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Performance Analysis of Asymmetrical Rotor Induction Motors
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
2011 (English)In: Proceedings of Portuguese-Spanish Conferenceon Electrical Engineering, 2011Conference paper, Published paper (Other academic)
Abstract [en]

Inter-bar currents can form a considerable part of stray-load losses in a skewed induction motor. A substantial reduction of these losses can be obtained by removal of the rotor skew. Removing the rotor skew will introduce parasitic effects such as increased noise level and increased magnitude of the harmonic torques during motor start. By introducing modulated rotor slots these negative effects can be reduced. In this paper, two different concepts of modulated slot rotors are studied. The starting performance and the losses at rated speed are simulated and compared with a standard motor using the Finite Element Method (FEM). The losses due to inter-bar currents in a skewed rotor are calculated from an analytical model. It is found that the additional losses introduced by the modulated rotor slots are small compared to the possible inter-bar current losses in the skewed rotor. Hence, an increased efficiency can be obtained by introducing modulated non-skewed rotor slots.

Place, publisher, year, edition, pages
2011.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-119611OAI: oai:DiVA.org:kth-119611DiVA: diva2:612095
Conference
XIICLEEE’11
Note

QC 20130320

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