Showing papers in "Electrical Engineering in 1940"

This culture

Abstract: Deploring the “uneasy self-consciousness” that afflicts many engineers in considering “culture,” Past President Parker suggests that the culture which consists of mental flexibility, sympathy with others' interests, and understanding of the relation of one's profession to society also may be instilled through great teaching of technical subjects.

Effective resistance to alternating currents of multilayer windings

Abstract: IN any multilayer winding carrying an alternating current, such as the windings illustrated in figures 1, 2, and 3, each layer of copper lies in the alternating magnetic field set up by the current in all the other layers. Eddy currents are set up in each layer in a direction to partly neutralize the magnetic intensities in the interior of the copper wire in each layer. As a result of the eddy-current losses in the copper, the effective resistance of the winding to the alternating current it carries may be many times its resistance to continuous currents.

The Ionosphere

Abstract: SOME YEARS AGO there was a flood of books bearing such titles as “The Doctor Looks at Love”, “The Lawyer Looks at the Law”, “The Poet Looks at Civilization”, etc., etc. I might have followed their precedent by naming this lecture “The Physicist Looks at the Ionosphere”. Better would have been to say “The Physicist Listens to the Ionosphere” for while the actual procedure is neither listening nor looking in the usual senses, it is rather more like listening. As a matter of fact we have all of us listened to the ionosphere — all of us excepting those who as yet have never hearkened to a broadcast from long distance, and who must by now be few. Any program which is heard from more than a few hundred miles, and does not come by wire, comes by courtesy of the ionosphere. When we are lending ear to such a program, we are listening both to the loud-speaker and to the ionosphere, since both take part in the transmission. Of course we are likely to be listening also to the news; but nowadays the news is generally dismal or frightful or both; and it should be happiness to be diverted for a while from what the ionosphere brings to the qualities of this innocent agent itself, which is not in the least to blame for the evil which it reflects.

Theory of hysteresis-motor torque

Abstract: THE object of this study is the development of a quantitative theory of hysteresis-motor torque, especially in relation to magnetic properties and dimensions. The theory is interpreted physically in an idealized case, and applied to a particular motor to verify the result experimentally.

Performance of traveling waves in coils and windings

Abstract: THE reaction of coils and windings to traveling waves which impinge upon their terminals is an ever-important problem in electric power systems from both the practical and the scientific point of view. Transformers as well as alternators are used at increasingly higher voltages and their insulation is thus subjected to switching and lightning surges of ever-increasing severity. A simplified but nevertheless rigorous conception of the wave propagation within such windings may therefore be advantageous. It may be used for coils in communication circuits as well.

Ultrahigh-frequency loop antennas

Abstract: ANTENNAS which are discussed in this paper were developed for two applications: (1) to serve as elements in radiating systems of localizers and radio ranges used to guide aircraft; (2) to act as receiving antennas carried by aircraft.

Surge characteristics of a buried bare wire

Abstract: BURIED bare wires are frequently used as grounds or counterpoises for transmission-line towers and also as shield wires for underground rubber-covered telephone wires. Experience has verified the effectiveness of such wires in reducing insulator flashovers for direct strokes to transmission towers and breakdowns of underground rubber-covered wires due to surges. Quantitative relations between surge characteristics of the wires and various fundamental constants are, however, incomplete. Theoretical considerations of surge characteristics appear to have been confined to empirical approximations of test results1,2,3 and do not reveal the relation to fundamental constants, such as the earth resistivity and dielectric constant of the earth.

A method for detecting the ionization point on electrical apparatus

Abstract: WHEN any part of the air path included in the insulating circuit of a piece of electrical equipment is overstressed, ionization occurs. The critical value of voltage is a function of the nature of the remainder of the dielectric circuit, the manner of use, surface conditions, the proximity of grounded conducting bodies, the temperature, and in some cases, the relative humidity. Ionization in air causes the formation of small quantities of ozone and oxides of nitrogen. The presence of ozone leads to accelerated aging of insulating materials, especially organic materials such as varnished cambric and paper.

