%0 Journal Article
%T Application of Wedges for the Reduction of the Space and Time-Dependent Harmonic Content in Squirrel-Cage Induction Motors
%A Konstantinos N. Gyftakis
%A Panagiotis A. Panagiotou
%A Joya C. Kappatou
%J Journal of Computational Engineering
%D 2013
%R 10.1155/2013/657425
%X The influence of the semimagnetic stator wedges of different sizes on the electromagnetic characteristics and the behavior of the induction motor is investigated. The study will be carried out with both analytical calculations and FEM analysis. The analytical calculations will take into account the stator and rotor slots, as well as the iron core saturation in order to study the spatial and time-dependent harmonic content of the air-gap magnetic flux density and electromagnetic torque. The size of the wedge plays an important role as it determines the tooth tips saturation, the high harmonic content of the air-gap magnetic flux density, and the electromagnetic characteristics of the induction motor. 1. Introduction It is well known that the existence of space and time harmonics in the electromagnetic variables of a symmetrical induction motor, fed by symmetrical three-phase voltage system, depends on several causes. Mainly, it depends on the presence of stator and rotor slots and the magnetic saturation of the stator and rotor core, especially at the tooth tips [1]. As a consequence, torque oscillations, high frequency losses, vibrations, and noise are generated. Those undesired phenomena lead to less efficiency, temperature increase, reduction of the induction motor life cycle, and higher maintenance cost. Since the induction motor is the most widely used electrical machine in industrial applications, there is a continuous research concerning the optimization of the motorĄ¯s electromagnetic variables and behavior, as well as improved design aiming at the motorĄ¯s longer life cycle [2¨C5]. Many methods have been proposed during the years, aiming at the reduction of higher rank harmonics. Such methods are the skewing, the construction of cage rotors with totally closed slots [6], and the construction of asymmetrical rotor slots [7]. Each one of these methods though, presents several disadvantages. Generally, the above methods have a negative impact on the power factor, due to the increased leakage flux. Furthermore, they result to reduced output power at nominal speed. Another method proposed for the reduction of the air-gap magnetic flux density harmonic content is the use of semimagnetic wedges for the closure of the stator slot openings. The wedges lead the flux in the slot opening and produce a more uniform flux density distribution in the air-gap but increase also the slot leakage flux. In [8¨C13], the authors have presented the influence of the stator slot openings on the induction motorĄ¯s efficiency, which is greatly improved by applying stator
%U http://www.hindawi.com/journals/jcengi/2013/657425/