Showing papers in "Transactions of The American Institute of Electrical Engineers in 1923"
TL;DR: In this paper, the causes of shaft currents in rotating electric machines were investigated, and it was shown that shaft currents can be caused by the use of poles and segments in certain ratios, such as 4, 8, 16, 24, 32, etc.
Abstract: This paper describes the causes of, and remedies for, the existence of “shaft currents” or “bearing currents” which sometimes flow across the rubbing surfaces of the bearings of electric machinery, thereby gradually damaging the shaft and bearings. Up to the present time the only cause of shaft currents that has attracted any particular attention has been the use of sectionalized stators, and the published discussions have been chiefly confined to synchronous alternators. Fleischman1 and others have shown that sectionalizing causes shaft currents for the reason that the extra reluctance of the joints causes an unequal division of the flux between the clockwise and counter-clockwise paths in the yoke, thus giving a resultant flux linking the shaft. Applying the same method of reasoning used in the case of sectionalizing to the general case of any machine with segmental punchings, the following facts are shown: 1. A principal cause of shaft currents in revolving electric machines is the use of poles and segments in certain ratios. 2. The frequency of the shaft current due to joints in the stator yoke is an odd multiple of the frequency of the stator flux, the frequency of the shaft currents due to rotor joints is an odd multiple of the rotor frequency, and these frequency multiples are determined by the ratios of poles to segments. 3. Machines with 4, 8, 16, 24, 32, etc., poles are especially likely to have shaft currents, and machines with 6, 10, 14, 22, etc., poles are relatively immune. 4. By the proper choice of the number of segments for use with any machine, or by the use of segments with offset dovetails, or both, shaft currents can be effectively eliminated in most cases. The possibilities of shaft currents being caused by homopolar action as the result of magnetic flux flowing in the shaft, or by other means, are discussed, and it is concluded that such causes are seldom important. A possible useful application for the theory of shaft currents in the design of a high-current transformer is mentioned, and the possibility of obtaining multiple frequencies from a stationary transformer in this way is shown to be dependent upon the presence of magnetic saturation. A table of combinations of poles and segments that will cause shaft currents is given, and a bibliography of the subject is appended.
103 citations
TL;DR: In this article, the authors deal with some of the more common types of ventilating and cooling systems used in the electric machines and particularly with the laws governing the flow of heat from the cooling surfaces.
Abstract: The elevation in temperature of the windings of any electric machine due to the internal heat losses is usually the dominating factor in limiting the rating of the machine. This limitation found in the heating, is primarily due to the effects of high temperatures on the various types of insulation used in such machines. The American Institute of Electrical Engineers Standards specify the maximum permissible operating temperatures for the various grades of insulation. The temperature of the windings in the machines then, must be kept below this maximum permissible temperature. The heat losses produced in a machine are the results of electrical and mechanical losses. These losses must be transferred from the source of generation to the cooling medium. The first step of the heat flow path is by conduction through the copper, iron or insulation to the ventilating or cooling surfaces. The second step in the transfer of the heat may be called the liberation or dissipation of the heat from these surfaces to the cooling medium. This portion of the heat flow may be divided into two or more stages by the use of an intermediate cooling medium, such as oil, in an oil-insulated transformer. This paper deals with some of the more common types of ventilating and cooling systems used in the electric machines and particularly with the laws governing the flow of heat from the cooling surfaces.
58 citations
TL;DR: The electric arc is now extensively used, and yet after more than a hundred years of study, there has been little crystallization of opinion as to certain phases of its fundamental theory as discussed by the authors.
Abstract: COMMERCIALLY the electric arc is now extensively used, and yet after more than a hundred years of study, there has been little crystallization of opinion as to certain phases of its fundamental theory. Absolute contradictions are frequently found in the literature, and premature generalizations have given rise to more disagreement among the investigators of the equation of the static characteristic of the normal1 arc than the experimental difficulties warrant.
58 citations
TL;DR: In this article, reduction formulas for Bessel functions, suitable for skin effect problems, are tabulated, and a table of values of the first five orders, for use in drawing curves, is given.
Abstract: Formulas are given, with examples, for the following new problems in proximity effect resistance ratio: Thin Tube and Infinitesimal Wire; Two Thin Tubes in Return Circuit; Two Thin Tubes in Parallel; Insulated Cable Sheaths in Single-Phase Circuit; Cable Sheaths in Three-Phase Circuit, Flat Spacing; Finite Wire and Infinitesimal Wire; Two Wires in Parallel; Three-Phase Circuit, Triangular Spacing, Three-Phase Circuit, Flat Spacing. Reduction formulas for Bessel functions, suitable for skin effect problems, are tabulated, and a table of values of the first five orders, for use in drawing curves, is given.
