Abstract
The operation of non-linear load leads to distortion on system and equipment. The nonlinear relation between voltage and current implies higher frequency components of current and voltage called harmonic. This may constitute distortion on the fundamental waveform. If this distorted waveform applies to a transformer, it may lead to additional losses and therefore reduces transformer efficiency. The losses occur due to the degree of harmonic distortion, commonly called total harmonic distortion (THD). This paper discusses the operating condition of three-phase transformer serving nonlinear load in the form of power converter. The related impacts of THD on voltage and current, additional power losses and its efficiency are analysed. The calculation is implemented on a 200 kVA three-phase transformer serving a rectifier supplying a balanced inductive load. For analysis purpose the system is simulated using Simulink in MATLAB environment. From the generated results it is identified the THD of voltage and current distortions of 19% and 18%, respectively. These distortion is analysed to confirm the standard of IEEE 519-2014 verifying the distortions exceeding the maximum limit for both voltage and current. The effect of harmonic on transformer loss is also observed. The loss is calculated taking into account all parameters ensuring the calculation is valid. The result indicates the increase of loss due to considering harmonic distortion from 0.62 kW to 1.854 kW causing reduction of efficiency from 99.65% to 98.97%. This loss addition implies a derating of the transformer to avoid transformer overload that may shorten the device’s lifetime.
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