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Measurements of stray losses in induction machines with die-cast aluminium rotors
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. (HPD)
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
2012 (English)In: ICEMS 2012 - Proceedings: 15th International Conference on Electrical Machines and Systems, IEEE , 2012, 6401766- p.Conference paper, Published paper (Refereed)
Abstract [en]

The rotor bars in induction machines are usually skewed in order to reduce parasitic effects created by the stator and the rotor slotting. In skewed rotors having uninsulated rotor bars, inter-bar currents can create large losses, reducing the efficiency of the machine. This paper presents results from calorimetric measurements of the total losses in an 11 kW induction machine, equipped with either a skewed or an unskewed die-cast rotor. The losses are segregated for a comparative study of the different loss components. It was found that, for the studied machine designs, the stray-load losses are redistributed rather than reduced when the rotor skew was removed.

Place, publisher, year, edition, pages
IEEE , 2012. 6401766- p.
Keyword [en]
Stray losses, Die-cast rotors, Rotor skewing, Calorimetric measurements.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-107594ISI: 000332791700068Scopus ID: 2-s2.0-84873456186ISBN: 978-488686077-4 (print)OAI: oai:DiVA.org:kth-107594DiVA: diva2:576820
Conference
15th International Conference on Electrical Machines and Systems, ICEMS 2012; Sapporo; 21 October 2012 through 24 October 2012
Projects
EKC2/HPD
Note

QC 20130218

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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