General Diagnostics in Direct-Drive Permanent-Magnet Synchronous Generators Using Two Magnetically-Coupled Search-Coils

This article aims to present a novel magnetic flux condition monitoring method based on two search coils. The proposed method can detect all the common faults occurring in Permanent-Magnet (PM) machines. The idea is based on two search coils, one placed in the rotor and one in the stator, which couple magnetically under faulty conditions due to their relative motion. The induced voltage distribution on the stationary search-coil is associated with the type of fault, and the amplitude with the fault severity. The studied faults are the local demagnetization, inter-turn, static and dynamic eccentricity. The induced voltage on the stator search-coil was derived under inter-turn fault and partial demagnetization to provide more insight into the mechanism of the proposed method. 2-D Finite-Element Analysis (FEA) simulation and experimental results by two radial-flux permanent-magnet machines with different power output classes support that the method can be used effectively for condition monitoring of all the faults under stationary and non-stationary speeds and loads.