Researches On Electromagnetic And Mechanical Characteristics Of Cup-Shaped Axial Magnetic Contacts

Vacuum circuit breaker is widely used in medium voltage distribution system as control and protection equipment,which has an important impact on the normal operation of power grid system.The working performance of vacuum interrupter has a decisive influence on the comprehensive performance of circuit breaker.In recent years,the development of vacuum switch towards high voltage and large capacity has become the consensus of researchers with the limitation of SF₆ gas and the wide application of magnetic control technology.Therefore,many scholars have done a lot of work on the structure of contact to make the vacuum circuit breaker break higher current under the premise of keeping its volume unchanged.However,it is not only the electromagnetic performance of the contact that affects the working performance of the vacuum interrupter.During the closing of the vacuum interrupter,if the contact structure is improperly designed,it is likely to produce fatigue damage after multiple closing operations when the closing impact is large.Therefore,the influence of contact structure on the electromagnetic performance and mechanical properties should be analyzed from a comprehensive perspective.In order to analyze the influence of the internal structure of vacuum interrupter on insulation performance,the overall structure size of the vacuum interrupter is determined according to the empirical formula in this paper.And the 2D model of vacuum interrupter is established to analyze the influence of the main shield on the electric field distribution.Then the structural parameters such as the thickness,diameter and skirt angle of the main shield are improved.Finally,the insulation performance of the vacuum interrupter under different shielding materials is analyzed.In order to analyze the influence of contact structure on the magnetic field characteristics,a 3D finite element model of contact structure is established by virtual prototyping technology.Ansoft Maxwell is used to calculate the magnetic field distribution characteristics.The current density distribution on the contact structure,the axial magnetic field distribution on the arc gap plane and the lag time distribution along the radius direction are obtained.The effects of the number of slots on the contact,the slot length of the contact plate,the rotation angle of the cup finger and the type of iron core on the magnetic field characteristics are discussed.In order to calculate the mechanical properties of the contact under the closing impact,the rigid body dynamic simulation model of VS1 vacuum circuit breaker is established in this paper.And the dynamic characteristics of the circuit breaker is calculated.The influence of spring parameters and contact mass on the dynamic characteristics of contact is analyzed.Then the 3D model of cup-shaped axial magnetic contact is established,and the collision process of contact is simulated by the nonlinear software LS-DYNA.The stress and strain of the contact structure at each moment are obtained.The change trend of contact collision force under different closing speed and contact spring pre-pressure is analyzed,and the improvement measures are proposed to reduce contact collision.The fatigue life analysis process of contact structure is established in n Code software.The fatigue life and dangerous area of contact structure are predicted by coupling the stress-strain results with n Code software.In order to avoid the influence of the change of the contact slot parameters on the magnetic field characteristics of the vacuum interrupter,the fatigue life of contact is optimized by changing the structure of the support plate in this paper.The optimization law of cup-shaped axial magnetic contact is finally summarized in this paper,which can provide theoretical support for the design and development of vacuum interrupter products.