Showing papers by "Dragan Poljak published in 2006"

Wire Antenna Model for Transient Analysis of Simple Grounding Systems, Part II: the Horizontal Grounding Electrode

Abstract: The paper deals with the transient impedance calculation for simple grounding systems. The mathematical modelmodel is based on the thin wire antenna theory. The formulation of the problem is posed in the frequency domain, while the corresponding transient response of the grounding system is obtained by means of the inverse Fourier transform. The current distribution induced along the grounding system due to an injected current is governed by the corresponding frequency domain Pocklington integro-differential equation. The influence of a dissipative half-space is taken into account via the reflection coefficient (RC) appearing within the integral equation kernel. The principal advantage of the RC approach versus rigorous Sommerfeld integral approach is simplicity of the formulation and significantly less computational cost. The Pocklington integral equation is solved by the Galerkin Bubnov indirect boundary element procedure thus providing the current distribution flowing along the grounding system. The outline of the Galerkin Bubnov indirect boundary element method is presented in Part II of this work. Expressing the electric field in terms of the current distribution along the electrodes the feed point voltage is obtained by integrating the normal field component from infinity to the electrode surface. The frequency dependent input impedance is then obtained as a ratio of feed-point voltage and the value of the injected lightning current. The frequency response of the grounding electrode is obtained multiplying the input impedance spectrum with Fourier transform of the injected current waveform. Finally, the transient impedance of the grounding system is calculated by means of the inverse Fourier transform. The vertical and horizontal grounding electrodes, as simple grounding systems, are analyzed in this work. The Part I of this work is related to the vertical

Nonlinear-coupled electric-thermal modeling of underground cable systems

Abstract: An original nonlinear-coupled electric-thermal model of underground cables with the solid sheaths is proposed. The model deals with the numerical evaluation of losses, heating, and ampacity. The computation of the current dependent losses is undertaken by means of the filament method, where conductors and sheaths are represented by a number of smaller subconductors or filaments. Furthermore, heat-transfer phenomena through an "infinite" domain beneath the soil surface are modeled combining the finite and the mapped infinite elements, respectively. The corresponding finite-element meshes are generated by the advancing front method. The numerical results presented throughout this work suggest that the International Electrotechnical Commission relation concerning the external thermal resistance for touching cables, placed in flat formation, having appreciable sheath losses, should be re-examined.

Numerical Methods in Electrical Engineering

Abstract: Skripta Numericke metode u elektrotehnici temelje se na visegodisnjem istraživackom, strucnom i nastavnom radu autora na podrucju primjene numerickih metoda u inženjerskom modeliranju.

A Simple Finite Element Model of Heat Transfer in the Human Eye

Abstract: A simple finite element 2D model of the human eye is developed to calculate the steady-state temperature distribution. The mathematical model of the eye is based on the Pennes bio-heat transfer equation. Problem is solved using the weak formulation and the Galerkin-Bubnov procedure. The study was performed to determine the effects of various values of thermal conductivity of lens on temperature distribution inside human eye and also the effects due to changes in ambient temperature and blood temperature.

A numerical~stochastic technique for underground cable system design

Abstract: A numerical–stochastic technique for an optimisation of underground cable systems is based on a finite-element mesh generator carried out by means of the advancing front method, a nonlinear coupled electric-thermal model, a multiquadric ampacity approximations including successive zooming steps, and a stochastic optimisation method involving differential evolution. The proposed technique provides the optimisation of cable systems for which neither accurate analytical nor empirical ampacity formulas are available, thus resulting in more economical design.

Finite element model of the human head exposed to electrostatic field generated by Video Display Units

Abstract: The goal of this paper is to investigate interaction between electrostatic field of Video Display Units (VDU's) and human head in front of it. Special attention is given to the field at the surface of the face. The finite element model for assessment of the electrostatic field, by solving Laplace equation for the electric potential, is implemented. The electrostatic field is calculated for two different faces and for two different types of the domain and then compared with results obtained by the finite difference method. The advantage of the presented numerical method is a high resolution and a higher accuracy.

Nonuniformity modelling of particular aluminum sheath temperatures and losses

Abstract: A nonlinear coupled electrothermal model of underground cables having aluminum sheaths is developed. The mathematical model deals with the numerical evaluation of losses, heating and ampacity. The filament method, the advancing front method as well as the finite-element method combined with the mapped infinite elements are used. In particular, an improved modelling of heat sources is carried out, taking into account the influence of the nonuniform losses distribution of a particular sheath on the cable heating. Moreover, the calculation of losses is performed with respect to the nonuniform temperature distribution of a particular sheath. Some illustrative computational results leading to clear-cut concluding remarks are given.

Computation of maximal electric field value generated by a power substation

Abstract: A procedure for a computation of the maximal value of extremely low frequency electric field from a power substation is presented.

