Towards the Selection of Balancing Planes to Attain Low Vibrations in Flexible Rotor Motor Systems

Abstract

Electric motors with variable frequency drives have several kinds of excitations, such as mechanical unbalance and electromagnetic forces between the rotor and stator. They cause undesirable lateral vibrations in induction motors during their operation. The vibration can be minimized by careful selection of balancing planes that are required to keep vibrations low at various operating speeds in the case of an induction motor rotor. It is important to note that arbitrary selection of balancing planes may not be feasible due to manufacturing, assembly and existing motor design constraints. In this research, a rotordynamic model is developed for simulating free and forced response of the industrial scale motor-rotor system operating at super-critical speed. The accuracy of this model is verified with the experimental modal analysis data. Subsequently, this model is used to design for selecting balancing planes to minimize the vibration at critical and operating speeds. This paper describes a complete process for achieving a suitable balancing through parametric study. The effects of residual unbalance on the vibrations at the super critical operating speeds are also highlighted. Research is currently underway in formulating and solving associated optimization problems for estimating optimal balancing for a range of operating speeds as well as multiple modes of interest.