An Investigation into Backup Bearing Life using Quantified Rotor Delevitation Severity Indicators

Safe and continuous operation of an active magnetic bearing (AMB) system relies heavily on its mechanical, electronic and software components. If one of these components fail, a rotor delevitation event (RDE) could be induced and possibly damage the backup bearing (BB) system. To improve BB reliability and safety, the usability of delevitation severity indicators (DVAL, VVAL and AVVAL) for predicting BB life is investigated. A small-scale active magnetic bearing system is used to generate BB degradation data by subjecting steel-caged rolling-element bearings to multiple RDEs. The RDEs are induced at specific initial conditions to analyze the statistical distribution of bearing failure. Delevitation severity indicators are subsequently used to compare a series of RDEs to find changes in BB performance characteristics. Using only shaft position and rotating speed data, this investigation showed that delevitation severity indicators change as the bearing degrades. A distinctive linear pattern of degradation is identified by calculating AVVAL for the duration when rotor whirl and bouncing occur. This linear degradation pattern is used to identify a failure zone wherein the probability of bearing failure is extremely high. A BB life prediction method based on this linear degradation pattern and AVVAL is developed and validated.