Energy storage roller press bearings

Why do stationary flywheel energy storage systems use active magnetic bearings?

(Image rights: Piller Group GmbH) Many of the stationary flywheel energy storage systems use active magnetic bearings, not only because of the low torque loss, but primarily because the system is wear- and maintenance-free, a characteristic that plays a central role, especially in continuous operation.

Why is the speed of a roller bearing limited?

This speed in turn is limited by design factors and material properties. If conventional roller bearings are used, these often limit the speed, as do the heat losses of the electrical machine, if it forms one unit with the flywheel in a so-called integrated design.

How does magnetic lifting reduce axial bearing load?

In the case of a vertical axis of rotation—as it is common in almost all FESS applications—the weight force of the rotor on the bearings can be reduced by magnetic lifting, which enables a reduction of the axial bearing load and thus the loss torque. This solution is described in more detail in Sect. 10.3.1.

Why do rolling bearings increase temperature?

Especially a rolling bearing experiences not only an increase in temperature due to internal friction (rolling friction of the rolling elements, cage friction, lubricant displacement dissipation, etc.) but also an external temperature input caused by the rotor.

Is a steel flywheel a low-speed or high-loss mechanical bearing?

Historically, steel flywheel was considered ‘‘low-speed’’ and ‘‘older’’ technology associated with high-loss mechanical bearing. There is less research in the steel/isotropic flywheel design [23,24]. These works fo-cus on improving the specific energy and energy density by finding the optimal geometric profile or utilizing a novel configuration.

How does unbalance induced bearing load differ from a rigid bearing system?

The most important finding is that the unbalance-induced bearing load in supercritical operation decreases at higher speeds, whereas in a completely rigid bearing system, it increases with the second power of the rotational speed. Figure 9.46 shows measurement results of bearing loads determined with the aid of the test setup shown in Fig. 9.39.