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Popular Articles (October 2014)

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  • 1. Fundamental considerations of power limits of transmission systems

    Page(s): 1045 - 1057
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    At this time the power limit of transmission lines is a live subject and presents such complications as to require very careful analysis. The paper points out the essential features to be considered in a study of the problem, and calls attention to some outstanding results of an experimental investigation of the subject with a view to clarifying some of the points that have been under discussion in the past two years. It is shown that the problem of stability is not necessarily confined to long-distance, high-voltage transmission, but may be present in any system where the impedance of the transmitting circuit is high compared with the load to be carried. While the impedance of the transmission line and transformers plays an important part in establishing the breakdown point of a system, the characteristics of synchronous apparatus with the method of voltage regulation used are of equal importance. It is shown that the synchronizing power of synchronous apparatus is largely dependent upon the field excitation at the time excess load is applied; that field excitation is determined by the circuit conditions under steady load, and, in order to provide for increase of excitation with increasing loads of considerable magnitude, some automatic means of controlling the field is essential. The rate at which mechanical load in large quantities can be added to a system is limited on account of the necessity of change in angular displacement between the generators and receiving bus; this changing angle requires relative speed change, which takes time. This fact, together with the inherent tendency of synchronous machines to “stiffen” under sudden applications of load, makes it possible to rely on the usual vibrating-type voltage regulator working on the field of the exciter to provide the necessary field change. It is brought out that the maximum load that a system can carry under steady conditions at normal voltage can be suddenly thrown on, and the voltage r- gulator, with the assistance of the factors mentioned, will provide the necessary excitation. Voltage regulators are practically a necessity where it is desired to approach, under operating conditions, the ultimate maximum power of the system. Transient load changes that occur on the usual system, such as throwing on or off load, cutting in or out transmission circuits, etc., can be easily taken care of, providing such changes do not exceed the steady state limits of the system. The effect of short circuits depends upon their nature, whether three-phase or single-phase, and upon the location and duration. This subject is discussed briefly and the conclusion drawn that successful operation can be obtained under usual short-circuit conditions if adequate relaying is provided. The possibility is discussed of increasing the limit of power transmission by improving the apparatus and the characteristics of the transmission circuits, and it is pointed out that no great development may be expected from any scheme yet proposed regarding a modification in line characteristics. With reference to the apparatus, it is possible to make some changes in the design of synchronous machines tending to “stiffen” them, such as higher saturation, larger air-gap, etc., but in general no radical improvement may be expected here that does not materially increase the cost and decrease the efficiency of the machine. Attention is turned therefore toward such schemes of regulation, or compensation, of the synchronous apparatus as would increase the maximum power. Among these is the use of reactors for locally controlling power factor and thus too the field excitation of the more important synchronous machines. However, the possible additional power thus obtained is limited, and, as it now appears, other methods which have greater promise will be resorted to. The use of a mercury-arc rectifier in the alternator field circuit seems to have great possibilities. By varying the fiel View full abstract»

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  • 2. Abridgment of effect of transient voltages on power transformer design

    Page(s): 357 - 361
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    When an ordinary transformer is subject to transient voltage excitation, local concentration of voltage takes place in which the capacitance charging current of the coils to ground is supplied through the winding. This is because the ratio of inductance and capacitance of the various parts throughout the winding is not constant. Calculations and tests of voltage distribution in the winding, caused by the impact of (a) damped high-frequency oscillations, and (b) unidirectional traveling waves, are given. In order to make the analysis clearer, the transformer winding is considered as a network of inductances and capacitances, and this term “network” is used throughout the paper. Certain simplified and typical networks are considered. Transformers having one terminal grounded, such as are used in three-phase star connection, particularly in high-voltage systems, are frequently built with the insulation graded to other windings and ground, in the order of the normal frequency voltage stress. The danger of such a practise is shown in power transformers which are subject to transient overvoltage, since voltage oscillation in the winding may raise the voltage to ground at intermediate points above the terminal voltage, unless the design of the winding eliminates oscillation. The theoretical and experimental data given show that the distribution and magnitude of voltage stresses existing during recognized standard insulation tests are essentially different from stresses created by transient voltages. This permits the construction of transformers that would satisfactorily pass standard insulation tests but at the same time would not be suitable for average service. A new type of a transformer called “non-resonating,” for use on grounded neutral systems, is described. In transformers of this type, voltages of all frequencies distribute uniformly along the windings, as the possibility of internal voltage resonance is eliminated by a proper bala- ce of distributed capacitance and inductance of the winding. This is accomplished principally by means of conducting surfaces (shields) placed outside of the winding and connected to its line terminal. The action of the shields is similar to that of the shielding ring on an insulator string. It neutralizes the effect of the capacitance current from the inside surface of the winding to ground, by supplying to every point of the winding a “charging” current equal to the “discharging” current of that point to ground. In some cases, the application of the shield reduces the local stresses to one-eightieth. Up to the present time, the total capacity of this new type of transformer exceeds half a million kva. View full abstract»

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  • 3. Synchronous machines I — An extension of Blondel's two-reaction theory

    Page(s): 974 - 987
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    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, Blondevs theory has been extended in the present paper to a comprehensive system of treatment in which the effect of harmonic m. m. fsy 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. The corresponding reactances are definitely defined in Appendix C in terms of permeance coefficients, and means are outlined for quantitative determination of such coefficients from graphically constructed field plots. Although, strictly, there areas many field plots required as there are significant m. m.f. harmonics, an approximation, developed in Appendix B, is given in which only one plot is necessary, other permeance waves being derived therefrom. It is shown that only the average term and the second space harmonic of the permeance series affect the fundamental voltage- Hence, unless it is required to calculate the harmonic voltages, only those two terms of the permeance series need to be determined. In the application of the results, the fundamental voltages thus produced by the armature currents are superposed upon that due to current in the field winding, which latter has been previously treated. This gives the vector diagram, Fig. 19, from which the steady state relations are set down in equations. In Part II, the steady-state angle-power relations are developed, including an interpretation of the “reluctance term11 in the power or torque equation. In Appendix D, the vector diagram for salient pole machines is interpreted in terms of the well-known Potier diagram for cylindrical rotor machines. Also the effect of saturation both on anglepower relation and on the value of excitation required under load is discussed. Subsequent papers in the near future will present results which have been obtained from the application of the method and point of view here outlined to the solution of problems relating to abnormal operating conditions of synchronous machines. View full abstract»

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  • 4. The most economical power factor: A practical design formula for distribution circuits

    Page(s): 904 - 912
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    The use of power factor corrective devices on distribution circuits is justified, under certain conditions, by rather substantial savings in investment charges and by a reduction in the power losses of the system. The object of the present paper is to develop a practical working formula for calculating the most economical corrected power factor for a distribution circuit. Most economical conditions are assumed when the total of such annual circuit costs as are directly affected by a change in power factor, is a minimum. The usual methods for computing separately, the saving in I2 R losses and the decrease in investment charges due to power factor improvement, are inadequate. Particularly in the design of new circuits and extensions has the need for a more accurate method for calculating optimum power factor and conductor sizes been expressed.2 Since these equations were originally worked out, two other solutions for the most economical corrected power-factor angle have been published, each having been obtained independently of the other. Menjelou3 obtained his formula in the form: α sin θ = 1 β tan θ in which θ is the power-factor angle and α and β are constants computed from the circuit costs. Stevenson4 obtained a similar expression: sin θ = δ − η tan θ the difference lying in the constants to be evaluated. The equation developed in this paper reduces to the simple form: sin θ = unit cost ratio That is, the sine of the most economical corrected power-factor angle is determined by the ratio of the annual cost of condenser capacity per reactive kilovolt-ampere of correction to the annual cost (fixed charges plus value of losses) per kilovolt-ampere delivered, of that portion of the supply circuit which is directly affected by the change in power factor. When the unit cost ratio is greater than th- sine of the original power-factor angle, it is found that no investment in corrective equipment is economically justified. The equation is set up in such a form that solutions are readily obtained for the most economical size of conductor as determined by the Kelvin law, and for the required kilovolt-ampere rating of the transformers and condensers. A method is suggested for including generating station costs with those of the individual circuit under consideration. In evaluating circuit costs, the effects of load factor and the shape of the typical daily load curve upon capital investment and power losses have been worked out after the methods used by Gear and Williams5 and by Reyneau and Seelye6. Equations for evaluating the circuit constants are included in the appendix. Several illustrative examples are worked out. View full abstract»

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  • 5. Abridgment of the reactances of synchronous machines