New instruments for recording lightning currents

Abstract: IN the early days of lightning investigations surge voltages on transmission lines were measured by a relatively crude device consisting of a number of parallel gaps with different spacings. The maximum gap broken down, which was indicated by markings on a thin piece of paper placed within the gap, was a measure of the voltage. Peters,1 by applying the phenomenon of Lichtenberg figures to photographic films, then developed the instrument called the klydonograph. Much information concerning the magnitude and frequency of voltage surges on systems was obtained with this instrument. At about this time the cathode-ray oscillograph was just emerging from its laboratory stage of development and several investigating groups adapted it to field work. A number of records were obtained with this device which showed the rate of rise of the voltage wave, its crest, and a limited amount of information regarding its tail. However, the quantity of data secured by this means was quite small, largely because of the initial cost of the instrument and the necessity of constant attendance for operation and maintenance.

Note on earnshaw's theorem

Abstract: Many have seen the “electromagnetic levitator” in the General Electric Company's “House of Magic” demonstration lectures. In this demonstration, an aluminum disk is stably supported in an alternating magnetic field under the repulsive force between the induced eddy currents and field.5 Another and related problem is reflected in several recent and serious, but inevitably (utile, attempts to achieve stable suspension in space under the forces of permanent magnets alone. This article sheds further light on the basic theory involved, which was formulated a century ago by Samuel Earnshaw and seems quite largely to have been overlooked.

The design characteristics of amplidyne generators

Abstract: COMPANION papers present some of the inherent possibilities and the useful applications for dynamoelectric amplifiers.1,2 They have also clearly pointed out that the inherent value of such an amplifier is determined by three characteristics: (1) ratio of response or sensitivity; (2) speed of response; and (3) stability.

Starting performance of salient-pole synchronous motors

Abstract: IN recent years, two papers on the subject of salient-pole synchronous motors have been published in which practical methods for calculating the starting performance are derived on the basis of considerations that take into account all the unsymmetrics of this type of machine; the authors of these two papers are respectively H. V. Putman and T. M. Linville. Application of the Putman method gives at small values of the slip torque values that are somewhat too high; on the other hand, application of the Linville method is rather laborious, especially when the damper cage has a relatively large number of bars per pole. In view hereof, the author presents in this paper another method of calculating the starting performance of a salient-pole synchronous motor, a method which also takes into consideration all the unsymmetrics of this machine. This new method is, on the one hand, much simpler to apply than the Linville method, while on the other hand, it leads to more accurate results than the Putman method. It has been used for many years in the calculation and design of machines of various ratings and speeds, and has always given satisfactory results.

Determination of short-circuit torques in turbine generators by test

Abstract: THE consideration of short-circuit stresses in turbine-generator shafts and frames must be preceded by a knowledge of the developed electrical torque. The theoretical work for this subject has been done by Kilgore and Stone, and Nickle, Pierce and Henderson. As far as is known there have been no extensive measurements of short-circuit torques on modern turbine generators. The object in performing these experiments was to obtain data to check previous equations derived from theoretical considerations and, if necessary, make revisions.

Analysis of factors which influence the application, operation, and design of shunt-capacitor equipments switched in large banks

Abstract: THE application of shunt capacitors to distribution circuits has been well treated in the technical press. These papers have in general dealt with conditions obtaining when relatively small banks of capacitors are connected to the circuit 24 hours of the day. The increase in knowledge of the benefits afforded by capacitors through experience and analysis, coupled with the price reductions effected through advances in design and manufacture, has logically stimulated their use in fields where switching during the day, as governed by load and voltage conditions, is advantageous, desirable, and economically sound. These types of applications impose different duties upon the capacitors as well as upon the disconnecting equipments and associated devices, and the question naturally arises in the engineers' mind as to their effect upon the design and operation of the equipment. This paper offers a discussion and an analysis of the more pertinent of these problems. The conclusions drawn pertain in general to installations of 6,900 volts and below. The higher-voltage equipments may require additional considerations.

