A simple method for calculating winding temperature gradient in power transformers

This paper presents a new method for calculating winding temperature gradient in large power transformers. A general formulation of the problem is made using the electrical analogy. An expression for the thermal resistance of the solid insulation is found using analytical methods. Expressions for the thermal resistance of the oil boundary layer for natural and directed oil flow are then found through correlation of test results from actual transformers. A comparison of the results of the new method and previous methods is presented. The new method is found to be a significant improvement.