J. F. Borges da Silva

Series-impedance of underground transmission systems

A general solution for the magnetic field in the soil is developed that satisfies arbitrary boundary conditions on an underground cylindrical surface at a finite depth below an earth/air plane surface. A quasi-steady state hypothesis is assumed. The series impedance of an underground cable with a perfectly conducting sheath is evaluated taking into account skin effect in the soil. The numerical results are compared with F. Pollaczeks (1926) classical solution. >

Wave Propagation in Polyphase Transmission Lines a General Solution to Include Cases Where Ordinary Modal Theory Fails

The solution of transmission line equations is usually written as a superposition of so called natural modes of exponential type. These are obtained through the use of a suitable transformation that decouples the original sets or N simultaneous 2nd order wave equations for voltages and currents into N independent equations. For such a transformation to exist the fundamental product matrix ZY must be diagonalizable. In a previous paper it has been shown that physically realizable transmission lines are possible for which ZY is not diagonalizable and to which ordinary modal theory does not apply. In the present paper a new generalized modal theory is developed for the purpose of including non-diagonalizing cases.

Series-impedance of underground cable systems

A general solution for the magnetic field in the soil is developed that satisfies arbitrary conditions on a set of underground cylindrical surfaces at a finite depth below the earth/air surface. The solution takes into account singularities of all orders located in the axis of each circular boundary, allowing boundary conditions on the earth/air plane to be satisfied and imposing regularity at infinity. The method is used to evaluate the series-impedance matrix of a system comprising three underground cables in a flat configuration. Numerical results are presented for the contribution of the Earth return path to the cable self-impedances as well as for the mutual impedances between cables. The results are compared with Pollaczeks classical solution. >

The effect of randomly earthed ground wires on PLC transmission-a simulation experiment

The analysis of an almost periodic lattice of cascaded line segments with individual lengths randomly distributed around a typical mean value is presented. The analysis considers an interphase balanced antisymmetric-type carrier transmission and makes use of a modal decomposition technique. Each line segment is assigned a two-port network representation whose intrinsic propagation parameters are established. The transmission matrix of the overall chain is obtained, and from it the chain propagation parameters (attenuation, velocity, surge impedances) are computed. The analysis and numerical results presented show that even slight random perturbations of line periodicity are sufficient to render unnoticeable any sharp variations in attenuation, velocity, and surge impedance. >

Q-factor and bandwidth estimation of sharp resonant phenomena in transmission line systems with grounding points

Transmission line systems exist with grounding points at both the sending and receiving ends; due to standing wave phenomena the transmission performance of such systems is critically affected in the neighbourhood of certain resonant frequencies — attenuation, phase constant and characteristic impedance showing large amplitude variations in a relatively small frequency range. In this paper a simple accurate method to estimate the quality factor and the bandwidth of the resonant curves describing the frequency behaviour of the transmission line propagation parameters is presented.

IRREGULAR EIGENVALUES IN THE ANALYSIS OF MULTIMODAL PROPAGATION

In the application of matrix methods, to the frequency domain solution of travelling-wave phenomena in poliphase systems, it is tacitly assumed that the basic matrix [ZY] has as many eigenvectors as eigenvalues.

Ground return effect on wave propagation parameters of overhead power cables

It is noted that the propagation properties of overhead three-phase cables are usually analyzed assuming that the pipe conductor establishes a perfect shielding between the inner conductor set and any outer conductor, i.e. the power cable is assumed to be an isolated system. The influence of a lossy ground plane in the neighborhood of the cable is examined in the present work. The propagation parameters for both approaches are compared, and significant differences are found to exist, in the zero mode, at low working frequencies. Relative errors up to 60% have been determined in the attenuation, velocity, and surge impedance. A physical interpretation of these results is presented. It is based on the imperfect screening action of the pipe which allows the magnetic field to spread outside the cable and penetrate the imperfect soil, giving rise to a higher series inductance and a smaller series resistance. >

Application of a first order perturbation method to the analysis of almost periodic multiport network chains

ContentsPropagation parameters of cascaded multiconductor transmission structures can be easily determined when the chain is strictly periodic. If periodicity is somehow perturbed, which is usually the real case, the evaluation of the chain propagation parameters becomes very complex, especially when the number of cascaded sections is large. To handle this situation we propose an approach based on a standard first order perturbation method allowing a simple relationship to be found between the chain parameters and those characterizing its component cells. The method is first developed for general 2n-port networks and later particularized for the special case of two-port transmission-line systems. Graphs with numerical results are presented allowing the accuracy of the method to be checked.ÜbersichtDie Berechnung der Wellenparameter von Ketten aus Mehrleiter-Übertragungsystemen bietet keine Schwierigkeit im Fall streng periodischer Ketten. Wird die Periodizität gestört, wie es in der Praxis häufig vorkommt, so wird die Berechnung sehr mühsam, besonders dann, wenn die Kette viele Glieder enthält. Um diese Schwierigkeit zu überwinden, schlagen wir die Anwendung einer gewöhnlichen Störungsmethode erster Ordnung vor, die es gestattet, eine einfache Beziehung zwischen den Wellenparametern der Kette und den Wellenparametern der einzelnen Glieder zu gewinnen.Die Methode wird zuerst für allgemeine 2n-Tore entwickelt und danach auf den Sonderfall der Zweitor-übertragungssysteme angewandt.Die Genauigkeit des Verfahrens läßt sich aus der graphischen Darstellungen numerischer Ergebnisse ablesen.

Automated measurement system to generate a Preisach-type model of ferromagnetic hysteresis

An automated measurement system for identification of ferromagnetic hysteresis based on Preisachs model is described. The data required consist of incremental permeabilities taken along symmetric hysteresis loops. Magnetic field values are determined by preset values of current in an excitation coil. Magnetic induction values are obtained using an analog integrator for the electromotive force (EMF) induced in a test coil. The integrator output is digitized. The acquisition of successive incremental permeability values as well as the data reduction and display of results are fully automatic. Details of hardware and software implementation as well as the calibration procedure and results obtained for soft iron samples of different composition are presented. The system is particularly suited to investigate the so-called statistical stability of Preisachs model by allowing use of different B-H plane scanning modes.

Analog circuit simulation of magnetic dipole behavior according to the Langevin-Weiss theory of ferromagnetism

An analog electronic circuit designed to illustrate the principles of ferromagnetism by simulating the behavior of elementary magnetic dipoles as described by the Langevin-Weiss theory is presented. The device is intended to help undergraduate students master the fundamental ideas that explain the properties of ferromagnetic materials. The circuit design is described and related to the concepts used in the Langevin-Weiss theory, which is briefly outlined. Results obtained with the simulator are presented as oscilloscope traces and illustrate some of its possible uses. >