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Article
Publication date: 10 August 2018

Nebojsa B. Raicevic, Slavoljub R. Aleksic, Željko Hederic, Marinko Barukcic and Ilona Iatcheva

The purpose of this paper is to present a new calculation method for increasing the shielded volume in which the external electromagnetic field is maximally reduced. In a space…

104

Abstract

Purpose

The purpose of this paper is to present a new calculation method for increasing the shielded volume in which the external electromagnetic field is maximally reduced. In a space shielded in the way mentioned in this paper, it is possible to introduce measurement instruments and increase the accuracy of results obtained with them, as well as reduce the risk of unwanted electrostatic field influence on living organisms.

Design/methodology/approach

A new numerical procedure for the optimization of the coaxial ring conductor system for electrostatic shielding is developed in the paper. The optimization of the functional that consists of electrostatic energy density and a system of equations derived from the equipotential character of the conductor system is used. The system of nonlinear equations is obtained and then numerically solved by minimizing this functional. The first presented optimization procedure is based on the analytical optimization method using the Lagrange coefficients and gradient of the objective function.

Findings

It is possible to design a large number of protective ring formations. Applying the differential evolution optimization method, an optimal arrangement can be obtained for any specific number of rings. The differential evolution optimization method, which belongs to the class of evolutionary algorithms, is used for solving this very complex optimization problem. In combination with the above-mentioned method, excellent results in the elimination of the external electric field have been obtained. Although a larger number of rings provides more efficient protection, this number is limited from the economic point of view. Therefore, it is necessary to achieve a compromise between the number of rings, the size of volume shielded and the quality of protection.

Research limitations/implications

There are few papers that address this problem, although the elimination of the influence of the external electromagnetic field has gained more importance lately. The presented method can be applied to increase the reliability of measured data, protection of the environment, in space research, etc. The main limiting factor for using a larger number of rings that provide better protection is the economical one.

Originality/value

The proposed method is suitable for the generalization of procedures, for the protection of the space where the external electric field needs to be reduced or eliminated.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 4
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 31 January 2020

Nebojsa B. Raicevic, Slavoljub R. Aleksic, Ilona Iatcheva and Marinko Barukcic

This paper aims to present a new approach to the numerical solution of skin effect integral equations in cylindrical conductors. An approximate, but very simple and accurate…

172

Abstract

Purpose

This paper aims to present a new approach to the numerical solution of skin effect integral equations in cylindrical conductors. An approximate, but very simple and accurate method for calculating the current density distribution, skin-effect resistance and inductance, in pulse regime of cylindrical conductor, having a circular or rectangular cross-section, is considered. The differential evolution method is applied for minimization of error functional. Because of its application in the practice, the lightning impulse is observed. Direct and inverse fast Fourier transform is applied.

Design/methodology/approach

This method contributes to increasing of correctness and much faster convergence. As the electromagnetic field components depend on the current density derivation, the proposed method gives a very accurate solution not only for current density distribution and resistance but also for field components and for internal inductance coefficients. Distribution of current and electromagnetic field in bus-bars can be successfully determined if the proximity effect is included together with the skin effect in calculations.

Findings

The study shows the strong influence of direct lightning strikes on the distribution of electrical current in cables used in lightning protection systems. The current impulse causes an increase in the current density at all points of the cross-section of the conductor, and in particular the skin effect on the external periphery. Based on the data calculated by using the proposed method, it is possible to calculate the minimum dimensions of the conductors to prevent system failures.

Research limitations/implications

There are a number of approximations of lightning strike impulse in the literature. This is a limiting factor that affects the reliability and agreement between measured data with calculated values.

Originality/value

In contrast with other methods, the current density function is approximated by finite functional series, which automatically satisfy wave equation and existing boundary conditions. It is necessary to minimize the functional. This approach leads to a very accurate solution, even in the case when only two terms in current approximation are adopted.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 39 no. 3
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 17 August 2018

Ilona Iatcheva

This paper aims to present application of electromagnetic field (EMF) modeling in the educational process of electrical engineering study. Special attention has been paid to…

104

Abstract

Purpose

This paper aims to present application of electromagnetic field (EMF) modeling in the educational process of electrical engineering study. Special attention has been paid to determination of specific parameters and characteristics as a function of device design. The aim is to introduce to the students the great opportunities for study and optimization of system behavior, based on the modeling of EMF distribution.

Design/methodology/approach

Illustrative examples have been considered, in which the students have to model the EMF distribution in relatively simple devices, using both analytical field determination and finite element method (FEM) analysis. The task includes also the determination of capacitances, inductances, magnetic fluxes, energies and forces. The problem has to be solved for different values of geometry parameters and material properties of the device. Thus, students can examine specific relation between field distribution and changes of the design.

Findings

The modeling of EMF distribution for different geometry and material properties allows determination of key factors, significantly influencing the behavior and processes in the studied device, which is the basic element in the computer-aided design systems and it can be used in subsequent system optimization.

Practical implications

The wide possibilities and advantages of the FEM simulations have been demonstrated in the modeling of EMF distribution and obtaining of device parameters. It enables students to significantly improve their knowledge in EMF theory and helps the future engineers to estimate the great advantages and possibilities for optimal device designing, which offer them the numerical simulation of electromagnetic processes.

