-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a parallel finite difference time domain (FDTD) code is developed for the calculation of the horizontal electric field above ground for three distances of 2 Km, 5 Km and 10 Km from the return stroke channel. An electromagnetic model of lightning is adopted for the purpose of simulation. The obtained results are compared with those simulated by Cooray-Rubinstein formula (CR). The effect of ground's conductivity on the electric field value is also investigated. The results show that the accuracy of CR formula decreases as the ground's conductivity decreases or distance of observation point from the lightning channel becomes larger.
General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper a new technique is presented to evaluate efficiently the Green's functions of filament sources radiating over a half-space. The technique is based on the annihilation of the asymptotic and branch-point singular behaviours of the spectral Green's function. The asymptotic and singularity terms are subtracted, then calculated analytically and finally re-added to the remaining integral. The annihilation leads to a very smooth remaining integral that is calculated adaptively by using Gaussian quadratures. In order to validate the accuracy and efficiency of the proposed technique, lossless and lossy half-space media are analyzed and the results are found to agree very well with literature.
Electrical Engineering (ICEE), 2011 19th Iranian Conference on; 06/2011
-
[show abstract]
[hide abstract]
ABSTRACT: This study presents a robust and efficient approach for derivation of non-symmetrical closed-form Green's functions for microstrip structures. In this method, the discrete complex image technique is used to extract the closed-form expressions for stratified Green's functions. The surface-wave poles in these expressions are first extracted using a recursive contour integration method. The remainder is then approximated by a series of complex exponentials using either the Prony's method or the generalised pencil-of-function (GPOF) along the extended rooftop-shaped path in k <sub>ρ</sub>-plane. An analytical identity is subsequently employed to obtain the new spatial-domain Green's functions. For calculation of the integral of GzxA with respect to x , it is observed that only a single approximate Green's function can accurately represent both the near and far fields. Moreover, the method generates accurate results in the near-field region when z '' z and ρρ0. A two-part expression for the non-symmetrical potential GzxA is introduced as well. This two-part approximation is very accurate and computationally fast for the entire range of distances, especially when z = z ''0 or z '' z .
IET Microwaves Antennas & Propagation 04/2011; · 0.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We review in this paper simplified analytical expressions derived by Wait using the concept of attenuation function for the analysis of the propagation of lightning radiated electromagnetic fields over a horizontally stratified ground. Considerations regarding the use of these formulations as well as their domain of applicability are given. For the case, where the upper ground layer has a lower conductivity than the lower layer, the magnitude of the attenuation function can take values greater than unity. Time-domain waveforms of the vertical electric field along a horizontally stratified ground, obtained using the simplified formulations feature, an oscillatory behavior in their early-time response. The peak value of the field is also found to be larger than that corresponding to the case of a perfect ground. The accuracy of the Wait's formulations is examined taking as reference full-wave simulations obtained using the finite-difference time domain (FDTD) technique. FDTD simulations confirm the oscillatory waveform of the far field above a horizontally stratified ground (with an upper layer characterized by a lower conductivity than that of the lower layer), as well as the enhancement of the field peak compared to the case of a homogeneous, perfectly conducting ground.
IEEE Transactions on Electromagnetic Compatibility 09/2010; · 1.18 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper proposes an improved method for reconfiguration of distribution systems based on a simple branch exchange method of single loop. In some previous works for reconfiguration of distribution networks with several loops, loops are one by one selected and reconfiguration at each matched loop is performed according to the simple branch exchange method of the single loop. Although the loops selection sequence affects the optimal configuration and the power loss of the network, the loops selection sequence is not incorporated in the network reconfiguration problems up to now. In this paper, the sequence of the loops selection is optimized for the maximum loss reduction and a simple branch exchange method is employed for reconfiguration in each loop. Discrete Genetic algorithm is used to optimize the sequence of the loops selection. The proposed algorithm is effectively tested on two feeder of a real 77-bus distribution network of the city of Sirjan in Iran.
