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COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

Publisher:
Emerald Group Publishing Limited
Emerald Publishing
ISSN:
0332-1649
Scimago Journal Rank:
32
journal article
LitStream Collection
Description of electrical machine windings in the finite element space

Andrzej Demenko

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878108

Purpose – This paper seeks to develop 3D finite element methods for the electromagnetic field calculation in electrical machines and to present the discrete methods of winding description. Design/methodology/approach – The 3D finite element models of electrical machine windings are considered. Attention is paid to the windings with stranded conductors. The finite element equations are considered as the equations of magnetic networks. The formulation of matrix that transforms winding currents into the field sources is discussed. This matrix is also used in the calculations of flux linkages. In the proposed method, the winding loops are replaced by a set of plane loops. The field sources are defined by the numbers of these loops around the element edges and loops associated with element facets. Findings – The presented description is the 3D finite element representation of MMF description used in the classical models of electrical machines. The advantage of the proposed approach is that the source description can be successfully applied in the FE method using single scalar potential. In addition, the presented approach guarantees a good convergence of ICCG procedure of solving edge element equations for ungauged formulation using magnetic vector potential. Originality/value – The applied analogies between the finite element formulation and the equivalent magnetic network models help to formulate an efficient method of field source description. The developed method allows one to apply single magnetic scalar potential in the 3D finite element analysis of electrical machines.
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Determination of critical thermal operations for high‐speed permanent magnet electrical machines

Zlatko Kolondzovski

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878117

Purpose – The thermal design of high‐speed electrical machines is a greater challenge in comparison with conventional electrical machines. When designing the machine, the calculated temperatures in all parts should be lower than their critical temperatures. This paper aims to perform thermal analysis for different rotor types according to the level of shield from eddy currents in order to achieve a safe thermal design of the machine. Design/methodology/approach – The machine under study in the paper is a high‐speed permanent magnet (PM) motor designed for speed n =31,500 rpm and power P =130 kW. A thermal‐network method was used for thermal analysis of the machine. Findings – The minimum value of the coolant flow in the air gap that provides an effective cooling of the machine was estimated. The coolant itself is not able to provide an effective cooling of the magnets if they are not shielded from eddy currents. Research limitations/implications – The results are obtained only by the thermal‐network method. Numerical techniques and practical measurements for comparison and validation of the existing results should be implemented in future. Practical implications – The paper offers useful practical information when a safe thermal design of a high‐speed PM electrical machine should be performed. Originality/value – The paper demonstrates how three different design types of a high‐speed PM electrical machine are thermally analysed in order to find out which type fulfils the rigorous thermal criteria. The practical significance of the paper is beneficial for the designers of high‐speed PM electrical machines.
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The investigation of electromagnetic field influence generated by mobile phones on cardiac pacemakers with the anatomically based human model

Arkadiusz Miaskowski; Andrzej Krawczyk; Andrzej Wac‐Wlodarczyk

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878126

Purpose – The aim of this paper is to investigate the coupling model which describes the relationship between the electromagnetic (EM) field emitted by a field source, in this case the mobile phone, and the interfering voltage at a cardiac pacemaker which is digitally implanted into the human body model. Design/methodology/approach – The research was carried out using two kinds of numerical phantoms with various configurations, i.e. the mobile placed in front of a trunk and the mobile placed near the human ear (totally 12 configurations). Moreover, the simplified homogeneous human model with numerically implanted cardiac pacemaker is considered (two configurations). The simulations are carried out using the finite difference time domain method according to international standards. Findings – From the investigation it was found that the interfering voltage at the cardiac pacemaker (for each of the considered models) was much smaller than the one proposed by IEC standard. A practical conclusion that can be drawn is that the highest interfering voltages occur when the mobile is in a vertical position. Research limitations/implications – The analysis was limited to the cardiac pacemaker with a unipolar electrode and could be carried out for other types of pacemakers. Practical implications – The evaluations such as those presented should be useful in the development of protection standards of human exposure to EM field with respect to humans with implants such as cardiac pacemakers. Furthermore, such a modeling allows for the evaluation of potential EM interference prior to an implantation of implants. Originality/value – Such a detailed analysis of a coupling model considering various configurations of mobile phone position to a human model has so far never been carried out.
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High frequency electromagnetic emissions of cylindrical laminated cores

