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  • 1.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nategh, Shafigh
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Stening, Alexander
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Grop, Henrik
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Measurement and Modeling of Iron Losses in Electrical Machines (Invited Paper)2012In: Proceedings of the 5th International Conference Magnetism and Metallurgy WMM'12, Gent, Belgium: Gent University , 2012, p. 101-119Conference paper (Other academic)
    Abstract [en]

    This paper gives an overview of nowadays used simulation models and measurement methods in order to determine iron losses in electrical machinery. The paper provides machine designers and system engineers with an overview of suitable iron loss models applicable for the machine design process and simulations. Furthermore, possible methods for iron loss measurements in electrical machines are presented from ongoing research projects. Besides standard electrical power measurements, iron losses are determined by thermal and magnetic property measurements, taking into account different IEC and IEEE standards.The goal is to emphasize the different possibilities of iron loss measurement methods and possible application areas for electrical machinery.

  • 2.
    Stening, Alexander
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Analysis and Reduction of Parasitic Effects in Induction Motors With Die-Cast Rotors2013Doctoral 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.

  • 3.
    Stening, Alexander
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On Inter-bar Currents in Induction Motors with Cast Aluminium and Cast Copper Rotors2010Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This thesis presents a study of the effects of inter-bar currents on inductionmotor starting performance and stray-load losses. The work is focused on theperformance differences between aluminium and copper casted rotors.A method to predict the stator current when starting direct-on-line isdeveloped. This includes modelling of skin-effect, saturation of the leakageflux paths and additional iron losses. The results are verified by measurements.An analytical model accounting for inter-bar currents is derived, andthe dependency of the harmonic rotor currents on the inter-bar resistivity isinvestigated. It is found that the inter-bar currents can have considerableeffect on motor starting performance and stray-load losses, the amount beingstrongly dependent on the harmonic content of the primary MMF.Based on measurements of inter-bar resistivity, the starting performanceof an aluminium and a copper casted rotor is simulated. The results indicatea higher pull-out torque of the aluminium rotor than for the equivalent copperrotor. This is rather due to an increase of the fundamental starting torque ofthe aluminium rotor, than due to braking torques from the space harmonicsin the copper rotor. The results are verified by measurements. It is foundthat the difference between the pull-out torques is even larger than calculatedfrom the model. Thereby, it can be concluded that the inter-bar currents havea considerable effect on motor starting performance.At rated speed the braking torques are larger in the aluminium rotor thanin the copper rotor. This is seen as increased harmonic joule losses in the rotorcage. Simulations have shown, that these losses can be as large as 1% ofthe output power for the studied machine.

  • 4.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Larsson, Björn
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Measurements of stray losses in induction machines with die-cast aluminium rotors2012In: ICEMS 2012 - Proceedings: 15th International Conference on Electrical Machines and Systems, IEEE , 2012, p. 6401766-Conference 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.

  • 5.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    A Comparative Study of Parasitic Effectsin Induction Motors With Die-Cast Copper and Die-Cast Aluminium RotorsArticle in journal (Other academic)
  • 6.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Performance Analysis of Asymmetrical Rotor Induction Motors2011In: Proceedings of Portuguese-Spanish Conferenceon Electrical Engineering, 2011Conference 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.

  • 7.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Reduction of synchronous torques in induction machines using asymmetrical rotor slots2012In: ICEMS 2012 - Proceedings: 15th International Conference on Electrical Machines and Systems, Institution of Electrical Engineers of Japan (IEEJ), 2012, p. 6401765-Conference 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.

  • 8.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Starting performance of induction motors with cast aluminium and copper rotors including the effects of saturation and inter-bar currents2009In: 2009 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS, 2009, p. 159-163Conference 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.

  • 9.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    The effects of inter-bar currents in cast aluminium and cast copper rotors2009In: ICEM: 2008 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES, NEW YORK: IEEE , 2009, p. 2381-2385Conference 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.

  • 10.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Shaukat, Usman
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    New Design Options For Induction Machines Using Modulated Rotor SlotsArticle in journal (Other academic)
1 - 10 of 10
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