WINDING THERMAL ANALYZING OF DRY TYPE TRANSFORMERS

Transformers are the most important power conversion units used in the electrical systems considering their prices. The life of transformers has a considerable economic impact on the operation of electrical systems. Though the transformer life expectancy depends on the operating temperature, the life expectancy at various operating temperatures is not accurately known. The information regarding loss of life of insulation is considered to be the best way through which the transformer life expectancy can be expected. The most important parameter in transformers life expectancy is the insulation temperature value. The aim of this paper is to present a new and more accurate winding thermal model for dry-type transformers based on heat transfer theory, application of the lumped capacitance method and the thermal-electrical analogy. The proposed model is verified using experimental results, which have been obtained from temperature rise test performed on a 5 kVA dry-type transformer