Stéphane Duchesne; J‐Ph. Lecointe; F. Périsse; Ewa Napieralska‐Juszczak

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878135

Purpose – This paper aims to propose a high‐frequency (HF) model able to compute the flux density in the vicinity of the laminated stator core of an AC machine. Design/methodology/approach – Experiments form the main approach. Analytical results previously obtained with a simplified rectangular laminated structure are confirmed with a standard cylindrical magnetic core. Findings – Three frequency domains are defined, depending on the skin depth relative to the thickness of the magnetic sheets. A methodological approach is proposed for each domain. For higher frequencies, the magnetic core can be considered as transparent for external field computation. Research limitations/implications – The HF model is valid for skin depths much lower than the thickness of the magnetic sheets. Practical implications – The proposed HF model provides a link between the weak field measured in the natural void existing between the stator core and the housing of large electrical machines. With such a link, it is possible to develop a new monitoring system able to detect and to localize the partial discharges in the stator winding of a large machine. Originality/value – The low‐frequency limit of the model has been measured. It corresponds to a ratio of 1/40 between the skin depth and the magnetic sheet thickness. Therefore this model offers a new perspective for maintenance applications.
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Attenuation of magnetic field components through an AC machine stator

D. Thailly; R. Romary; D. Roger; J‐F. Brudny

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878144

Purpose – Non‐intrusive magnetic measurements in AC machines are possible with small flat coils stuck on the external surface of the housing of a running motor. The aim of the paper consists in determining transmission coefficients able to give a direct relationship between the weak external flux density and the airgap one. Design/methodology/approach – An experimental approach shows that the decoupling principle can be applied. Transmission coefficients are determined separately for the stator yoke, the motor housing and the external air. Findings – For low frequencies and a housing made of steel, eddy current can be neglected. The transmission coefficient depends strongly of the mode (number of poles) of the rotating field. Conversely, for higher harmonic ranks, the additional attenuation caused by eddy currents in the housing does not practically depend on the mode but is strongly dependant on the frequency. Research limitations/implications – The transmission coefficients are determined considering a 2D electromagnetic model and several simplifying hypothesis. Experiments prove the validity of the proposed approach up to 550 Hz. Practical implications – Up to now, many fault detection systems are based on the presence of additional harmonics in the external magnetic field spectrum. With the knowledge of simple transmission coefficients, an analysis of the variation of the magnitude of critical spectrum lines is now possible for a more precise fault detection in AC machines. Originality/value – To the authors' knowledge, the only alternative way for the interpretation of external field measurements consist in using a numerical method with a full model of the machine which takes a lot of computation time. The proposed transmission coefficients provide a faster method valid for most of the interesting spectrum lines.
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3D finite element analysis of skewed squirrel‐cage induction motor using novel mesh modification method

Yoshihiro Kawase; Tadashi Yamaguchi; Masashi Watanabe; Naotaka Toida; Tu Zhipeng; Norimoto Minoshima

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878153

Purpose – This paper aims to describe a novel 3D finite element mesh modification method for motors with the skewed rotor in detail, the method having been developed by solving the Laplace equation. Design/methodology/approach – Using the mesh of the skewed squirrel‐cage induction motor created by the novel method, the torque, the bar‐current, the electrical losses and so on are analyzed by the 3D finite element method. Findings – It was found that the torque ripple, the bar‐current ripple and the losses of the motor with the skewed rotor are smaller than those of the motor with the no‐skewed rotor. In addition, the validity of the analysis is clarified by comparing the calculated and the measured results. Originality/value – The usefulness of the method is clarified by the 3D finite element analysis of a skewed squirrel‐cage induction motor.
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Shape design of a MEMS device by Schwarz‐Christoffel numerical inversion and Pareto optimality