54 citations
TL;DR: In this article, the authors present the theoretical basis for a theorem by which the practical analysis and visualization of short-circuit phenomena can be greatly simplified, which follows from the approximation of neglecting resistance in the application of Kirchhoff's Law to closed circuits.
Abstract: This paper presents the theoretical basis for a theorem by which the practical analysis and visualization of short-circuit phenomena can be greatly simplified. The theorem follows from the approximation of neglecting resistance in the application of Kirchhoff's Law to closed circuits. Thus in any problem of short circuits in which the effect of resistance is negligible in the initial moment, and this includes many of them, the theorem applies. It is: If the resistance of a closed circuit is zero, then the algebraic sum of the magnetic linkages of the circuit must remain constant. Illustrative examples are given, including the transformer, the single-phase and polyphase alternator, and the induction motor.
43 citations
TL;DR: In this article, the authors considered the problem of convection in a viscous fluid and showed that the viscosity is a factor of first importance which cannot be neglected, and therefore adopted a film theory as an approximation.
Abstract: THE general problem of heat transfer requires a knowledge of the laws of conduction, radiation and convection. In 1822, Fourier gave us the first thoroughly scientific definition of conductivity and reduced the problem of heat conduction to an exact science, with a power and completeness which left little room for extension or improvement even to the present day. The law of radiation was first suggested by Stefan in 1879 as a result of an analysis of some experiments made by Tyndall. In 1884 Boltzman deduced the law theoretically from the principles of thermo-dynamics and electromagnetics. Thus the laws of conduction and radiation have been accurately known for a long time, while the problem of convection has received relatively little study. This fact is surprising when we consider the important part played by convection in almost all cases of heat transfer. A complete mathematical solution of a convection problem would require a knowledge of the hydrodynamic laws of viscous fluids for stream line and turbulent motion, combined with the Fourier equations of heat conduction in a moving medium. At present our lack of the hydrodynamic laws for turbulent motion renders a rigorous solution impossible. Therefore in most of the theoretical work so far attempted the simplifying assumption of an in-viscid fluid has been found necessary. The theoretical results obtained when viscosity is neglected are in general far from the experimental facts. Langmuir's study of the problem showed that the viscosity is a factor of first importance which cannot be neglected. He therefore adopted a film theory as an approximation. The reason for the existence of a film around a hot body may be seen as follows: Consider a horizontal wire maintained at a given temperature in a fluid, the fluid adjacent to the wire will become heated and rise while the cooler fluid of greater density will flow into its place. Thus a convection current is set up by the difference in density between the hot and cold fluid. This condition is usually referred to as free convection. At the surface of the wire the fluid is stationary due to viscosity. As we proceed from the surface of the wire the velocity of the convection currents increase until a distance is reached at which the critical velocity conditions in the fluid are exceeded and the stream line flows bursts into turbulent motion. The discontinuity between the stream line and turbulent motion constitutes the outer boundary of the film. At the inner boundary the fluid has the temperature of the hot surface and at the outer boundary the temperature of the ambient fluid. The actual configuration of the outer boundary is unknown. As an approximation we might assume that it was an eccentric ellipse or cylinder, etc., and determine the size and eccentricity so as to best fit the experimental results. For ease of calculation Langmuir adopted the simplest approximation and assumed that the outer boundary of the relatively stagnant film was a cylinder concentric with the wire. He thus reduced the hopelessly complex problem of convection to one of conduction in the steady state.
39 citations
TL;DR: In this paper, Sorensen et al. make a plea for a more strenuous use of insulating materials, in the light of a request in another paper given this morning, in which the author recommends a decrease in the test voltage applied to transformers with one terminal grounded.
Abstract: R. W. Sorensen: My first point is in connection with the statement that we use our insulations under stresses which rarely exceed the breakdown voltage of air, though tests show a strength of 10 to 20 times that of air for many of the insulations used. This plea for a more strenuous use of insulating materials is interesting in the light of a request in another paper given this morning, in which the author recommends a decrease in the test voltage applied to transformers with one terminal grounded.
34 citations
TL;DR: In this article, it was shown that the effect of the radiation on the attenuation and distortion of the waves along the line must also be negligible, compared to the effects of the joulian losses, and in this result a proof of the correctness of the initial assumption is seen.
