Showing papers in "Electromagnetics in 1988"
TL;DR: In this paper, basic principles and validity limits of the field-to-transmission line coupling calculating using Transmission Line (TL) theory are discussed, and the effect of shield overhead wires on the response of a power transmission line to an electromagnetic pulse is investigated.
Abstract: The paper discusses basic principles and validity limits of the field-to-transmission line coupling calculating using Transmission Line (TL) theory. Attention is given to the EMP-power lines interaction. A review of the fundamental equations and method of solution is given, considering that two equivalent formulations are possible. These result in two equivalent circuits for an elementary section of the transmission line, each characterized by different excitation source terms. The excitation sources for the case of a nuclear EMP excitation are modeled, and the solution of the equations is given taking into account the effect of a lossy earth serving as a return conductor. In order to assess the validity limits of the TL approximation, a comparison is made between results obtained by the authors using this approach, with those published in the literature using the scattering theory. The effect of shield overhead wires on the response of a power transmission line to an EMP is investigated. It is shown that overhead shield wires, placed in the vicinity of phase conductors for the purpose of providing protection of the system from lightning surges, can be considered effective also when the power line is illuminated by an incident electromagnetic pulse.
47 citations
TL;DR: In this paper, an exact analytical solution for the two-dimensional problem of electromagnetic (EM) scattering by a composite and anisotropic circular cylindrical structure is presented, where closed form expressions are derived for the EM fields in the biaxial layer, induced currents on the conducting core and on the impedance sheet.
Abstract: Exact analytical solution for the two-dimensional problem of electromagnetic (EM) scattering by a composite and anisotropic circular cylindrical structure is presented in this paper. The scatterer consists of a metallic cylinder coated by a lossy anisotropic layer and by an impedance sheet. In the anisotropic layer both permittivity and permeability tensors, when referred to principal axes (ρ,Φ,z), are biaxial and diagonal. The impedance sheet is also anisotropic and is characterized by a surface admittance tensor . The primary EM source is an arbitrarily polarized plane wave, normally incident on the cylinder. Closed form expressions are derived for the EM fields in the biaxial layer, induced currents on the conducting core and on the impedance sheet, and also the scattered fields in the exterior region. The axial components of the EM fields are expressed in terms of Fourier series whose terms are products of radial eigenfunctions and azimutal harmonic functions. It is shown that, in the anisotr...
29 citations
TL;DR: In this paper, a general expression for the Laplace transform of the end voltages and currents was derived by means of the telegrapher's equation model, and the results of a computer program that can handle lines with sufficiently general characteristics (e.g., losses, finite conductivity of the ground, and pulses of arbitrary shape).
Abstract: This paper deals with the study of transients in multiconductor lines excited by interfering plane wave disturbances. By means of the telegrapher's equation model, we derive a general expression for the Laplace transform of the end voltages and currents and show that it. depends on the line characteristics, on the geometry of the interfering wave, and on the terminal loads, which are assumed to contain linear non-reactive elements. Additional assumptions lead to expressions that can be analytically transformed in the time domain. These closed-form results, despite their apparent limited applicability, provide a useful insight into the electromagnetic mechanisms of the interferences and constitute a valid check for more complex all-numerical simulations. Finally, we present the results of a computer program that can handle lines with sufficiently general characteristics (e.g., losses, finite conductivity of the ground, and pulses of arbitrary shape).
15 citations
TL;DR: In this article, the analysis of the coupling of electromagnetic pulses with transmission lines is rigorously formulated in the spectral domain by means of a Fourier transform, on the line axis, of the currents and of the total electromagnetic field.
Abstract: The analysis of the coupling of electromagnetic pulses with transmission lines is rigorously formulated in the spectral domain by means of a Fourier transform, on the line axis, of the currents and of the total electromagnetic field. By means of this formulation, the validity of the telegrapher model and its limitations are clearly assessed; and the spectral domain counterpart of the telegrapher model is presented along with the modifications required to deal with transmission lines over an unperfectly conducting ground. To demonstrate the usefulness of the spectral theory on a practical case that cannot be studied by the telegrapher model, the formal solutions of the problem of a single buried wire of arbitrary length are obtained, by means of the Wiener-Hopf technique. A discussion of the numerical methods that can be used to solve the general equations obtained by the spectral theory is also included.
