Impact of 2D and 3D Rotor Eccentricity on End Winding Mechanics Behavior in Synchronous Generators

Investigations on static air-gap eccentricity (SAGE) faults about magnetic field variations, current/ voltage changes, and stator/ rotor vibrations have been widely carried out, while the mechanical properties of the end windings have been rarely studied, especially in 3D eccentricity cases. This article provides a detailed study on the stator end winding mechanics behavior in synchronous generators at typical rotor eccentricity running conditions. Such mechanics behavior includes not only the electromagnetic force (EF) properties, but also the end winding vibrations as well as the stress/strain/deformation responses due to the uneven EF excitation. The typical rotor eccentricity running conditions include: 1) radial static air-gap eccentricity (RSAGE), 2) axial static air-gap eccentricity (ASAGE), and 3) hybrid static air-gap eccentricity (HSAGE). The theoretical analysis, finite element analysis calculation and experimental verification are performed respectively, by taking a 5kVA synchronous generator as the research object in this paper. It is shown that in normal and SAGE cases, the end winding EF/vibration contains the DC component and even harmonics, especially the 2nd harmonic. RSAGE increases the end winding EF/vibration, whereas ASAGE increases the end winding EF/vibration at the extended end of the rotor while decreasing the EF/vibration on the retracted end. Under HSAGE, both RSAGE and ASAGE will affect the variation trend of end winding EF/vibration with the rule of single direction SAGE fault. The nose part and the joint to connect the end part and the linear sections are the most dangerous positions to afford the mechanics responses, and the occurrence of SAGE will make these parts more vulnerable.