۱- Introduction

۲- Experimental rotor/AMB system

۳- Strain measurement system

۴- Strain measurement calibration

۵- Dynamic results

۶- Conclusions

References

Abstract

Active magnetic bearing systems provide contact-free rotor levitation, which allows near frictionless rotation and high rotational speeds when they operate normally. Under certain operational conditions, a transient fault, overload condition, or disturbance may occur. Touchdown bearings or bushings are therefore implemented in such systems to prevent contact between rotor and stator laminations. If the rotor makes contact with a touchdown bearing, the rotor dynamics may become transient or persistent in contact. Appropriate control strategies through the magnetic bearings to restore contact-free rotor operation may extend the life of touchdown bearings, and minimise operational downtime. To achieve this, an understanding of the contact dynamics is required, together with the relationship between contact and magnetic bearing forces. In this paper, rotor/touchdown bearing contact conditions are investigated experimentally using an active magnetic bearing system with a flexible rotor. Design methodology is presented for a measurement system capable of providing rotor/touchdown bearing contact related data, based on strain measurement. Strain induced contact signals are calibrated against applied magnetic bearing forces. The frequency dependent behaviour of the active magnetic bearing system is considered using evaluated force and phase measurements. The measurement data represent system identification for the potential of active magnetic bearing force-based contact control.

Introduction

The ability of Active Magnetic Bearings (AMBs) to provide contactless rotor levitation with vibration control has a number of benefits, including high-speed rotor operation, the elimination of the need for lubrication, long life and reliability, and energy efficiency due to the low friction losses. However, passive bearings are also used in AMB systems as Touchdown Bearings (TDBs) to prevent potentially damaging rotor/magnetic bearing stator contact from occurring. TDBs support the rotor while the AMB system is not operating, but also limit excursions of the rotor during operation, such as in cases of power loss, component failure, rotor mass loss, or other significant external disturbances. Such cases may cause rotor/TDB contact. Since TDBs are functional components of AMB systems, it is crucial to understand their influence on rotor dynamic behaviour in contact cases, in order to minimise potential damage. This is particularly important as TDB life and condition impacts directly on the reliability of AMB systems.