    Page(s): 345 - 348
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    Until somewhat recently, synchronous machine theory has been satisfied with a relatively few characteristic constants, or reactances, in terms of which the behavior of machines has been calculated. Present theory, however, requires many more coefficients. There are now generally recognized two values each of leakage, synchronous, and transient reactance, which correspond to the two symmetrical axes of magnetization of the armature current and which refer to balanced operation. Negative and zero phase-sequence reactances are also employed to determine operation under unbalanced conditions, and it is possible and desirable to distinguish other reactances. In view of the increasing complexity of the subject it is felt that a critical survey of it is in order and the object of the paper has been to provide that survey. The paper has been divided into two parts. Part I describes and treats of the subject with regard to those factors which are important to application or operating engineers, and to designers. In particular, the major types of reactances which include the synchronous, transient, and phase-sequence reactances, are discussed. These quantities are defined and their methods of test outlined. It appears necessary to consider a second type of transient reactance; namely sub-transient reactance. Both reactances may be determined from short-circuit oscillograms as illustrated in the paper. A table is included which gives the numerical range of reactances for the various types of synchronous machines. Part II discusses the theoretical considerations, with a view to broadening and classifying existing conceptions of reactance. It includes the effect of external reactance on negative phase-sequence reactance and the variation in this latter quantity, depending upon whether current or voltage is impressed on the machine. An important aspect of the division of synchronous reactance into armature reaction and leakage reactance is discussed. Transient reactance is shown- to be the difference between synchronous reactance and the ratio of the mutual reactance between armature and field and the total field reactance. Calculations are included to show that the short-circuit and open-circuit time constants are related to each other in a simple manner. The appendixes cover the following subjects: a. Application of the Principle of Superposition to Synchronous Machine Analysis. b. Replacing the Effect of Induced Field Currents by Employing Transient Instead of Synchronous Reactances. c. Significant Rotor Circuits in Addition to the Main Field Winding (which effect transient reactances). d. The Negative Phase-Sequence Reactance of a Synchronous Machine with Negative Phase-Sequence Voltage Impressed. e. Construction of Equivalent Circuits: Concept of Field Leakage Reactance. f. Calculation of Total Field Reactance. g. Relation of the Mutual Reactance Between Armature and Field to the No-Load Excitation Current. h. Relation Between Three-Phase and Single-Phase Reactances. i. Discussion of the System of Notation Used in the Paper. j. Per-Unit Representation of Quantities. View full abstract»

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  • 6. Equivalent single-phase networks for calculating short-circuit currents due to grounds on three-phase star grounded systems

    Page(s): 1014 - 1020
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    This paper presents a method for calculating the steady state value of the short-circuit current in a fault to ground on a power system operated with grounded neutral, and the distribution of this current throughout the system. Constant impedances and electromotive forces in the system, and electrically short lines, are assumed, and line capacitance is neglected. If, at the time the fault to ground occurs, the distribution of the load current in the system is known, the total current in any portion of the system under the short circuit condition may be calculated by means of this method. By “total current” is meant here the sum of that part of the fault current which appears in the branch considered, and the normal current in the branch due to the loads. The latter current, of course, does not appear in the fault. Formulas and equivalent circuits for the usual three-phase transformer and generator connections used in practise, are given. The use of such circuits permits the calculation of the fault current and its distribution in the power system from an equivalent single-phase network. Since currents in a three-phase network under balanced conditions may also be calculated from a single-phase network, it is accordingly possible to calculate, entirely on a single-phase two-wire basis, the total current in any branch of a star grounded network for a ground on any phase. The setting up of equivalent 2-wire single-phase networks similar to those for the three-phase case is not generally possible where the number of phases exceeds three. The value of the method lies in its enabling one to calculate on a single-phase two-wire basis the short circuit current (steady state) due to a ground on a three-phase grounded neutral system, as regards both magnitude and distribution and taking into account all system loads. In the usual approximate method of making short-circuit calculations, a single-phase-to-neutral network is substituted for the actual network. W- ile this method involves less labor than that proposed in the paper, the results obtained by it are inexact, the effect of non-grounded loads being usually ignored. The method of the paper involves much less work than that required by three-phase calculations giving equal accuracy. An illustrative example is given. View full abstract»

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  • 7. Transmission stability: Analytical discussion of some factors entering into the problem

    Page(s): 951 - 961
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    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 sub- ect 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 View full abstract»

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  • 8. Abridgment of generalized theory of electrical machinery

    Page(s): 302 - 305
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    In the following pages, electrical machinery is analyzed from a new point of view. Analytical quantities, like magnetizing current, armature reaction, leakage flux, transient reactance are not introduced; only such quantities are used as actually exist in the machine at one particular load. Thereby the theory of electrical machinery is expressed in terms of the minimum possible number of quantities. No hypothetical currents or fluxes are used and no actual physical quantity is left out. The concept of “free energy,” used in thermodynamics, is introduced and generalized. The criterion of good design of all electrical machines is expressed by a constant, the “thermodynamic efficiency” which gives a measure of the effective utilization of iron and space for the transformation of energy. This constant plays a most fundamental role in the steady and transient behavior of the machine. A method is given by which the direction of flow of energy between different parts of any complicated machine can easily be read from the diagrams. The theory of constant-potential and constant-current electromagnets is used as a stepping stone to show that the theory of the polyphase alternator is identical with the theory of the constant-potential polyphase transformer if flux linkages and magnetomotive forces are interchanged. The circle diagrams of the transformer and the alternator are developed, as well as the elliptical locus diagram of the alternator with salient poles. Problems in the sudden short circuit and the sudden load variation of the polyphase alternator are also solved. Blondel's diagram for the circular locus of the synchronous motor is derived in a more extended form together with its elliptical locus with salient poles. The elliptical loci of the reaction machine and the synchronous converter are also developed. The circular locus for the polyphase induction motor, the single-phase induction motor and the repulsion motor are derived. The- method of attack used in the paper is applicable not only to circular and elliptical loci, but also to loci of higher curves. The method is used to develop the complete theory and locus diagram of the double squirrel-cage induction motor and the split-phase induction motor with or without condenser (or the so-called condenser motor). Besides those mentioned above, the writer has also developed with this method the loci of commutator machines such as the polyphase induction motor with commutator rotor, the series polyphase and the shunt polyphase commutator motors, and the compensated series motor, including the effect of the short-circuited brush currents, also the locus of induction motors in cascade. An extension of the concept of free energy establishes the four-line vector diagram and the locus characteristics of any transmission system or any four-terminal network, showing the voltages and currents at both sending and receiving ends. Due to the length of the article, however, their discussion does not appear here. All locus diagrams show the speed and the torque at all loads. They also show the magnitude and phase relation of all actual currents, fluxes, and e. m. fs. A relation of the form r/x is found for the ratio of the work done to the free energy and this one simple formula is sufficient to find the locus diagram and the complete performance of all electrical machinery and transmission lines. It is the only formula used in the paper. In the appendix, the relation of the design constants used to the constants of other methods is shown. View full abstract»

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  • 9. A two-speed salient-pole synchronous motor

    Page(s): 339 - 346
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    The design features and performance characteristics of salient-pole synchronous motors are well known and have been thoroughly covered in the technical press. The synchronous motor has been handicapped in the past because it is inherently a single-speed machine, and a change in speed could be obtained only by a change in the frequency of the power supply. Changing the frequency, however, is not practical in most applications. The special pole described in this paper which allows two-speed operation of a synchronous motor to be obtained at high efficiency is a new feature2. The same principle applied to a generator enables two frequencies to be obtained at the same speed or the same frequency at two different speeds. All that is necessary to change the speed (or frequency) is a pole-changing switch for the stator winding and a reversing switch for the rotor winding. A 5000/2500-h. p., 600/300-rev. per min., two-speed synchronous motor was built without having first constructed a model of any kind. This motor proved to be entirely satisfactory and its characteristics obtained by test agreed very closely with the calculated characteristics. At either speed the two-speed synchronous motor functions exactly as the ordinary synchronous motor. There is nothing special or complicated about its construction, it does not require any more attention than the ordinary synchronous motor, and its expense of maintenance is just the same. The first cost of such a motor is only slightly more than that of the ordinary synchronous motor whose rating is equal to the low-speed rating of the two-speed motor. Therefore, the two-speed synchronous motor is a practical machine and it should open a new field for synchronous motor application. View full abstract»

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  • 10. Power limitations of transmission systems

