The characterization of the severity of rotor delevitation events: A parametric study

Active magnetic bearing (AMB) failure and the ensuing rotor behavior is a very important aspect of AMB safety. A model for this rotor behavior was developed and was used to characterize the severity of rotor delevitation events. The characterization was done by means of severity indicators derived from the rotor behavior within the backup bearings. The indicator is a quantitative value that can be used to compare different delevitation events. The indicator presented in this paper is the non-dimensionalised velocity of the geometric center of the rotor (Vval). This indicator only requires the rotational speed and position data of the rotor to determine the Vval quantity. This ensures that this value can be determined for most current operational systems and on historical data logged from previous rotor delevitation events. In order to validate Vval, a comparison was done between simulated and experimental rotor drops and their associated Vval values. The model used to produce the simulation results is BBSim. Experimental results were obtained on a 4-axis suspended rotor, modified to use rolling element backup bearings.