Estimation of Dissipation Factor and Moisture Content of Kraft Paper Used in Transformer Bushing from Leakage Current

The bushing part of power transformers is usually exposed to very high electrical stress. This may cause unwanted failure, which will put the entire power distribution network at risk. The major part of the bushing insulation is comprised of oil-impregnated paper. A significant drawback of oil-paper insulation is that it accumulates moisture with service aging. High moisture content is also accompanied by high dielectric losses i.e. dielectric dissipation factor. This paper presents a method to predict moisture content and dissipation factor from leakage current data. Leakage current monitoring is a simple, low-complex monitoring method that can be used in online conditions. An attempt has been made in the present work to predict moisture content and dissipation factor from leakage current data. For this purpose, the harmonic content of the leakage current, especially the 3rd/7th harmonic ratio is the insulation-sensitive parameter.