Causes and characteristics of the electromagnetic vibration of a squirrel cage induction motor under load

Abstract

Three-phase squirrel cage induction motors (IM) have been used in all types of industry, because of their robustness and simplicity of structure, low cost, and ease of maintenance. Due to the resultant air gap flux wave, an IM produces electromagnetic vibration and noise more or less regardless of the slot combination. Recently, reduction of electromagnetic vibration and noise has become important from the standpoint of environmental improvement. Vibration caused by an IM at no-load has been studied for many years and its basic factors have been analyzed. However, electromagnetic vibration under load has not been analyzed sufficiently. Since vibration under load conditions is affected by load and installation, analysis of this vibration is a rather difficult task. But study of the electromagnetic vibration of the motor itself under load is basically the most important item. This paper clarifies, theoretically and experimentally, the causes and characteristics of the electromagnetic vibration of an IM under load conditions. First, general equations are derived for the dominant electromagnetic force waves that produce electromagnetic vibration. Causes and vibration modes are clearly classified and a theoretical analysis provides a basic concept for electromagnetic vibrations. Second, electromagnetic vibrations for various loads are measured taking the effect of natural frequency of the motor into consideration. The measured data are classified and analyzed in detail, based on the proposed theory. © Scripta Technica, Inc. Electr Eng Jpn, 120(4): 81–89, 1997