Design On 24kV Vacuum Interrupter With Cup-Shape And Axial Magnetic Field

The vacuum circuit breakers (VCBs) have been widely applied in the middle voltage level power systems for their advantages, such as smaller volume, green energy, long life, fine reliability and free maintenance, and the VCBs have the control and protection dual task. The operation performance of the VCBs directly influences the reliability, the stability and the safety of the entire power system. However, the vacuum interrupter (VI) is the most important unit in the VCB. Therefore, the design of higher parameter VI has theoretical and engineering significance for the insulation and breaking performance research of the VCBs.In this thesis, the structure parameters of the 24kV VI have been calculated by the experience formulas. Firstly, two VI models have been proposed based on the different opening direction of the arc end of the floating shielding cover. And the electric field distribution in the VIs have been computed and analyzed using the finite element method (FEM). The results show that the maximum electric field strength of the VIs are at minimum when its direction opens upside, and the electric field strength distribution is more uniform in the VIs and greatly influenced by the floating shielding cover. Then, the structure has been presented according to the numerical computation and comparative analyses. Finally, based on the structure parameters of the floating shielding cover and contacts, the optimal value of the variable parameters were achieved using the improved genetic algorithm. And the insulation performance of the optimization model was validated.Based on the structure parameters, the cup-shape contact model was proposed. And the current density and AMF strength were obtained using the EFM. And the current density distribution, AMF distribution, conductor resistance and phase-shift time caused by eddy current were considered and illustrated. According to the simulation analysis results, the AMF strength is the smallest on the contact edge and the gradient gap is relatively high, and the AMF strength of the center plane between contacts gap is only half on the surface of contacts. In order to improve the AMF strength at the contact surface and between the two electrodes, the iron-core in which the slot is not fully slotted and it is embedded into the edge of contacts. And the average value of the AMF strength increases on it, the electrode surface has been completely used; the distribution of the AMF is more uniform, but the phase-shift time increase a little. Because the contact structure parameters greatly influences the phase-shift time, its parameters can been optimized by the further research work. And the optimal VI structure can be obtained.