C. L. Fortescue

Lightning Discharges and Line Protective Measures

This paper describes the mechanics of the development of a lightning stroke in a cloud and the formation of a surge on a line. It shows that the energy of a stroke can vary between wide limits so that the actual surge on the line may be of practically any magnitude. Fundamental types of high-tension line construction are analyzed to show the performance that would be obtained with them. Experience obtained on the 220-kv. lines of the Public Service Electric and Gas Company is offered to substantiate the belief that induced surges are of relatively small importance and that the direct stroke is the criterion for good design. The effects of line construction on the character of surges impressed on the terminal substation apparatus is discussed to indicate the degree of protection that would be required.

Transmission Stability Analytical Discussion of Some Factors Entering into the Problem

The subject of stability has been much discussed lately, because it has an important bearing on future large power developments. In the early stages of a large program, such as the proposed superpower program, good engineering and common-sense dictate that each step should be very carefully considered from all points of view, since a blunder or failure to give proper weight to some important factor, such as stability, might set back the development program for many years. A brief historical review of the subject of stability follows; for those who are not familiar with “static” stability there is a review of the subject in the Appendix. A criterion of stability is suggested based on present operating conditions, namely, that for reliability each unit of the superpower shall be at least equal to the best that has heretofore been obtained with similar power systems. The necessity of a careful study of the characteristics of all machinery connected to the transmission line is pointed out. The necessity of proper inherent characteristics in generators and synchronous condensers is emphasized, and particular stress is laid on the necessity of proper volt ampere characteristics both inherent and with the exciter. The action inside a generator during the transient following a change in load is discussed; it is pointed out that the true field is a resultant due to several magnetomotive forces in addition to that of the field circuit; the combined effect is a marked tendency to self-excitation, and inherent self-excitation would take place if it were not for the damping effect of resistance in the different circuits. A brief review of other factors entering into the problem is given. These factors comprise inertia of moving parts, mechanical torque, speed of relays, circuit breakers, etc. The difficulty of correlating all these quantities is pointed out, and a basis on which it is practical to make computation is suggested. Those who have not studied the subject of stability are recommended to read the Appendix before proceeding with the subject of transient stability. The subject of transient stability is opened with a definition of stability of a power system. The elements of the problem are discussed in some detail. The problem is one of obtaining the conditions of equilibrium, taking into account mechanical or applied torque, electrical or counter torque, inertia torque and damping factors, in addition to the electrical characteristics of the system. The action of a generator under suddenly applied load is discussed in some detail. The “transient” stability of a simple system is discussed, use being made of a new diagram known as the power angle diagram which may be derived from the circle diagram as obtained for static stability. Three diagrams are required for the simple investigation but the method may be elaborated to include all the factors affecting the problem including the characteristics of governors, exciter systems, and so forth. The difference between the problems of switching operations, load swings and short circuits is pointed out. In the last case the effect of different values of ground resistance is discussed at some length and also the effect of length of time before circuit breaker opens. The necessity of obtaining reliable data on ground resistance with faults is stressed. Throughout this paper the essentiality of delivering the necessary kilovolt-amperes to the line either by adequate exciter systems or by proper modification of machine characteristics in order to maintain a high order of stability is insisted on. It is pointed out in the Appendix that while inherently compensated generator, synchronous condensers, etc., are future possibilities, our main concern is the problem of getting the most out of present day designs as our present day problems depend on these and not on something that may be commercially developed five years from now. Consequently the conclusions refer to means that may be made quickly available and the two most important are: a. Improved inherent regulation of machines. b. Increased speed of excitation.

Theoretical and Field Investigations of Lightning

This paper gives a review of some recent developments in the methods of studying lightning phenomena. The Norinder form of cathode ray oscillograph and its application in Tennessee are discussed, together with the information secured. The second part gives the theory of traveling waves along transmission lines. Reflections at open and grounded ends are considered. A mirror scheme of an infinite series of waves on a double infinite line equivalent to actual waves along a finite line is developed. The third part discusses the manner in which surges are actually produced on lines by lightning and the effect of ground resistance on the protection afforded by ground wires, both with respect to induced and direct strokes.

Polyphase Power Representation by Means of Symmetrical Coordinates

THIS paper is a more complete presentation of the subject of power representation by means of symmetrical coordinates, which was briefly outlined in the authors paper on Symmetrical Co-ordinates presented at the 30th Annual Convention, 1918.

Power, Reactive Volt-Amperes, Power Factor

The relation between power, reactive volt-amperes, and power factor is discussed for sinusoidal electromotive forces and currents. Reactive volt-amperes is defined as the flow of stored energy into the circuit and is deduced from the stored energy cycle. It is shown to be a cyclic flow of power which is 90 deg in advance of the cyclic part of the dissipation or power input cycle which with the stored energy cycles is positive at all instants. This leads to the vector equation ?I? + ?? derived for the equation of total inflow of energy given by Ri2 + d/dt (1/2Li2)or (Ri2 + L di/di i) for an inductive system or Ri2 + d/dt (1/2 q2/C) or (Ri + q/C) i for a capacitor system. Non-sinusoidal electromotive forces and currents are discussed and it is shown that there is no simple relation between the volt-amperes as obtained by voltmeters and ammeters and power as obtained by wattmeters and reactive power. The inflow of stored energy for double frequency fundamental can be obtained but it appears to bear little relation to the product of mean square volts and amperes and true average power. It is concluded that the ratio of power to mean square volt-amperes is a useful practical factor with non-sinusoidal waves encountered in practice but should not be used to define reactive volt-amperes. Polyphase power and reactive volt-amperes are defined. In a balanced system power is continuous and the instantaneous reactive volt-amperes are zero.

Abridgment of rationalization of station insulating structures with respect to insulation of the transmission line

The purpose of this paper is to present a logical basis for the insulation of transmission lines and substations using as a basis the characteristics of traveling waves produced by lightning discharges. The method presented was formulated from the data obtained from the cathode ray oscillograms of actual line surges and upon the laboratory work in which the impulse flashover characteristics of insulating structures was determined. The breakdown volt — time characteristics of various forms of insulation are presented. Using these curves of various forms of gaps in the known characteristics of traveling waves, insulation of the transmission line at various distances from the gap is determined so that flashover will be unlikely to occur at these points. A similar method of analysis is made upon substations and lines protected by lightning arresters, but with the known characteristics of lightning arresters, the insulation on the line up to points 1000 to 5000 ft. away can be apportioned so that the lightning arrester will take the discharge, preventing the flashover of insulation. The system set forth in the paper enables the transmission engineer to design the line and substation in an economical manner and obtain adequate protection for all points desired.

Abridgment of theoretical and field investigations of lightning

This paper gives a review of some recent developments in the methods of studying lightning phenomena. The Norinder form of cathode ray oscillograph and its application in Tennessee are discussed, together with the information secured. The second part gives the theory of traveling waves along transmission lines. Reflections at open and grounded ends are considered. A mirror scheme of an infinite series of waves on a double infinite line equivalent to actual waves along a finite line is developed. The third part discusses the manner in which surges are actually produced on lines by lightning and the effect of ground resistance on the protection afforded by ground wires, both with respect to induced and direct strokes.

Transmission line stability: Analytic deduction of the condition for stable operation for transmission lines

In the body of the paper by Fortescue and Wagner, presented at the recent Midwinter Convention, and in the companion papers by Evans and Bergvall, E. B. Shand, and Evans and Sels the conditions of stability are discussed by means of graphs. This method has been chosen as that best fitted for presenting these important factors in the problem of power transmission before the engineering public in the form best adapted for practical application.