Analysis of Radial Magnetic Forces in Hydrogenerators with Fractional-Slot Windings

This paper investigates radial magnetic forces in two hydrogenerators with fractional-slot windings. Using time-stepping finite element analysis, time and space distributions of the flux density in the airgap are computed. Maxwell stress tensor is then employed to calculate the radial forces analytically. Spatial harmonic orders of radial force density at one time instant and time-varying mean value of radial force density are studied. Using simple structural equations, stator deformations due to the zeroth and lowest non-zero modes of vibration are calculated and compared. Simulation results are discussed to identify the major cause of vibration in the hydrogenerators under investigation.