Study on longitudinal vibrations in turbomachinery coupled with skewed slotted bar cage induction motors

Venkatesham, B. and G, Krishna Reddy and G, Rami Reddy (2021) Study on longitudinal vibrations in turbomachinery coupled with skewed slotted bar cage induction motors. Journal of Vibroengineering, 23 (3). pp. 572-586. ISSN 1392-8716

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The present paper discusses the study of longitudinal vibrations in turbomachines coupled with skewed slotted bar cage induction motors and which are of the typical configurations in refinery industries. Based on vibration data, the severe longitudinal vibrations in tilting pad thrust bearing assembly and its failure mechanism during start up transient and steady-state operations has been observed. The excitation sources for these longitudinal vibrations originates from asymmetric air gaps in cage induction motors. Hereby, the study of longitudinal vibrations in turbomachines with thrust bearing is found to be necessary. A simplified Single degree freedom (SDOF) analytical model is proposed to estimate the peak response based on tuned variable stiffness method. Uniform air gap with rotor skew causes fixed thrust and is proportion to square of the load current. Static eccentricity across the rotor motor air gap causes variations in gap length and intern creates the torque fluctuations. This value is proportional to variance in square of the load current. In the proposed model evaluates the cascade effect of preloaded thrust due to rotor motor skewness and followed by compressor thrust due to differential pressure across the impeller in the form of the variable stiffness. This model has advantage in analysing the coupled motor and turbomachinery system response in longitudinal direction in a simple manner. The longitudinal vibrations estimate at thrust bearing and compared with experimental vibration data obtained from the field machinery. There is a good convergence between results of the analytical model and experimental field vibration data.

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IITH Creators:
IITH CreatorsORCiD
Venkatesham, B
Item Type: Article
Uncontrolled Keywords: Asymmetric air gaps; Electrodynamic currents; Induction motor; Longitudinal vibrations in turbomachinery; Rotor skew; Thrust bearing hydrodynamics;Cage induction motors; Differential pressures; Excitation sources; Longitudinal direction; Longitudinal vibrations; Static eccentricities; Steady-state operation; Tilting pad thrust bearing
Subjects: Physics > Mechanical and aerospace
Divisions: Department of Mechanical & Aerospace Engineering
Depositing User: . LibTrainee 2021
Date Deposited: 24 Jun 2021 04:35
Last Modified: 01 Mar 2022 07:08
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