Effect of power system harmonics on transformer loading capability and hot spot temperature

Under harmonic conditions, caused by nonlinear loads, losses and temperature inside the power transformer increase. The hot spot temperature is one of the major limiting factors that affect the transformer life time and its loading capability considerably. This paper presents the determination of field distribution on the transformer components as well as its losses using finite element method (FEM). The hot spot and top oil temperature are computed under harmonic conditions according to two techniques, i.e. the dynamic thermal model and IEEE guide. The effect of harmonics on the useful life of transformer is then analyzed. Finally, an algorithm is proposed to determine the loading capability of transformer under harmonic conditions.