The physics of lightning

Ultraviolet pulses of 200 fs duration and low energy (/spl ap/0.2 mJ) have a sufficiently high peak power to ionize oxygen and nitrogen by three- and four-photon ionization, respectively. It is shown that the resultant ionization channel induces a lightning like discharge at half of the natural self-breakdown voltage in nitrogen or air. The laser triggered discharging process is studied by monitoring the voltage between two planar electrodes. The effects of oxygen on the induced breakdown is investigated. A complete theoretical model is presented to simulate: (1) the electron seeding; and (2) the evolution of the plasma of electron-ion in the applied field. The results of the theory verified by small scale experiments-are used to simulate the process of laser triggered lightning in atmosphere, and helps to define the parameters of a laser system for lightning protection. >

Femtosecond ultraviolet laser pulse induced lightning discharges in gases

We test the two most commonly used lightning return stroke models, Bruce-Golde and transmission line, against subsequent stroke electric and magnetic field wave forms measured simultaneously at near and distant stations and show that these models are inadequate to describe the experimental data. We then propose a new return stroke model that is physically plausible and that yields good approximations to the measured two-station fields. Using the new model, we derive return stroke charge and current statistics for about 100 subsequent strokes.

Lightning return stroke models

We present correlated measurements of the voltage induced on a power line by nearby lightning and the vertical electric field intensity from that lightning. Data are given for more than 100 first strokes and more than 200 subsequent strokes with the lightning ground strike point located by triangulation using a network of television cameras and by thunder ranging. Voltages were measured at one end of a 460 m unenergized distribution line which was open-circuited at both ends. A neutral wire was located beneath the line and was grounded at both ends. The time-domain voltaqe and vertical electric field waveforms were detected and recorded on a system having a frequency response from less than 1 Hz to over 1 MHz. Only about half of the vol tage waveforms resemble the "classical induced positive surges" described in the literature. The magnitude and polarity of the peak induced voltage is a strong function of the location of the lightning ground strike point.

Lightning Induced Voltages on Power Lines: Experiment

A critical review is presented of the currents and the electric and magnetic fields characteristic of each of the salient discharge processes which make up cloud-to-ground and intracloud lightning. Emphasis is placed on the more recent work in which measured waveform variation is in the microsecond and submicro- second range, since it is this time-scale that is of primary importance in lightning/aircraft interactions. The state of the art of the modeling of lightning currents and fields is discussed in detail. A comprehensive bibliography is given of all literature relating to both lightning measurements and models.

A Review of Natural Lightning: Experimental Data and Modeling

An experimental station for research on lightning and lightning effects was built in the Massif Central (France) in 1973. The experimental procedure is an application of artificial triggering of lightning flashes by means of the wire and rocket technique, which has previously been shown to be valid by M. M. NEWMAN.

Research on Artificiallyu Triggered Lightning in France

After a brief description of the physical phenomena of ionization, charge movement, and ionic recombinations, a very schematic description of the corona cycle results in a loss law which, in particular, shows the influence of the conductor capacity. A more accurate calculation method is then described, the results of which agree very well with experience. This law enables the conductor losses to be determined beyond the critical voltage by the sole determination of its critical gradient.

Calculation of Corona Losses Beyond the Critical Gradient in Alternating Voltage

The essential instability of the radio noise level generated by a transmission line is well known. Its main cause is the fluctuation of the surface state of the conductors and thus, the exact prediction of the radio noise field is very illusory.

Predetermination of the Radio-Interference Level of High Voltage Transmission Lines I - Predetermination of the Excitation Function

This paper presents a simple demonstration and the physical meaning of the excitation function due to corona effect on EHV conductors. Its purpose is to promote and to make easier the application of the excitation function, in order to improve the calculation methods of Radio Interference of EHV lines.

The Theory of the Excitation Function: A Demonstration of its Physical Meaning

A new method of predetermining corona losses under rain is suggested. Instead of setting up empirical formulas based on experimenting according to customary proceedings, a quantitative analysis of the loss mechanism is discussed. In this way networks of losses which are valid for any kind of conductor or line are obtained, but in a slightly idealized form due to certain simplifying hypotheses. Further on application is made to show how the new calculation method was tested by way of a very careful experimentation; then it is explained how to pass from idealized networks to directly applicable loss networks. The limits and possibilities of the usage is also specified.

Claude H. Gary

Papers

Research on Artificiallyu Triggered Lightning in France

Calculation of Corona Losses Beyond the Critical Gradient in Alternating Voltage

Predetermination of the Radio-Interference Level of High Voltage Transmission Lines I - Predetermination of the Excitation Function

The Theory of the Excitation Function: A Demonstration of its Physical Meaning

Predetermination of Corona Losses Under Rain: Experimental Interpreting and Checking of a Method to Calculate Corona Losses