Research On Space Charge Characteristics Of Cellulose Insulating Paper

In recent years,HVDC project has been widely used in China.Converter transformer is one of the most important equipment in power system,so it must be operated safely and stably.During its long running time,space charge is easy to be accumulated in its inner oil-paper insulation and electric field distortion will be caused,which can accelerate the deterioration process of insulation system.It is easier to replace aged insulating oil,the replacement of aged insulating paper wounded on the windings must be carried out after the transformer has been stopped and returned to the factory,so the service life of the insulating paper determines the service life of the transformer.Therefore,from the viewpoint of transformer safety,it is necessary to study the space charge characteristics of the insulating paper.The net charge density can be obtained by measuring space charge distribution in the insulating paper,but it can’t reflect the transport process of space charge in medium.Based on the transport model of bipolar carriers,the space charge characteristics of cellulose insulating paper are simulated by using COMSOL Multiphysics software.Firstly,the one-dimensional simulation model of the insulating paper is established and the physical process of charge motion is analyzed.Secondly,the distribution characteristics of charge density and electric field intensity in the insulating paper are analyzed,and the distortion effect of space charge on the electric field is quantitatively analyzed based on the simulation results.Then,the influence of the polarity inversion and their features such as aging degree and thickness of insulating paper on space charge characteristics is received.Finally,the feasibility of improving its mechanical properties with nano-silica modified insulating paper is explored,which indicates that nano-modified insulating paper could improve its mechanical properties,thus reducing the generation or development of internal defects within the insulating paper,so the ability to resist the space charge accumulation can be improved to a certain extent.The results show that,the same polar charge accumulation is formed in the insulating paper when the charge is injected by the electrode,the same polar charge weakens the electric field on both sides of the insulating paper and enhances the internal electric field,and this distortion effect increases the breakdown voltage across the insulating paper.The more serious the aging status is,the more space charge accumulates in the insulation paper,and the stronger the distortion of electric field is.When the thickness turns small,the speed of charge accumulation becomes faster.The deformation quantity of the nano-modified insulating paper decreased obviously compared to the unmodified one.