14 citations
TL;DR: In this article, the authors developed two alternate unclassified high altitude nuclear electromagnetic pulse (EMP) environment descriptions: one arising from a simple radiating dipole moment model, and the other resulting from curve-fitting the calculated fields from a computer code named CHAP.
Abstract: Being able to accurately determine the response of an electrical system which is excited by a high altitude nuclear electromagnetic pulse (EMP) requires a knowledge of the time history of the incident EMP field strength, as well as its angle of incidence and polarization. A commonly used, unclassified, description of this environment is provided by the ''Bell Laboratory waveform.'' Recent studies have shown, however, that this EMP waveform tends to overestimate the response of an above-ground transmission line by more than an order of magnitude. As a result, other unclassified high altitude EMP environments have been developed. This presentation discusses the development of two alternate unclassified EMP environment descriptions: one arising from a simple radiating dipole moment model, and the other resulting from curve-fitting the calculated fields from a computer code named CHAP. For both of these EMP models, the electric field at two earth observation points are compared. These fields are then coupled to an above-ground line and the resulting open-circuit voltage responses are compared. Using the CHAP EMP environment, a limited parametric study of the peak positive and negative open-circuit voltage is then performed and surface plots of these peak voltages are presented. 8 refs., 21 figs., 1more » tab.« less
9 citations
TL;DR: In this paper, a procedure based on trasmission-line theory is presented for the evaluation of the effects produced by an EMP wave on a multiconductor power line, where the high-altitude nuclear EMP is considered as an incident wave towards the ground; the total field is the sum of the incident wave and the wave reflected from the ground surface.
Abstract: A procedure based on trasmission-line theory, is presented for the evaluation of the effects produced by an EMP wave on a multiconductor power line. The high-altitude nuclear EMP is considered as an incident wave towards the ground; the total field is the sum of the incident wave and the wave reflected from the ground surface. The transmission system is represented in the frequency domain by an accurate simulation model, which takes account of earth and conductors skin effect. Non-linear phenomena, such as corona and flashover, are not considered. The EMP-line coupling results in per-unit length series-voltage and shunt-current sources. Analysis of the multiconductor circuit with distributed impressed sources is performed by using matrix operators in integral expressions, which are calculated numerically. The transient voltages and currents are obtained by a discrete inverse Fourier transform. The EMP effects induced on a distribution power line with different terminal conditions are computed.
8 citations
TL;DR: In this article, a technique for the optimization of peak directivity under side lobe level constraints was proposed, where the antennas treated are rectangular grid arrays of isotropic sources, and the directivity of such an array was expressed as a ratio of two functionals, called the Rayleigh quotient.
Abstract: This paper deals with a technique for the optimization of peak directivity under side lobe level constraints. The antennas treated are rectangular grid arrays of isotropic sources. The directivity of such an array may be expressed as a ratio of two functionals, called the Rayleigh quotient. By means of the projection matrix, the constrained maximization problem is transformed into the problem of an unconstrained maximization of a normalized quadratic function. A closed-form solution for the optimum peak directivity and the corresponding current distribution are found by solving for the biggest eigenvalue and the corresponding eigenvector in the generalized eigenvalue problem. Two types of arrays are considered. First, for linear arrays, the peak, directivity in the main beam is optimized under side lobe level constraints. Second, for square arrays with a rectangular grid, with the array pattern generated via the Baklanov transformation, a technique for optimizing the peak directivity under desire...
7 citations
6 citations
TL;DR: In this paper, a perfectly conducting uniform two-wire transmission line of finite length illuminated by a plane incident electromagnetic wave is considered, where the external excitation is modelled by distributed voltage and current sources.
Abstract: Consider a perfectly conducting uniform two-wire transmission line of finite length illuminated by a plane incident electromagnetic wave. The resulting voltage and current response is calculated by using the transmission line theory where the external excitation is modelled by distributed voltage and current sources. The line equations form a set of coupled linear nonhomogeneous ordinary differential equations which are transformed into a more convenient compact decoupled form. Analytical approaches to solve the compact line equations as well as the appropriate boundary conditions are presented. The compact formulation may be easily generalized to consider more complex systems than two-wire lines. In the frequency domain great importance is attached to the mathematical aspects (in the sense of analytic functions) of the line theory. The solutions are expanded in terms of residues and singularities by using a special application of Mittag-Leffler's theorem. Two inversion methods of the Laplace tra...
