| The rapid raise of the voltage level and system capacity requires the high voltage interrupters, which are the most important apparatus used to control and protect the power delivery system, have better operation performance and higher reliability. The vacuum circuit breakers (VCBs) adapting the multi-break technology combined with the phasing switching technology can withstand high transient recovery voltage (TRV) and interrupt high current upto200kA, moreover, they are environmentally friendly, so they have the potential to replace the SF6interrupters, though which still play a great role in the high voltage area, use the greenhouse gas SF6, to essentially impove the operation performance and reliability of interrupters. Therefore, they are the development trend of extra high voltage and high capacity switchgears. The investigation of the physical process of vacuum arc in short gaps is related to the essential theories of the multi-break and the phasing switching technologies, and is also the key problem which seriously restricts the development of the new type of VCBs. In order to discreate the theorical impediment for the reasearch and development of high voltage and intelligent VCBs, this dissertation used the numerical simulation method combined with the experimental research to investigate the distributions of plasma parameters, the variations of arc appearance and their influence on the anode thermal process during the arcing period.According to the basic fluid dynamics equations consisting of mass conservation, momentum conservation and energy conservation, combined with the Maxwell equations, a two-temperature Magneto Hydro Dynamic (MHD) model related to the fully ionized gas was establised firstly. Then, a vacuum arc MHD model was developped based on the two-temperature MHD model. The new model took the actual flowing status of arc into account and added in the standard k-ε turbuence equations which is suitable for the supersonic arc. After loading the boundary conditions and initial conditions, the supersonic arc and subsonic arc were numerically simulated using the CFD software—COMSOL. The flow field, temperature field and electromagnetic physical characteristics of the two types of arc were calculated and analyzed. Calculation results shown that the flow of supersonic arc is significant different with that of subsonic arc. From the cathode to the anode, for the supersonic arc, the plasma pressure increase gradually, but the velocity decrease gradually; the variations of these paramters of subsonic arc are in contrast with those of supersonic arc. The influence of arcing parameters, such as arc current, contact radius, gap length and axial magnetic field (AMF), on the flow of plasma and the radial distributions of axial current density jz at the anode side and energy flux density s on the anode surface were further discussed in detail. Both of the increasing of arc current and the decreasing of contact radius make the jz and s increase significiately and intensify their constrictions toward the center of arc column. The extension of gap length also aggravates the constrictions of jz and s in the central region of arc, but reduces them in the radial edge of arc. The enhancement of AMF restricts the constriction of arc obviously and makes the radial distributions of the jz and s more homogeneous, thus subdues the erosion of anode efficiently. Therefore, it is an importance method to control vacuum arc and improve the interruption capacity of VCBs. In addition, the simulation result s could be used as a boundary condition of the anode thermal process model.Utilizing the CMOS high-speed camera, the appearance variations of arc which were generated by the separation of contacts and the ignition of high voltage pulse discharge were contrasted and analyzed in detail. It is valided that the raise of initial opening speed of contacts and the application of AMF could accelerate the transition from constricted arc to diffuse arc. The variations of arc light intensity, the diffusion of arc diameter, and the voltage-current characteristic of arc were calculated with the same conditions of experiments, thus it is possible to analyze the macroscopical appearance variation of arc from the microcosmic level of plasma parameters. The comparative analysis illustrated that the calculation results are in reasonable agreement with those of experiments.Thus the vacuum arc MHD model is feasible.In order to quantificationally investigate the influence of inter-electrode plasma on the thermal process of anode, a two-dimension anode thermal model was built. The model taken into account the molten and phase change of anode, the effection of Joule heating, the thermal conduction and the heat radiation. Using the arc simulation result s of chapter3as the heat flux density boundary condition on the anode surface, calculation of the variations of anode temperature distribution and the molted pool depth during the arcing period were then conducted. The calculation results indicated that the time of peak anode temperature has about2-3ms delay relative to that of peak current. Next, the impact of arcing parameters including the thickness of anode on the anode thermal process was further discussed. According to the temperature and the status of anode at current zero, the dependence of the arcing parameters on the maxium interruption capacity of VCB was derived.All in all. in this dissertation, the spatial distributions of inter-electrode plasma parameters, the variations of arc appearance, and their influence on the anode thermal process were further investigated, the arc controlling methods about the restraining of arc constriction, the fast transition of arc mode, and the improvement of the interruption capacity of VCB were then proposed. The research work contributes to supply the theoretical support for the optimization designs of multi-break VCBs and phasing switching VCBs, and to promote the application of them in the supervoltage and high capacity field, thus it has an important theoretical value and practical signification. |
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