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Analysis and Reduction of Parasitic Effects in Induction Motors With Die-Cast Rotors
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
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 [en]
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: urn:nbn:se:kth:diva-119603ISBN: 978-91-7501-682-5 (print)OAI: oai:DiVA.org:kth-119603DiVA: diva2:611816
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
List of papers
1. The effects of inter-bar currents in cast aluminium and cast copper rotors
Open this publication in new window or tab >>The effects of inter-bar currents in cast aluminium and cast copper rotors
2009 (English)In: ICEM: 2008 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES, NEW YORK: IEEE , 2009, 2381-2385 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, a study of the influence of inter-bar currents on induction machines with aluminium and copper casted rotors is presented. The resistance between the rotor bars and the iron core is measured on five different rotors. An analytical model to predict the influence of inter-bar currents on machine performance is developed, and the results are verified by measurements. It is found that the measured inter-bar resistance is lower in cast copper rotors than in cast aluminium rotors. This leads to a reduced pull-out torque and increased stray-load losses.

Place, publisher, year, edition, pages
NEW YORK: IEEE, 2009
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-30704 (URN)10.1109/ICELMACH.2008.4800258 (DOI)000269315000440 ()978-1-4244-1735-3 (ISBN)
Conference
International Conferece on Electrical Machines, Vilamoura, PORTUGAL, SEP 06-09, 2008
Note
QC 20110310Available from: 2011-03-10 Created: 2011-03-04 Last updated: 2013-03-20Bibliographically approved
2. Starting performance of induction motors with cast aluminium and copper rotors including the effects of saturation and inter-bar currents
Open this publication in new window or tab >>Starting performance of induction motors with cast aluminium and copper rotors including the effects of saturation and inter-bar currents
2009 (English)In: 2009 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS, 2009, 159-163 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, a study of the starting performance of induction machines with aluminium and copper casted rotors is presented. Models are developed to predict the starting current. Based on measurements of inter-bar resistivity, an analytical model is used to predict the influence of inter-bar currents on machine starting performance and stray-load losses. The results are verified by measurements. It is found that the inter-bar currents increase the pull-out torque in the aluminium rotor, but at the expense of increased stray-load losses.

Series
International Conference on Electrical Machines and Systems ICEMS
Keyword
Copper rotor, inter-bar current, starting torque, stray loss
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-29844 (URN)10.1109/ICEMS.2009.5382966 (DOI)000277826700032 ()2-s2.0-77950602851 (Scopus ID)978-1-4244-5177-7 (ISBN)
Conference
12th International Conference on Electrical Machines and Systems, Tokyo, JAPAN, NOV 15-18, 2009
Note
QC 20110222Available from: 2011-02-23 Created: 2011-02-17 Last updated: 2013-03-20Bibliographically approved
3. A Comparative Study of Parasitic Effectsin Induction Motors With Die-Cast Copper and Die-Cast Aluminium Rotors
Open this publication in new window or tab >>A Comparative Study of Parasitic Effectsin Induction Motors With Die-Cast Copper and Die-Cast Aluminium Rotors
(English)Article in journal (Other academic) Submitted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-119610 (URN)
Note

QS 2013

Available from: 2013-03-20 Created: 2013-03-20 Last updated: 2013-03-20Bibliographically approved
4. Measurements of stray losses in induction machines with die-cast aluminium rotors
Open this publication in new window or tab >>Measurements of stray losses in induction machines with die-cast aluminium rotors
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
Keyword
Stray losses, Die-cast rotors, Rotor skewing, Calorimetric measurements.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-107594 (URN)000332791700068 ()2-s2.0-84873456186 (Scopus ID)978-488686077-4 (ISBN)
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
5. Performance Analysis of Asymmetrical Rotor Induction Motors
Open this publication in new window or tab >>Performance Analysis of Asymmetrical Rotor Induction Motors
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.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-119611 (URN)
Conference
XIICLEEE’11
Note

QC 20130320

Available from: 2013-03-20 Created: 2013-03-20 Last updated: 2013-03-20Bibliographically approved
6. Reduction of synchronous torques in induction machines using asymmetrical rotor slots
Open this publication in new window or tab >>Reduction of synchronous torques in induction machines using asymmetrical rotor slots
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
Keyword
Synchronous Torques, Starting Torque, Modulated Rotors, Asymmetrical Rotor Slots.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-107595 (URN)000332791700067 ()2-s2.0-84873458181 (Scopus ID)978-488686077-4 (ISBN)
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
7. New Design Options For Induction Machines Using Modulated Rotor Slots
Open this publication in new window or tab >>New Design Options For Induction Machines Using Modulated Rotor Slots
(English)Article in journal (Other academic) Submitted
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-119612 (URN)
Note

QS 2013

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

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