Vesna Arnautovski-Toseva

Grounding systems modeling for high frequencies and transients: some fundamental considerations

In spite of large amount of research work in the last decades on the grounding systems modeling for high frequencies and transients there is no consensus on its practica applicability. This work points to some issues that may be important in the systematic approach to determine the validity domains of the different existing methods for analysis. In particular, the following topics are discussed: the evaluation of the upper frequency of interest in the transient study, the limitations due to the electrical dimensions of the system, and due to the underlying circuit concepts, especially in relation to the definition of impedance to ground. As a basis for the evaluation of the validity domains of more simplified quasi-static and circuit based models a full-wave electromagnetic model is described. Validation by comparison with experiment and illustrative numerical results are presented.

Comparison of Image and Transmission Line Models of Energized Horizontal Wire Above Two-Layer Soil

The paper presents comparison between two approximate models of energized horizontal thin-wire conductors above two-layer soil. The formulation is posed in frequency domain by using two approaches. The first one is based on quasi-static image theory within Mixed Potential Integral Equation. The second one is based on transmission line theory with approximation of per unit length parameters. The authors compare currents computed by the both approximate models of a center fed wire to establish the computation errors over a wide frequency range. The main objective is to validate the proposed image and transmission line models for various lengths of wire conductors, and various cases of low and high conductivities of two-layer soil. The verification of the results is done by comparison with exact model based on full-wave theory. Detailed parametric analysis clearly illustrate validity domain and problems when using both approximate models with respect to their use in practical EMC studies.

High frequency current distribution in horizontal grounding systems in two-layer soil

This paper presents the ongoing research results of the high frequency grounding system analysis in two-layer soil structure. On the basis of rigorous electromagnetic field theory, which involves Sommerfelds integrals, the mathematical model is formulated by the mixed potential integral equation (MPIE). Detailed analysis of a high frequency performance of a typical short and long horizontal grounding conductor placed in the upper layer is given. It is shown that because of the presence of two distinct layers the current distribution is not only function of frequency, but also a function of the reflection factor and the upper layer height

Image and Exact Models of a Vertical Wire Penetrating a Two-Layered Earth

In this paper, we investigate the validity of image theory in modeling a vertical wire penetrating a uniform or two-layered earth. First, a rigorous full-wave electromagnetic model is described that may be used as a standard for comparison. The model is based on the method of moments (MoM) and exact Green functions for the layered earth that involve Sommerfeld-type integrals. Next, we derive the image model from the exact model and analyze the approximations. We compare the current along a vertical wire as computed by the MoM using the exact Green functions, with the current computed using the image Green functions. The image model is accurate at dc, and the error is generally low at low frequencies but rises at high frequencies. We show that the image model leads to smaller errors when the wire is embedded in one layer. However, the error is larger in cases of penetration through different layers. We also show a strong dependence of the error on the resonant frequencies.

High frequency electromagnetic analysis of horizontal grounding conductor and near-by passive parallel conductor within two-layer soil

This paper presents the ongoing research results of the high frequency grounding system analysis in two-layer soil structure. On the basis of rigorous electromagnetic field theory, which involves Sommerfelds integrals, the mathematical model is formulated by the mixed potential integral equation (MPIE). Detailed analysis of a high frequency performance of a typical horizontal grounding conductor placed in the upper or in the bottom layer is given. It is shown that because of the presence of two distinct layers the current distribution and the impedance to ground are highly affected by the parameters of both soil layers. Also, the current distribution in near-by passive horizontal conductor is analyzed. At the end of the paper some observations about the effects of two-layer soil structure at high frequencies are given.

Transient analysis of grounding systems without computer

Recently simple empirical formulas have been introduced that estimate the impulse impedance, impulse coefficient and effective length/area of different arrangements of grounding electrodes (horizontal and vertical electrodes and grounding grids) under typical lightning currents. Soil ionization and inductive effects are both included in the formulas for smaller simple arrangements of grounding electrodes, while soil ionization is ignored for grounding grids. To illustrate and validate the new formulas, we compare the results from the formulas with experimental data recently published by different research groups.

Antenna mode currents and radiated emissions of in-door PLC line within wall structure

It is known that the total currents flowing in a given circuit may be decomposed into differential or transmission mode currents and common or antenna mode currents. The second ones are generally supposed to be the main source of emission problems related within PLC. In this paper the main objective of the authors is to analyze the frequency dependence of antenna mode currents in a PLC unbalanced circuit. The unbalance is a result of a changing the circuit from symmetrically to asymmetrically driven. Of interest is the relationship between the change of the amount of antenna mode currents due to source asymmetry and the effect on the radiated electric field. The numerical analysis is based on the full-wave theory that is solved by the method of moments. The studied theoretic example is a simple 5m long PLC line placed within a concrete wall structure.

Three-dimension method of moments analysis of radiated field from DC-DC converters

The radiated electromagnetic field of a modern high frequency switching DC-DC converter has been analyzed using a three dimension Method of Moments (3D-MoM). The print circuit board (PCB) of the converter is modeled with equivalent thin-wires. The analytical results from MoM are validated by comparison with the results from a well-known commercial software. The software developed offers great flexibility for parametric optimizations such as loop area and frequency, which are not supported with existing software.

Analysis of electrophysiological activities using Matrix Pencil Method

This paper presents a high resolution method for analyzing of electrophysiological activities using Matrix Pencil Method (MPM). This approach identifies measured signal from nerves to better understanding the functional organization of neuronal ensembles that form the peripheral nerves or the cerebral cortex. Matrix Pencil Method which is used to extract original signals and benefits from minimum exponential functions while having excellent reproducibility feature. MPM also can eliminate the noise part of the system and return pure original signal. In this paper, MPM is used to reconstruct recorded action potential from cockroach by using Matlab environment which shows less than 4% error.

On the Image Model of a Buried Horizontal Wire

It is common practice in the engineering analysis process to use an approximate image method for the computation of the current in buried horizontal conductors (in the literature, this is often referred to as the “modified image” or “reflection coefficient” method). According to this approach, the earth/air interface is replaced by a positive mirror image of the charge and current in the conductor, and its field is multiplied by a suitable reflection coefficient. Different opinions on the validity of this approximation have been expressed in published debates, but more systematic analysis of the error introduced by this approach is not available in the literature. To establish the amount of error, we compare the computation results of the image model with the rigorous Sommerfeld integral method for a wide range of parameters. Contrary to widespread opinion, our results suggest that the modified image (or reflection coefficient) method in EFIE-based solutions (e.g., the Pocklington equation) leads to a large error (larger than 20%) in the low-frequency range for the computation of the current distribution in conductors longer than 10 m. In such a case, MPIE-based methods are preferred for use to achieve a smaller error (approximately 5%). Guidelines for the application of image models related to the conductor, earth and excitation parameters, upper frequency limit, and modeling method are presented.