Numerical and experimental analysis of the thermal behavior of dry-type transformer supplying nonlinear loads

Abstract

Thermal behavior of the transformers is affected by distorted loads caused by the influence of electronic equipment in the electric current. The aim of this work is to analyze the thermal behavior of a 5 kVA dry-type transformer working with linear and non-linear loads. Thermocouples and PT100 were used to measure the temperatures inside the cores. In addition, fans were used inside the transformers to analyze the influence of forced convection in the temperatures. Empirical correlations from literature were used to determine the average heat transfer coefficient used in the numerical analysis and to validate the results obtained in this work. The emissivity of the core surface was measured with a thermal camera. COMSOL software was used for the numerical simulation of the heating of transformers under the effect of certain loading and cooling conditions. Comparisons between experimental and numerical temperatures were carried out to validate the methodology. Hot Spots temperatures and their locations were also possible to be estimated with this methodology. The Hot Spots temperature in the core reached 20 °C above the transformer insulation limit. These temperatures and locations will serve in the future to optimize cooling projects of shell-type transformers.