    Page(s): 45 - 51
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    Review of the Subject — Several independent studies have been made recently to determine the economies of a large, uniform power system. The two studies of more general interest were those conducted by the Department of the Interior, under the direction of W. S. Murray, for the Superpower Zone, and by F. G. Baum for the United States. Both of these investigations are available in published form. During the progress of the Superpower Survey, one of the longest transmission lines proposed was that extending 350 miles from the Niagara Falls Development to New York City. Under emergency conditions on this line, the power limit for the maximum amount of power was approached by two twin-circuit lower lines with three circuits carrying the emergency load. The maximum power limit would have been exceeded if two single-circuit tower lines had been employed, even though the transmission voltages and the total copper cross-section were the same as with the two twin-circuit lower lines. Similarly, several long, high-voltage lines will be required in a nation-wide system, especially through the middle western region as shown by Mr. Baum's report. The tendency to extensive transmission systems has emphasized the necessity of considering the factors which will limit the amount of power that can be transmitted any distance with the highest practical transmission voltage. On account of the transmission line characteristics, the power limits will be greater when the system is regulated by synchronous apparatus than when those such apparatus is used so that two power limits will be considered in this paper; first, for an unregulated system; and second, for a regulated system. However, while we are primarily interested in high-voltage systems in this paper, it should be kept in mind that these same methods of calculation may be applied to lower voltages in determining the power limitations of station tie lines. It is commonly accepted that different types of networks have cer- ain power limitations. For example, a very simple case quite generally known is that of a simple resistance circuit in which the power delivered is a maximum when the resistance of the load is equal to that of the line. Another familiar case is that of the electric arc furnace where the maximum power occurs when the resistance of the furnace arc is equal to the reactance of the electric furnace leads. The general phenomenon of maximum power limit in circuits of fixed reactance and variable resistance or load has been recognized and Us theory worked out for numerous cases, such as short transmission lines, rotating machines, and transformers. A power transmission system may be regarded as a special type of network. Ordinarily it consists of long, high-tension transmission lines and apparatus connecting generating stations with distant load centers which may be either at the terminus or at intermediate points on the high-tension lines. In large systems, the high-tension lines may form a network similar to an ordinary local distribution system. Where synchronous condensers are not installed, the problem of the maximum amount of power which may be delivered through the system is similar to the simple resistance and reactance cases cited above in that additional load or shunt impedance simply alters the load and voltage in accordance with the relative impedances of the system. The employment of synchronous condensers at the load centers or along the transmission lines to alter the power factor and maintain the voltage at the load materially increases the maximum amount of power that may be desired over a given transmission network. The theoretical maximum amount of power however, cannoi be obtained under operating conditions because the synchronous equipment at the receiver drops out of step with the supply. Also, fluctuations in load will produce unstable conditions, which may accumulate sufficiently to cause the momentary swings in load to exceed the power limit, resu View full abstract»

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  • 11. The rotating magnetic field theory of A-C. motors

    Page(s): 170 - 178
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    The predetermination of the performance of a polyphase a-c. machine is greatly facilitated by the fact that at constant voltage and frequency its magnetic field is of constant intensity and rotating with uniform velocity. It is easy to form a mental picture of lines of ferce moving in space and being cut by conductors, which may be moving or stationary. Furthermore, the rate of cutting, and therefore the generated voltages, which form the basis for quantitative analysis, are readily determined by the relative motion of the flux and the conductors. Because of the ease with which a physical conception can be formed of a rotating magnetic field, the idea of considering a single-phase alternating field as made up of two oppositely rotating fields has been found very useful. In a paper entitled “A Physical Conception of the Operation of the Single-phase Induction Motor” Transactions A. I. E. E., Vol. XXXVII), Mr. B. G. Lamme has given an excellent description of single-phase induction motor operation based on a conception of two oppositely rotating magnetic fields. From the discussion of Mr. Lamme's paper, it appears to be the concensus of opinion that the method he uses furnishes the simplest and clearest physical conception of the single-phase motor. However, this is not the method usually employed in the quantitative analysis. Reference to text books will show that the mathematical treatment is usually based on the so called “cross field” theory. In this method the secondary induced voltage is considered made up of two components, one the voltage induced by transformer action of the alternating field and the other the voltage generated by rotation of the secondary conductors in the magnetic field. It has been argued against the method based on two oppositely rotating fields, also known as the “Rotating Field” theory, that it is more apt to lead to erroneous results, requires more expert handling and that it is an indir- ct method, being based on the previously determined performance of the polyphase motor. However, the main argument against it seems to be its limitation to induction motors only, and that it must be abandoned when we come to motors of the commutator type. Even those who otherwise favor the method appear to agree that it is not applicable to commutator motors as we are then no longer dealing with induction machines, but with shunt or series motors, as the case may be. The objection to the rotating field theory, that it is applicable to induction motors only, would be a serious one if it were valid. However, it will be shown in this paper that the theory can be readily applied to commutator machines also, and that so far from being more apt than other methods to lead to erroneous results, it undoubtedly furnishes the simplest and most direct means for mathematical deductions in the more complicated problems where three or more circuits are inductively related and moving with respect to one another. View full abstract»

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  • 12. Underground alternating-current network: Distribution for central station systems

    Page(s): 545 - 554
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    1. Certain experimental arrangements for an underground alternating current distribution system are covered in the paper. 2. Low costs and characteristics satisfactory for general utilization of alternating current are contrasted with difficulty of obtaining reliability. The advantage of adopting system characteristics which will make each service suitable for lighting, appliances, and motors is indicated. There is described experience with a combined light and power network on one set of mains. Effect of voltage variation on incandescent lamp illumination is discussed. An appendix covers tests on this subject. 3. Reliability in service of standard distribution materials is considered. Tests on cables are described which indicate that for underground distribution conditions, low-voltage cables will eliminate arcing faults while high-voltage cable will not do so. An appendix of arcing tests is attached. 4. Certain factors are discussed relative to size of mains and location of transformers necessary to make the low voltage network clear its own faults. 5. There is a description of an experimental system consisting of several radial high-voltage feeders, the distribution transformers of all these being connected on the low-voltage side to a common low-voltage cable network. 6. The reactance of the transformer circuits is almost three times that of standard distribution transformers. 7. The only protective devices used are automatic circuit breakers installed in the low-voltage cables between the distribution transformers and the network. The switches open on a reversal of energy from the network and close when the transformers are in a condition to supply power to the network. The devices are sensitive enough to open on transformer magnetization energy. 8. Great reliability is obtained for the network as a switch failure an a high-voltage fault is the equivalent of a short-circuit on the secondary network. 9. Ability to switch automatically all transformers by contro- ling the supply end of the feeder to which they are connected allows a higher all-day efficiency due to the saving of iron loss at periods of light load. This feature also makes it easy to work on high-voltage equipment. 10. A description of the equipment used in this experimental installation and operating results of switch equipment from date of installation in April 1922 to March 1924 are given. 11. It is believed that with low-voltage a-c. underground networks arranged as described, the reliability is the same as the reliability of the sources supplying the various radial high-voltage feeders. The possibility in the future of a protected network arrangement of the supply system is mentioned. View full abstract»

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  • 13. The M. M. F. wave of polyphase windings: With special reference to sub-synchronous harmonics

    Page(s): 118 - 127
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    The m. m. f. waves of fractional slot windings or other irregular windings are found to contain harmonic components having wavelengths greater than two pole pitches. These are designated as sub-synchronous harmonics since their harmonic order is lower than that of the synchronously rotating wave. They induce currents in the damper windings of synchronous machines which may produce noticeable loss. Some test data concerning losses are included. These harmonics have an effect upon reactance and, under certain conditions, they may cause vibration. An appendix covers the calculation of the m. m. f. of three-phase fractional slot machines. View full abstract»

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  • 14. Ionization studies in paper-insulated cables — I

