Remarks on Load Dependency of the Voltage Quality of a 500 MVA Synchronous Generator with Fractional Slot Windings.

Abstract

The induced voltage shape of an electrical generator is mainly depending on the used materials, the electromagnetic design and the actual operational state. Especially large synchronous hydro generators are often equipped with a fractional slot stator winding in order to fulfill the high requirements of a sinusoidal voltage output. However, due to such a stator winding, many different harmonic field wave components are circulating along the airgap. Additionally to the fundamental harmonic wave and the higher harmonics with wavelengths 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 resulting voltage quality of a 500MVA salient pole synchronous generator is investigated with finite element methods separately for higher harmonics and sub-harmonics in dependence of various operational states.