On the Effects of Subsynchronous Interharmonic Voltages on Power Transformers: Three Phase Units

The effects of subsynchronous interharmonic voltages (SIVs) on three phase power transformers are presented and discussed. In a companion paper, the results of an experiment study a single phase transformer highlighted the need for accurate modeling of the magnetization curve. This study focuses on the magnetizing currents, rms values, and spectral components in the presence of SIVs. A suitable time domain model based on the physical phenomena, as well as a circuit analysis, is presented for both three and five limbs core configurations. The model is experimentally validated and the results of numerical simulations, carried out for different power transformers, are utilized to determine the SIV effects for a variety of magnetizing curves, core geometries, SIV magnitudes, frequencies, and symmetrical components. A compact index able to give a first quantitative estimation of the SIV effects is introduced.