Lightning Discharge Currents Research Articles

A study of lightning electromagnetic effect on the metal roof constructions

Metal roofs are often seen as substitute of traditional materials such as concrete these years. But there have been few researches on the lightning electromagnetic effect on these constructions. This work adopts the Finite Difference Time Domain (FDTD) method to carry out numerical simulation of Lightning Electro-Magnetic Pulses (LEMP) generated by lightning discharge current. A substation was taken as an example, the distribution of LEMP field with metal roof and non-metal roof were calculated separately by 3-Dimentional FDTD method. The results show that the metal roof has a reflection effect on the LEMP field, which makes the LEMP field significantly weakened compared to traditional concrete buildings. But for constructions of windows and doors, the intensity of LEMP field inside the construction is still destructive. This work also discussed effects of doors and windows on the electromagnetic distribution and came to conclusions that the amplitude of LEMP field decreases significantly with distance from the door (or window) increasing. The size of the windows or doors was positively related to the LEMP amplitude in the construction.

Analytical Representation of Measured Lightning Currents and Its Application to Electromagnetic Field Estimation

Lightning discharge currents waveshapes and their derivatives with multiple peaks are measured in artificially triggered lightning experiments and at instrumented tall towers. Such waveshapes are represented in this paper by the N -peaked analytically extended function ( N P-AEF) and Marquardt least-squares method is applied for the estimation of its nonlinear parameters. Typical channel-base currents of the first negative, subsequent negative strokes, and positive strokes, based on comprehensive measurements by Berger et al. at Monte San Salvatore in Switzerland, are approximated by N P-AEFs and used in the computation of lightning electromagnetic fields. A new attenuation factor introducing nonlinear current attenuation along the channel is applied within the modified transmission line model (MTLSIN). A lightning return stroke is assumed to have a vertical discharge channel at the perfectly conducting ground. In order to validate this model, calculated lightning electromagnetic fields are compared with the typical, as measured by Lin et al. at various distances from the discharges. Lightning currents and their derivatives measured at the tall towers are also approximated by N P-AEFs. For the measured artificially triggered lightning currents, MTLSIN is applied for the calculation of their electromagnetic fields. These are compared with the measured fields of specific lightning strokes, so as to results of other models.

Application of Genetic Algorithm to Estimation of Function Parameters in Lightning Currents Approximations

Genetic algorithm (GA) is applied for the estimation of two-peaked analytically extended function (2P-AEF) parameters in this paper. 2P-AEF is used for approximation of measured and typical lightning discharge currents. Lightning discharge channel is often modeled as thin-wire vertical antenna at perfectly conducting ground. Engineering lightning stroke models assume that the current along that channel is related to the channel-base current which may be measured at the instrumented tall towers and in triggered lightning experiments. Mathematical modeling of lightning currents is important in verification of lightning strokes models based on simultaneously measured electromagnetic fields at various distances, so as in lightning protection studies, computation of lightning induced effects and simulation of overvoltages in power systems. Typical lightning discharge currents of the first positive, first negative, and subsequent negative strokes are defined by IEC 62305 Standard based on comprehensive measurements. Parameters of 2P-AEF’s approximation of the typical negative first stroke current are determined by GA and compared to approximations obtained by other functions. Measured currents at Monte San Salvatore in Switzerland, at Morro de Cachimbo Station in Brazil, and in rocket-triggered lightning experiments at Camp Blanding in Florida are approximated by 2P-AEFs, and good agreement with experimentally measured waveshapes is obtained.

Experimental modeling of lightning discharge into soil

We present measurements of the electrical properties of soil using a complex designed for testing of lightning protection systems and for measuring the conductivity of soil, including ground electrodes, at currents close to the lightning discharge current. The working resistance of soil is in the range from 10 to 100 Ω at a discharge current of 50 kA and a pulse energy of approximately 4 MJ. The results of experiments in an open field area at the voltage on a circuit of 2 MV are presented. Based on the data obtained, we plot the time profile of the soil resistance upon passing a current pulse of the amplitude of tens of kiloamperes through the soil. A dynamic change in soil resistance with time, a “degradation” of soil resistance, and the formation of a spark channel along the soil surface are reported.

Computer simulation of the electric field structure and optical emission from cloud-top to the ionosphere

Computersimulations are carried out to study the ‘sprite’ onset mechanism. Both electrostatic and electromagnetic codes are developed to calculate the electric field structure and optical emission intensity between the top of the thundercloud and the ionosphere. The optical emission is composed of two structures. One peaks at 70 km height and its lateral dimension is 50–60 km; the other peaks at 90 km height and the lateral dimension extends beyond 200 km. It is found that the nitrogen first positive band, which has a red colour, dominates over the nitrogen second positive band except at the bottom of the optical emission. The upper part of the optical emission is caused by a horizontally travelling electromagnetic pulse induced by a lightning discharge current. The lower structure is caused by electrostatic effects induced by the unneutralized charge left after the lightning discharge current flows. The electromagnetic codes developed can simulate the self-consistent response of the upper atmosphere to the lightning discharge current. The electrostatic treatment can predict only the optical emission at heights less than ∼80 km. The optical emission intensity has a strong nonlinear dependence on the electric field strength through the enhanced electron density, and is increased for a long discharge path, a large current, and a short pulse. Also, the higher the lightning discharge is initiated, the brighter the optical emission is, because the electrostatic field is stronger for high altitude lightning.