Abstract: The aim of this investigation was to contribute something to our knowledge of traveling electromagnetic waves. Among the transient phenomena that occur along transmission lines, these are still little known, especially as far as their “attenuation” and “distortion,” or change in shape near the “wave front” are concerned. It is first seen that the “classical theory” of the propagation of electrical disturbances along lines, as it has been chiefly developed by Heaviside and Poincare, does not give a correct representation of the facts near the wave front, because it assumes an instantaneous penetration of the current in the wires. It is shown that this theory is an “unidimensional” one, as it considers only one space variable, the coordinate along the line, and, from an electromagnetic point of view, amounts to identifying the traveling waves with plane wave phenomena. Steinmetz's theory of the radiation from traveling waves (Trans. A. I. E. E. Feb., 1919) is then examined, and, as Carson pointed out (Jour. A. I. E. E., Oct. 1921), found based on a misconception of the propagation of the electromagnetic field near the wires of a line. It is remarked that this theory amounts to propagating longitudinal electric waves, a conception in conflict with the basis of Maxwell's theory. This latter proves very easily that, along a perfect line, i. e., without ohmic or leakage losses, plane electromagnetic traveling waves are propagated without distortion and without attenuation; hence that there is no radiation. Losses do not change anything from the radiation point of view (Mie. Ann. Phys. 2, 1900). In the theory of Steinmetz, the radiation was the controlling factor at high frequencies. Although the question could be considered as settled, in so far as Steinmetz raised it, it is felt that the conditions under which traveling waves are started must be elucidated, in order to decide whether, during the transient process of establishing a plane electromagnetic traveling wave, any loss of energy can occur by radiation in free space. This would reduce the radiation to a transient phenomenon instead of to a steady one, as assumed by Steinmetz, i. e., to an effect produced when the condition of plane wave is departed from, as at the origin or the end of a line (“end effect”). The problem, considered in its broad aspect, i. e., from the electromagnetic point of view of Maxwell, appears to be of great complexity. It involves a study of what might be called time-three-dimensional space transient, while the most complicated transients considered in electrical engineering are time-one-dimensional space transients, as was already noticed. It was found possible, however, to decide whether the radiation is a factor of enginering importance in attenuating and distorting waves. There, first, the distribution of current along the conductors of a line is shown to be a very close approximation to the actual, unknown, distribution, with regard to the possibly existing radiation. Then, from this assumption, the radiation of the system is calculated at a corresponding approximation, and its amount found to be negligible compared to the heat dissipated in the line during the same time. From this it is concluded that the effect of the radiation upon the attenuation and the distortion of the waves along the line must also be negligible, compared to the effect of the joulian losses, and in this result a proof “a posteriori” of the correctness of the initial assumption is seen. The first idea of that procedure, but limited to stationary waves, is probably to be credited to M. Abraham (Phys. Zeit. 2-p. 329–1901) who applied it to the calculation of the radiation from a single isolated wire (oscillator), and found it in practical agreement with a more elaborate theory, based on Maxwell's equations. As in this latter application the radiation is larger than the ohmic dissipation, the conclusions of this investigation are even strengthened. An application to the steady radiation from a transmission line oscillating freely at one of its natural frequencies shows, even at very high frequencies, that the power radiated is negligible compared to the heat dissipated. For instance, a 100-kilometer transmission line, No. 00 B. & S. wire, oscillating at three million cycles per second, wastes by radiation only 1/3600 of what is wasted by heat. This is in accordance with the results giren for steady a-c. traveling waves along a line by Carson, (loc. cit.). In the case of a traveling wave suddenly started at the origin of a perfect line, it is found that, when the wave has become plane, the amount of energy ${3 \over 2}\ d\ 10^{-9} I_2\ joules$ is wasted by radiation. d is the distance in cm. between the two wires of the line and I the constant current suddenly flowing in the line, in amperes. This energy is carried to infinity by an electromagnetic field limited to a thin spherical shell of variable depth, (not thicker than d), expanding at the speed of light. A reflection of the wave at a free end of a line is shown to add to the preceding an amount of radiated energy $4\ d\ 10^{-9}\ I^2\ joules$ and only half that amount for a grounded line. A complete transposition causes a radiation four times as large as the sudden starting of the wave. Compared to the joulian dissipation during the time the wave takes to travel once along the line, the radiated energy is of the order of 1/10,000th. The influence of the radiation on the attenuation and distortion of traveling waves is thus found entirely negligible in engineering practise. Other possible factors are suggested.
30 citations
TL;DR: In this paper, the authors considered it well worth while to attempt in the laboratory to duplicate the conditions of an arcing ground on a transmission system and by spark gap determinations of voltages and by oscillograms to determine the maximum voltages developed and to discriminate between the various theories proposed.
