Impact of different harmonic loads on distribution transformers

The increased usage of electrical load devices causes non-sinusoidal waveforms of currents and voltages in the power system. These harmonic loads have a significant impact on distribution transformers. The primary effect of harmonic currents are the additional power losses in transformer components, which result in increase in generated heat, as well as reduction of transformer's life-expectancy. This study examines the effects of different nonlinear loads on а dry-type three phase distribution transformer with rated power of 4.5kVA and rated voltage 440/380V. Measurements are done to several relevant parameters, such as: current and voltage high order harmonics, active and reactive power, power factor, total harmonic distortion etc. with sophisticated instruments in laboratory conditions. Using the measurement data, additional power losses are calculated according to the mathematical model proposed in the IEEE Std. C57.110-1998. This study shows an experimental confirmation of theoretically expected results.