New developments in current-transformer design

Abstract: VERY noteworthy progress has been made in recent years in the design of current transformers for medium and high voltages. Previously most current transformers were designed and built according to the same general practices as a small power transformer, and its size, weight, and general appearance was that of a conventional transformer. The latest current transformers, described below, scarcely resemble their prede-cessors — their weight, size, etc., are but a small fraction of the older designs. A comparison of the principal data of two current transformers — one designed in 1929 and the other of recent development — may be of interest (table I).

A graphical solution of transient stability

Abstract: An extension of the equal-area method of determining transient stability limits, applicable to power systems that can be reduced to two equivalent machines

An extension of the method of symmetrical components using ladder networks

Abstract: IN his now classical paper on symmetrical components Fortescue analyzed the behavior of synchronous and induction machinesoperating under unbalanced conditions. In this analysis Fortescue assumed that the stator and rotor windings themselves were symmetrical, that the rotor windings were either short-circuited or connected to balanced static circuits, and that the stator windings were connected to unbalanced circuits. Under these conditions there are unbalanced currents of a single frequency in the stator, and balanced currents of two different frequencies in the rotor. It has since been shown how the method of symmetrical components is applied when the rotor windings are connected to unbalanced circuits and the stator windings are connected to balanced circuits. Under these conditions there are unbalanced currents of a single frequency in the rotor, and balanced currents of two different frequencies in the stator.

The output and optimum design of permanent magnets subjected to demagnetizing forces

Abstract: THE recent development of new permanent-magnet alloys having a high available energy has extended considerably the field of permanent-magnet applications. Prominent among these new materials is the group of aluminum-nickel-iron alloys which has been given the name “Alnico”. These alloys are characterized by coercive forces of 400 to 700 oersteds, residual inductions of 6,500 to 7,800 gausses, and available energy values ranging from 1.3 × 106/8π to 1.7 × 106/8π ergs. Corresponding values of these quantities for three other well-known magnet materials are given in table I, and characteristic curves for these materials are shown in figure 1.

Fractional-slot and dead-coil windings

Abstract: THE expression “fractional-slot windings” is commonly applied to machines where the number of slots is not an integer multiple of the product of the number of poles and phases. Dead-coil windings (D.W.) refer to windings where some of the slots contain wedges instead of coil sides. We shall use the term (F.W.) in this paper to comprise all windings which are not (D.W.). The term (F.W.) therefore comprises both whole-slot as well as fractional-slot windings which contain no dead coils.

Dielectric strength of insulating liquids in a continuously circulating system

Abstract: THE electrical properties of liquid dielectrics have been studied by theoretical and experimental physicists for a long time. Of the various properties one of the most important, and probably the least understood, is the mechanism of electrical breakdown. To become acquainted with the voluminous literature in this field one must read not only monographs1–4 but also more recent important summaries and experimental contributions.5–13 One of the important concepts in the past has been that breakdown is initiated by ionization in gas bubbles thrown out of solution or suspension in the liquid. As a new experimental approach to this problem we set up a closed system in which the liquid could be continuously circulated through the dielectric strength cell with filters, dryers, and a degasifier in series in the system so that solid particles, moisture, and dissolved gas could be removed.

