| As the main part of oil-immersed type transformer,laminated pressboard is made of thin layers of insulating paperboard by applying insulating glue.Due to the complex bonding and pressing process,and the negative effects of different kinds of insulating adhesives on the insulation performance,the interlayer adhesive becomes the weak point of surface flashover and partial discharge fault.The research on the influence of insulating adhesive on the surface flashover and partial discharge characteristics of oil impregnated laminated paperboard,and the analysis of the change of insulating adhesive in the discharge process from the micro morphology and molecular structure are helpful to correctly understand the discharge mechanism and essence of the composite insulation system,so as to provide the basis for the selection of insulating adhesive,the structural design of laminated paperboard and the improvement of bonding process.In this paper,the effects of the type of insulating adhesive,the distribution of electric field,the number of brushing layers,the bonding process and the direction of adhesive layer on the flashover characteristics of laminated paperboard were studied by simulation experiment;Secondly,the effects of different types of insulating adhesives on the partial discharge characteristics of laminated paperboard were studied;Finally,the micro physical morphology and chemical functional groups of the viscose interface before and after discharge were compared and analyzed(1)The influence of phenolic resin adhesive,casein adhesive and phenolic adhesive paper on the flashover characteristics of laminated paperboard was obtained.It was found that the phenolic resin adhesive had the best insulation performance among the three adhesives.The whole surface adhesive was more suitable as the brush coating method of insulating adhesive than the point adhesive.The adhesive layer was the weak link in the insulation structure of laminated paperboard,and the compressive strength of the adhesive layer was higher when it was perpendicular to the applied electric field.It is found that the more uneven the electric field is,the higher the flashover voltage is,and the greater the probability of discharge along the adhesive layer is;In terms of the type of insulating adhesive,the compressive strength of phenolic resin adhesive is 6% higher than that of the worst phenolic adhesive,and the compressive strength of casein adhesive is between the two;The less the number of laminations(the number of adhesive layers),the higher the flashover voltage.The flashover voltage of 5-layer paperboard is 7.8% lower than that of 3-layer paperboard;The results show that the flashover voltage of the laminated paperboard is about 14% higher than that of the point bonding;When the direction of the adhesive layer is parallel to the applied electric field,the compressive strength is 18% lower than that of the vertical layer.(2)The partial discharge characteristics of laminated paperboard bonded with phenolic resin adhesive,casein adhesive and phenolic adhesive paper were obtained.It was found that the existence of insulating adhesive made laminated paperboard more prone to partial discharge than single-layer paperboard.The partial discharge resistance of phenolic resin adhesive was stronger than casein adhesive,and phenolic adhesive paper was the worst.The results of partial discharge test show that the average initial discharge voltage of the laminate without adhesive brush is 56 k V,which is 27%,26% and 51%higher than that of the laminate bonded with phenolic resin adhesive,casein adhesive and phenolic adhesive paper,respectively;Compared with phenolic resin adhesive,casein adhesive and phenolic adhesive,the maximum discharge capacity and discharge times per unit time of non brushing laminated paperboard decreased by 10.4%,19.6% and 39.1%respectively,and the discharge times per unit time decreased by 32%,30% and 43%respectively.The maximum discharge capacity and discharge times per unit time of the laminate bonded with phenolic adhesive paper were significantly higher than those of other laminates(3)It is found that the bonding state of the adhesive layer and the functional group structure of the insulating adhesive molecules are the important reasons for the laminated paperboard to discharge easily.Through SEM observation and analysis,it is found that there are physical defects such as pores and bubbles in the adhesive area.The tiny oil gap formed by these defects bears higher electric field strength than solid insulation,which distorts the local electric field strength and leads to the occurrence of partial discharge.During the discharge process,the insulating glue molecule is easy to break the bond,which leads to the change of the corresponding chemical group content.The broken bond generates low-carbon organic compounds in the form of methane,ethylene and other gases.The formation of new bonds releases energy,which intensifies the gasification of transformer oil.In addition,the insulation defects of the adhesive itself further lead to the distortion of the local electric field,It promotes the formation of gas channel,accelerates the discharge process,and finally leads to the formation of flashover channel on the surface of laminated paperboard. |
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