Research On Nozzle Optimization Of High Voltage Circuit Breaker

The dielectric recovery in interruption process is an important qualification to judge the performance of the high-voltage circuit breakers. The arc nozzle of SF₆ circuit breaker is the kernel part in arc quenching chamber, because of its controlling effect on gas flow property during the breaking. Consequently, design of the nozzle in arc chamber is the core of SF₆ high-voltage circuit breaker design. And nozzle design includes downstream and upstream optimum.The 252kV SF₆ circuit breaker with two-stage nozzle is taken as the investigation object in the nozzle downstream optimum design. Through the optimization of the nozzle downstream it can improve interruption capacity by controlling the gas flow effectively during the breaking. The objective function of the nozzle optimization is the dielectric recovery characteristics, which satisfy the specification of the SF₆ circuit breaker. Based on the analysis of traditional method of calculating dielectric recovery strength, a simplified numerical computation method of dielectric recovery for electric apparatus has been proposed, which chooses pressure in flow field in stead of dielectric recovery to represent interruption performance. Due to the higher nonlinear global mapping relationship between interruption performance of SF₆ circuit breaker and the nozzle structural parameters, artificial neural network (ANN) were applied to achieve the parameter global mapping of SF₆ circuit breaker on the basis of the nonlinear mapping properties of ANN. The feasibility and validity of the research work have been verified by the demonstration examples. The foundation for nozzle structural optimization of the circuit breaker is provided.The design variables involved in the inverse problem of the nozzle optimization are highly nonlinear, and the solution of the objective function with higher precision is relatively difficult to obtain. In this thesis, genetic algorithm (GA) was adopted to realize the optimization design of nozzle with different structures. And the validity of the optimization is verified. It has been indicated that the nozzle structural parameter optimization method based on the artificial neural network and genetic algorithm approach is feasible. It simplifies the nozzle optimization, and overcomes the computing of the electric field, flow field. And this optimization strategy provides a feasible scheme for the complex structural optimization.The nozzle upstream optimum design focuses on how to control the arc gas flowing mode to improve the velocity of arc energy diffusion. A novel chamber structure with rotary-gas grooves in the upstream of the nozzle was presented, using the novel rotary flowing arc. It can be shown that, SF₆ circuit breaker with rotary-gas groove has strong arc extinguishing capacity. Under the circumstances of keeping the flow unchanged, the flow characteristics in arc quenching chamber of the SF₆ circuit breakers with different number and shape of the rotary groove was studied. The optimum number and shape of rotary groove can be obtained. The theoretical analysis basis for the novel rotary gas SF₆ circuit breakers and the design method of gas rotary nozzle is provided.