Wetting characteristics for kraft paper immersed in mineral and biodegradable insulation oils

Abstract

Moisture in power transformers are undesirable but yet unavoidable; hence necessitating its continuous study. The kraft paper of the oil filled transformer absorbs much of its moisture from the insulation oil in which it is immersed. The dielectric properties of the paper can be determined as a function of the wetting, penetration and saturation of the paper by the aqueous liquid in the oil. This paper compares the absorption characteristics of aqueous substances into kraft paper in two commercial insulation oils; palm based Palm Fatty Acid Ester (PFAE) biodegradable oil and petroleum based Hyrax Hypertrans mineral oil. Kraft paper thicknesses used in this study were varies from 0.2 mm to 0.5 mm and 1.0 mm. Test oil samples are taken directly from drum given by the suppliers. The study result shows that substances absorbed by kraft paper immersed in both insulation oils is dependent on paper thickness and chemical composition of the oils. The result shows that 0.2 mm thick paper absorbs the same aqueous percentage from both insulation oils irrespective of their constituent moisture content while the substance absorbed in both the 0.5 mm and 1.0 mm thick papers immersed in PFAE is higher that immersed in Hyrax Hypertrans by about 1 %. It also shows that the rate of absorption reduces as the paper thickness increases. This concludes that irrespective of the high initial moisture content of PFAE being higher than that of Hyrax Hypertans, same aqueous substance is diffused into kraft paper.