Harmonics effect on Transformer

Harmonics distortion effect on Power System and their impact on Induction Motors are already discussed. 
Some of the disadvantages of harmonics and their impact on the transformers are:

• RMS current increase
• Eddy Current loss increases
• DC offset current saturation

RMS current Increase:

Harmonics currents in the system will increase the RMS current in the transformers. This increase in the RMS current will increase the losses (copper losses) in the transformer which results in the reduction of the overall efficiency of the transformer

Eddy Current Loss Increase:

Eddy currents loss is proportional to the square of the applied frequency. As the harmonic components will have the frequencies of the order of multiples of the fundamental frequency eddy current losses will increase with the presence of the harmonic components in the current and voltage waveforms. Therefore because of the increase in the eddy current loss overall efficiency of the transformer comes down. Harmonic component also increase the temperature of the windings.

DC offset current saturation:

Due to the presence of dc component in the harmonics tend to saturate the core of the transformer.