Originality/value

This work illustrates possibilities, advantages and many years of author’s experience in application of EMF modeling in the teaching process in the study of electrical engineering specialties. The work problems presented have been solved analytically and on the basis of computer FEM simulations, which allows comparison of the opportunities and necessary efforts, offered by both kinds of methods.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 5
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 8 August 2018

Tin Benšic, Marinko Barukcic, Željko Hederic, Venco Corluka, Nebojsa Bozidar Raicevic and Ilona Iatcheva

The purpose of this paper is to develop a system for estimating the position of the active magnetic bearing (AMB) shaft. A new approach using the static and dynamic inductances…

128

Abstract

Purpose

The purpose of this paper is to develop a system for estimating the position of the active magnetic bearing (AMB) shaft. A new approach using the static and dynamic inductances and complex analytic signal to simplify the estimation procedure. Finite element (FE) simulations are introduced as a part of the system synthesis.

Design/methodology/approach

The paper presents an AMB displacement estimation system. The system is created with three inductive sensors. The position is computed from refined static and dynamic inductance obtained from complex analytic signals of flux and current. FE simulation is used to relate refined inductances to the displacement and to verify the model.

Findings

This paper shows the applicability of complex analytic signal transformation on estimation systems. The use of new refined inductance is presented in contrast to the classical approach of static and dynamic inductances. The paper shows that classical approach of static and dynamic inductance is not usable for the presented estimation system.

Practical implications

For the practical implementation of the presented system, it is necessary to know the exact dimensions of the AMB stator and the voltage and frequency used to supply the inductance estimation system.

Originality/value

The paper presents a system for estimating the displacement of AMB. The paper introduces the application of complex analytic signal to the estimation of AMB displacement. The mentioned signal is used to compute the new refined inductances. The comparison to the classical approach of static and dynamic inductances is given in this paper. The paper introduces FE simulations to the estimation system synthesis.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 8 August 2018

Ilona Iatcheva, Malina Dimitrova and Nikolina Petkova

The purpose of this study is to model the electric field distribution in 3D in the vicinity of 400 kV power line to determine the field impact on the environment and on the human…

174

Abstract

Purpose

The purpose of this study is to model the electric field distribution in 3D in the vicinity of 400 kV power line to determine the field impact on the environment and on the human body depending on the person location and presence of other objects.

Design/methodology/approach

The real 3D geometry of the three-phase line because of the line sag presence and existence of additional objects in its vicinity is considered. The time-harmonic electric field has been modeled, taking into account 1,200 phase shifting between the three-phase, 50 Hz currents. The study has been carried out using the finite element method (FEM) and COMSOL Multiphysics 5.2 software package. Special attention was paid to the field at a height of 2 m from the ground, to estimate the field influence on the located human body in the studied area (in relation to the limits for permissible electric field values).

Findings

3D map of electric field in the line vicinity and the electric field strength distribution along the observation surface (2 m from the ground) are determined for several region configurations: without additional objects, human presence just under the line, human at a certain distance from the line and presence of human and a tree. The simulation model was validated on the basis of comparison with computed and experimental data presented in the literature.

Originality/value

3D FEM modeling makes it possible to consider the real environment configuration, presence of line sag and additional objects with different material properties and obtaining of field quantities at any point of observation.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 11 September 2009

Rumena Stancheva, Ilona Iatcheva and Angel Angelov

The purpose of this paper is to introduce a method for evaluating the production tolerances influence on the practically realized optimal solution of electrotechnical devices. The…

175

Abstract

Purpose

The purpose of this paper is to introduce a method for evaluating the production tolerances influence on the practically realized optimal solution of electrotechnical devices. The influence is estimated by the optimal solution range defined with a given probability.

Design/methodology/approach

Because of the tolerances nature, the paper is in probabilistic categories. The accent is put on the cases when the mathematical description of the cost function is analytical, for example polynomial found on the basis of the design of experiments and response surface methodology. The optimal solution range is defined with a given probability. The governing equation is Chebychev's inequality. In some cases, Chebychev's inequality would be rather weak but the advantage is that it is valid for all kinds of probabilistic distributions.

Findings

A numerical example – an electrical machine – is considered with respect to variances in the magnetic characteristics of the stator and rotor core electrotechnical steel and tolerances in the geometrical dimensions of the machine. An analytical expression for the variance of the optimal solution is obtained in the case of a second order polynomial cost function. It is found that the energetic characteristic of the realized optimal design is expected to be negligibly different from its value in the proposed optimal project.

Originality/value

Although the example concerns the field of electrical machines, the methodology can be of interest for other domains and for different electrotechnical devices.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 5
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 4 May 2012

Rumena Dimitrova Stancheva and Ilona Ilieva Iatcheva

The purpose of this paper is to evaluate the rate of discrepancy between the group of expected project results and the group of corresponding results realized preliminarily at the…

106

Abstract

Purpose

The purpose of this paper is to evaluate the rate of discrepancy between the group of expected project results and the group of corresponding results realized preliminarily at the design stage.

Design/methodology/approach

The authors formulate and solve the problem to determine the values of two assemblies of independent variables guaranteeing the project with the best (X→*) and as well this one with the worst (X→**) tolerance field of the expected Zx realization. The problem is formulated as an optimization one in nonlinear mathematical programming and it is solved by applying the flexible tolerance method.

Findings

By the use of basic relations in statistical science an expression of standard deviation σZx of Zx is found and proposed. The limits in which are expected to be change in the deviations between the main project results and the corresponding ones of the implemented design, mathematically defined previous to its realization.

Research limitations/implications

The accent is put on the cases when the device characteristics are presented as polynomials, obtained on the bases of the design of experiments (DOE) and the response surface methodology. An arbitrary technical characteristic Zx=Z(x→) is presented.

Practical implications

A researcher could confine numerically the tolerance field between project results and expected realized ones in the whole investigated region.

Originality/value

The paper is characterized by an original approach and a new expression of standard deviation is proposed which will be of interest to designers.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 31 no. 3
Type: Research Article
ISSN: 0332-1649

Keywords

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