Calculation And Analysis Of Charge Amount Of Particles With Dielectrically Coated In SF₆ Gas Under DC Voltage

Free moving metal particles is the main factor that causes the safety accident of gas insulated line(GIL).In the study of deactivation of spherical free moving particles,dielectrically coated on the surface of low pressure electrode is a measure that limits the lifting movement of metal particles in electric field and reduces the opportunity that metal particles close to the high pressure electrode.In this paper,the parallel plate electrode is used as the model.And experimental method is adopted to investigate the lifting of metal particles before and after the dielectrically coated on the electrode.Then simulation is used to analyze the charge distribution and force of the particle surface under two conditions of bare electrode and dielectrically coated electrode.Finally,the theoretical basis of improving the lifting voltage of metal particles can be provided.The experiment in this paper is carried out from the parallel plate electrode,and explores the movement of metal particles under the bare electrode condition.According to the characteristic of constant acceleration motion between the electrodes,establishes a method for calculating the charge amount of particles from the kinematicformula.Although the charge amount of the particles placed on the electrode will change at the same electric field strength after the surface of low pressure electrode coated.The metal particles will still keep constant acceleration motion when they are lifting up.Therefore,the calculation method of charge amount derived from the kinematic formula has certain universality under the electrode model,and has nothing to do with coating.Based on the above calculation method,the charge amount of metal particles at the moment of lifting movement is figured out under the conditions of different materials and different thickness of coating.The experimental calculation shows that the charged amount of metal particles when lifting is significantly lower than that under bare electrode,and the lifting voltage of metal particles can be significantly improved after coating.In response to above phenomena,the calculation model of the electric field distribution of particle under the conditions of the bare and dielectrically coated electrodes was established respectively with the help of Comsol.The results show that the maximum value of the electric field under the bare electrode appears at the top of the particle and is subjected to an upward electric field.The maximum value of the electric field under the dielectrically coated electrode appears between the particle and the coating,and the direction of the electric field force is related to the electrical charge,and there are two kinds of situations,downward and upwards.When the voltage achieves the lifting voltage under the bare electrode,metal particles may still be subjected to the downward electric field force.Therefore,the decrease of charge and the downward of the electric field force are the reasons for enhancing the particle lifting field.