Showing papers in "Transactions of The American Institute of Electrical Engineers in 1926"

Cipher Printing Telegraph Systems For Secret Wire and Radio Telegraphic Communications

Abstract: This paper describes a printing telegraph cipher system devetoped during the World War for the use of the Signal Corps, U. S. Army. This system is so designed that the messages are in secret form from the time they leave the sender until they are deciphered automatically at the office of the addressee. If copied while en route, the messages cannot be deciphered by an enemy, even though he has full knowledge of the methods and apparatus used. The operation of the equipment is described, as well as the method of using it for sending messages by wire, mail or radio. The paper also discusses the practical impossibility of preventing the copying of messages, as by wire tapping, and thte relative advantages of various codes and ciphers as regards speed, accutracy and the secrecy of their messages.

Rural Electrification

Abstract: This is a paper on rural electrification, discussing some of the problems connected with this important development. The paper points out the effect of power and machinery on the living conditions of the American farm and the part electricity may play. It discusses the things being done by the agricultural and electrical industries to direct and bring about a proper development of this service.

Synchronous machines I-an extension of blondel's two-reaction theory

Abstract: Blondel treated salient pole machines by resolving the fundamental space component of m. m. f. along the two axes of symmetry-the direct axis of the pole, and the quadrature axis between poles. Using this idea, and applying harmonic analysis, Blondel's theory has been extended in the present paper to a comprehensive system of treatment, in which the effect of harmonic m. m. fs., as well as the fundamental, and also of field m. m. f. in the quadrature axis, as well as in the direct, have been taken into account. It is shown that the "armature leakage flux" which causes reactance voltage drop in synchronous operation, comprises all fluxes, due to armature currents, which generate fundamental voltage, except the space fundamental component, the latter constituting the total flux of "armature reaction." Impressing upon the variable air-gap permeance those space harmonics of m. m. f. which are due to the fundamental time component of current and which therefore rotate at various fractional speeds, produces odd space harmonics of flux rotating at many different speeds and in opposite directions. Some of these, listed in Table I, produce fundamental voltage, but most of them generate time harmonics. The former, which are reactive voltages, are only those of the nth space order rotating at one nth speed-that is, those which correspond in space order and speed to the harmonic m. m. fs.

Cipher printing telegraph systems

Abstract: L. F. Morehouses This work on the development of arrangements for secretly transmitting telegrams was done during the War under the direction of Mr. Gherardi. The problem was to see if a simple and effective means that would be entirely secret could be devised for handling telegraph business. The method used should be such that an enemy could not decipher the messages even if he could capture the mechanism used, thoroughly understand its operation, and obtain contact with the line circuits.

Vacuum Switching Experiments at California Institute of Technology

Abstract: Successful experiments in switching or breaking a circuit in a high vacuum have been made at the California Institute of Technology. This paper is a report on three sets of these experiments, which extended over a period of three years. The conclusions drawn from the experiments may be summed up in the statement that vacuum breakers of laboratory type have been successful in breaking circuits and offer a possible solution of the circuit-breaker problem. The results show that switching in vacuum affords the advantages of no pitting of contacts, quick break, the arc always going out on the first half-cycle, small voltage rise across the switch, and small distance of travel necessary for the switch blades. Making the vacuum switch practical calls for a solution of the problem of making commercial apparatus with vacuum-tight joints, and the elimination of the use of liquid air with the vacuum pump.

Methods of High Quality Recording and Reproducing of Music and Speech based on Telephone Research

Abstract: The paper deals with an analysis of the general requirements of recording and reproducing sound, with the nature of the inherent limitations where mechanical records are used, ana a detailed description of a solution involving, frst, the use of electrical equipment for the purposes of recording and, second, the use of mechanical equipment based on electric transmission methods for reproducing. Probably the most useful feature of the paper is the complete description of the application of electrical transmission theory to mechanical transmission systems. A detailed analysis is made of the analogies between the electrical and the mechanical systems.

Studies of Transmission Stability

Abstract: Stability may be defined as the capacity of a power system to remain in equilibrium under steady load conditions, and its ability to regain a state of equilibrium after a disturbance has taken place. The lack of stability first manifested itself in the cases of overloaded machines and high impedance tie lines. The transmission of large blocks of power over long distances has presented the problem in a new form. Attention was directed to this problem in a group of papers before the Institute at the Midwinter Convention of 1924. These papers gave a general discussion of the stability problem and pointed out the necessity of considering the limitations imposed not only by the line alone but by the transformers, rotating machines and load. Extensive and pertinent discussions followed which emphasized the importance of the limitations imposed on power transmission by stability conditions. The papers and discussions at the 1924 Midwinter Convention established a method for the determination of power limits under steady load conditions assuming fixed excitation. The limit so determined is due to the inherent characteristics of machines and does not take into account the possibility of changes in excitation due to the action of voltage regulators. The possibility of exceeding the ``inherent stability limits'' by the operation of the voltage regulators and exciters was pointed out. This condition of ``artificial stability'' was not at that time believed to be attainable.

