Computer simulation tool for the design and optimation for UHV SF6 circuit breakers

The capacity of the electric grid in China is undergoing rapid expansion to keep pace with the fast economic growth. The annual gross production of the UHV products exceeded 100 billion RMB (approximately 12 billion Euro). Therefore the design and optimization technology for UHV SF6 gas circuit breakers are very demanding. Based on the two-dimensional magneto-hydrodynamic (MHD) model and a commercial CFD (computational fluid dynamics) software, FLUENT, a computer simulation tool for the design and optimization for UHV SF6 gas circuit breaker is established. Nozzle ablation effect is considered by introducing an independent mass conservation equation for the ablated material to the overall conservation equations of mass, momentum, and energy. The ohmic heating and the radiation of the electric arc are considered in the model by adding relevant source terms. Both the thermal interruption capability and the dielectric interruption capability can be numerically predicted. To predict the thermal interruption capability, the arc conductance 200ns before current zero is used as an indicator. The CFD model is applied for the high current arcing phase, and Mayr arc model is used near the current zero period. To predict the dielectric interruption, both the reduced electric field strength and the reduced critical electric filed strength everywhere inside the interrupter are computed and compared, to judge the occurrence of the electric breakdown. The validity of the present simulation model is verified by comparison of the simulation results with the experimental results such as voltage, currents of the arc and pressure rises Type here the email address of the main author as a footnote. inside the interrupter during the arc interruption. The numerical prediction by the simulation tool is verified by the direct interrupting test of 550kV GCB, too. The developed computer simulation tool was applied in the design of a 550kV GCB. Significant benefits have been achieved in terms of both the cost saving and shorten of the development cycle. The paper is organized as follows: the governing equations of the simulation model based on the 2-dimensional MHD model are presented in section 2. The numerical prediction of the thermal interruption capability of the SF6 GCB is described in section 3. The numerical prediction of the dielectric interruption capability of the SF6 GCB is described in section 4. In section 5 the experimental set-ups as well as the experimental results are presented and compared with the simulated ones. The numerical predictions agree well with the experiments. Finally conclusion is drawn in section 6.