Raul Montano

Resistance of Spark Channels

A study undertaken to measure the resistance of spark channels in air with two different current waveforms is presented. In one experiment, the spark was created by a Marx generator. In this case, the gap length was maintained at 12.8 cm, and the current flowing through the spark had a peak current lying in the range of 0.2-2.2 kA. The decay time of the current was larger than 100 mus. In the other experiment, the spark was created by a current generator. In that experiment, the gap length was maintained at 1 cm, and the current flowing through the spark had peak-current amplitudes in the range of 35-48 kA. The decay time of the current was larger than 500 mus. The results show that the resistance of spark channels initially decreases, reaches a minimum value, and then recovers as the current in the spark gap decreases. The minimum resistance of the spark channel decreases with an increasing peak current. The results are compared with various theories that attempt to predict the temporal variation of the resistance of spark channels. The comparison shows that further developments in the existing theoretical models are needed in order to reproduce with better accuracy the dynamic behavior of the channel resistance

On the Relationship Between the Signature of Close Electric Field and the Equivalent Corona Current in Lightning Return Stroke Models

Engineering return stroke models can be categorized either as current generation (traveling current source type) models or current propagation (transmission line type) models. The current generation models are described among other parameters by a corona current distributed along the channel. Recent studies show that there is equivalence between the models of current generation and current propagation types. Due to this equivalence, any engineering return stroke model of current propagation type can be described in terms of an equivalent corona current per unit channel length. The measurements conducted within 10-500 m from triggered lightning flashes show that the electric field of subsequent return strokes at these distances flattens within 15 mus or so. In this paper, the constraints imposed by this feature on the temporal and spatial variation of the equivalent corona current are investigated. The results show that in order for the close fields to flatten within 15 mus or so, the equivalent corona current, should be bipolar and the corona current wave shape at late times should be identical to that of the longitudinal current time derivative. This is in contrast to most of the engineering models of current generation type, in which the corona current is assumed to be unipolar.

An Efficient Implementation of the Agrawal Model for Lightning-Induced Voltage Calculations Using Circuit Simulation Software

One of the popular, simple, and accurate field-to-wire coupling models for studying transmission-line lightning interaction is the Agrawal model . In this model, the coupling mechanisms are represented by distributed sources along the line, wherein each distributed source is due to the horizontal component of the illuminating electric field at that point on the line. These sources give rise to the propagating scattered voltage along the line, while the total voltage at any instant at a given point along the line is the sum of scattered voltage and the voltage at that point due to the illuminating vertical component of the electric field. There is a difficulty in applying the Agrawal model with the built-in transmission-line models of various circuit simulation software such as the Alternate Transients Program-Electromagnetic Transients Program , PSpice , Simpow , PSS/E , etc., as the voltage source due to the horizontal component of the electric field in the Agrawal model is in series with the line impedance , and not in between two transmission-line segments. In this paper, a simple circuit approach for efficient implementation of the Agrawal model using any circuit simulation software that has built-in transmission-line models is proposed.

Experimental Investigation of Lightning Transients Entering a Swedish Railway Facility

Transients caused by lightning in railway facilities have not received much attention. In this paper, we describe the measurements of lightning transients entering a Swedish railway facility during the summer of 2003. The measurements of the transients were made in a technical house that provides an uninterrupted power supply for telecommunication systems and the signal systems. An analysis of the data has shown that transients in excess of 7 kV (peak to peak) can appear across the line-to-neutral supply system due to an indirect lightning strike. Some typical characteristics of the line-to-neutral transient voltages in terms of stroke locations and stroke amplitudes are presented. Further, from the experimental data, an empirical relation for predicting the line-to-neutral transient voltage in terms of stroke location and stroke current amplitude is obtained. Simple induced voltage calculations are presented to identify the levels of induced voltages appearing at the input of the technical house. The influence of ground conductivity on those induced voltages is also presented. The information presented in the paper is an important electromagnetic-compatibility issue associated with the lightning protection for railway systems

Parameters that influence the crosstalk in multiconductor transmission line

Transient surges in one of the overhead conductors, due to direct lightning strike, causes crosstalk (interference) in other adjacent conductors. Its a common phenomenon observed in power lines, communication lines and electrified railway lines. In this paper we investigate the crosstalk in multi-conductor transmission lines (MTLs) above finitely conducting ground as a function of ground conductivity, height of the receptor conductor, position of emitter source and the terminal loads. It is shown that ground conductivity has a significant influence in the amplitude and wave shape of the crosstalk currents in MTLs, which has not received sufficient attention earlier. In general finite ground conductivity increases the crosstalk current magnitudes in the receptor circuit loads both at the near end and far end. There are situations in which far end crosstalk is larger than the near end crosstalk for identical loads at both ends. These observations have important implications in electromagnetic interference studies of outdoor systems such as railway signaling systems subjected to lightning strikes.

Modeling direct lightning attachment to electrified railway system in Sweden

Direct lightning attachment to a single-track electrified railway system in Sweden is modeled in this paper. Using this model the induced voltages in each of the nine conductors at heights varying from 0.5 m (tracks) to 10 m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance. The main interconnection between the conductors and the flashover strength of the supporting insulators are included in the simulations. A simple model for the arc channel during flashover of the insulators and the ionization of the soil around the pole foundations are also included in the model to assess the possible realistic surge voltage distribution in the system. It is shown in the paper that finite ground return parameters, interconnections between the conductors, and arcing phenomena like insulation flashover, and ionization at the pole footing decide the voltage/current distribution in the conductors.

On the response and immunity of electric power infrastructures against IEMI — Current Swedish initiatives

IEMI is not a new research topic especially for military applications. However, not much attention has been paid in the past to the possibility that this type of threat could be used against civilian critical infrastructure by terrorist groups or other rough elements. Moreover, just a few research programs, mainly conducted in the U.S., have been reported combining power systems and high altitude nuclear high-altitude electromagnetic (HEMP) pulse. The present manuscript is aimed to present various Swedish research activities planned to provide the necessary knowledge to improve the electromagnetic requirements/susceptibility level against IEMI threats of future digital and electronic components used on different critical infrastructures system.

Crosstalk in multiconductor transmission line in the presence of finitely conducting ground

Transient surges in one of the overhead conductors, due to direct lightning strike, causes crosstalk in other adjacent conductors. This is a common phenomenon observed in power lines, communication lines and electrified railway lines. The presence of finitely conducting ground influences the magnitude and wave shapes of the crosstalk currents and voltages and this phenomenon has not received sufficient attention earlier. In this paper, we investigate the crosstalk in multi-conductor lines above finitely conducting ground as a function of ground conductivity, height of the receptor conductor, and position of emitter source. It is shown that ground conductivity has a significant influence in the amplitude and wave shape of the crosstalk currents in multiconductor transmission lines.