Effect of harmonics on iron losses

Abstract

This thesis investigates the effect of non-sinusoidal flux waveforms on iron losses through Epstein frame measurements. The report includes a survey of empiric loss calculation methods. First, it is investigated how to find the loss coefficients for calculations of losses with sinusoidal wave forms. For this purpose, both new and previously obtained measurement data is used. Different methods to find the coefficients are studied and their short comings are pointed out. It is found that the curve fitting method using a series of measurements, ±4% agreement between empiric and experimental values is possible for wide range of frequencies (e.g. up to 400 Hz). This can be compared to ±30% difference for the constant coefficient method utilizing experimental data for only two test points. Consequently, an experimental investigation is made on the iron loss in presence of harmonics. One or two harmonics are superimposed on the fundamental flux wave. The effects of both the harmonic amplitudes as well as the phase angles on iron losses are studied experimentally. It is observed that the phase angle between fundamental and harmonic waves is important for low order harmonics (e.g. 5th /7th) but has minor effect on higher order harmonics. Further, a time domain analytical expression for calculation of iron losses with distorted waveform is recommended and it is found that the recommended expression gives ±10% agreement with the experimental results. However, it is shown that the impact of the phase angle is not covered using the said expression. The results also show that iron loss coefficients found using measurements with sinusoidal wave forms can be used for distorted waveforms as well.