Research On Mechanism Of Non-equilibrium Plasma Arc And Breaking Characteristics In High-Voltage SF₆ Circuit Breakers

With the rapid development of UHV construction, there are some technical problems in their own building and running. Especially UHV capacitors bank dedicated circuit breaker, which is not only to meet the 40kA short-circuit current breaking, but also to ensure small 1600A rated current breaking 3000-5000 times, the repeat breakdown phenomenon does not occur. The arcing characteristic and dielectric recovery characteristic of capacitor bank circuit breaker small current breaking process were main research topics. Circuit breaker operating strategy was given and chamber structure was optimized by mechanism and experimental research of circuit breaker small current non-equilibrium arc characteristics, dielectric recovery characteristics and closing pre-strike characteristics. The results were applied to the design and development of SF6 circuit breakers, to meet the operational requirements of circuit breaker high electrical life.This dissertation mainly conducts work in the following several aspects:(1) The mechanism study of non-equilibrium thermodynamics arc plasma space transport and time relaxation process in high voltage SF6 gas were carried out. The non-equilibrium thermodynamics double temperature plasma arc mathematical model was established, and the relaxed time of arc plasma non-equilibrium were getted. The transport coefficient of each transport process were cleared, such as conductivity coefficient; thermal conductivity coefficient; viscous coefficient, etc. The microscopic parameters were getted, such as density and composition of gas, temperatures of electronics and heavy particle, etc. The connection between thermodynamic parameters and switch electrical parameters in the process of operation was established. The pressure and temperature boundary conditions were given when arc plasma transformed non-equilibrium to equilibrium state.(2) The high voltage SF6 circuit breaker non-equilibrium arc extinguish characteristics were analyzed. A model of non-equilibrium plasma arc physical field coupling calculation was established, and the dynamic changes of the plasma arc parameters were simulated under flow, energy and electromagnetic process. The compressed characteristic, flow characteristic and arc characteristics in the process of load breaking were calculated, and the distribution of pressure, temperature, density, transport parameters and thermodynamic parameters in the arc chamber at the time of arc extinguished were getted. The influence of different physical process to arc extinguished characteristics were analyzed, through the coupling calculation of flow field and temperature field.(3) The mechanism of dielectric recovery characteristics were researched when the circuit breaker open small current. A mathematical model of dielectric recovery characteristics based on double temperature ionization equilibrium equation was established. The breakdown electric field strength and the voltage values were get by calculated the transformation law of electron density and temperature under different pressures and electric field in cold breaking process. The influence of arc contact ablation, arc energy, gas pressure and breaking speed to dielectric recovery characteristics were analyzed. Interrupter structure was optimized and operating strategy of high electrical life was proposed, to meet the demand of 3000 times operation.(4) Experimental study on the high voltage circuit breaker dielectric recovery characteristics were carried out. The dynamic breakdown characteristics test loop of the the switch of capacitor set was established. The test method of dielectric recovery characteristics in the process of the opening and closing of circuit breaker was improved. The dielectric recovery characteristic test curves and closing pre-strike characteristic test curves were given for the first time. The effects of the factors such as pressure, close speed, voltage polarity on dielectric recovery characteristics were analyzed, and the results guided simulation calculation method of circuit breaker. The parameters of close selection phase control were given, which directly applied to research and design of the circuit breaker. The closing phase angle, pre-strike time, voltage and option control strategy were given by compared the results of the test and simulation calculation.