    Page(s): 337 - 347
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    A research investigation of the ionization phenomena which occur in paper-insulated, high-voltage power cables is being made at the Harvard Engineering School under the auspices of the Impregnated Paper-Insulated Cable Research Committee, The paper presents some of the preliminary results which have been obtained, certain tentative conclusions that are suggested by the data and a description of the method developed for making the measurements. It is a preliminary report and in subsequent papers it is intended to record the progress of the investigation as it proceeds. The paper consists essentially of four parts as follows: (a) A number of curves of power, power factor and capacitance taken on samples of cable at two frequencies and over a wide range of temperature. These curves show well-known characteristics, but in order to exaggerate these effects, cable models were made up to simulate the general conditions in a cable — one model consisting of glass and air only and another of glass, air and paper. Tests of these cable models gave very interesting results, particularly with reference to power factor. They also show rather clearly the baffling action of paper and the effects on power, power factor and capacitance when this baffling action is eliminated. In practically all the curves, the power and power factor begin to increase rapidly at a lower voltage gradient than the capacitance. (b) Discussion of the results obtained and certain tentative conclusions which may be drawn from the results so far obtained and reported herein. 1. Ionization in the dielectric of an air condenser increases its capacitance slightly at first and then rapidly as the electron is separated from the atom. In our measurements we accordingly found that the power and power factor increase rapidly at a lower voltage gradient than the capacitance. 2. Ionization which occurs within air spaces in a dielectric may be called “restricted ionization” in that the current i- limited because of the remainder of the dielectric in series. 3. With “restricted ionization,” the voltage across each air space reaches a constant finite value with indefinite increase in the over-all voltage. The resistance of the ionized space, therefore, must be inversely as the current. 4. Consequently when this condition is reached, the ionization loss may be proportional to the charging current. 5. The increase of power factor with increase in voltage gradient with subsequent decrease of power factor is due to the fact that the capacitance of the solid dielectric, which is substantially constant, is in series with ionized air spaces whose resistances are inversely as the current. A simple mathematical analysis of this type of electric circuit shows that power-factor curves should have the form obtained in the measurements. Hence power factor alone is not a criterion of the degree of the completeness of saturation by compound. 6. Ionization by its bombarding action may destroy the baffling action of paper. 7. Ionization may produce potential gradients tangential to the surface of the layers of paper which, in conjunction with the bombarding action, may be the cause of the so-called “tree designs.” (c) Discussion of methods for measurements of this sort and a description of a new type of bridge which was devised for the measurement of dielectric losses at these extremely low power factors with the necessary high degree of accuracy. A large air condenser used as a standard and a vibration galvanometer of unusually high sensitivity and wide range of tuning were designed for use as a detector. The bridge is quickly and accurately balanced by varying a resistance and a mutual inductance. The angle of defect of the standard air condenser, although extremely small, is nevertheless very important in measurements of this character. This angle was measured by a substitution method and corrections made accordingly. (d) Four appendixes di View full abstract»

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  • 15. The electric arc and its function in the new welding processes

    Page(s): 1404 - 1410
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    The subject of this paper is a phenomenon of great interest and very great complexity. The electric arc is a tool of extreme power and flexibility. The electric arc can be used to melt the most refractory substances, cut the armor plates of battleships or weld together the ends of wires no thicker than a human hair. It is a wonderful tool that makes or breaks almost anything. It may unite the most indifferent elements such as nitrogen and oxygen, or break the molecule into its constituent atoms. In this paper we shall discuss only one type of application of the electric arc; namely, the application of the arc to the welding of metals, but even in these limits the field is very wide. The electric arc was discovered by H. Davy who in 1810 was experimenting with the sparking between two horizontally disposed carbon pencils. The density of the current was such that on short circuit the tips of the carbon pencils were heated to incandescence. When the electrodes were separated the electric current continued to flow across the air-gap between the carbon pencils. The air-gap was bridged by some sort of an extremely bright band which under action of the accending currents of hot air was bent upwards and formed a bow or an “arc.” This is the origin of the term, the “electric arc.” For many years the electric arc was used only as a source of light. It was only years later that the electric arc was applied for the purpose of melting and welding metals together. In 1881 de Meritens for the first time used a small carbon arc for melting and welding the lead terminals of storage batteries. The more extensive application of the carbon arc was done by Bernardos. This process was modified by Dr. Zerener of Berlin, Germany, who shortly prior to 1890 invented a process of welding with a flaming arc. In this process two carbon electrodes are disposed to form a “V”. The arc is drawn between the two electrodes and caused to impinge upon th- metal to be welded by being forced down by a powerful electromagnet. This arrangement caused the arc to act in a similar manner to the flame of an oxyacetylene flame. The energy developed in this arc is only partly transmitted into the weld and the efficiency of the method is very low. The third type arc welding known now as a metallic arc process was discovered about 1890 by H. Slawianoff. This engineer conceived the idea of producing steel ingots by an electrical casting process. Metal was deposited from a steel rod into a mold, an electric arc being maintained between the rod and the metal of the mold. Means were provided whereby the metal rod could be fed forward as it was consumed and a solenoid arrangement was provided for maintaining the arc length substantially constant. The ingots obtained under such conditions proved to be sound and free from shrinkage pipes. However, the cost of electrical energy in Russia in those days was very high and the process was commercially uneconomical. The information obtained by Slawianoff in this work led to the application by him of the metallic arc to the uniting together of metal plates, the repairing of cracked and broken machines, etc. Thanks to the work of Slawianoff we now possess a method of welding with metallic electrodes which at present is by far the most used of all arc welding processes. View full abstract»

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  • 16. Effects of time and frequency on insulation test of transformers

    Page(s): 145 - 155
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    Permanently grounded transformers must be given the insulation lest by inducing the necessary voltage across the windings. The A. I. E. E. Standards specify that the time of induced voltage tests be the same as for high potential test. In certain cases where the transformers are of very large capacity the induced voltage must be made at a frequency several times higher than normal. Since the dielectric strength of most insulating materials decreases with an increase in the frequency, an investigation has been made to determine the proper and fair length of time to make induced voltage test when the frequency is higher than normal. Following are the main points brought out in the investigation. Above a certain voltage, time of voltage application as well as voltage causes failure of insulation. The dielectric strength can be expressed as a function of both time and voltage by an equation of the form $Kv. = A(a + {1-a over root {1} of T})$ in which A is the kilovolts necessary to cause failure in one minute, “a” is a constant representing the ratio of strength for infinite time to the one minute strength and T is time in minutes. The value of “a” varies for different materials apparently depending mostly on the dielectric loss. The breakdown by creepage over solid insulation with the electrodes either on the same side or on opposite sides of the sample (arranged in such a manner that the solid insulation is under considerable stress) is not affected by time nearly so much as is the puncture voltage of solid insulation. The behavior of oil without barriers is so erratic that no very definite relation can be obtained between time and dielectric strength. In general time decreases the strength quite rapidly for the first few seconds after which the effect decreases and probably disappears entirely after two or three minutes. The momentary strength ranges from 25 to 30 per cent higher than the one minute strength. The effect - f time on the strength of solid insulation and oil in series is about the same as for solid insulation alone until the oil distance exceeds the solid insulation thickness after which it begins to be the same as for oil without barriers. The strength-time curves for solid insulation are of approximately the same shape for all frequencies from 60 to 420 cycles, although the strength decreases with an increase in frequency F approximately in accordance with the formula kv. = 1.75/ F0·137 Failure by creepage over the surface of solid insulation which is under no stress (i. e., with the electrodes on the same side of the barrier) takes place at approximately the same voltage for all frequencies from 60 to 420 cycles; but if the electrodes are so arranged (on opposite sides) that the insulation is under considerable stress the failure voltage decreases with an increase in frequency in about the same order as the puncture voltage of solid insulation does. The rupture voltage of oil is the same for both 60 and 420 cycles. The effect of frequency on the puncture voltage of solid insulation and oil in series is the same as for solid insulation until the oil distance exceeds the thickness of solid insulation, after which the effect decreases and as the oil distance increases the effect approaches that for oil without barriers. By considering the effects of both time and frequency on dielectric strength it is shown how to determine the proper length of time to make the voltage strain at higher frequencies equal to the strain at 60 cycles for one minute. 8. ACKNOWLEDGEMENTS It is desired to acknowledge the valuable assistance rendered in the Testing Department by Messrs. N. M. Albert, H. L. Garver, C. F. Green, L. D. Martin and W. F. Weikel in carrying on the long and tedious tests, covering a period of three to four months. View full abstract»

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  • 17. Failure of disk insulators on high-tension transmission lines

    Page(s): 474 - 475
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    A PAPER under the above title was presented by the writer at the Pacific Coast Convention of the Institute in the summer of 1922, and was printed on page 740, Vol. XLI, 1922 Transactions of the Institute. This article and the included curves comparing the frequency of failure of the various disks of the assembly with the voltage gradient curve has been of sufficient interest to engineers connected with the high-tension insulator industry for the author to be requested to bring his investigation up to date by including the results of insulator tests of 1923 and 1924. View full abstract»

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  • 18. Coordination of insulation as a design problem

    Page(s): 449 - 452
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    The factors having influence on insulation design of transmission line and station are briefly reviewed, and it is pointed out that the progress of the art does not yet allow of close design of the insulation structure for insulation strength. The prominent part played by the lightning arrester is stressed, and the fact that it has a marked effect on the coordination of station insulation. Examples of a typical 110-kv. station where no coordination was made, and of a 220-kv. station where a deliberate coordination was attempted, are given, as well as the experience obtained with each. View full abstract»