Abstract: THE subject of arcing grounds in transmission systems is one of the greatest interest to operators of power systems of any extent. The almost universal grounding of the neutral in this country is done primarily to alleviate the destructive effects produced by arcing grounds. However, in spite of its great importance, a clear understanding of what happens in an arcing ground in not general. There is no agreement as to the magnitudes of voltages and surges produced, and the various theories proposed call for different properties of the arc. The authors therefore considered it well worth while to attempt in the laboratory to duplicate the conditions of an arcing ground on a transmission system and by spark gap determinations of voltages and by oscillograms to determine the maximum voltages developed and to discriminate between the various theories proposed.
29 citations
TL;DR: In this article, a graphical method of correcting the errors in the standard formulas for calculating the thermal resistance and geometric properties between the conductors and the sheath is obtained in terms of what is called the "geometric factor," the results are tabulated for 2, 3 and 4-conductor cables throughout the range of practical sizes and an empirical formula is given.
Abstract: The main purpose of this article is to express the calculation of current-carrying capacity in simple formulas. The allowable current for underground cables is usually limited by the maximum permissible temperature of the insulation. The temperature rise is of course a function of the ability of the cable system to dissipate the heat generated. The chief difficulty in the calculation of current-carrying capacity is the determination of the thermal resistances of the path through which the heat must flow. The main part of this paper deals with the errors in the standard formulas for calculating the thermal resistance and geometric properties between the conductors and the sheath. A graphical method of correcting the errors is obtained in terms of what is called the “geometric factor,” the results are tabulated for 2, 3 and 4-conductor cables throughout the range of practical sizes and an empirical formula is given. The check between the results of the graphical correction method and the published experimental data on this subject is very satisfactory, and emphasizes the errors in the standard formulas. The thermal resistance between the sheath and the duct is mentioned briefly, and an approximate method of finding the resistance between the duct and the region at base temperature is outlined. The previous work is then combined into a simple formula giving the allowable current for n-conductor cables, there being any number of similar cables in the duct bank. The formula is also enlarged to cover the case of cables in the metric and square inch systems, and cables buried directly in the ground. The method of including the effect of induced sheath currents in single-conductor cables and of dielectric losses is shown. Finally, the procedure to use in case the cables in the duct bank are not all of the same type is outlined. In Appendix A the geometric factor for three-conductor cables under three-phase voltage is discussed, Russell's formula for this geometric factor being compared with the experimental determinations and an empirical formula for it is given. A formula is also given for the calculation of dielectric losses in three-conductor cables. The geometric factors for three-conductor cables in all other connections (i. e., the geometric factor for one conductor against the other two and sheath, or between any two conductors, etc.) are then derived in terms of the two geometric factors already obtained. In Appendix B are given examples of the calculation of current carrying capacity under various conditions, and of dielectric loss. In Appendix C an example is given which shows the error introduced by using an approximate formula for the calculation of the thermal resistivity of the insulation of a three-conductor cable based upon experimental measurements, the case taken up being a table in the Research on the Heating of Buried Cables.
25 citations
TL;DR: In this article, a general picture of the long toll cable system which is being projected for use in the northeastern section of the United States was presented, including automatic means for adjustment of the repeater gains to compensate for changes in the resistance of the conductors caused by temperature changes.
Abstract: The applicatton of telephone repeaters has made it possible to use small gage cable circuits to handle long distance telephone service over distances up to and exceeding 1000 miles. A general picture of the long toll cable system which is being projected for use in the northeastern section of the United States was presented recently by Mr. Pilliod before this Institute.* Many of the circuits in these toll cables are so long electrically that a number of effects, which are comparatively unimportant in ordinary telephone circuits, become of large and sometimes controlling importance. For example, the time required for voice energy to traverse the circuits becomies very appreciable so that reflection of the energy may produce ``echo'' effects very similar to echoes of sound. The behavior of the circuits under transient impulses, even when two-way operation is not involved so that ``echoes'' are not experienced, is very important. In order to keep within proper limits of variation of efficiency with frequency over the telephone range special corrective measures are necessary. Owing to the small sizes of the conductors, the attenuations in the longer circuits are very large. Special methods are, therefore, required to maintain the necessary stability of the transmission, including automatic means for adjustment of the repeater gains to compensate for changes in the resistance of the conductors caused by temperature changes.
TL;DR: In this paper, a new and simple general law is proposed, based on one of the fundamental universal laws of physics, which leads to the existence of a force longitudinal to the conductor, which our older laws deny.
