Thermal model for a low-speed flywheel in medium vacuum

This paper presents a model aimed to predict the temperature inside a flywheel energy storage system, and more specifically the temperature of the permanent magnet bearings of the system. The windage losses are evaluated by supposing an incompressible Couette flow between the flywheel and the enclosure. The eddy current losses inside the permanent magnet bearing are evaluated by a finite element (FE) electro-mechanical model. Those losses are injected into a FE thermal model. It shows that, in stationary low vacuum conditions, the temperature remains at acceptable levels. The sensitivity of the model to various parameters is also studied. Finally, the case of a loss of vacuum is examined, and it is shown that the system has a high time constant, and that the temperature of the magnets raises slowly enough.