A Thermal Equivalent Calculation of the Overload Time of Medium Voltage Distribution Transformers

This paper aims at the proposal of two methods for temperature calculation of the top of the oil for medium voltage distribution transformers. The first method, based on a simplified thermal equivalent circuit, considers the data of the temperature rise testing and resulting parameters. The second considers various load conditions and also the knowledge of the constructive characteristics of the transformer for determining thermal parameters and provides, through an iterative tool, the temperature of the top of oil. The advantages and disadvantages of each model is presented and discussed.