The cross-field theory of alternatingcurrent machines

Abstract: P. L. Alg´er: Mr. West has presented in his paper a businesslike and accurate way of obtaining the characteristics of an a-c. motor. The method is particularly adapted, and, in fact, was especially intended, for use by engineers having to do with large numbers of motors. Probably we all agree that the circle diagram, or some similar graphical method, is most suitable for college instruction, and for use by persons only dealing with motors occasionally. When large quantities of motors are to be

Ionization Studies in Paper-Insulated Cables---III

Abstract: This is the third report to be presented before the Institute of the research investigation of ionization phenomena in paper-insulated, high-voltage cables, which is being conducted at the Harvard Engineering School under the auspices of the Impregnated Paper-Insulated Cable Research Committee. This paper is a report of progress and will be followed by further reports as the work continues. The total power dissipated in impregnated-paper insulation may he separated by the graphical method into the component dissipated in the solid dielectric and that dissipated in the ionized gas films, and also may be separated analytically into these two components by selecting three suitable points on the power curve. This separation gives the three characteristic cable constants. When the power curve of a cable is analyzed into its two components, the ionization-power curve itself should be a straight line. Frequently, however, the ionization-power curve is concaved upwards. This is probably due to the non-linear characteristic of power loss caused by longitudinal and tangential stresses. Hence, it may be assumed when the ionization-power curve is concaved upwards, that longitudinal and tangential stresses exist within the cable. This theory is substantiated by investigations with cable models. The value of the maximum power factor and of the voltage at which it occurs are shown to be very simple functions of the three characteristic cable constants. With a considerable number of cables, the calculated and the experimental values of these quantities are in close agreement.

Steady-State Stability in Transmission Systems Calculation by Means of Equivalent Circuits or Circle Diagrams

Abstract: The maximum load on a proposed transmission system must be within the steady-state power limit of the system for stability of operation. Two methods of calculating steady-state stability are given in detail and illustrated by examples. (1) The given transmission system is replaced by a simple equivalent system; then the steady-state power limit of this equivalent system is determined graphically. (2) By means of a circle diagram the system is tested for stability with the maximum proposed load on the system. All formulas from published references necessary for the calculations are included and all calculations are given in full so that similar studies can readily be made by an engineer who has not previously made a study of the subject of stability.

Surface Heat Transfer in Electric Machines with Forced Air Flow

Abstract: Since the insulation of windings in electric machines has comparatively low temperature limits, the problem of cooling these machines with the most economical use of material becomes one of major importance. The design of such machines from a temperature standpoint is usually based on tests of a previously made similar machine or else is of the ``cut arnd try'' type where such tests are not available. The predetermination of the operating temperature depends a great deal upon the rate at which the heat losses can be liberated from the ventilating surface to some cooling fluid such as air, which is considered in this paper. Some data are available regarding this rate of heat dissipation with forced air convection currents; a comparison of the various results published, however, shows them to be inconsistent. The purpose of this paper is to submit additional information that should be of value to the industry and that will also explain some of the inconsistencies in the past tests. Extensive experimental tests were made regarding the rate of surface heat transfer with air flows of various velocities for radial and axial ducts. The influence of shape, size, cross-section, condition of surface, mean temperature, and other factors were investigated. The most important factor found was that this rate of heat transfer was not constant along the air flow path but that its value varied from point to point along the duct.

Notes on the Vibration of Transmission-Line Conductors

Abstract: This paper describes tests made with a graphic recorder to show the vibration of transmission-line conductors under various conditions of wind velocity, conductor tension and span length. The method of taking the records is discussed. Formulas are given for determining the velocity of propagation of transverse waves along a conductor, the wavelength of a vibration, and the frequency of vibrations caused by ``eddies'' formed at a conductor subjected to air currents.

