C. F. Wagner

The Relation Between Stroke Current and the Velocity or the Return Stroke

The velocity of the return stroke is an important element in estimating (1) the surge impedance of the return stroke, (2) the potential of the downward leader, and (3) the length of the last striking distance. The energy required to establish an arc plasma can be determined from laboratory tests. By equating this quantity to the energy required to retard the velocity of a traveliing wave, the consequent velocity of the return stroke can be evaluated in terms of the stroke current.

Effects of Corona on Traveling Waves [includes discussion]

THE effect of corona on traveling waves is to retard any given point on a voltage wave above the corona threshold value by an amount proportional to the distance traveled. Thus the effect is equivalent to a reduction in velocity. If a linear circuit can be characterized by assigning to it a certain inductance L and capacitance C, per unit length, then a wave impressed upon such a circuit will propagate along the circuit with a velocity v, such that

The Lightning Stroke

IN RECENT YEARS renewed interest has developed in the effect of lightning on electrical transmission lines. The most vital characteristic of lightning in most methods of calculating its effect is the current measured at the ground terminal. A large amount of data is available about the stroke current crest magnitude and a considerable amount of data is available which covers the time-to-crest of the stroke current. Despite these data there is still controversy over the time-to-crest. Measurements in the region of a microsecond are admittedly difficult. The industry is still seeking new data. In approaching this problem, it was felt that it might be conducive of results to analyze the mechanism of the return stroke and then, from the factors governing the mechanism, try to synthesize the stroke. Perhaps certain limits to the rate of rise could be ascertained. Some of the characteristics of the component factors could be obtained in the laboratory, others by computation. It was with this in mind that the present investigation was undertaken.

New instruments for recording lightning currents

J. H. Hagenguth (General Electric Company, Pittsfield, Mass.): The paper is of considerable interest, as it presents a variety of instruments for measuring lightning currents and charges. Although considerable progress has been made in our knowledge of lightning currents, there still remains considerable work to be done before lightning is fully understood.

Effect of Predischarge Currents Upon Line Performance

The magnitude of predischarge currents of gaps under impulse conditions have been determined. For gaps formed by two parallel pipes the magnitude is found to be approximately proportional to the length and to the spacing. These currents, which must be drawn through the impedance of the line, produce drops at 2 or 3?sec (microseconds) that may be equal to or greater than the gap voltage. Adaptation of these properties improves the lightning performance of transmission lines.

Standard Decrement Curves

Standard decrement curves in use for a number of years in the calculation of power system voltages and currents under fault conditions now have been revised and are presented herewith. Their use enables the determination of the magnitudes of voltages and currents for various intervals of time subsequent to the occurrence of a fault.

Lightning phenomena: III — Field studies

In this concluding article in a series of three, field studies of lightning disturbances on electric-power systems, made with the aid of instruments described in part II (September issue), are reviewed. (Part I, in the August issue, reviewed the general characteristics of lightning phenomena.) The qualitative and quantitative information obtained in these studies has enabled remedial measures to be devised and the lightning performance of systems improved, thereby reducing the system outages from this cause. FROM the standpoint of the lightning performance of electrical systems the frequency of occurrence, as well as the magnitude and wave shape of the voltages and currents produced on systems, is important.

Calculation of short circuits on power systems

CURVES presented in the companion paper “Standard Decrement Curves” are sufficiently accurate for most commercial work, particularly circuit breaker applications. Many special cases arise, however, for which these curves are not applicable. Of this character are relay applications on power systems involving several machines having different time constants and located unsymmetrically with respect to the fault. The individual branch currents in systems of this character may have widely different decrements and even may increase with time. Need, therefore, exists for a method of calculation which will take these individual variations into consideration. Such a method has been developed and has been termed the “internal voltage” method of calculation. It is particularly valuable in that it lends itself to the use of the calculating board and thus minimizes the labor involved.

Insulation co-ordination

Certain changes in United States practice are proposed, while the practices in the United States and Canada are presented for the benefit of engineers of other countries.

Lightning phenomena: I — General characteristics

Although Franklin conducted his famous lightning experiments about the middle of the 18th century, little more was learned until about a generation ago when lightning outages on expanding electric-power systems made an intensive study of the phenomena imperative. Many investigators in different parts of the world have studied lightning during that period, many special instruments have been devised for recording various characteristics of the phenomena, and from information obtained through the use of these instruments remedial measures have been devised — to the end that in spite of the continuously expanding network of electric-power lines, outages caused by lightning have been greatly reduced. In a series of three articles, the authors have reviewed and described: (I) the general characteristics of lightning, the accumulation of the charge, and the mechanism of the discharge; (II) instruments available for measuring the properties of lightning; and (III) results of field investigations in which the instruments described in part II were used. Part I appears on this and the following pages; parts II and III are scheduled for subsequent issues. THE physical manifestations of lightning have been with us from the remotest times, but only comparatively recently have the phenomena become even partly understood. Franklin in his electrical experiments between 1740 and 1750 succeeded in identifying lightning as the static electricity of his time. Beyond this fact little was learned until within the past 25 years. The real incentive to obtain additional knowledge lay in the necessity of the electrical industry to protect against its effects. As longer transmission lines were built the need for reduction in outages due to lightning became more acute. This placed more stringent requirements upon lightning arresters and other protective devices. Largely through the co-operation of the utilities and manufacturers and through the use of special instruments such as the klydonograph, cathode-ray oscillograph, surge-crest ammeter, Boys camera, and fulchronograph, information of a very valuable character has been obtained regarding stroke mechanism and the voltages and currents associated with lightning.