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  • 19. Abridgment of two-reaction theory of synchronous machines generalized method of analysis — Part I

    Page(s): 194
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    STARTING with the basic assumption of no saturation or hysteresis, and with distribution of armature phase m. m. f. effectively sinusoidal so far as regards phenomena dependent upon rotor position, general formulas are developed for current, voltage, power, and torque under steady and transient load conditions. Special detailed formulas are also developed which permit the determination of current and torque on three-phase short circuit during starting, and when only small deviations from an average operating angle are involved. View full abstract»

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  • 20. Theory of three-circuit transformers

    Page(s): 345 - 355
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    The characteristics of three-circuit transformers, the literature of which is very meager, is discussed here in considerable detail. The features of the scheme of treatment are as follows: 1. The scope and general aspects of the problems of three-circuit transformers are reviewed. 2. Some peculiar phenomena of considerable theoretical interest are cited. 3. An electrical network equivalent to the magnetically interlinked circuits of a three-circuit transformer is developed, useful in visualizing the problem and in predicting by inspection a number of its characteristics. 4. Two physical interpretations of the equivalent network are given to assist the understanding of its principle and its applications. 5. The case of auto transformers interconnecting three circuits is interpreted so that the formulas developed for three-circuit transformers become universally applicable regardless of the presence or absence of metallic interconnection among the three circuits inside the case. 6. Formulas are developed for the calculation of regulation with various loads in the different windings. 7. Formulas are developed for the division of load between two primary circuits, or two secondary circuits in parallel. 8. Formulas are developed for the equivalent effective impedance for short circuits. 9. The behaviour of a three-circuit transformer operating in parallel with a two-circuit transformer is analyzed so as to determine the flow or distribution of load kv-a. in the network. 10. The problem of unsymmetrical loads, particularly that of single-phase line-to-neutral short circuits on a polyphase system are discussed in an appendix, with a simplified method of solution, deriving formulas for some representative cases. When the transformer is interconnecting two polyphase generating systems, the division of single-phase line-to-neutral loads and short circuits between the two systems is considered and solved by the same method and formulas. 11. The theory of three-circuit transfo- mers is extended to four circuits in another appendix illustrated by an example, and is then generalized to n-circuit transformers. 12. For convenient reference, the more important formulas and symbols are collected in another appendix. View full abstract»

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  • 21. Abridgment of a new system of speed control for A-C. motors

    Page(s): 930 - 933
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    The drive unit of this system consists of a constant-speed a-c. motor supplemented by an adjustable-speed d-c. machine of much smaller size. Both rotor and frame of the a-c. motor are mounted on bearings. The d-c. machine is mechanically connected to the frame of the a-c. motor so that the d-c. machine may drive or be driven by the frame. The d-c. machine is electrically connected through a motor-generator set of equivalent rating, to the source of a-c. energy. The shaft speed of the a-c. motor is increased above the fixed speed by rotating the frame of the a-c. motor in the same direction as the rotor, and it is decreased by rotating the frame in the opposite direction. The direction of rotation and speed are governed by adjusting the voltage impressed on the armature of the d-c. drive machine by the generator of the motor-generator set. When the unit is used to drive fans, the speed range is obtained by a combination of armature voltage control and field control of the d-c. drive machine. This permits a still further reduction in the rating of the d-c. drive machine so that for comparatively wide ranges of speed, it forms but a small percentage of the total drive unit rating. Twenty-four units of this type, aggregating 7020 hp., are now being built for Powerton Power Station for driving forced and induced draft fans. This system of fan drive is being installed in preference to the two-speed squirrel-cage type induction motor system previously used, because it shows large savings in energy, costs little more, and provides a simple method of fan control which permits the adoption of a simplified system of automatic combustion control. The versatility of the system is further illustrated by a description of a 2500-hp. unit of this type designed to drive a high-pressure reciprocating boiler feed pump. During the first seven months of 1930, orders were placed for 35 of these units ranging in size from 166-hp. to 2500-hp., aggregating 16,000 hp. for installation in fou- different power stations. View full abstract»

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  • 22. Abridgment of “synchronized at the load” — II: Calculations of system performance

    Page(s): 603 - 607
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    This paper describes the results of calculations made for operating the Hell Gate and Sherman Creek generating stations of the United Electric Light and Power Company, synchronized at the load. After reducing the numerous branches of the system to a simpler equivalent, calculations were made on the operation of an isolated section. These calculations indicated ample static stability and transient stability under fault conditions representing the maximum which might normally be expected. Other calculations were made indicating that the entire system with synchronizing paths completed through the substation low-voltage busses, would likewise meet the required stability conditions. Tentative system design factors based on the calculations and experience to date are suggested as a guide to system planning. This paper shows a practical application of the theories and principles developed in the studies of transmission stability. In the present case, a somewhat different object was in view inasmuch as it was desired to substantiate ideas as to the feasibility of the plan of synchronizing at the load rather than to obtain numerical limits. View full abstract»

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  • 23. Practical aspects of system stability

    Page(s): 142 - 151
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    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 is necessary. 3. Requisite equipment for obtaining such data is not now available. 4. Studies of models and artificial transmission lines are not adequate because too little is known about the relative importance of the several factors to allow intelligent duplication. 5. Proper relay equipment and action is vital. 6. Oil-switch operation is an important factor. 7. Only a certain part of the stored energy of a system is available in any given case of trouble. 8. Operating distribution of excitation current is one of the major problems. View full abstract»

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  • 24. Steady-state stability in transmission systems calculation by means of equivalent circuits or circle diagrams

    Page(s): 365 - 373
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    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. View full abstract»

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  • 25. Abridgment of shielding and guarding electrical apparatus used in measurements — General principles

    Page(s): 453 - 457
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    Electrical measuring apparatus is shielded and guarded to protect it from the following external influences; namely, leakage currents, electrostatic fields, magnetic fields, and electromagnetic waves. Apparatus is guarded against leakage currents which may flow over or through the solid insulators on which the apparatus is supported. It is shielded against leakage currents which flow through the fluid in which the instrument is immersed. By a proper arrangement of guards and shields any apparatus can be completely protected against leakage currents. Any apparatus can be completely shielded from electrostatic fields by placing it in a metallic case. However, there may be electrostatic reactions between the apparatus and the shield, thus introducing errors in the measuring apparatus. Shielding apparatus from magnetic fields requires that the apparatus be surrounded by a thick enclosure of magnetic material. The theory of this magnetic shielding has been developed and formulas for producing the most satisfactory shielding are given. The shielding of an apparatus from electromagnetic waves is largely accomplished by means of eddy currents which these waves set up in the shield. The theory for the production of these eddy currents has been developed and the best location of shields is discussed. Some attention is given to the errors which may be introduced by shielding and some methods are outlined for obviating the necessity of shielding. View full abstract»

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  • 26. Theory of action of the induction watthour meter and analysis of its temperature errors

    Page(s): 511 - 512
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    W. H. Pratt: I think it should be emphasized that the present paper, except so far as it describes a particular mechanism for effecting compensations, is a restatement of material most effectively presented by Kinnard and Faus at the midwinter convention two years ago. Previous to that time, meters having much smaller Group II errors than those used for a background of this paper were used in predominant numbers, and since then the whole output of one of the largest producers of meters has been substantially without Group I errors. So that, presented at this time, the background of this paper must not be looked upon as a picture of general present-day practise. View full abstract»

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  • 27. Cipher printing telegraph systems: For secret wire and radio telegraphic communications

    Page(s): 109 - 115
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    This paper describes a printing telegraph cipher system developed 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 the relative advantages of various codes and ciphers as regards speed, accuracy and the secrecy of their messages. View full abstract»

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  • 28. Electrical definitions

    Page(s): 565
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    Report No. 2 in the A. I. E. E. Standard's series was issued in August 1927. This report was made up of all the definitions appearing in the approved sections of the A. I. E. E. Standards of t h a t date. It was issued t a obtain criticisms and suggestions and if possible to eliminate inconsistencies. In a number of cases definitions of the same thing had developed, varying only slightly in wording. Such differences will unquestionably be necessary in some instances due to varying applications but in most cases can be eliminated through agreement of the committees having the standards affected in hand. A new report dated June 1929 is now available in which part of such coordination work has been included. The new report has also been carefully cross-indexed and brought up to date by the insertion of definitions from Standards approved since original date of publication. Copies of this new Report No. 2 may be obtained without charge by writing, H. E. Farrer, Secretary, Standards Committee, A. I. E. E., to whom all criticisms or suggestions should also be addressed. View full abstract»

