Harmonics has effect on transformer in various ways, e.g.:
1. Core loss: Harmonic voltage increases the hysteresis and eddy current losses in the lamination. The amount of the core loss depends on harmonic present in supply voltage design parameter of core materials and magnetic circuit.
2. Copper loss: Harmonic current increases copper loss. The loss mainly depends on the harmonics present in the load and effective ac resistance of the winding. Copper loss increase temperature and create hot spots in that transformer. The effect is prominent in the case of converter transformers these transformers do not benefit from the presence of filters as filter are normally connected on the AC. system side.
3. Stress: Voltage harmonics increase stresses of the insulation,
4. Core vibration: Current and voltage harmonics increase small core vibrations.
5. Saturation problem: Sometimes additional harmonic voltage causes core saturation.