Steady‐state analysis of electromagnetic field by vertical electrical dipole over lossy ground

AbstractThe lightning discharge effect is shown by a model in which a lightning current climbs to a lightning cloud from the ground. The electromagnetic field induced at the observation point is the integration of the contribution due to an infinitesimal vertical dipole placed on the discharge path integrated along the path from the ground surface to the height of the cloud. When the conductivity of the ground is taken into account, the expression of the electromagnetic field due to the infinitesimal electric dipole contains a term given by a complicated infinite integral called the Sommerfeld integral that includes the Bessel function. For a wave source with an isolated waveform lasting for a short period of time such as the lightning discharge current, the frequency components exist over a broad range. Hence, in the analysis of the transient electromagnetic field by the lightning discharge, the frequency changes significantly with the source location. As a result, the behavior of the integrand in the Sommerfeld integral changes significantly. This paper treats a case in which the wave source varies sinusoidally so that the transient analysis is anticipated and a useful result is obtained for the steady state. To this end, the analysis of the electromagnetic field induced by a vertical electric dipole on the lossy ground is described with special attention given to the numerical processing of the Sommerfeld integral.

1967 The Magic of I2t

Evaluation of the effects of a short-time irregular-shape current pulse on the conductors and devices through which such current pulses pass can be a perplexing problem to the industrial power system engineer, as well as to those working in other areas. The adverse effects may range from a nuisance malfunction in the overall circuit to a catastrophic explosive failure in power circuit equipment. Common sources of short-time, nonsinusoidal wave-shaped current pulses in industrial systems include: 1) current-limiting fuse let-through current 2) surge discharge current pulse created by short circuiting a charged capacitor 3) lightning discharge currents 4) controlled current let-through of solid-state switching devices. To a surprising degree, the aggregate effect of a particular short-time current pulse can be evaluated in terms of a single composite quantity ∫i <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> dt, called I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> t, and generally expressed in ampere-square-second units. This paper describes and explains a multiplicity of circumstances in which the simple I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> t value can serve to evaluate the severity of the effects as related to conductors, switches, circuit breakers, switching assemblies, and even electric shock effects on human beings.

Magnetic and microstructural properties of some lodestones

An iron ore which behaves as a permanent magnet is lodestone. The intrinsic magnetic properties and the microstructual characteristics which are responsible for the permanent-magnet properties of the lodestone have never been described or explained. Iron ores capable of being charged sufficiently strongly to behave as permanent magnets are defined here as proto-lodestones and fall into two categories — Class I which contains Fe as the only significant cation, and Class II which contains considerable Ti, Mg and Al as well. Proto-Lodestones are magnetically hardened by oxidation and precipitation processes which produce the microstructure responsible for the permanent-magnet properties. Lodestones are charged proto-lodestone iron ores. Lodestones have R H values (ratio of remanent coercive force, H R, to coercive force, H C) between 2.0 and 2.5; R I values (ratio of saturation remanence, I SR, to saturation magnetization, I S) >0.1–0.25 and the ratio of NRM/SIRM (natural remanence to saturation remanence) is 0.15–0.7. The intrinsic magnetic properties and microstructural characteristics of proto-lodestones and other iron ores are described and explained. The mechanism of charging the proto-lodestone appears to be either transient magnetic fields associated with lightning-discharge currents or presently obscure aspects of magnetization intensity enhancement associated with maghemitization of massive iron ores.

Amplitude statistics of lightning discharge currents and ELF and VLF radio noise

The received noise is considered as a result of integrating several atmospherics during the response time of the receiver. The probability distributions of this noise and of current in the lightning flashes are related by a twofold Hankel transform. The measured amplitude distribution of the received noise is inversely proportional to the squared amplitudes for very large signals, and the derived distributions of the effective source current exhibit a similar behavior. The large-amplitude source currents are associated with return strokes of lightning discharges. Their statistics exhibit such a behavior if they are computed in the presence of the more frequent, lower amplitude K pulses and if the velocity dependence of large-amplitude strokes is taken into consideration.

