic particle collision is proposed based on the Boltzmann equation and the solvingmethod based on Particle in cell-Monte Carlo collision is utilized. Based on the equationsabove, the one-dimensional before-arc process of single-atomic structure dielectric issimulated by self-programmed codes. Compared with the classical example, the accuracyof the algorithm and self-programming is verified. By this model, the impacts of electronand ion motions on before-arc process are analyzed and the formation processes of sheatheand ionization layer are also acquired.(2) The model of before-arc process in a simplified two-dimensional vacuum circuitbreaker when high current interruption is established in this dissertation. Metal vapor ischosen as the research object, microscopic physical essence of vacuum metal vapor arcgeneration is analyzed by self-programmed codes. The electron avalanche developmentprocess in metal vapor, the distribution of space charges density, the sheath formation process and the change of dynamic electric field by the space charge are obtained. Fromthe micro point of view, the main reason for the contraction of electron during the metalvapor arc formation prophase is explained in this dissertation. The physical essences thatthe effects on the microscopic before-arc process produced by the macroscopic parameterssuch as the opening range, secondary electron emission coefficient, interruption currentand electron collision at proximal region are analyzed.(3) According to the field emission theory and the hot electron emission theory,According to the field emission theory and the hot electron emission theory, the model ofbefore-arc process in a simplified two-dimensional vacuum circuit breaker when smallcurrent interruption is established in this dissertation. The metal vapor generated in thesmall current breaking process and breakdown process are simulated by self-programmedcodes. The absolute effect of the electrode process on small current vacuum arc generatinghas already been obtained.(4) The simulation model of polymolecule SF6is established by considering the elasticmomentum transfer, vibrational excitation, electron attachment, ionization and otherdifferent physical and chemical changes in before-arc process. The effects of spatial andtemporal variation on micro dynamic electric field are studied further by self-programmedcodes. The avalanche producing and development time and changes in the electron energyof SF6fore-arc are quantitatively calculated in this dissertation and the plasma internalmovement of SF6arc formation stage has also been obtained.