Effect Of Aging Pressboard On The Characteristics Of Creepage Discharge In Oil/Pressboard Insulation

The traditional view that aging mainly affects the mechanical properties of pressboard, and little effect on the electrical properties is proved. However, in recent years, research data tends to show an increase of the failure caused by creepage discharge on the oil/pressboard interface in aged transformer. It is therefore of importance to carry out the study on the characteristics of creepage discharge on the differently aged oil/pressboard interfaces, in order to understand how the aged pressboard play a role in the evolution process of creepage discharge.In this paper, various aged pressboards had been made up by thermal aging method, and a set of video and image recording system for the phenomenon during creepage discharge was established, and a set of joint monitoring platform for partial discharge was also established, including impulsive current detection method, ultra high frequency detection method, ultrasonic detection method, and dissolved gas analysis method. Using the constant voltage method, the evolution process of creepage discharge on the differently aged oil/pressboard interface has been studied, pressboard layer and surface microstructure has been analyzed, the mechanism of the effect on the characteristics of creepage discharge by aged pressboard has been presented and proved, the changing law of the detection information for partial discharge has been summarized.The results showed that the effect of aging pressboard will bring the decreasement of compactedness and increasement of cavity amount and volume between cellulose layer by the effect of aging, which prompting the formation and development for the gas channel of creepage discharge, and quicken development average velocity of creepage discharge and white mark, and weaken significantly anti-creepage discharge performance in pressboards layer direction. Surface structure of aging pressboard was not damaged, nothing but deeply aging pressboard (80℃equivalent to running30years) will be damaged that the cavity turned up, which reduce insulating property in the perpendicular direction of surface pressboard.There are the distinguishing characteristics for the detection information of partial discharge between the early and later stage of creepage discharge, which is able to be used to diagnose the severity of creepage discharge.