5 citations
TL;DR: In this paper, the authors address the problem of bounding signal levels at terminations of a multiconductor transmission-line network and formulate the overall network equation in terms of the combined voltage supervector (a special combination of the voltage and current vectors).
Abstract: Starting from the norm concept for vectors and matrices, this paper addresses the problem of bounding signal levels at terminations of a multiconductor transmission-line network. The overall network equation is formulated in terms of the combined voltage super-vector (a special combination of the voltage and current vectors). Utilizing the scattering and propagation supermatrices for the waves on the transmission-line network and the combined voltage supervector for sources, the BLT equation is used to express the combined voltage supervectors and the voltage and current supervectors at the junctions. The upper and lower bounds for the combined voltage supervector, voltage supervector and current supervector are obtained in terms of the norms of the propagation and scattering supermatrices and the norm of the combined voltage source supervector. Various properties of the propagation and scattering supermatrices are discussed for two cases, namely, a uniform section of a multiconductor transmissio...
5 citations
TL;DR: In this article, three aspects of the problem of electromagnetic interaction with transmission lines are reviewed, including the coupling of common to differential mode, and two simple phenomenological corona models are proposed.
Abstract: Three aspects of the problem of electromagnetic interaction with transmission lines are reviewed. The various source terms appearing in the transmission line equations are discussed, including the coupling of common to differential mode. The interaction of an electromagnetic pulse with above-ground multi-conductor power lines is treated directly in the time domain by keeping an account of each scattering term. Finally, two simple phenomenological corona models are proposed, results derived from which are compared with recent experimental data.
TL;DR: In this paper, an application of the transmission-line theory to determine the coupling of disturbing waves on coaxial or multi-wire shielded cables is presented, where the influence of geometrical or electrical parameters such as the cable length, the angle of illumination and the ground conductivity are examined.
Abstract: This paper presents an application of the transmission-line theory to determine the coupling of disturbing waves on coaxial or multiwire shielded cables. First the external problem is analyzed in the case of a line parallel to the ground and examples are given for an illumination either by the field radiated by a lightning stroke or due to a nuclear electromagnetic pulse. The influence of geometrical or electrical parameters such as the cable length, the angle of illumination and the ground conductivity are examined. Penetration of energy into the cable is studied for a coaxial cable. Then some experimental results on multi-wire shielded lines are presented in order to highlight the various mechanisms which can cause a differential voltage between each pair of the inner lines. Lastly, application of a simple numerical model shows the relative influence of dissymmetries either in the structure of the cable or in the load impedances connected at both ends.
TL;DR: In this article, the early-time responses of overhead lines to an exponentially decaying electromagnetic transient are considered and it is found that peak currents of over 5kA and associated voltage crests of several megavolts occur for small incident wave angles.
Abstract: The early-time responses of overhead lines to an exponentially decaying electromagnetic transient are considered. The early-time current, voltage, and radial electric field induced in a wire is investigated. A. transient electromagnetic plane wave produces the driving electromagnetic force for the wire. The wire is assumed to be infinitely long and perfectly conducting. The wire is situated above a finitely conducting plane earth. The plane wave is assumed to have its magnetic field perpendicular to the axis of the wire. The time history of the plane wave is described by a 5O kV/m decaying exponential pulse. It Is found that peak currents of over 5 kA and associated voltage crests of several megavolts occur for small incident wave angles. These values are comparable to small lightning strikes to power transmission line structures. The rates-of-rise of the induced currents are greater than 100 kA per microsecond which exceeds the maximum rate-of-rise of nearly all lightning negative first strokes.
TL;DR: In this work, a least-squares preprocessing technique is utilized for the modeling of data where the signal-to-noise ratio is less than 20 dB and the procedure will ascertain the validity of the analytical model.
