Transient Response of Active Magnetic Bearing Rotor During Rotor Drop on Backup Bearings

Abstract

Backup bearing is a key safety component of the rotating machinery with the active magnetic bearings (AMBs). Owing to many unexpected reasons, the AMB rotor running at the full speed may drop onto the backup bearings. Sometimes, the full clearance whirling motion is induced, which is harmful to the machine. Therefore, it is quite important to know the transient behaviour of the AMB rotor and the backup bearing. Till date, a lot of works have been performed on the AMB rotor drop and various mathematical models were established. However, most of them took into account only the interaction between the rotor journal and the backup bearing but neglected the interaction between the shaft and the stator component. As we know, for a real AMB machinery, there should be seal components, and the clearance of the seal component is very small to avoid the leakage. If an AMB failure occurs, the interaction between the shaft and the seal component is likely to happen. Thus, it is more reasonable to include this factor into the AMB rotor drop model. The problem is addressed in this work. The previous model is extended to include the shaft-stator contact. The numerical analysis based on two sets of AMB rotor data shows that the dynamic behaviour of the AMB changes greatly, if the shaft-stator contact is considered. There is no longer an optimum support damping to prevent the harmful full clearance whirling motion, and at this time, a well-balanced AMB rotor is preferred.