The Cross-Field Theory of Alternating-Current Machines

Abstract: It is the purpose of this paper to show how analysis by the cross-field theory may be used to obtain accurate, purely numerical methods of calculating performance characteristics of alternating-current machines Methods of calculation are derived and sample calculations are given for the single-phase induction motor and the repulsion motor

Practical Aspects of System Stability

Abstract: During the past few years there has been much discussion regarding the behavior of long transmission lines under transient conditions, such as flashovers, short circuits, arcs and grounds which would tend to make them unstable, but unfortunately this discussion has been largely theoretical due to the absence of any actual operating data upon which to base assumptions. It has only been recently that an opportunity has been afforded to make field tests on one of the two existing 220-kv. systems and the results of such a series of tests made on the system of the Pacific Gas and Electric Company, are presented in the paper. This is the first instance where tests of this nature have been attempted and the lack of proper testing equipment proved a serious handicap. It was necessary to develop a special high-speed oscillograph wattmeter, a high-speed oscillograph filmholder and a pilot generator. Moreover the technique of testing was developed so that it was possible to secure oscillographic records 200 mi. apart by telephone signal. The tests established the following important facts: 1. System stability as a problem is inextricably entangled with operating economics, and cannot be handled solely as a problem in design, except for very simple cases. 2. For any adequate conclusions to be reached much more fundamental data are necessary. 3. Requisite equipment for obtaining such data is not nov available. 4.

Development and Application of Loading for Telephone Circuits

Abstract: A review of the art of loading telephone circuits as practised in the United States. The introductory section briefly reviews the theory of coit loading, and summarizes the principal characteristics of the first commercial standard loading coils and loading systems, thereby serving as a background for the description of the various improvements of outstanding importance which have been made in the loading coils and loading systems during the past fifteen years to meet the new or changing requirements in the rapidly advancing communication art. These major improvements are described in detail under the appropriate headings (1) Phantom Group Loading, (2) Loading for Repeatered Circuits, (3) Incidental Cables in Open-Wire Lines, (4) Cross-talk, (5) Telegraphy over Loaded Telephone Circuits, (6) Loading for Exchange Area Cables, and (7) Submarine Cables. The discussion of these various developments sets forth the relations between the loading features and the associated phases of telephone development, such as the cables, repeaters, telegraph working, and carrier telephone and telegraph systems. The concluding part of the paper gives some general statistics regarding the extent of the commercial application of loading in the United States, and a brief statement indicative of the large economic importance of loading to the telephone using public.

Lightning and Other Experience with 132-Kv. Steel Tower Transmission Lines, and its Bearing on Tower-Line Design from the Continuity of Service Standpoint

Abstract: A large number of transmission lines have been erected without adequate consideration having been given to the ability of the line to stay in circuit electrically during the occurrence of lightning or other disturbance conditions. These come, however, within the range of the transmission engineer's field of action. The authors' experience with a 55-mi., 132-kv. transmission line since 1917 to date is cited, the particular line being one which has been very successful from a standpoint of continuity of service. Further experience with other lines built with variations on the original design and placed in service in 1924 and 1925, is given. A detailed analysis is given of eighty-eight cases of lightning trouble on one of these lines during 1925, the various steps taken to reduce the frequency of this trouble, the effect of increased clearances and separations, of additional insulators, of flux control units, and of arcing horns and shields on the amount of trouble and on the damage to insulator and conductor. These are discussed both from the standpoint of actual experience and from the laboratory analyses and investigations made. A general discussion of the ground wire and its effect on lightning voltages is given and the arguments for and against it are discussed. The importance of paying attention to the mechanical side of the ground wire and the effect of such attention on continuity of service is pointed out.

Measurement of Transients by the Lichtenberg Figures

Abstract: The paper gives the results of a comprehensive study of the effect of transients on the size and appearance of Lichten berg figures. Sixteen different rates of voltage rise were used, varying from about 20 minutes to 0.1 microsecond to reach a crest value of 25 kv. Results were obtained with transients the crest voltages of which ranged from 5 to 25 kv. The steeper wave fronts were checked with the Dufour cathode-ray oscillograph. Calibration curves are given, showing that the positive figures are not much affected by changes in wave front, while the negative figures vary considerably with changes in wave front, especially at the lower voltages. The positive figures are divided into three types according to their appearance which is found to depend on the rate of voltage rise. It is concluded that for most conditions the size of the positive figures will give a determination of the crest voltage of the applied transient to within approximately 25 per cent.

No-Load Copper Eddy-Current Losses

Abstract: One of the factors which is sometimes responsible for very considerable losses in rotating machines is that of eddy-current losses in the copper conductors resulting from slot leakage flux produced by the main flux. These losses occur at no-load as well as under load and should not be confused with the copper losses resulting from the slot leakage flux produced by the load current. These no-load copper losses occur in salient pole machines, both d-c. and a-c., and in induction motors. This paper is an attempt to remove the calculation of no-load copper eddy-losses from the field of empiricism where it has previously been and to place it on a firm theoretical foundation. Test results are presented which show that the theoretical formulas which have been developed are correct. Some of the consequences of this analysis are rather unexpected where the frequencies are sufficiently high to produce large skin effect. For instance, laminating the copper may produce increased or decreased losses, depending upon the conditions.