Abstract: Time domain measurements are limited In bandwidth and spectral resolution by the sampling rate and the record length. Typically a compromise is necessary for broadband signals. Moreover, the simple extension of the record length may result in a noise dominated signal at late time. These problems can be avoided by using system modeling to analytically extend the data record. A linear combination of complex exponentials is used to model the data at late time. In order to handle noisy data, a least-squares preprocessing technique is utilized. This enables the modeling of data where the signal-to-noise ratio is less than 20 dB. Moreover, the procedure will ascertain the validity of the analytical model. Results are obtained for simulated noisy data and actual data (with unknown noise characteristics) to Illustrate the technique presented.
TL;DR: In this paper, a two-dimensional transient lens synthesis problem is considered, where the formal electric field or formal magnetic field has only a u3 component while the remaining field has a u2 component with both field components a function of u1 only.
Abstract: In transient lens synthesis, there are a variety of ways of specifying inhomogeneous media such that simple electromagnetic waves, such as TEM waves, can propagate in the medium. In the simplified situation considered here, we have a two-dimensional problem in which u3 = z, and either the formal electric field or formal magnetic field has only a u3 component while the remaining field has only a u2 component with both field components a function of u1 only. The uniform TEM wave then propagates in the ui direction. Two-dimensional lenses can then be specified and these lenses are suitable for launching TEM waves on two parallel perfectly conducting plates.
TL;DR: In this paper, the authors compared the actual variation of induced current with angle of incidence, depth of burial, and wire diameter compared with the variations predicted from the transmission-line approximation.
Abstract: Laboratory measurements of the current induced in buried conductors were made and are compared to predictions based on the transmission-line approximation. The measurements were made in a test region of salted soil that was illuminated with a repetitive transient wave from a Large Linear antenna. The small wires buried in the salted soil are electromagnetically similar to larger conductors in typical natural soils. The actual variation of induced current with angle of incidence, depth of burial, and wire diameter are compared with the variations predicted from the transmission-Line approximation.
TL;DR: In this article, a linear convolution integral equation to the incident E-field value V(t), its integral and first moment was derived using Laplace transform techniques, and simple approximations to the current waveform were obtained.
Abstract: When a wire of length L is struck broadside by an electromagnetic pulse, the current at the centre of the wire is independent of L during the initial period of time t≤;L/2c. The current behaviour in this initial period is related by a linear convolution integral equation to the incident pulse. Using Laplace transform techniques the large time behaviour of the current is derived. In practice this is very useful since the large time approximation is valid when t > > a/c, where a is wire radius, and for thin wires a/c is very small indeed compared to pulse duration. On this basis, simple approximations to the current waveform are obtained, involving only the incident E-field value V(t), its integral and first moment The various approximations are compared to previously published numerically exact solutions and observed to be very satisfactory. Finally a comparison with experimental data is made.
TL;DR: In this paper, a waveguide model is proposed for the evening type transequatorial propagation mode, where field aligned irregularities observed in equatorial ionosphere are assumed to form dielectric waveguides.
Abstract: A waveguide model is proposed for the evening type transequatorial propagation mode. Field aligned irregularities observed in equatorial ionosphere are assumed to form dielectric waveguides. A local Champan type layer electron density distribution is taken inside the guide. The transequatorial wave propagation is treated by using this model and the propagation theory of dielectric waveguides. The total attenuation is computed between two points located in opposite hemispheres. The analytic form of the results permits easy interpretation of the propagation characteristics. A good agreement is observed between the experimental results and the theoretical calculations for the total attenuation. Comparisons have also been done for the propagation delay and the incoming elevation angle at the reception point.
TL;DR: In this paper, the authors show how one can interpret the manner in which an overhead line above a perfectly conducting ground responds to an electromagnetic pulse, function of its extremities, leading to display the various phenomena involved and allowing the identification of mechanisms actuating these phenomena.
Abstract: The rigorous study of scattering problems due to the coupling of electromagnetic waves with wire structures can be done directly in time domain by means of various methods, namely by using integral equations and finite difference solutions. Accurate results are being obtained by using these methods in both time and frequency domains, leading to display the various phenomena involved and allowing the identification of mechanisms actuating these phenomena. This paper shows how one can interpret the manner in which an overhead line above a perfectly conducting ground responds to an electromagnetic pulse, function of its extremities. Other more complex applications are also presented.