Critical aspects of demagnetization faults in multi-stage direct drive permanent magnet generators for renewablesCritical aspects of demagnetization faults in multi-stage direct drive permanent magnet generators for renewables Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2025-07-292023enDemagnetization of permanent magnet machines is a fault that evolves over time leading to an eventual catastrophic failure. This condition is of particular interest in renewables, with emphasis on remote applications such as offshore wind, tidal, and wave energy harvesting. Moreover, the demagnetization fault can be either uniform or non-uniform. The strong majority of research articles are focusing on non-uniform demagnetization and typically study the case of a single faulty magnet. This is because, the uniform demagnetization does not create harmonics that can be detected with spectral methods. Despite the above, the study of single magnet demagnetization studies have been criticized due to being unrealistic to describe most practical cases where permanent magnet machines are subjected to demagnetization due to overloading and/or overheating conditions and leading to uniform demagnetization. This article sheds some light into such theories, while studying a realistically induced in the lab, demagnetization case of a direct-drive C-GEN permanent magnet generator. The goals of this research are to examine the generated harmonic index due to the fault, the distribution of the demagnetization in space and the impact of the fault on the multiple generator stages due to the circulating currents.Paper 2023-EMC-0116.R1, presented at the 2022 IEEE Energy Conversion Congress and Exposition, Detroit, MI, USA, Oct. 09–13, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Electric Machines Committee of the IEEE Industry Applications Society [DOI: 10.1109/ECCE50734.2022.9947661]. This work was supported by the EPSRC under Grant MU-EDRIVE EP/V040758/1.http://creativecommons.org/licenses/by/4.0/IEEE Transactions on Industry Applications5966655-6663 Gyftakis Konstantinos Γυφτακης Κωνσταντινος Skarmoutsos Giorgos Barajas-Solano Ignacio Burchell Joseph Mueller Markus Institute of Electrical and Electronics Engineers Condition monitoring Demagnetization Direct drive generators Fault diagnosis Permanent magnet machines