Compressed powdered molybdenum permalloy for high-quality inductance coils

Abstract: THE introduction of loading coils in the telephone system at about the turn of the century brought special demands on magnetic and electrical properties of core materials, and set in motion investigations which have had wide influence on the theoretical and practical aspects of ferromagnetism. The first step in this development led to cores of iron wire, which sufficed for loading coils on circuits of moderate length.1 With the development of telephone repeaters and the extension of circuits to transcontinental length some 25 years ago, there arose need not only for loading coils, but also for network coils, which would have high stability with time, temperature, and accidental magnetization. Magnetic stability was at first secured2 by employing iron-wire cores provided with several air gaps. Later, commercial and technical considerations led to a core structure made from compressed insulated powdered material, first electrolytic iron3 and later Permalloy powder.4 This type of core is mechanically stable; it introduces in an evenly distributed fashion the requisite air gaps, while avoiding undesirable leakage fields; and it subdivides the magnetic material so as to reduce eddy-current losses. Although other means have been suggested,5,6 no way has yet been devised which provides these features so well and at so low a cost as the compressed powdered type of core.

A study of short-time ratings and their application to intermittent duty cycles

Abstract: VARIOUS American standards for electrical apparatus provide, in addition to continuous ratings, certain short-time ratings, based on 5-, 15-, 30-, and 60-minute runs with the apparatus starting cold. Usually these short-time runs do not correspond to conditions met in service; for example, a motor very seldom starts cold, operates for a limited period of time, and then remains at rest until it has cooled to ambient temperature. Often these short-time ratings are applied to intermittent loads, such as shown in figure 1, in which T represents the total time for each cycle of operation; T r = kT, the running time; and T i = (1−k)T, the time the motor stands still. Since the short-time ratings do not indicate the type of operating cycle with varying values of T, k, and operating current I, for which these ratings are suitable, suggestions have been made from time to time to establish standard intermittent load ratings, especially for motors. Efforts along these lines have so far not led to any definite action because it is difficult to find practical standard provisions applicable to the many variations encountered in operating cycles. Furthermore, the present standard short-time ratings are so simple and convenient for acceptance-test ratings that there naturally is considerable hesitancy in adopting a complicated system of intermittent ratings. This raises the question of the possibility of devising various reasonably simple means for applying short-time ratings to intermittent load conditions without resorting to time-consuming temperature calculations, for instance, those used in the application of railway motors. In many industrial applications the cost of these calculations would be entirely out of proportion to the total cost of the motor and any slight saving in the size and cost of the motor resulting therefrom.

Dynamoelectric amplifier for power control

Abstract: THE USE of amplifiers has become common knowledge in radio, but on the other hand, the term amplification has seldom been applied to processes in power engineering. Strictly speaking, we may say that a radio amplifier is only a form of control because we always tap a new source of power and the function of the amplifier is to control this power so as to reproduce the changes of energy flow at a higher power level. On this ground we might say that an ordinary d-c generator is an amplifier because we control the power output by the current in the field winding. Such a terminology would, however, be rather misleading because when we say amplification, we imply something more specific than when we say control. An amplifier should give accurate reproduction both of intensity and time intervals, whereas, controlled power circuits used so far have not met these requirements. In the radio-frequency amplifier we are dealing with a time element of less than a millionth of a second. In an audio amplifier the time element is about 1/5,000 of a second. The only device we know of that will respond in such a short time is the high-vacuum electron tube. In power circuits, on the other hand, the time element is seldom less than one-tenth of a second.

Some problems in the standardization of temperature ratings of fractional-horsepower motors

Abstract: AT the winter convention of the AIEE in New York in January 1939, there, were presented a number of papers on temperature rating of electrical apparatus.1–6 Since that time AIEE Standards No. 1 has been tentatively revised to favor the resistance method for determining the temperature rise and changing the limits for this method from 55 degrees to 60 degrees centigrade. Little data have been published on how the proposed changes in standardization might affect fractional-horsepower motors. For this reason the study out-lined in this paper was undertaken. It is hoped that the information given herein will be of some assistance in standardization problems affecting fractional-horsepower motors. It is further hoped that others who have similar data on fractional-horsepower motors will make them available, regardless of whether they may support or differ with the data in the paper, in order that correct information representative of the industry may be available to those who make the standards, or any future revision of them.

