Vibration and Noise Analysis of Squirrel Cage Induction Motors with Double Non-Skewed Rotor Structure

Electromagnetic vibrations that are produced by the adjacency of force's frequency and natural frequencies of the system usually cause a number of problems in electrical machines, including mechanical vibration and acoustic noise, which lead to the equipment lifetime reduction. The slot skewing method effectively alleviates the vibration/sound issue in induction motors; however, it has some disadvantages, such as a decrease in output torque, intensified stray losses due to inter-bar currents, and an increase in iron loss. In this regard, this paper studies a double non-skewed rotor (DNSR) as a possible alternative to skewed designs. The study, first, investigates the electromagnetic force and vibration modes of the proposed design. Later, a coupled analysis is used to study the vibration and sound pressure level of the system. The results show that the new method could avoid the disadvantages of the conventional skewing and significantly reduce the vibration and acoustic noise.

I. Introduction

Induction motors (IM) have been widely used in industrial and household applications thanks to their low-cost production, robust construction, and low maintenance requirements. However, IMs have some drawbacks as well; parasitic effects such as pulsating torques, mechanical vibration, and acoustic noise still remain challenging issues for machine designers. Besides, modern electric motors are designed with higher magnetic flux density in the air gap than motors manufactured fifty years ago, and, consequently, the electromagnetic vibration and noise are higher in newer motors, regardless of the stator/rotor slot combination [1]. On the other hand, with the increasing environmental concerns, vibration and noise issue has become more challenging for machine designers. In this regard, both industrial and academic communities are looking for a solution to minimize the torque ripple, noise and vibration in electrical machines.