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

The effects of subsynchronous interharmonic voltages (SIVs) on single phase power transformers are presented and analyzed. The phenomena of hysteresis loop asymmetrization and core saturation are described. The accuracy of the different approximations used to model magnetization curves are evaluated against experimental measurements. The results obtained from both no-load and load tests demonstrate that very low frequency SIVs, even with magnitudes of less than 1% of the rated voltage, cause a significant increase in the rms value of magnetizing current and its harmonics and interharmonics.