Effects of current and voltage harmonics on distribution transformer losses

The drive to improve energy efficiency and reduce electrical loading has resulted in energy efficient lighting such as compact fluorescent lamps (CFLs) replacing conventional incandescent lamps. However, the presence of such non-linear loads has brought about the injection of voltage and current harmonics into electrical networks. As transformers are the interface between the supply and the non-linear loads, the investigation of their effects on transformer losses is of great importance. These harmonics can cause excessive loss and abnormal temperature rise in the transformers, thus reducing their operational life span. This paper investigates the impact of current and voltage harmonics of the loads on a single-phase 25kVA distribution transformer. Harmonic spectra of a range of non-linear loads including CFL, LED tube, PC and fluorescent lamp are obtained. A single-phase inverter is used for harmonic generation to simulate power supply harmonics injected into the transformer. Open circuit and short circuit tests are conducted on the transformer under the effect of harmonics, and the impacts on core loss are analyzed.