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  • 29. Abridgment of the law of corona and dielectric strength of air — IV: The mechanism of corona formation and loss

    Page(s): 1390 - 1398
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    The mechanisms of corona and corona loss have been studied with the cathode-ray oscillograph. High voltage power of the order of 0.1 watt can be measured with an accuracy of 1 per cent with this instrument. The measurements show that the loss follows the quadratic law above the visual critical voltage. On polished wires there is no loss until the visual critical voltage is reached. The loss then starts quite suddenly and takes a finite value on the quadratic curve. On cables and imperfect conductors there is a loss below the visual critical voltage on brushes at local “rough” spots. The loss due to these irregularities can be represented by the probability law. This is quite in accord with former work. In practise it is important not to mutilate the conductors in stringing. The really important factor in design is the irregularity factor, mo, for weathered conductors. No line should be operated with a corona loss under fair weather conditions. It is not necessary from the economic standpoint since large diameters can be obtained with special types of conductors. The visual critical corona voltage can be calculated with great accuracy. As the applied a-c. voltage is increased above the visual critical value, the instantaneous critical voltage becomes lower and lower until finally corona starts at the zero point of the wave. This occurs when the applied voltage is twice the visual critical voltage. At still higher voltage, corona starts below zero or on the falling wave. The effect is as if the instantaneous critical voltage is reduced by an amount approximately equal to the excess of the applied voltage above the visual critical voltage. Thus when the excess is equal to the visual critical voltage the instantaneous voltage is zero. This occurs when the applied voltage is twice the visual critical voltage. The reason for this is clearly shown as well as many other interesting facts. Artificial corona was readily produced with all of the characteristic- of real corona after the mechanism was determined. The quadratic law seems to be the rational expression for the loss. Details of measurements are given in the supplemental paper on measurements by Starr and Lloyd, “Methods Used in an Investigation of Corona Loss by Means of the Cathode Ray Oscillograph.” View full abstract»

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  • 30. Three methods of measuring dielectric power loss and power factor

    Page(s): 556 - 563
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    The paper presents a brief description of the methods of measuring dielectric power loss and power factor in commercial use at the Electrical Testing Laboratories. The several methods are handled individually and their advantages and disadvantages listed. Appendixes are included on the use of the shunted electro-dynamometer as an ammeter, determination of compensation, effect of incorrect compensation in the wattmeter shunt, effect of slightly unbalanced voltages on three-phase measurements, a three-phase wattmeter switch and shielding, grounding, etc. View full abstract»

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  • 31. Abridgment of induced voltage of electrical machines

    Page(s): 191 - 194
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    The object of this paper is to describe and discuss a general equation for the induced voltage of electrical machines having parallel coil sides, and which includes as special cases single- and polyphase-induction motors, synchronous generators, d-c. generators, synchronous converters, and static transformers. The application of the general equation to most of these cases is illustrated, and a number of interesting problems which may be solved by means of it pointed out. A characteristic of this equation is that no restrictions are placed on the velocity of the moving conductors, or on the rates of pulsation and rotation of the flux; but these may vary in any arbitrary manner which can be given a suitable analytic expression. The several methods for the reduction of harmonic voltages are classified and their limitations discussed in such a way as to leave in mind a vivid picture of the process. Tables and curves have been prepared for comparing the effects of the skew, pitch, distribution, and phase connection harmonic reduction factors. A new method for summing the finite series of the distribution summations is given in Appendix II of the complete paper. View full abstract»

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  • 32. General light and power supply of Chicago

    Page(s): 608 - 609
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    The development of a distribution system is largely determined by the load density and Us rate of change. The following is a discussion of these factors and their influence on the Chicago distribution system: The d-c. system which supplies the central part of the city includes an area of about one sq. mi. in which the load is expected to reach 200,000 kw. in 20 years. This would economically require substation supply of about 10 substations of 25,000 kw. each. Surrounding the small d-c. area the general light and power supply over the city is by means of 60-cycle, 4,000-volt circuits, except for the larger industrial loads which are supplied from 12,000-volt lines. The load density of the greater part of the 4,000-volt system is about 4,000 kv-a. per square mile, and the economical supply would be from 7,000 kv-a. remote controlled substations spaced about 1.3 miles. The maximum density of load on this system is 10,000 kv-a. which would require 10,000-kv-a. substations. Calculations indicate that, with increasing load densities, the economy of this intermediate distribution voltage disappears, and in the ultimate development higher distribution voltages are necessary. View full abstract»

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  • 33. Current limiting reactors with fire-proof insulation on the conductor

    Page(s): 137 - 141
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    In a previous paper, tests were described which proved conclusively that if conducting material were lodged between the turns of a reactor having bare conductor, the reactor would flashover at the instant a failure occurred on the circuit in which the reactor was placed. In this paper, tests are described which were made during the development of a proper insulation for the conductor of reactors. Short Circuit Tests. Reactors tested consisted of one reactor with enameled conductor and two reactors with asbestos insulated conductor; one having a thin covering of asbestos; the other a thicker covering. The reactor with enameled conductor flashed over during the first short circuit test. That with a thin covering of asbestos stood one short circuit and arced over in the second short circuit. The reactor with the thick covering stood many short circuit tests without any failure or sign of distress. These tests established the fact that thin insulation on the conductor will not prevent such failures, even though it has sufficient dielectric strength to withstand the voltages placed across it for the reason that the magnetic force exerted on iron and steel objects will cause them to break through thin insulation. On the other hand, thick insulation will adequately protect the reactor from failure due to foreign substances. Thermal Tests. Thermal tests on the asbestos insulation established the following facts: First: That this insulation does not smoke excessively at temperatures below 350 deg. cent. Second: That it does not burn even at temperatures of melting copper. Third: That its insulation and mechanical strength is not appreciably affected when heated rapidly as high as 350 deg. cent. Thermal Capacity. The thermal capacity of the conductor is affected by the insulation, as follows: First: Under the effects of extremely high short circuit currents for a very brief interval, the thermal capacity is not affected by the asbestos. Second: With a moderate short-circuit - urrent for a longer length of time, the thermal capacity of the insulated conductor is increased due to the storage of heat in the insulation. Third: During normal operation, at rated current, the temperature rise of conductor is increased due to the drop in temperature in the insulation. Costs. The asbestos insulation increases the cost of the reactor directly by the addition of the cost of the insulation itself and indirectly by making it necessary occasionally to increase the size of the conductor. However, this increase in cost is not a large percentage of the total cost of the reactor. View full abstract»

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  • 34. An electrified railway substation of the Pennsylvania railroad

    Page(s): 431 - 433
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    This paper contains a description of one of the outdoor substations of the Philadelphia-Wilmington electrification of the Pennsylvania Railroad, recently placed in service. It describes the initial installation of apparatus provided in the substation for the present suburban electrification, as well as the steps taken to accommodate the additional apparatus necessary for the through electrification when it takes place. The location and control of the substation is described as well as the types of protective apparatus utilized and the method of operation. Attention is called to certain operating necessities which control the design and location of a substation of this character. The means provided for handling the heavy apparatus into and out of a substation of this character and the facilities for handling, cleaning and restoring oil to the different pieces of apparatus are described in some detail. View full abstract»

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  • 35. Distribution networks

    Page(s): 414
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    After much debate the system most favored is the three-phase, four-wire alternating-current network for the supply of light, power or the combination of light and power. Bur, unfortunately, most services and equipments are 110 volts or 220 volts today, and the electrical relations in the three-phase circuit make it possible only to obtain service at either 115 and 199 volts or 120 and 208 volts with simple transformation ratios. The relative merits of these combinations have been debated thoroughly and especially their effects on service using present standard equipment. No unanimous decision has been reached and both types of networks are in service. Both systems give satisfactory service when standard equipment is used, for, fortunately, lamps may be had at either 115 or 120 volts and single-phase and polyphase motors have tolerances whereby satisfactory operation may be had between, roughly, 110 and 120 volts single-phase and 200 and 240 volts three-phase. But, of course, when operated at points near the tolerance limits the margins of departure from the average motor characteristics are changed, and a design based on either system as a standard would have a wider field of satisfactory application. Electrical World. View full abstract»

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  • 36. High-voltage oil circuit breakers for transmission networks

