Novel insights into the nonlinear dependency of the airgap magnetic flux density of synchronous generators with fractional slot windings in case of various operational states

To fulfill the requirements of the voltage shape quality, a fractional slot stator winding is often applied within large synchronous machines. Due to such a stator winding, a lot of different harmonic field wave components are circulating along the air gap. Additionally to the fundamental harmonic wave and the higher harmonics with a wavelength shorter than two pole pitches, the armature reaction of a fractional slot winding creates harmonic field components with a wavelength larger than two pole pitches, the so called subharmonics. The paper investigates the field harmonics of a 500 MVA salient pole synchronous generator in dependence of various operational states obtained from finite element analyses.