Research On Motion And Inhibition Of Spherical Metal Particles In SF₆ Gas Under DC Voltage

Metal particles may be inevitably produced in the process of production,transportation,installation and operation in GIS/GIL.Under the action of electric field,metal particles may lift and move in GIS/GIL cavity,even adhere to the insulator surface,initiating gas gap breakdown or insulator surface flashover and reducing the insulation performance of GIS/GIL.Relative to the AC voltage,metal particles will move more violently under DC voltage as the direction of electric field force is fixed,so metal particles contamination is even more serious.In view of metal particles contamination in GIS/GIL,the paper had made a certain idealization of the shape of metal particles in actual engineering from the perspective of mechanism research,and studied the motion and inhibition of spherical metal particles in SF6 gas under DC voltage.The main contents are as follows:An experiment platform of metal particles motion was setup,and a method to obtain key parameters of particles motion was proposed.With the SF6 gas tank as the main body,the high speed camera,ultrasonic sensor and ultra high frequency sensor were used to collect the motion figures,ultrasonic signals and ultra high frequency signals in the process of particle motion respectively.The combination analysis results of ultrasonic signals and ultra high frequency signals showed that the ultrasonic signals ars mainly caused by the collision between the particle and the electrode,and the influence of the micro-discharge between the particle and the electrode on the ultrasonic signal can be neglected.An image processing method was proposed to accurately obtain the instantaneous displacement of the particle motion.The calculation method of the coefficient of restitution when the particle collides with the electrode was proposed,and the specific value was obtained.The characteristics of the electric field distortion on the particle surface during the particle motion in the coaxial cylindrical electrode were studied.The electric field distribution of the particle in the coaxial cylindrical electrode was calculated,the force of the particle was analyzed,and the ordinary differential equation of the particle motion was proposed.By treating particle motion as finite element mesh motion,the electrical and mechanical field coupling solution of particle motion was realized in the COMSOL Multiphysics,and the electric field distortion during particle motion was obtained.The influence of voltage,particle diameter,and position of particle on the distortion of the electric field was investigated.On the basis of obtaining the electric field distortion,the mechanism of micro-discharge and gap breakdown induced by particle motion was calculated basing the starting criterion of the streamer and the breakdown criterion of gas gap.The ultrasonic properties of the particles when colliding with the external cavity in a coaxial cylindrical electrode were studied.Based on the elasto-plastic collision theory,the three physical phases of collision between the particle and outer cavity were analyzed:elastic deformation,elastoplastic deformation,and elastic recovery.The contact force model was established when the particle collides with the electrode and the collision process was calculated.The contact force changes and the maximum contact force were obtained.The correlation coefficient method was used to analyze the relationship between the maximum contact force and the amplitude of the ultrasonic signal obtained experimentally,and the fitting formula of the maximum contact force,collision velocity,and particle diameter were obtained.Further dimensionless analysis of the fitting formula revealed the effect of voltage and particle diameter on the ultrasonic signals.The reason why the dielectrical coated electrode can enhance the particle lifting field was studied.The lifting field of the aluminum particle with a diameter of 1mm under different SF6 gas pressures,film materials and thicknesses were obtained,and the motion figures of the particle after lifting were obtained.A method to calculate the amount of charge when the particle lifted was proposed,and the charge amount was obtained.The deficiencies of the lifting field calculation model proposed by Parekh were analyzed and corrected.From the point of view of the particle charge and force,the reason why the dielectrical coated electrode can enhance the particle lifting field was revealed.