Mechanical Force Between Electric Circuits

Abstract: A general equation is developed for the mechanical force exerted by a system of n electric circuits, upon any part of that system. The electric circuits are assumed to contain resistances, and the reluctance of the several magnetic circuits is assumed to be a function of both the currents and the relative positions of the circuits. The equation is therefore applicable to circuits involving saturated iron. Special cases of a single circuit and of n circuits are treated, in which a method of graphical solution is given. Also an approximation is made, which results in fairly simple analytical expressions for the force in the case of circuits involving saturated iron. The results are preliminary to an investigation of the forces existing in synchronous machines under the condition of short circuit, which subject will be treated in a forthcoming paper.

Tests of Paper-Insulated High-Tension Cable

Abstract: The paper deals with those tests which are involved in specifications. The discussion is from the standpoint of the purpose and significance of the various standard tests which are made rather than that of the technique of the details of testing. A considerable number of data are given. The subjects treated are purpose and importance of tests of cable; insulation resistance test; high-voltage test; dielectric loss and power-factor test; ``ionization'' test; bending test; accelerated life test; preparation of samples for high-voltage tests and tests of components. The possible significance of wide variation in some of the properties of cable is discussed. The relation found between time and voltage based on a large number of tests of both three-conductor and single-conductor cable is discussed at considerable length. A test for stability of the impregnating compound is described as is also a proposed standard load for dielectric-loss testing. Some data are given showing the effect of repeated bending on lead and how that effect is influenced by the tensile stress in the lead. The paper concludes with a list of the ways by which, in the author's opinion, progress can be made in the improvement of the quality and the design of paper-insulated high-tension cable.

Development and application of loading for telephone circuits

Abstract: Bancroft Gherardi: The invention of loading and the development of telephone repeaters have, together, revolutionized the engineering of toll-line plants in the United States. For the invention of loading we are indebted to Dr. Pupin.

Polarization of Radio Waves

Abstract: UNTIL rather recently, the practise of radio communication was confined to the use of long, earth-bound waves. These waves are preferred on account of the regularity of day and night operation and the absence of fading. The characteristics of the earth-bound wave were extensively explored and there was a tendency to generalize these results assuming that they apply to all radio wave transmission.

A High-Frequency Voltage Test for Insulation of Rotating Electrical Apparatus

Abstract: For many years the need for a higher test voltage between turns of individual coils or complete windings has been recognized. To obtain this higher test voltage, high frequency has been introduced. The high frequency used for this test is produced by damped oscillating discharge from a condenser and applied directly to the leads of the coil or winding. Practically any desired voltage can be applied to a coil or winding provided a sufficientty high frequency is used. As a shop method for checking defects in material, or poor workmanship, the high-frequency test method has been found very effective in those classes of windings so far tried. The method used for detecting short circuits on the principle of the radio receiving set are described.

Mechanical force between electric circuits

Abstract: J. Slepian: The relation which is perhaps most frequently used by electrical engineers for calculating mechanical forces between circuits is that due to Maxwell, which states that, in any displacement in which currents are kept constant, the mechanical work received during' the displacement is equal to the increase in magnetic energy of the system. This relation is readily derived from the principle of conservation of energy by taking into account the electrical input during the displacement. As Professor Karapetoff puts it, there is a “fifty-fifty” rule here; half the electrical input goes to increasing the magnetic energy and half is given up to mechanical work.

The Space Charge that Surrounds a Conductor in Corona at 60 Cycles

Abstract: An exploring potential wire was used to locate the radial position and to determine the potential of the space charge that surrounds a conductor in 60-cycle corona. The familiar concentric cylinder set-up was used. The potential of the exploring wire due to the applied voltage and its position in the electric field between the conductor and cylinder was maintained at zero so that the potential on the wire was due only to the presence of the space charge. The cyclic potentials of the exploring wire at various radial distances from the conductor in corona at the center of the cylinder were observed with an electrometer of low capacitance connected through a phase-shifting synchronous contactor to the exploring wire and through its own capacitance to ground. The location of the space charge and the potential it sets up in the electric field in the space surrounding the conductor in corona were thus determined. The paper contains four sections: I?The Problem and Results, II?Description of the Apparatus Used and the Method of Application, III?Discussion, IV?Conclusions.