Experimental Validation of a Method of Drying Cellulose Insulation in Distribution Transformers Using Circulating Synthetic Ester

Abstract

The article concerns a method of drying cellulose insulation of distribution transformers with the use of synthetic ester. This method uses the high solubility of water in the ester compared to other dielectric liquids. The method is based on the striving of the oil-paper insulation system for a state of moisture equilibrium. Water migrates from the cellulose insulation of the high moisture content to the synthetic ester which is subjected to continuous drying. The research was carried out on a complex laboratory model reflecting the transformer insulation system. In this model, the drying of the ester was carried out using a molecular sieve with an appropriately selected adsorber weight. To check the drying efficiency of the cellulose insulation, the water content in the pressboard strips taken from the model, both before and after the drying process, was determined. The water content was measured using the Karl Fischer titration method. The research showed the high efficiency of the proposed method of drying. With the ester moisture in the range of 110-130 ppm and the insulation system temperature of about 70 °C, the loss of water in the samples dried for 7 days was over one percentage point. The obtained test results constitute the basis for the validation of the method on distribution transformers.