Research On Three-Dimensional MHD Arc Characteristic Of High-Voltage SF₆ Circuit Breaker

SF6 circuit breakers (HV SF6 CBs) are widely applied in the high voltage (HV), extra high voltage (EHV) and ultra-high voltage (UHV) power system to control and protect the system and the equipments. With the development of the electric power industry and the increase of the electricity load, the power system constantly tend to high voltage, large capacity, and higher requirement for the HV SF6 CB design and performance have been put forward. The development of higher insulation ability and interruption performance for the HV SF6 CB is the key consideration to ensure the safety, the reliability, stability and efficiency of the electrical power systems, and it is also the protection to interrupt the fault in the system operation process, and minimize the economic loss.HV SF6 CB is inevitable to produce the arc during the open and close the circuit. By applying the numerical solution and simulation method, the numerical simulation of the mathematical and physical model of the electric arc is an effective way to study the insulation performance, the dielectric recovery and interruption performance of the HV SF6 CBs. To research the pressure variations in different region of the arc quenching chamber during the breaking process, the finite volume method is used in this thesis, based on 3D magneto-hydro-dynamic (MHD) mathematical model, and the arc parameters varying with different opening stroke and the arc temperature distribution are obtained. And the pressure difference between the upstream and the downstream because of arc jam effect, and the influence on the gas flow breaking the arc have been analyzed.The PTFE insulation nozzle of the arc quenching chamber is the key structural component, which can control the gas flow inside the tubes and the capacity of dielectric strength during the breaking process for the HV SF6 CBs. Therefore, the structure design of the nozzle is very important to the design of gas flow path in the HV SF6 CBs. In order to effectively control the gas flow, and improve the breaking capacity, a 550kV EHV SF6 CB is used as the research object in this thesis, and different nozzle structure with different flow path are proposed, and the numerical simulation of cold gas flow inside the interrupter has been computed using the finite volume method. By comparing the pressure distribution and velocity distribution of different observation points in the region of the upstream and the downstream nozzle, a quantitative description of pressure difference and velocity difference between the upstream and the downstream is obtained, to reflect the flow behavior during the breaking process. From the simulation results, it can be seen that the nozzle length and surface structure are the main parameters to control the gas flow.