Bezier curve-based shape optimization of SF₆ gas circuit breaker to improve the dielectric withstanding performance for both medium and maximum arcing time

This paper presents the optimization scheme to improve the interruption performance of a gas circuit breaker, which must carry out the interruption duty within specific arcing time for successful operation. The systematic process of design optimization was proposed by using the Bezier curve and sequential approximation technique for satisfying both medium and maximum arcing time. Depending on the specific arcing time, the position of moving part is different and that position directly affects the gas flow in the circuit breaker. Consequently, temperature, pressure, density, and flow rate between electrodes and tank changes accord to the position, which determines success or failure of the interrupting operation. To satisfy the design criteria for successful interruption, it is necessary to satisfy more than one arcing time at the same time. The diameter and the shape of the nozzle in the circuit breaker is a key part in securing the successful interruption. Thus, the nozzle shape design requires high expertise and proficiency. To solve this problem, we used the finite volume fluid in cell (FVFLIC) for flow analysis and the Bezier curve based optimization to design nozzle shape. The control points in the Bezier curve were selected as design variables and the optimization process was performed employing the sequential approximation technique. Based on the experimental results, the validation the optimization results was confirmed, and finally we can analyze the relationship between the fixed contact at each arcing time and the inflection point of the downstream of the nozzle.