    Page(s): 1340 - 1348
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    THE standards of the American Institute of Electrical Engineers define an oil circuit breaker as a “device (other than a fuse) constructed primarily for the interruption, in oil, of a circuit under infrequent abnormal conditions.” Common usage, however, has sanctioned the use of the term “circuit breaker” as applying to a device for the regular and usual interruption of an energized circuit as distinguished from a switch used only for opening circuits which are de-energized or not carrying load. This paper will consider only high-voltage oil circuit breakers, the term “high voltage” being taken as applying to potentials of 25,000 volts or above. View full abstract»

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  • 37. Lightning and other transients on transmission lines lightning

    Page(s): 403 - 407
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    F. W. Peek, Jr.: In some respects Mr. Creighton's conclusions are not as far from my own as might appear at first glance. The effect on transmission lines is determined wholly by the gradient. The fact that he has very high energy values is due to the high voltages or high cloud heights that he has assumed. View full abstract»

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  • 38. Abridgment of flux linkages and electromagnetic induction in closed circuits

    Page(s): 219 - 223
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    It is shown that the flux linkages of a circuit may be changed in two very different ways — either the flux may be varied causing a voltage to be induced according to Faraday's Law of Electromagnetic Induction, or the turns may be varied by a substitution of circuit without inducing a voltage. In the Appendix, it is mathematically shown that the flux may be changed either by transformer or cutting action, but that the presence of one or the other of these actions is dependent on the choice of reference axes. Thus, any argument to the effect that one of them in particular is a necessary part of all induction phenomena is futile. It is possible to identify in every d-c. machine the building up of flux linkages so as to generate a voltage, and the reduction of flux linkages by a substitution of circuit so as not to generate a voltage. The alternate working of these two methods for changing the flux linkages of a circuit is an essential and necessary feature of every d-c. dynamo-electric machine. General criteria are introduced for ascertaining in any given case the nature of the changes in inter-linkages which occur, and whether voltages are induced thereby. By way of application, a new restriction on the use of coefficients of inductance is pointed out, the sliding contact and homopolar machine are discussed, and finally a table has been prepared illustrating the various types of flux linkages found in familiar apparatus. View full abstract»

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  • 39. Parallel resonance and anti-resonance

    Page(s): 662 - 665
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    There seems to be a certain amount of uncertainty among authors as to just what is a correct definition of resonance in a parallel circuit such as shown of Fig. 1. The most common definition is that resonance is that condition which makes the total reactance, or susceptance, equal to zero. This is the condition for unity power factor. In some definitions the further condition is added that at resonance the total impedance of the circuit is a maximum. The A. I. E. E. Standardization Rules,1 for instance, say that resonance is the condition of maximum impedance obtained by varying L or C, and nothing is said about zero reactance or unity power factor. These differences in definitions have led to this investigation. View full abstract»

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  • 40. Cable charge and discharge

    Page(s): 525 - 530
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    Conductivity determinations of insulating materials, and therefore the determinations of the leakage resistance of a cable, condenser or similar structure, have always been more or less unsatisfactory, due to a phenomenon often called “soaking in of the charges.” In general, if a constant direct voltage is impressed upon a circuit, in the first moment large transient currents flow, representing the energy storage and adjustment in the magnetic and dielectric fields of the circuit. These transient currents however vanish very quickly, usually in a very small fraction of a second, and all the currents in the circuit or circuits then become constant. If a constant direct voltage is impressed upon a cable or similar structure, large transient currents also flow momentarily; but after these currents of energy adjustment in the electromagnetic field of. the system have vanished, usually after a small fraction of a second, the remaining current is not constant, as in the usual electric circuit, but continues to decrease-slowly, for minutes or even hours. If then the cable is discharged by short-circuiting it, after the large initial transient discharge current has passed and the voltage on the cable has become zero — in a small fraction of a second — the current coming out of the cable does not entirely vanish, but a small discharge current continues to flow for many minutes or even hours. Or, if the cable has been discharged by short-circuiting it for a short time, until its terminal voltage has become zero, and the short circuit is taken off, a terminal voltage and an electrostatic charge gradually build up again at the cable, reach a maximum after some minutes, and then gradually decrease again. Various explanations have been proposed of this phenomenon as a hysteresis effect of the dielectric, etc. It is shown in the following, that this phenomenon of the “soaking in of the charges” or the “electrification of the- cable” is a true electric circuit transient, has nothing to do with hysteresis effects, but is the result of, and explained by the energy adjustment of a system with constant values of resistance, inductance and capacity, that is, is in no essential different from the usual rapid starting or stopping transient of the ordinary circuit, except that it is many thousands of times slower. This great slowness is due to the fact that the resistance in the transient circuit is the leakage resistance of the cable dielectric, and therefore extremely high, measured not in ohms but in hundreds of megohms. If the dielectric of the cable consists of two or more materials, having different resistivities, or different specific capacities, or both, then the distribution of voltage through the dielectric gradually changes. At the moment of voltage application, the voltage distributes between the component dielectrics in proportion to their specific capacities; gradually however this voltage distribution changes to a distribution proportional to the resistivities of the component dielectrics, and electrostatic charges build up in the interior of the dielectric, at the boundaries between the component dielectrics. The electric quantity has to be conducted through the dielectric, and due to the very high resistivity of the dielectric, this energy readjustment within the dielectric occurs with extreme slowness, giving a transient of a duration of many minutes, but a true electric transient nevertheless, like the usual transients of a duration of milliseconds. In the discharge of the cable, the reverse occurs, and the internal charges gradually disappear by conduction through the dielectric. This phenomenon is discussed in its various aspects, and the equations of the slow transient derived, in the following: It is shown that this slow transient always is impulsive or exponential, and consists of (n — 1) terms, if the insulation is composed of n materials. A number of con View full abstract»

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  • 41. Starting characteristics and control of polyphase squirrel-gage induction motors

    Page(s): 153 - 159
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    In the application of squirrel-cage induction motors to such severe service as frequent start and stop or frequent plugging operation, it is desirable to know how much loss the motor will be required to dissipate. Plugging being understood as changing the motor from any speed in one direction to any speed in the opposite direction, by reversing the rotation of the field only. The subject of starting loss is also of interest from the control standpoint; such as the application of auto-transformers for starting purposes; or where an external resistance is inserted in the primary as is done in the control of elevator motors. Consideration is given, to the part that the primary and secondary resistance and the total reactance play in the determination and the manipulation of the starting losses; and, as it is true that in many applications the time spent in accelerating the rotor from rest is useless from the production standpoint, consideration is given to the value of secondary resistance that will give minimum starting time for a given field strength. This involves a method for the determination of the time taken to attain a given speed in general. There are many cases where a motor has already been designed and tested, and is about to be applied on a given job where the cycle of operation is known and includes either starting and stopping or plugging. In such an event, instead of working with the various test values to get the constants of the machine, it is much more convenient and accurate to work from such values as starting torque, maximum torque, slip at full load, locked current and primary resistance. It will be shown how the proceeding short-cut method can for most cases be made more simple without sacrificing the accuracy of the result to any appreciable extent. When a motor is plugged the problem is complicated by the difficulty that eddy currents flow in the rotor which give a slight increased effect to the torque at negative speeds. Although this paper - oes not show how to predetermine its amount, it does show how to handle the losses and the time of reversal, if the test speed-torque values are known or can be estimated from another machine. View full abstract»

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  • 42. Transformer tap changing under load

    Page(s): 1331 - 1335
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    Attention is called to the need for voltage and power-factor regulating equipment on lines used for tying together large generating stations and for interconnection of systems. Such lines must be capable not only of transferring large amounts of energy in either direction, but must also be suitable for connecting generating sources operating at essentially equal voltages. The important characteristics of the three principal methods for voltage regulation on interconnecting lines, — namely, synchronous condensers, tap changing under load, and induction regulators, — are presented, discussed and compared. The comparison includes such factors as first cost (including installation) reliability, ease of operation, losses, effect on system power factor and losses, maintenance, adaptability to reversible energy transfer and ability to give close voltage regulation. The requirements of regulating equipment, particularly from the operator's standpoint, are discussed with the idea of bringing out the necessity of obtaining a high degree of reliability, ease of operation and flexibility to meet the various operating conditions. The fields of application of various methods of regulation are discussed, showing the advantages of each for different requirements and pointing out that in some cases the best solution of the problem lies in the application of a combination of two different methods of regulation to secure the best overall results. Brief descriptions of three installations (two of tap changing under load, and one of induction regulators) for voltage regulation and power factor control on lines of The Philadelphia Electric Company are included. View full abstract»