E. Costamagna; P. Di Barba; A. Savini

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878162

Purpose – This paper sets out to provide a numerical procedure for field analysis and shape design for a class of MEMS devices. Design/methodology/approach – The proposed numerical procedure for field analysis relies on numerical inversion of Schwarz‐Christoffel (SC) transformations for doubly‐connected regions: the geometry of a given micromotor is mapped into an annulus, where the non‐radial field excited by the transformed electrodes is computed. In turn, the shape design relies on the definition of non‐dominated solution according to the Pareto optimality conditions. Findings – The SC approach proposed here allows the designer to evaluate both driving torque and radial force characteristics of the device with suitable accuracy within short CPU times. In turn, this allows one to perform repeated field analyses for a large number of feasible geometries and to use enumerative approaches to design optimization. By this means, a 3D objective space is investigated to identify the optimal shape of an electrostatic micromotor, subject to prescribed constraints. Originality/value – To the best of one's knowledge, the combination of SC transformations and Pareto optimality is an unprecedented method for MEMS design. In particular, it is expected that the proposed SC tools will supply a fast and accurate computation to compare or supplement results from FEM tools, when a large number of geometries should be analysed. This could be particularly useful in the preliminary steps of a design procedure for a given class of devices.
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Three‐phase distributed constants model of induction machines for EMC and surge propagation studies

Francesco Della Torre; Sonia Leva; Adriano Paolo Morando

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878171

Purpose – This paper aims to provide a complete three‐phase distributed constants model of cable‐induction machine systems useful for EMC and overvoltages propagation studies. Design/methodology/approach – The paper considers a three‐phase distributed constants model for the supply cable and a model of the same type for the induction machine. All the magneto‐electric links between phases are considered. The Clarke transform is applied in order to reduce the analytical complexity of the obtained model. A new numerical method is also proposed for the integration of the resulting whole three‐phase model, very similar, in terms of methodology, to the well‐known finite differences models. Findings – The whole model for the three‐phase drives is used for EMC and overvoltages propagation studies. The proposed examples highlight how, thanks to the Clarke model, the dynamic analysis of the three‐phase drives in case of application of a standard fault source or an equivalent pulse width modulation (PWM) impulse, become easy to implement on a standard PC and with standard software (i.e. Matlab). The obtained results, compared with those that are presented in the literature, confirm the validity of the proposed model and numerical approach. Originality/value – The developed model is of a three‐phase type because it is not possible to consider a single‐phase equivalent model in case of asymmetric voltage sources (i.e. asymmetric faults or PWM inverter voltage supply). The model also includes all the magneto‐electric couplings between phases that play a fundamental role in the considered applications.
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Modelling of vertical electrostatic comb‐drive for scanning micromirrors

Renata Sulima; Slawomir Wiak

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878180

Purpose – The main aim of this paper is to build an equivalent circuit model of a comb drive microactuator, while the phenomenon of generating the electric fringing field at electrode edges is taken into consideration. Design/methodology/approach – The approach to the comb drives design requires the “leakage capacitance” (appearing at electrode edges) to be introduced to the complex equivalent circuit model. Introducing these capacitances leads to defining the circuit model properly. Findings – Such a complex approach by use of the equivalent circuits model could make it possible to reduce the discrepancy between the field and circuit models. These results were obtained after comparing both field and circuit models. Originality/value – MEMS microdrives are in the area which is being developed very dynamically. Improvements in the mathematical models would permit more precise microdrive design, leading to optimal structure.
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Characteristics investigation of a new type AFPM machine according to the geometric structure of rotor using 3D FEM

Byung‐Jun Lee; Byoung‐Kuk Kim; Yun‐Hyun Cho; Yon‐Do Chun; Dae‐Hyun Koo

2008 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

doi: 10.1108/03321640810878199

Purpose – The purpose of this paper is to present the performance characteristics analysis of a new type axial flux permanent magnet (AFPM) machine according to the geometric structure of rotor such as permanent magnet dimension, the air‐gap length and so on. Design/methodology/approach – The 3D finite element method (FEM) is used to analyse electromagnetic fields with the aid of an ANSYS software package. The FEM is based on the magnetic vector potential and the governing equation can be obtained from the Maxwell equation. Using the dynamometer system, the characteristics of the AFPM machine were estimated according to load torque. Findings – The AFPM machine characteristics with static torque, cogging torque and flux density according to rotor geometric dimensions are analyzed using a 3D FEM software package. And then, the prototype of an AFPM machine and several rotors with different PM structure are manufactured and tested. Resulting from the experiment, the characteristics such as EMF waveform, speed and efficiency curves according to load torque, and efficiency curves according to PM thickness, are obtained. The measured performance results verified the overhang effects and improved the efficiency of the motor. Originality/value – The paper proposes a new type AFPM machine structure with T‐shape teeth and laminated back yoke and two types of rotor with fan‐shaped permanent magnets. It presents the results of characteristics of the proposed AFPM machine throughout the simulation and experiment.
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