Losses Analysis of Direct Drive PM Generators Suffering from Demagnetization

Direct drive PM generators are critical machines and gain ground in the field of renewables, especially in remote applications. It is therefore important to guarantee their reliability and long uninterrupted operation. One faulty condition that may propagate over time, if undetected, is the demagnetization one. This paper studies the impact of partial demagnetization on the electromagnetic and thermal performance of PM generators. More specifically, the fault will create a magnetic imbalance leading to the creation of circulating currents in the stator coils. The circulating currents will in turn increase the machines’ losses and drop of efficiency and consequently increase the severity of the fault. Finally, the paper offers a fault severity analysis and relates it with the electromagnetic and thermal stress of the faulty PM machines.