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Reduction of synchronous torques in induction machines using asymmetrical rotor slots
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. (HPD)
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
2012 (English)In: ICEMS 2012 - Proceedings: 15th International Conference on Electrical Machines and Systems, Institution of Electrical Engineers of Japan (IEEJ), 2012, 6401765- p.Conference paper, Published paper (Refereed)
Abstract [en]

Removing the rotor skew in induction machines reduces the negative effects created by inter-bar currents. On the other hand, synchronous torques at low rotor speeds may appear, this can prevent the rotor to reach its rated speed. This paper presents a new method for the reduction of synchronous torques in unskewed induction machines. By introducing modulated rotors, having an asymmetrical rotor slot distribution, these parasitic torques can be suppressed. A simple numerical model is used to find suitable modulation coefficients for an efficient reduction of synchronous torques. This method is verified by FEM-simulations of different rotor designs. The results show that the synchronous torques can be controlled by the modulation coefficients used.

Place, publisher, year, edition, pages
Institution of Electrical Engineers of Japan (IEEJ), 2012. 6401765- p.
Keyword [en]
Synchronous Torques, Starting Torque, Modulated Rotors, Asymmetrical Rotor Slots.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-107595ISI: 000332791700067Scopus ID: 2-s2.0-84873458181ISBN: 978-488686077-4 (print)OAI: oai:DiVA.org:kth-107595DiVA: diva2:576821
Conference
15th International Conference on Electrical Machines and Systems, ICEMS 2012; Sapporo; 21 October 2012 through 24 October 2012
Note

QC 20130220

Available from: 2012-12-13 Created: 2012-12-13 Last updated: 2014-10-14Bibliographically approved
In thesis
1. Analysis and Reduction of Parasitic Effects in Induction Motors With Die-Cast Rotors
Open this publication in new window or tab >>Analysis and Reduction of Parasitic Effects in Induction Motors With Die-Cast Rotors
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a study of inter-bar current effects on induction motors with die-cast aluminium and die-cast copper rotors. The parasitic effects introduced by these currents are analyzed and possible solutions to these problems are presented. This is realized by developing analytical tools for the simulation of inter-bar current effects. The methods used are verified by measurements on prototype machines. It is shown that the inter-bar currents can have a considerable effect on the motor starting performance, which can result in a reduced pull-out torque. At rated operation, this is seen as increased harmonic rotor currents, having a negative effect on the motor performance.

Results from calorimetric measurements show, that the efficiency gained when substituting a skewed die-cast aluminium rotor with a skewed die-cast copper rotor, is less than the theoretical expectation. It is shown that this is a result of a reduced power factor for the copper rotor. High inter-bar currents are believed to be the origin of this effect, increasing the harmonic content in the rotor magnetomotive force. This would be seen as an increased rotor leakage reactance. Results from locked-rotor tests, and simulations using measured values of inter-bar resistance, support this theory.

It is shown, that these negative effects are suppressed to a negligible level by the use of an unskewed rotor, but to the expense of a large synchronous torque at a low speed. By using a modulated rotor concept, having an asymmetrical rotor slot distribution, an unskewed rotor is designed to reduce this parasitic torque. Measurements on a prototype machine show that the modulated rotor suppresses both the inter-bar currents and the synchronous torque, resulting in an improved starting performance, without any significant change of the motor efficiency. The presented results strengthen the potential of the modulated rotor concept, introducing new possibilities for the reduction of negative effects appearing in induction machines.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 47 p.
Series
Trita-EE, ISSN 1653-5146 ; 2013:011
Keyword
Aluminium rotors, asynchronous torques, copper rotors, die-cast rotors, induction machines, inter-bar currents, modulated rotors, starting torque, stray losses, synchronous torques
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-119603 (URN)978-91-7501-682-5 (ISBN)
Public defence
2013-04-04, F3, Lindstedsvägen 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20130320

Available from: 2013-03-20 Created: 2013-03-18 Last updated: 2013-03-20Bibliographically approved

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