Derivation of Dynamic Characteristics for Induction Motor Support

In induction motors, the rotor rotates within the supporting structure i.e. bearing support. The dynamic behavior of the rotor depends on the rotor itself, dynamic characteristics of the bearings, and supports structure. To perform rotordynamic analysis, the rotor elastic properties i.e. mass, inertia, stiffness from the rotor elements, bearings, and supports should be derived. In rotordynamic analysis, each support is reduced to two single degree of freedom spring-mass system in both the horizontal and vertical directions. In this paper, the dynamic characteristics of the supports are studied. We present a finite element method to calculate the equivalent mass and stiffness of the supports in a typical induction motor. We assume the equivalent supports properties remain unchanged regardless of the rotor speed or any dynamic excitation. The supports stiffness is computed based on static deflection of the bearing pedestal and the supports equivalent mass is derived from the modal analysis of the supporting structure.

Keywords:

dynamic coefficient , reduced model , bearing pedestal , rotordynamic