Unbalanced Magnetic Radial Pull During Module Open Circuit Fault in a Multi-Modular, High Voltage PM Synchronous Direct Drive Generator for Offshore Wind

This paper compares an analytic and finite element method (FEM) for calculating unbalanced magnetic pull in a multi-modular PM synchronous generator with tangential air gaps between the segments. The radial force density from the Maxwell stress sensor and resulting unbalanced magnetic pull amplitude are calculated for a 10 MW generator with one segment open circuited, operating at no-load condition, and the remaining segments operating at nominal load. The analytic model and the FEM model corresponded well for the mean unbalanced magnetic pull, but the analytic model was not able to predict the lower harmonics in the ripple. The methodology in this paper may be useful for first iteration fault tolerant design of multi-modular machines with tangential gaps between stator segments.