Diagnosis of present-day cellulosic insulating materials used in electrical power industry

Failure of solid dielectric materials in power equipment usually results into undesired outages and expensive replacements due to absence of recovery unlike in liquid and gas counterparts. It is therefore, necessary to assess the electrical insulating properties of the solids materials. This research work was aimed to determine if a relationship could be found between breakdown strength and other properties of solid insulating material on an empirical basis by using variables predicted by basic theory. A simple equation to predict dielectric strength using ASTM electrode system, considering the effect of stray or edge capacitances has been proposed for cellulosic insulating materials like diamond dotted paper, paper phenolic sheets, cotton phenolic sheets, leatheroid, and presspaper which are in use present time. The equation defines a relationship between dielectric strength and other properties like loss tangent, volume resistivity, dielectric constant and thickness. Values of the parameters required in the equation may be obtained by performing non-destructive dielectric diagnostic measurements. For a given material, calculated electric strength using the proposed equation and experimentally measured values are also compared and found close to each other. This is expected that the suggested equation will be useful to practicing engineers and designers for quick estimation of electric stresses in cellulosic materials studied in this research work.