Recently, adjustable speed hydroelectric power systems have been developed. In those power systems, AC exciting synchronous generators are used, instead of ordinary salient-pole type synchronous machines. However, some higher harmonic sequences are included in the distribution of air gap magnetic flux density and in the terminal voltage waveform of the AC exciting synchronous machines, because these machines have open winding slots. In order to develop better machines without terminal voltage waveform distortions, an evaluation method of the terminal voltage harmonics has been needed.
The authors describe mechanism of higher harmonics generation qualitatively and propose an analytical method of no-load terminal voltage waveforms, on the basis of two-dimensional magnetic field analysis considering movement of the rotor, for quantitative higher harmonics analysis. The analytical results of higher harmonics show good agreement with the experimental ones.
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