Importance of gas in electrodes for the glow-to-arc transition

Abstract: IN an earlier work1 on the probability of glow-to-arc transitions in a low-pressure mercury-vapor discharge it was pointed out that these transitions occur in a completely random fashion and that the probability of a transition increases with an increase of pressure, cathode-current density, or glow voltage. In particular, cathode temperature was found to be very important, the transition probability being several times higher in a narrow temperature range near 425 degrees centigrade than it is at either lower or higher temperatures. The possible causes of these transitions were also investigated and the only explanation that seemed consistent with the experimental results obtained was that each transition was due to a burst of gas from the electrode surface. It was felt that even if the amount of gas given off in each burst was very small, the random appearance of these bursts from various parts of the electrode surface could explain the experimental results obtained.

The dielectric strength and life of impregnated-paper insulation — II: The influence of the thickness of the paper

Abstract: PAPER as used in the spiral laminated impregnated insulation of high-voltage power cables is available over wide ranges of density and thickness. There result important variations in the ordinary physical properties of the paper such as flexibility, tearing, tensile, and bending strength. Variations in the electrical properties of conductivity, dielectric constant, and breakdown strength also result. The peculiarly severe conditions imposed by the manufacture, transportation, installation, and operation of high-voltage cables have emphasized the importance that full attention be paid to all physical properties of the insulation, especially those relating to permanence of mechanical structure and of high insulating properties. Manufacturers of cables often utilize the several types of variation referred to in designing cable insulation to meet the particular requirements of cables for different types of service.

Synchronizing transients and synchronizers for large machines

Abstract: IT IS a curious fact that the phenomena encountered in synchronizing operations have received scant attention in the technical literature even though the phenomena have been encountered ever since two synchronous machines were first operated in parallel, and even though a large number of synchronizing operations are performed every day. Possibly the explanation is due to two facts; first, that the ideal conditions introduce no disturbance, and, second, that the synchronizing transients are usually not large but for analysis require consideration as a stability problem of considerable complexity. A review of the synchronizing problem has become desirable because of the development of new types of automatic synchronizers and because of the progress in the analysis of system transients in connection with system stability. This study includes only those synchronizing operations for which the voltage, phase, and frequency conditions are matched before the connection is made; it does not include self-synchronizing methods.

Application of and operating experience with hydrogen-cooled synchronous condensers and alternators

Abstract: UNTIL about ten years ago the only cooling medium utilized for electrical rotating machinery was air. Obviously this was occasioned not by the fact that air has any particularly suitable characteristics but because it is the daily common surrounding medium which, of necessity, must be used for open-type machinery. Before that time, the need for construction of machines of constantly increasing size and speed had brought about the development of closed systems of ventilating. In these, facilities had been provided for conditioning the cooling air, but this had been primarily for the purpose of removing dust particles. The elimination of the particularly objectionable oxygen had not been attempted although for some time inert gas had been used in transformers to prevent oxidation of oil or insulation.

Industrial applications of amplidyne generators

Abstract: ACONSIDERABLE number of “amplidyne”∗ generators1,2 have been applied in conjunction with other electrical apparatus to industrial processes within the past few months. A summary of these applications indicates that the amplidyne generators are of particular value in conjunction with so-called “closed-cycle” control systems. A closed-cycle system may be defined as one in which the controlling agency is actuated in part by some function of the final output in such a manner as to minimize any deviation of this output from an ideal value.

Generalized bridge network for dielectric measurements

Abstract: RECENT experience with bridges for the determination of power factor and dielectric constant of small oil samples over a range of frequency has indicated the desirability of improving their characteristics. These improvements or developments have to do principally with changes in circuit arrangements, a generalized representation of the bridge network in terms of controllable impedances, an increased sensitivity inherent in the bridge itself, and an effective means for controlling the influence of inherent impedances extraneous to the bridge measuring arms on the accuracy, precision, and dependency of the bridge measurements and balances.