| The vacuum switches are the key components in the power systems for the roles of control and protection.The vacuum switches have many advantages,such as environmental friendliness,powerful extinction capability,miniature,long lifecycle and free maintenance.And the vacuum circuit breakers(VCBs)are widely applied in the generator protective systems and medium voltage distribution and utilization power systems.During the breaking process of the VCBs,the arc plasma is inevitably generated and influences the insulation,the dielectric recovery property and the interrupting performance.The investigation of the derivation mechanism and the variation principle of the vacuum arc plasma is the key consideration to design the VCBs with large capability and high technical specification.In this dissertation,a 40.5kV/31.5kA/2500A vacuum interrupter(VI)with cup-shaped axial magnetic field is taken as the research object,and the finite element numerical analysis and simulation of the electro-magnetic field has been carried by the COMSOL commercial software.Moreover,based on the experiment of the short-circuit current breaking,the developing process and the variation principle of the arc resistance under the different breaking conditions and arcing time are explored to improve the interrupting capability of the VCBs.Furthermore,the design scheme of the VI is proposed for observing the vacuum arc variation under the short-circuit current breaking.In which,the floating electrode is drilled every ninety degrees evenly in the circumferential direction to obtain the dynamic variation images of the vacuum arc during the arcing process.For verifying the rationality of the VI design scheme,a three-dimensional electro-magnetic model of the VI have been established.The finite element commercial analysis software COMSOL is used to obtain the internal electric field.And the influence of four holes on the floating electrode to the electric field distribution is compared and analyzed with no hole case.According to the VI contact parameters,a three-dimensional cup-shaped axial magnetic field calculation model is established and COMSOL software is used to simulate the axial magnetic field(AMF).The axial magnetic field distribution on the dynamic contact surface,the static contact surface and the break center plane is analyzed at peak current and current zero.The phase shift time distribution of the axial magnetic field on the break plane center is calculated.By introducing the iron core into the cup axial magnetic contact to analyze and improve the magnetic field distribution.And the different core structure models are established to compare and analyze the influence on the characteristics of axial magnetic field.Based on the short-circuit current interrupting experimental platform for the VCBs,including the experimental circuit,the permanent magnet repulsion mechanism control system and the high-speed image acquisition system,the short-circuit current interrupting experiments are carried out under T30 and T60 operation conditions.Through the experiments,the vacuum arc images are collected and the arc voltage and current during the arc extinguishing process are acquired,and the arc resistance curve is obtained.By analyzing the variation of the arc resistance and combing with curve fitting method,the physical-mathematical expression of the vacuum arc resistance and arc energy have been obtained.By comparing the experimental data with the dynamic arc resistance expression,the dynamic arc resistance expression can effectively describe the variation of the vacuum arc resistance. |
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