Effects of Thunderstorms and Earthquakes on the Hyderabad Magnetographs

Effects of nearby thunderstorms and earthquakes recorded on the Hyderabad magnetograms during the period January 1, 1965, to June 30, 1966, are discussed in the light of available literature.The thunderstorm effect caused by the magnetic field of the lightning discharge currents appears as a sudden change (kick) of 2-10γ in H or D or both and sometimes 1-2γ in Z also which is followed by very rapid oscillations decaying exponentially in 2-5 minutes.Earthquakes of moderate and great intensity with epicentres in India and its neighbourhood produce characteristic effects on the Hyderabad magnetograms (H, D and Z). The oscillations grow to a maximum of about 30γ in the middle of the effect and then die off gradually over 15-20 minutes. Sometimes the arrivals of seismic body waves P and S and the Rayleigh surface waves LR are clearly seen in the effects recorded on the magnetograms, indicating that the response of the variometers to earthquakes is primarily mechanical. However, a small amount of magnetic effect due to piezomagnetic fluctuations in the rocks underneath the observatory at the time of passage of earthquake waves seems to be inseparably mixed with the mechanical effect.

Lightning and Lightning Protection on Distribution Systems

THE CONCEPTIONS of lightning and of lightning discharge currents through arresters have been altered and enlarged by recent studies. Until not long ago the most complete information available on the magnitude and wave shape of lightning surges on electric systems has been that obtained by the cathode-ray oscillograph investigations of lightning voltages, reported and discussed before the AIEE,1 and elsewhere. Besides this there exists a large mass of data on the crest magnitudes but not the durations of currents in lightning strokes and arrester discharges. Based on the data available two conclusions have been generally held: one, that in a small percentage of discharges, the currents may be high, perhaps 65,000 amperes or more; and two, that the total duration of the discharge might be of the order of 100 microseconds, but not much more. Lightning-arrester design was based principally upon these conclusions. Arresters available during the past six or eight years have in general been able to discharge high currents of the durations cited without damage. In the field, the over-all experience with such arresters has been good. Throughout the country the average failure rate of Autovalve distribution arresters manufactured during that period has been less than a quarter of one per cent per year. However, in rural locations in some parts of the country failure rates of three to four per cent have occurred. This is considered excessive. The variation in failure rates led to the suspicion, several years ago, that there are characteristics in arrester discharge currents that had not been taken into account and which are themselves influenced by such factors as lightning exposure, stroke characteristics, ground resistance, and system characteristics. It is true that to some extent the significance of the data may be obscured by failures from abnormal system voltages and by the performance of obsolete arresters, but these factors were not sufficiently weighty to explain the observations.

Lightning and lightning protection on distribution systems

THE CONCEPTIONS of lightning and of lightning discharge currents through arresters have been altered and enlarged by recent studies. Until not long ago the most complete information available on the magnitude and wave shape of lightning surges on electric systems has been that obtained by the cathode-ray oscillograph investigations of lightning voltages, reported and discussed before the AIEE,1 and elsewhere. Besides this there exists a large mass of data on the crest magnitudes but not the durations of currents in lightning strokes and arrester discharges. Based on the data available two conclusions have been generally held: one, that in a small percentage of discharges, the currents may be high, perhaps 65,000 amperes or more; and two, that the total duration of the discharge might be of the order of 100 microseconds, but not much more. Lightning-arrester design was based principally upon these conclusions. Arresters available during the past six or eight years have in general been able to discharge high currents of the durations cited without damage. In the field, the over-all experience with such arresters has been good. Throughout the country the average failure rate of Autovalve distribution arresters manufactured during that period has been less than a quarter of one per cent per year. However, in rural locations in some parts of the country failure rates of three to four per cent have occurred. This is considered excessive. The variation in failure rates led to the suspicion, several years ago, that there are characteristics in arrester discharge currents that had not been taken into account and which are themselves influenced by such factors as lightning exposure, stroke characteristics, ground resistance, and system characteristics. It is true that to some extent the significance of the data may be obscured by failures from abnormal system voltages and by the performance of obsolete arresters, but these factors were not sufficiently weighty to explain the observations.

Discharge Currents in Distribution Arresters-II

TWO YEARS ago, the authors of this paper described to the AIEE a co-operative investigation by the Boston Edison Company, the Commonwealth Edison Company of Chicago, the Detroit Edison Company, the Georgia Power Company, and the General Electric Company, having as its object the determination of data relative to lightning discharge currents through distribution lightning arresters. At that time the results were based upon records obtained over a 13-month period from August 1934 to August 1935, inclusive. The object of this paper is to present the results from August 1934 to September 1937.

Effect of Near Lightning Discharges on a Magnetometer

DURING two thunderstorms at the beginning of the present monsoon, the recorded curves of the Copenhagen declination magnetograph recently installed at Alibag showed some characteristic features which on examination appear to be due to the effect of the magnetic field of the lightning discharge currents on the magnetometer. The magnetograms are reproduced in Fig. 1. The variations occurred between 2 hr. and 4 hr. and between 18 hr. and 22 hr. I.S.T. The storm was most intense in the second of the two intervals at about 20 hr. The magnetometer needle experienced a number of sudden kicks, and the subsequent oscillations gradually died down in 2–3 minutes. The maximum first deflection was about 1·5 mm.