Strength Analysis And Non-Destructive Evaluation Using Creeping Wave For Porcelain Rod Suspension Insulator Served

The invention and application of electricity are a great revolution in human's history, which not only create more facilities for human's daily life, but also promote a chain of development in other fields, impel human being to explore further. Electrical insulator is one of the important parts in transformer substation and transmission line, plays a role in connecting the lead with the bracket, as a kind of electrical insulator, mechanical connection and support. The key to safe operation of electrical transmission line is the quality of suspension insulator. Frequent fracture accidents have already happened to a great deal of insulators used in our country from the beginning of 1970's, with about 30 years history from then on, which brought our country economy and production out a great deal of loss, being a great hidden trouble to electrical department. Electrical porcelain insulator (EPI) is mostly made up of cast-iron flange, electrical porcelain and cement, the cement is gripped between the cast-iron flange and electrical porcelain, restrained when expansion, then produces stress on electrical porcelain insulator. It is numerical stated that the site near the flange oral part is the main position where the crack initiate and EPI rupture ultimately. In order to reduce the expansion stress resulting from cement's expansion and prolong the life-span of porcelain insulator, a thin asphalt buffer layer is coated between the porcelain and the cement. Electrical porcelain is a kind of classical brittle materials; the velocity of crack's growth is quite rapid so it's very important to prosecute non-destructive testing termly to avoid damage. The main aim of non-destructive testing about EPI is to detect inner micro-flaws as soon as possible, especially micro-crack, in order to forecast the length of life or replace the bad insulator, and eliminate hidden trouble resulting in accident. But because of structural complexity, the common examining measurement can't be used to get satisfying result. In this paper, the porcelain material's features are discussed first, and then the cause of EPI's deterioration is discussed: the failure of EPI is resulted from multiform factors which interact, except flaws which are taken in the process of manufacture, machining and self gravitation,mechanical load which are endured in the course of operation, environmental factor can't be ignored. It is the prime reason that the buffer layer's thickness isn't thick enough in the process of cementing or the buffer layer loses its elasticity in the course of operation, which results in nowhere does swelling stress's release produced by the cement. FEM analysis software-ANSYS is used to analyze temperature-structural stress in this location, and the analysis shows that the stress is reduced and changed by the asphalt buffer layer, and then the maximum stress is found, the minimum critical crack size is computed in the help of fracture mechanics, which offers guidance for non-destructive testing about the EPI. The examination about the EPI with the help of creeping wave probe is discussed not only in theory but also in experiment. The feasibility of examining EPI with the help of creeping wave is analyzed, and then the special test block is made, through experiment the advantage and disadvantage between the single crystal creeping wave probe and the twin crystal creeping wave probe with examining EPI are compared, which provide a kind of new means for non-destructive testing about the EPI.