High Speed Backup Bearings for Outer-Rotor-Type Flywheels - Proposed Testrig Design

Magnetic levitated rotors for high speed applications need backup bearing (BB) for safe spin down or relevitation after magnetic bearing failure or overload situations. Especially in flywheel energy storage systems long spin down times due to the high kinetic energy content and the vacuum environment complicate the use of conventional bearings as BBs. Depending on the geometric dimension, the rotational speed of the rotor and associated rotordynamic effects today’s available bearings (usually rolling element bearings) cannot fulfill their task with the desired lifetime. This paper shows mechanical and thermal problems as well as approaches to mitigate them. For a built and tested Outer-Rotor-Type flywheel its BB system is discussed. For an increase of the surface velocity limit and the extension of the BB lifetime several design improvements are suggested. Properties of a test rig and its special rotor design for BB testing are described and proposed for further experimental investigation. A design of the test-BB is proposed and the data acquisition as well as the dynamic behavior of the rotor is described.