An online eccentricity fault detection method for Axial Flux machines

An eccentric air-gap creates an electromagnetic force between the rotor and the stator of electrical machines. This force is known as unbalanced magnetic pull (UMP). This force leads to further increase the eccentricity and may severely reduce the performance of the machine, producing acoustic noise, vibration, excessive wear of bearing, rotor and stator rubbing. This paper presents a universal online method for diagnosing eccentricity in Axial Flux Permanent Magnet (AFPM) Machine. It is based on measuring the induced voltages of three search coils positioned above the coils of three phases as a suitable criterion for fault detection. Using this number of search coils enables not only the Static Eccentricity Factor (SEF) but also the minimum air-gap position to be estimated. The Three-Dimensional Finite-element Method (3D-FEM) was used to accurately analyze the machine and to validate the method. This study indicates that the induced voltages of the search coils suggest an online method for indirectly measuring eccentricity during machine operation.