Power Engineering and Optimization Conference (PEOCO), 2010 4th International; 07/2010
-
[show abstract]
[hide abstract]
ABSTRACT: This paper proposes a hybrid Genetic Algorithm-Simulated Annealing technique for optimal design of grounding grids. The technique aims to minimize the installation cost while ensuring the safety of personnel. The safety indices are obtained; using an electromagnetic formulation based on the well-known quasistatic complex image method together with a closed form of Green's function. This method provides fast and accurate results when it is used in the low-frequency analysis of multilayer grounding systems. The main feature of the proposed technique is its ability to escape from local minimums with good convergence. To examine the performance of the proposed technique, the results associated with an optimal design of a typical grounding grid in a power substation are presented. It is shown that the proposed design complies with the IEEE safety standard, keeping the installation cost as low as possible.
Power and Energy Engineering Conference (APPEEC), 2010 Asia-Pacific; 05/2010
-
[show abstract]
[hide abstract]
ABSTRACT: The (numerical) solution of a rectangular crack in a perfectly conducting surface is appropriate for non-destructive testing (NDT) applications to model faults. The paper presents a direct modeling technique for determining the H and E-polarized backscattering signatures of a two-dimensional crack in a metallic surface that is suitable for inverse scattering problem. The governing field integral equations (FIE) with logarithmic and hyper singular kernels is first discretized and solved by a collocation method based on Chebyshev polynomials. By using ad hoc quadrature rules, the integral equation is then reduced to a linear system of algebraic equations. This approach does not have the size or frequency limitations of the regular techniques such as modal expansion and quasi-static manners. The results are in good agreement with the entirely numerical and non-reversible solution of a finite element method.
IEEE Transactions on Antennas and Propagation 03/2010; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A modelling technique is proposed for direct use of the discrete complex image method (DCIM) to derive closed-form expressions for electric field components encountered in the electric field integral equation (EFIE) representing a lossy half space problem. The technique circumvents time consuming numerical computation of Sommerfeld integrals by approximating the kernel of the integrals with appropriate mathematical functions. This is done by appropriate use of either the least-square Prony (LS-Prony) method or the matrix pencil method (MPM) to represent electric field expressions in terms of spherical waves and their derivatives. A comparison is made between the two methods based on the computation time and accuracy and it is shown that the LS-Prony method performs two-three times faster than the MPM in approximating the integral kernels depending on the platform. The main feature of the proposed technique is its ability for direct inclusion in the kernel of computational tools based on the method of moments solution of the EFIE. This can be viewed as an advantage over the conventional DCIM approximation of spatial Green's functions for mixed potential integral equation for cases where the problem in hand can be more efficiently represented by the EFIE (e.g. the thin-wire EFIE). The accuracy of the proposed technique is validated against numerical integration of Sommerfeld integrals for an arbitrary electric dipole inside a lossy half space.
IET Microwaves Antennas & Propagation 03/2010; · 0.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a new technique is developed to evaluate efficiently the Sommerfeld integrals arising from the problem of a current element radiating over a lossy half-space. The annihilation of the asymptote and the branch-point singular behavior of the spectral Green's function is used in this technique. The contributions of the subtracted asymptotic and singularity terms are calculated analytically. The annihilation results in a remaining integral that is very smooth and can be calculated adaptively by using Gaussian quadratures and extrapolation methods to accelerate the convergence of the oscillating integrand. The accuracy and efficiency of the new technique has been confirmed by comparison with literature, and the commercial software NEC. The application of the proposed technique provides a robust and rapid procedure to calculate spatial Green's functions which can be used in ground-wave propagation, and lightning return stroke channel modeling.
Progress In Electromagnetics Research. 01/2010; 109:139-157.
-
[show abstract]
[hide abstract]
ABSTRACT: Distributed nonlinear resistive elements are incorporated into an antenna theory (AT) model with fixed inductive loading (ATIL-F) to realistically model the current wave propagation along the lightning return-stroke channel (RSC). Resistive elements are considered as a nonlinear distributed load whose resistance is a function of both current and time. This is adopted from the numerical models of a spark channel and consequent shockwave from a lightning discharge, yielding a changing value of the channel radius from the base to the cloud along the RSC. It is demonstrated that the proposed model is more consistent with the nonlinear behavior of a lightning channel inferred from experimental physical observations. The model also satisfies most of the well-known characteristics of RSC, including the temporal and spatial current and charge distributions, some important features observed in radiated electromagnetic fields, and wave propagation speed profiles along the channel when compared with those predicted by the ATIL-F model.