Comparison of Wire Antenna and Transmission Line Model for Transient Analysis of Grounding Electrodes

Abstract: The paper deals with different methods for the transient impedance calculation of simple grounding systems. The approach based on the thin wire antenna theory, i.e. antenna model (AM) and transmission line model (TLM), respectively, is used in this work. The formulation based on wire antenna theory is posed in the frequency domain (The transient response obtained by means of the inverse Fourier transform), while the corresponding transmission line approach is related to the time domain. The integro-differential relationships arising from the wire anntena thoery are handled via Galerkin-Bubnov scheme of Indirect Boundary Element Method (GB-IBEM) while the time domain transmission line equations are treated using the Time Domain Finite Element Method (TD-FEM). A number of illustrative numerical results is presented in the paper.

Boundary element modeling of radio base station antennas

Abstract: The paper presents an accurate and efficient boundary element procedure for the analysis of radiation from base station antennas. The base station antenna system is represented by the vertical antenna array in front of perfectly conducting (PEC) ground plane reflector. The formulation of the problem is based on a set of coupled Pocklington integro-differential equations for vertical antenna array. This set of coupled equations has been numerically treated by the indirect Galerkin–Bubnov boundary element method (GB-IBEM). The numerical results for the currents induced along the wires obtained via GB-IBEM are compared to the results computed via numerical electromagnetic code (NEC). Knowing the current distribution along the antenna array the corresponding radiated field is calculated. Some illustrative numerical results are presented in the paper.

Geometrical aspects of 3D human body exposed to extremely low frequency high voltage electric fields. A BEM approach

Abstract: The paper deals with the three dimensional modelling of the human body exposed to Extremely Low Frequency (ELF) high voltage electric fields by mean of the Boundary Element Method (BEM). Numerical results along head, neck, torso, abdomen, arms, legs and ankles are presented and discussed in the case of grounded subject standing under power distribution lines. The objective is to characterise the influence of different shape and geometrical factors on the current distribution inside the body and electric field in the near field. The inclusion of legs and arms with different orientations with respect to the incident field are considered. The main contribution is to present new results of the BEM for Extremely Low Frequency Exposure and to evaluate the relationship between degree of detail in 3D modelling and the corresponding fluctuation of results for induced currents.

Time Domain Measure for Power Flow of Thin Wire Electromagnetic Field

Abstract: Time domain power measure associated with the currents and charges induced on straight horizontal wires above perfect ground is proposed. The formulation is based on a set of coupled space-time Hallen integral equations. The time domain power flow measure is given by the negative time derivative of the spatial integral of the squared current and charge along the wires.

Time domain analysis of the energy stored in the near field of finite length wires embedded in a dielectric half-space

Abstract: Time domain energy measures assiciated with the currents and charges induced on the finite length wires embedded in a dielectric half-space are calculated. The formulation is based on the corresponding space-time Hallen integral equation. The effects of two media configuration are taken into account via the Fresnel reflaction and transmission coefficient, respectively. Currents and charges along the wires are obtained by solving the Hallen integral equation via time-domain Galerkin-Bubnov scheme of indirect Boundary Element Method (GB-IBEM). The assesment of time domain energy measures involves spitial integration of the squared current and charge along the wires.

Modeling panel antenna in NEC

Abstract: The paper deals with the panel antenna modeling using NEC Win PRO v. 1.1 package. Base of antenna modeling would be wire construction. To achieve better performance and characteristics, several solutions for reflector and dipole will be proposed. Antenna with best results and attributes will be compared with technical data of APX907016 RFS antenna given by producer. The challenge in the design of a suitable antenna is overcoming the inherent relationships between gain, pattern beam width, the presence of pattern side and back lobes, and also the size of the antenna.

Assessment of Human Exposure to Power Substation Electric Field

Abstract: The paper deals with human exposure to extremely low frequency (ELF) electric fields generated by transformer substation. The problem is twofold, i.e. it requires the calculation of power substation electric field and current density induced inside the human body. ELF electric field generated from a power substation is assessed by solving the Scalar Potential Integral Equation (SPIE) using the Source Element Method (SEM), a variant of the Indirect Boundary Element Method (IBEM). Knowing the electric field due to the substation the current density induced within the human being exposed to such field is obtained by solving the Laplace equation variant of the continuity equation using the direct Boundary Element Method with domain decomposition (BEM-DM). Some illustrative computational results for external electric field and internal current density are presented.

Analytical model of human body when exposed to high frequency electromagnetic fields

Abstract: Analytical model of human body is used to calculate the electric field and current density induced in human body when it is exposed to high frequency electromagnetic fields (50-200MHz). Especially, of interest are frequencies used by radio amateurs (50 - 200 MHz). Formulas used in this study are derived by using a cylindrical model of human body. Tabulations and graphical representations illuminate the results. The intent of this work is to draw more attention on possible health effects that RF fields from radio amateur antennas might have on human body.