| Whether the power grid can operate reliably and safely is closely related to the safe operation of all kinds of transmission and transformation equipment which constitute the main body of the power grid,and the operation condition of large oil-immersed power transformer,as the key equipment,is directly related to the safety and stability of the power grid.The life of power transformer depends largely on the state of its oil-paper insulation system.Insulation failure is the main factor affecting the normal operation of power transformer in actual production.There will be a variety of bubbles in the oil-paper insulation of transformers,and the existence of bubbles will lead to partial discharge in the in sulation,and even lead to breakdown with the deepening of the discharge degree.Therefore,it is of great significance to study the influence of bubbles on the insulation of power transformers to ensure the stable and safe operation of the power system.At present,based on the insulation theory,the appearance of bubbles will inevitably affect the performance of oil-paper insulation,but the influence characteristics of surface discharge and flasover caused by bubble defects of oil-paper insulation need to be further studied,and the influence of temperature and moisture in the test is often simplified or ignored.Therefore,a surface discharge test platform for oil-paper insulated bubbles was built in this paper,and the electrode model was reasonably optimized to meet the experimental requirements.Firstly,the characteristics of initial discharge voltage,flashover voltage,discharge spectrum and partial discharge statistical parameter of oil-paper insulation with different bubble content under the action of power-frequency AC voltage were summarized.The results show that the increase of bubble content accelerates the development of discharge,which is characterized by the decrease of boost time and initial discharge voltage.The degree of discharge deepens,showing that the mean square rate of discharge increases when discharge occurs.At the same time,in the process of partial discharge,the bubbles in the oil-paper insulation will fuse.Although the content of bubbles does not change,the initial discharge voltage will decrease gradually in the form of increasing the size of bubbles,making the surface discharge more likely to occur.The influence of bubbles on surface flashover of oil-paper insulation is further studied.It is found that the bubbles in oil-paper insulation are mainly affected by electric field in two aspects.One is that the bubbles in oil-paper insulation will be broken down and broken into more small bubbles.The other is to promote the occurrence of surface flashover,the size of the oil paper insulation bubble.The existence of bubbles will reduce the flashover voltage along the surface,promote the flashover and even breakdown of the oil paper insulation,and destroy the insulation strength.The existence of bubbles will increase the carbonization degree of insulating oil after flashover,but weaken the damage degree of cardboard to a certain extent.The influence of different moisture and temperature on the surface discharge characteristics of oil-paper insulation bubbles was tested on the test platform,and the influence of moisture and temperature on the dielectric characteristics of oil-paper insulation was verified.The influence of bubble content,temperature and moisture on the surface discharge characteristics of oil-paper insulation was analyzed.The results show that the initial discharge voltage of oil-paper insulation decreases and the development of discharge is promoted under the gradient of oil temperature at 10 ℃,20℃ and 40℃.However,the water content in oil has little influence on the surface discharge of oil-paper insulation at the gradients of 15 ppm,20ppm and 35 ppm,which can be almost ignored.The main reason is that the oil temperature has a significant effect on the dielectric properties of insulating oil in the test range,while the water content in the oil has little effect on the dielectric properties of oil.Through correlation analysis,can be found in the selected test range,the change of the bubble content for the paper insulation creeping discharge more obvious the influence of the initial discharge voltage,oil temperature less correlation,and the moisture content in the oil and the initial discharge voltage into extremely weak relevant or irrelevant,in studying the characteristics of bubble effect on oiled paper insulation discharge can be ignored in the influence of the influence of water content in oil. |
PDF Full Text Request