IEEE Transactions on Electromagnetic Compatibility 09/2009; · 1.18 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a new design of an S-band, self-phased, one-turn quadrifilar helical antenna (QHA) has been presented. The antenna has been analyzed in purposed of desired radiation pattern by numerical method. A new matching technique has been used to improve VSWR of the QHA. The experimental results show the radiation pattern has Nadir null of about 6 dB and Axial Ratio is better than 1 dB. In addition, VSWR is less than 2 in frequency bandwidth of 120 MHz. The antenna has low weight, size and cost which is suitable for satellite communication systems.
Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting, 2009. ANTEM/URSI 2009. 13th International Symposium on; 03/2009
-
[show abstract]
[hide abstract]
ABSTRACT: Flicker is one of the main indexes in power quality. With increasing of the modern consumers requirements and industrial units that use sensitive loads, the need of high quality power that cover the power quality standards is very essential. In this paper, an algorithm for flicker sources detection is presented by simulating of flicker sources such as arc furnace in PSCAD/EMTD. Using this algorithm, detection of the flicker sources is possible by installing minimum number of monitoring equipments. Location and minimum number of monitoring equipments is found in two stages by this algorithm. A method is also proposed to determine the flicker power propagation in the power network. In addition, to detect the flicker loads, a flicker meter is simulated according to IEC-868 standard and located in the positions which are determined by the algorithm. Finally, the flicker loads can be detected at any time by using a written program in Mfile/MATLAB. The simulation results show the capability of the proposed methods.
Harmonics and Quality of Power, 2008. ICHQP 2008. 13th International Conference on; 11/2008
-
[show abstract]
[hide abstract]
ABSTRACT: A modeling technique based on the frequency-domain spectral balance method is proposed for analyzing nonlinearly loaded antennas in the presence of a lossy ground. The modeling involves two stages. First, the problem is transformed into a nonlinear microwave equivalent circuit with the circuit parameters of the antenna extracted by the method of moments. Then, the nonlinear microwave equivalent circuit is treated using the arithmetic operator method. To efficiently perform basic arithmetic operations in the frequency-domain, a linear matrix transformation of the spectra is introduced. The main feature of the proposed technique is its efficiency in dealing with problems involving strongly nonlinear loads, the presence of a lossy ground, and multitone excitations. It is also suited for the analysis of array antennas, considering the mutual effects between array elements. The accuracy of the proposed model is confirmed by comparing the simulation results of several case studies with those obtained using the conventional methods available in the literature. Mutual coupling effects, multi-frequency excitation, strong nonlinear loads, and the presence of a lossy ground are included in the simulations to cover all of the asserted aspects of the paper.
IEEE Transactions on Antennas and Propagation 07/2008; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A frequency-domain spectral balance technique is utilized in this paper to analyse orientation effects on the performance of a non-linearly loaded antenna located over a lossy dielectric half-space. The technique involves two stages. First, the problem is transformed to a nonlinear microwave equivalent circuit with the circuit parameters of antenna extracted by the method of moments (MoM) solution of the electric field integral equation (EFIE). Then, the arithmetic operator method (AOM) is applied to solve the nonlinear microwave equivalent circuit. The main feature of the proposed technique is its efficiency in analyzing the transient response of the antenna with strong nonlinear loads over a lossy dielectric half-space. The technique works purely in the frequency domain, so the effects of lossy dielectric half-space can be considered properly by using method of moment in conjunction with Sommerfeld asymptotic method.
