Abstract
Faults in electrical machines can vary in severity and affect different parts of the machine. This study focuses on various kinds of short-circuits on the terminal side of a generic 20 kW surface mounted permanent magnet synchronous generator and how successive faults affect the performance of the machine. The study was conducted with the commercially available finite element method software COMSOL Multiphysics ® , and two time-dependent models for demagnetization of permanent magnets were compared, one using only internal models and the other using a proprietary external function. The study is simulation based and the two models were compared to a previously experimentally verified stationary model. Results showed that the power output decreased by more than 30% after five successive faults. In addition, the no-load voltage had become unsymmetrical, which was explained by the uneven demagnetization of the permanent magnets. The permanent magnet with the lowest reduction in average remanence was decreased by 0.8%, while the highest average reduction was 23.8% in another permanent magnet. The internal simulation model was about four times faster than the external model, but slightly overestimated the demagnetization.
Highlights
Permanent magnet synchronous machines, PMSMs, are widely used both as industrial motors and as power generators
Faults on the rotor side of the generator may be caused by bearing failure, eccentricity, damage of permanent magnets (PMs), asymmetries or mechanical looseness
The main purpose of this paper is to investigate the transient behavior of surface mounted uniformly magnetized Nd-Fe-B permanent magnets in a synchronous generator during several successive fault conditions
Summary
PMSMs, are widely used both as industrial motors and as power generators. PMSMs usually have a long expected lifespan and are likely to be exposed to one or several faults during its lifetime. Faults on the rotor side of the generator may be caused by bearing failure, eccentricity, damage of permanent magnets (PMs), asymmetries or mechanical looseness. Causes of failure can be, for instance, asymmetries, mechanical looseness or winding insulation breakdown. The generator can be subject to short-circuit events, either originating from internal faults, within the machine, or external faults. In cases when a PMSM is connected to an inverter, faults in switches and sensors may occur
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