Comparison of Distribution Transformer Losses and Capacity under Linear and Harmonic Loads

The significance of harmonics in power systems has increased substantially due to the use of solid state controlled loads and other high frequency producing devices. An important consideration when evaluating the impact of harmonics is their effect on power system components and loads. Transformers are major components in power systems. Supplying non-linear loads by transformer leads to higher losses, early fatigue of insulation, and reduction of the useful life of transformer. To prevent these problems rated capacity of transformer supplying non-linear loads must be reduced. This paper reviews the non linear loads effects on the transformers and the standard IEEE procedures for derating of the transformers which are under distorted currents. The equivalent losses and capacity of a typical 25 KVA single phase transformer is then evaluated using analysis and simulations in MATLAB/Simulink-based on useful model of transformer under harmonic condition- and results are compared.