Electromagnetic Compatibility and 19th International Zurich Symposium on Electromagnetic Compatibility, 2008. APEMC 2008. Asia-Pacific Symposium on; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents a new method to find minimum number of Phaser Measurement Units (PMUs), to determine the fault locations on transmission network lines in a power system. Considering the installation cost of PMUs, it is important to investigate the placement scheme of the PMUs at minimal locations on the network in the sense that the fault location observability can be achieved over the entire network. In this paper a new algorithm is introduced to find an optimization problem for determining the place and minimum number of PMUs in order to find accurate place of any fault in power systems. The accuracy of suggested algorithm is independent from the fault type and its resistance. Optimization problem is solved by branch and bond method. 41-bus 230 kV Tehran Transmission Regional Electric Network is used as a real case study.
Electric Utility Deregulation and Restructuring and Power Technologies, 2008. DRPT 2008. Third International Conference on; 05/2008
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a modification of the antenna theory (AT) model of the lightning return stroke to include inductive loading is presented. The distributed inductive energy-storing elements are used in the modified AT model (designated as ATIL model, where IL stands for inductive loading) to control the propagation speed of the upward traveling current wave without using an artificial, higher permittivity dielectric medium, as done in the original AT model. The variation of the propagation speed along the channel is also considered in the proposed model. As in the original AT model, resistive loading is used to account for the current attenuation with height. Numerical solution of the electric field integral equation in the time domain using the with appropriate boundary conditions yields a time-space distribution of current along the lightning channel. This current distribution and the resultant electromagnetic fields for the ATIL model are compared with those predicted by other time-domain and frequency-domain electromagnetic models. The current distribution predicted by the ATIL model exhibits features (such as current dispersion) that are more consistent with optical observations of lightning compared to the predictions of the original AT model.
IEEE Transactions on Electromagnetic Compatibility 03/2008; · 1.18 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A neural-network-based technique is described to determine the depth profile of a fatigue crack in a metal from the output signal of an alternating current field measurement (ACFM) probe. The main feature of this technique is that it requires only the measurements along the crack opening. The network uses the multilayer perceptron structure for which the training database is established by systematically producing semi-elliptical multi-hump cracks with narrow openings and random lengths and depth profiles. A fast pseudo-analytic ACFM probe output simulator is also used to produce network input data around each crack for a specified inducer. To demonstrate the accuracy of the proposed inversion technique, the simulated results of cracks with both common and complex geometries are studied. The comparison of the actual and reconstructed depth profiles substantiates the technique introduced here. To further validate the technique, the experimental results associated with several fatigue cracks of complex geometries are presented.
IET Science Measurement ? Technology 02/2008; · 0.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A modification of the Antenna Theory (AT) model of lightning return stroke channel is proposed to realistically represent its nonlinear behaviour. In this model, the constant channel distributed resistive loads are replaced by an appropriate set of non-linear resistors. The model is used to compute current distribution along the channel and the resultant electromagnetic field in various distances. It is shown that the modified model can accurately predict those features in measurement data which are not seen in the conventional theoretical results.
Electromagnetic Compatibility, 2007. EMC Zurich 2007. 18th International Zurich Symposium on; 10/2007
-
[show abstract]
[hide abstract]
ABSTRACT: In a power system, some disturbances can cause abnormal system conditions leading the system to huge damages. Special protection systems (SPS) can detect these abnormal conditions and initiate pre-planned corrective action to mitigate their consequences. However, excessive reliance on SPS can result in increased risk. In this paper, a flexible generator rejection scheme (GRS) for Tehran Transmission System is designed. Using the results of the system transient stability simulation and reliability evaluation of GRS, risk assessment of this scheme is made. Based on this assessment, economic effects of this GRS are analyzed. Furthermore, two methods for making GRS-related decisions are proposed and compared with each other.
Power Tech, 2007 IEEE Lausanne; 08/2007
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper a new method based on discrete wavelet transform is proposed. The method can determine the line voltage notch indices for the power quality monitoring purpose. One cycle of the line voltage is decomposed with discrete wavelet transform and then obtained details are used for calculation of the notch indices. Various wavelet functions are tested and the suitable function is specified. This method is applied to some simulated and real waveforms and results confirm its accuracy.
Power Tech, 2007 IEEE Lausanne; 08/2007