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  • 43. Oliver heaviside

    Page(s): 316 - 317
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    Oliver heaviside, of Torquay, England, Honorary Member of the Institute, recently died, at the age of seventy-seven, as the result of a fall from a ladder. Mr. Heaviside has been recognized as one of the most eminent exponents of electrical science, particularly for his development of the electromagnetic theory. His retiring character and desire to avoid society, partly due to almost complete deafness since childhood, has resulted in his name being unknown to the general public but those who have come in contact with his work regard him as an illustrious successor to Wheatstone, Maxwell, and Kelvin. He lived alone in a cottage at Lower Warberry, Torquay, England, in poverty, a pension of £200. a year having practically been forced upon him. While, he wrote papers of great value for the Philosophical Magazine of the Royal Society of London and for the London Electrician, for which he received but scant remuneration, these papers were difficult to read and little known. No pictures of him exist and few of his admirers ever met him. His writings however, had considerable practical value, particularly his mathematical theory of the value of distributed self-induction in long distance telephony, a theory of which Dr. Pupin availed himself in this country for practical application to telephony, and establishing a new epoch in this field. The Royal Society elected him to Fellowship, and the Institute on February 14, 1918, to Honorary Membership. The resolution adopted by the Board of Directors at the time of his election to Honorary Membership follows: View full abstract»

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  • 44. Application of electric propulsion to double-ended ferry-boats

    Page(s): 1077 - 1082
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    The double-ended ferry-boat propelled by means of a bow and stern propeller has become the recognized standard type, due to its maneuvering possibilities and general handiness in congested harbors. In all cases in which the prime mover is directly coupled to the two propeller shafts which must necessarily turn at the same revolutions per minute, the over-all propulsive efficiency is lowered due to the performance of the bow propeller. The electric drive system permits of applying power when and where required and to any degree desired. Tests on the double-ended ferry-boat W. R. HEARST show a material gain in propulsive efficiency when driving the bow propeller electrically at a speed which gives neutral thrust. Later tests indicate, however, that there is no substantial difference in the propulsive efficiency, whether the bow propeller is driven electrically at neutral thrust, or is electrically disconnected and driven by the water. Sufficient tests have not been made, however, to show that this is true in all cases. The reciprocating steam-engine or Diesel-engine type of drive, in which both shafts are direct connected, require approximately 19 per cent more horse power at the propeller shafts than the electric system, due to the difference in propulsive efficiency. The calculated fuel consumption of a typical reciprocating steam-engine drive with the direct-connected system shows that it requires approximately 40 per cent more fuel than the steam turbine electric system, due to the difference in propulsive and thermal efficiencies. The electrical transmission losses are less than the propulsive efficiency losses of the direct systems. In addition to the more efficient method of power application, electric drive also has many inherent advantages, such as rapid maneuvering qualities and ease of control. The Ward Leonard system, similar to that used on the Chicago fire boats which were put in operation in 190%, permits of the use of pilot-house control, eliminating - he personal factor which is always present with the engine-room telegraph. The operating records of ferry-boats in service prove electric drive to be reliable. The respective field of application of turbine electric drive or Diesel electric, drive for double-ended ferry boats depends upon the relationship of first cost to the operating changes and needs of the service. View full abstract»

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  • 45. Papers on rural electrification

    Page(s): 1166 - 1171
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    Eugene Holcomb: I notice the difference in the rate schedules in these two papers. The rates shown by Mr. Post seem undoubtedly too low for average rural territory. View full abstract»

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  • 46. Abridgment of automatic voltage regulators: Application to power transmission systems

    Page(s): 525 - 528
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    Within a relatively short time conditions in transmission systems as regards continuity of service and maximum power have radically changed. A few years ago, the amount of power transmitted over important lines was relatively small compared with their ultimate transmitting capacity. In such cases, the systems were inherently stable, and there was a reasonable margin of power with respect to load swings and short circuits. Automatic voltage regulators were used at that time chiefly for maintaining more uniform voltage conditions than could be obtained by intermittent adjustment by hand control. Different types of regulators for this purpose have given satisfactory service for a number of years. However, conditions have gradually changed. Within the last few years the power to be transmitted has increased to such an extent that it has now become necessary to consider means seriously for increasing the maximum power and for insuring continuity of service during transient disturbances, such as load swings and short circuits. The object of this paper is to present the results of an extended investigation along these lines. A new regulator is described which will accomplish the above purposes, and the theoretical analysis is confirmed by test results. View full abstract»

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  • 47. Abridgment of extinction of a long A-C. arc

    Page(s): 310 - 314
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    The extinction of an a-c. arc is analyzed as depending on two factors — the rate of recovery of dielectric strength of the arc space after current zero, and the rate at which voltage tending to re-ignite the arc is applied by the external circuit. In the short arc, most of the recovered dielectric strength resides in a deionized layer next to the cathode, but in the long arc, the rest of the arc space contributes largely to the dielectric strength. The breakdown gradient of the still ionized arc space is defined, and using a thermal ionization theory, a formula for growth of breakdown gradient is derived. The extinction of long a-c. arcs in the open is greatly influenced by the sectional area which the arc stream has at current zero. By confining arcs to slots and holes, the rate of deionization at current zero is greatly increased, and so large voltages per cm. of arc can be interrupted. A gas blast passing turbulently through an arc stream greatly accelerates deionization at current zero and so is effective in increasing the capacity of the a-c. arc to interrupt high-voltage circuits. The expulsion fuse is an example of a gas blast circuit interrupter, the gas blast resulting from the decomposition of the fiber fuse case. The oil circuit breaker is also a gas blast circuit interrupter, the blast arising from the gases produced by the decomposition of the oil. Means which increase the rate of oil decomposition improve the operation of the breaker. The magnetic blow-out in oil breakers is effective by causing an increased rate of oil decomposition. Electrostatic unbalance may lower the volts per cm. which a long arc can interrupt. The use of static balancing devices may then become advisable. View full abstract»

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  • 48. Synchronous machines — III: Torque-angle characteristics under transient conditions

    Page(s): 1339
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    This is the third part of a series of papers on the subject of synchronous machines. The first two were I. An Extension of Blondel's Two-Reaction Theory, II. Steady State Power-Angle Characteristics. The present paper deals with the power-angle, or torque-angle, characteristics under transient conditions, namely, A. Cyclic variation of impressed torque, B. Sudden angular displacement, C. Synchronizing out of phase. View full abstract»

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  • 49. Methods of voltage control of long highvoltage lines by the use of synchronous condensers

    Page(s): 263 - 264
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    A.W. Copley: In amplification Mr. Koontz's paper and xcarrying out the thought a little farther, it may be pointed out that there is a very definite power limit on a transmission line on which the values of generator and receiver voltage are fixed. The addition of synchronous condenser capacity beyond a certain limit does no good as far as increasing the capacity of the line is concerned. For instance, on a 200-mile line with 200 kv. maintained at both ends, the addition of synchronous condenser capacity beyond the point which allows a load of about 220,000 kw. at the receiver end, does not increase the capacity for transmitting power. The power limit of such a line being in the neighborhood of 220,000 kw., it can be seen that, at least on projected lines, the limit is being approached. It is, however, possible to increase the power limit of the line by making, in effect, two lines in series. For instance, on a 400-mile line, with synchronous condenser capacity at the receiver end, the limit of capacity is around 120,000 or 125,000 kw. By breaking the line in two parts of 200 miles each, the power limit of the upper end of the line is about 220,000 kw. and with that power delivered to the middle of the line, the balance of it again has the oipacity of 220,000 kw. minus the losses, which bring the delivered power down to about 200,000 kw. That is, by the introduction of condenser capacity in the middle as well as at the receiver end, the line capacity is increased from 125,000 to 200,000 kw. View full abstract»

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  • 50. Dry batteries for radio use

    Page(s): 445
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    Among the standard assemblies of dry cells adopted by the conference held at the Bureau of Standards, 1921, there were included two batteries for radio use. Since that date the demand for dry batteries for radio purposes has increased very greatly and the conditions of use have been considerably changed. It appears desirable, consequently, to revise the specifications for the performance of such batteries. In anticipation of another conference to consider this problem the Bureau and a number of battery manufacturers have been carrying out extensive tests in order to determine the type of performance tests to be established and proper numerical values for these requirements. The matter has also been taken up by a committee of the American Electrochemical Society on which the Bureau is represented. It is planned to call a conference of dry cell manufacturers and others interested to meet at the Bureau within the next few months. View full abstract»

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Aims & Scope

The Journal of the American Institute of Electrical Engineers (AIEE) contains articles published between 1924 and 1930. Contents are devoted to the advancement of theory and practice of electrical engineering and the allied arts and sciences.

This Journal ceased publication in 1930. The current retitled publication is IEEE Spectrum.

Full Aims & Scope