J.L. Bermudez

Determination of reflection coefficients at the top and bottom of elevated strike objects struck by lightning

Reference LRE-ARTICLE-2008-027doi:10.1029/2002JD002973View record in Web of Science Record created on 2008-02-06, modified on 2017-05-10

Nonuniform transmission tower model for lightning transient studies

This paper presents a new approach to model a transmission tower for lightning performance studies. It consists of representing each part of the tower by equivalent vertical and/or horizontal transmission lines as required. While horizontal line parameters are obtained from standard line formulas, specific expressions are derived for the parameters of vertical lines. Moreover, mutual coupling between any two parallel vertical transmission lines is taken into account. Transient waveforms obtained using the proposed method are compared with experimental data obtained using a reduced-scale model and field experiments. The agreement between simulated results and experimental measurements is satisfactory.

On the use of transmission line theory to represent a nonuniform vertically-extended object struck by lightning

In this study, we present an experimental validation of the transmission line representation of an elevated object struck by lightning. The experimental results are obtained using a reduced-scale model and injected signals with narrow pulse widths (down to 500 ps). The validation is performed using a reduced scale structure representing the Toronto CN Tower in Canada. Two models consisting, respectively, of 1-section and 3-section uniform transmission lines were considered for the comparison. It is shown that the 3-section model is able to accurately reproduce the obtained experimental data. The overall agreement between the 1-section model and the experimental results is also satisfactory, at least for the early-time response.

On the mechanisms of differential-mode to common-mode conversion in the broadband over power line (BPL) frequency band

The conversion between the common and the differential modes is of great importance in the transmission of data over poorly balanced cables such as electrical wiring. In this paper, we have studied some of the mechanisms involved in this conversion, both experimentally and theoretically. The results show that along-the-line variations in the line parameters be it gradual or abrupt, are responsible for part of the common mode in electric cables. Asymmetries at the source are also responsible for part of the common mode conversion and they can be dominant in certain cases

On the enhancement of radiated electric and magnetic fields associated with lightning return strokes to tall structures

We propose in this paper new expressions relating lightning return stroke currents and far radiated electric and magnetic fields, taking into account the presence of an elevated strike object. The derived expressions show that the presence of an elevated strike object enhances the radiated electromagnetic field. The enhancement with respect to a return stroke initiated at ground level is expressed simply through a factor equal to (1+c//spl nu/), where /spl nu/ and c are the return stroke speed and the speed of light, respectively. The computed results using the proposed expression are compared with sets of simultaneously-measured currents and fields associated with lightning strikes to the Toronto CN Tower, and a reasonable agreement is found.

Review of the Electromagnetic Compatibility PLC Work at the Swiss Federal Institute of Technology (Lausanne) and the University of Applied Sciences of Western Switzerland (Yverdon)

In this paper, we give an overview of the experimental and theoretical PLC-related research work carried out in close cooperation by the Swiss Federal Institute of Technology and the University Of Applied Sciences Of Western Switzerland. The work is conducted in the framework of the OPERA project and of a research contract with OFCOM. It is the EMC aspects of data transmission over power cables that are essentially are covered in this research. Much of the effort is dedicated to the experimental and theoretical characterization of conducted and radiated emissions from poorly symmetrical cables in the LV and MV networks. Our investigations focus in part on the evaluation and possible improvement of the k factor concept. For both, the radiation and the conducted emissions problems, a key issue studied is the common/differential mode conversion phenomena in the lines. Other work includes the study of emissions mitigation techniques and immunity test methods

Influence of the height of an elevated strike object on the enhancement of lightning radiated fields

We discuss in this paper the influence of the height of an elevated strike object on the magnitude of lightning radiated electric and magnetic fields. For the analysis, the transmission line (TL) return stroke model for the lightning channel is adopted and the strike object is represented by a uniform lossless transmission line. Analytical expressions derived recently by the authors for the radiated electric and magnetic fields are used to investigate the influence of the height of the elevated strike object Two specific cases of electrically-long and electrically-short strike objects are considered in the analysis. It is shown that, for both cases, the presence of a strike object results in an enhancement of the radiated electromagnetic field, compared to that of return strokes initiated at ground level. However, the enhancement is considerably larger for tall structures compared to short ones. The paper investigates additionally the effect of other parameters such as return stroke speed and reflection coefficients at the top and at the bottom of the strike object on the field enhancement.

Impact of the Symmetry of Coupling-Decoupling Networks on the Conducted Immunity Testing of PLC Modems

For conducted immunity testing, the injection of the test common mode signal is achieved by way of the couplingdecoupling network (CDN) whose symmetry is not defined in the standards. Due to the low symmetry of PLC cabling, part of the injected common mode test signal is converted into a differential mode signal that interferes with the wanted signal at the input of the modem being tested. We show in this paper that the expected bit error rates due to the differential mode current from the CDN are of the order of 1×10−5 to 5×10−5, which can be handled by coding and MAC ARQ procedures. We also show that it is unlikely that the differential mode signals from the CDN#2019;s finite LCL will overload the modems.