Abstract: Reasons are given why it is desirable to revise some of our older laws regarding electromagnetic forces and motions which are the basis of all electromotive devices, in order to conform better to more modern developments. Researches with high-current densities in such mobile conductors as liquids and arcs, have brought out some heretofore unnoticed forces, the existence of some of which had been denied. Some of our older laws are claimed to mislead, to be inaccurate, incomplete, to involve unnecessary complications such as the forced definitions of a sliding contact, are based on the wrong fundamentals, specify results contrary to the facts, and are not universal, thereby checking possible progress if accepted as universal. A new and simple general law is proposed, based on one of the fundamental universal laws of physics. It is shown how this might also be made the basis of a much desired universal law of induction. It leads to the existence of a force longitudinal to the conductor, which our older laws deny. Numerous experiments are described illustrating and bearing out the arguments. Suggestions are made showing how the laws and the present usual methods of mathematical treatment of such forces might be revised in order to make them more satisfactory, easier for the student to understand, and for the engineer to use. If the alleged improper restrictions imposed by former laws are removed, developments in new fields may become possible. In conclusion a tentative plan for revision is suggested.
TL;DR: In this paper, the authors describe methods by which base metals may be sealed to and through glass, even though the metal and glass have different coefficients of thermal expansion, by providing a large surface of contact between the glass and the metal, and in so proportioning the metal that the stresses resulting from the difference in coefficients of expansion are less than the ultimate strength of the joint between glass and metal.
Abstract: Methods are described by which base metals may be sealed to and through glass, even though the metal and glass have different coefficients of thermal expansion. The method consists in providing a large surface of contact between the glass and the metal, and in so proportioning the metal that the stresses resulting from the difference in coefficients of expansion are less than the ultimate strength of the joint between glass and metal. Four different types of seals are discussed: First, the flattened wire seal for small electrical conductors. Second, the ribbon seal for special purposes. Third, the disk seal for commercial manufacture of seals for carrying currents of the order of 100 amperes. Fourth, the tube seal in which metal and glass tubing are joined together.
TL;DR: In this paper, Dreyfus et al. used the vector method for determining transients in rotating electric machines and applied it to fixed combinations of resistances, inductances, and capacitances by Kennelly and others.
Abstract: The vector method is just as useful in solving problems involving transient conditions in electric circuits as it has proved to be when the currents and potentials are steady sinusoids. As far as the writer is aware, the vector method for determining transients in rotating electric machines was first used by L. Dreyfus. Previously the method had been applied to fixed combinations of resistances, inductances and capacitances by Kennelly and others. By making certain assumptions that are, however, quite reasonable in many cases, the transient currents in nearly all of the common types of electric machinery are damped sinusoids. Fortunately the damping is exponential and is thus readily accounted for. It is interesting to trace the development of the method. In the solution of all problems in direct currents the potentials, currents, and circuit constants are real numbers. In the corresponding problem in which the applied potentials are steady sinusoids, these quantities are all represented by complex numbers. In all other respects the working out of the solution is identical with that followed in the direct-current case. When the currents are damped sinusoids, they and the potentials and the circuit constants can still be represented by complex numbers. There is this difference, however; the vectors which represent the currents and potentials shrink exponentially as they rotate and the values of the circuit constants depend not only upon the frequency of the current, but also upon its rate of shrinking. Again the solution of any problem follows the same procedure that would the corresponding one in which the currents are steady sinusoids. In both the steady and damped sinusoidal cases the circuit constants depend upon the angular velocity of the vectors which represent the currents. In the former, the angular velocity is purely imaginary while in the latter it is complex, the real part being the rate at which the current vector shrinks and the imaginary portion, its angular velocity. In electric machinery in which rotating magnetic fields are produced, these fields shrink exponontially as they rotate when the currents are damped sinusoids. If these rotating magnetic fields are represented by vectors, the vectors will have a complex angular velocity just as do the currents. The e. m. f. which is produced by a steady sinusoidal variation of flux lags the flux by 90 degrees, whereas if the flux variation is a damped sinusoid, the angle of lag is less than 90 degrees, depending upon the damping. The mathematical relation, however, is the same, vis., the e. m. f. is proportional to the negative of the product of the flux and its angular velocity. It is then readily appreciated that the form of the solution for the transient state is the same as that which is used for the steady state. Before the method can be expected to give as accurate results as are obtained when predicting the steady operation, considerable experimental data must be obtained in order to determine the best methods of measuring the necessary constants, for these may be somewhat different during the transient period than during steady operation.
TL;DR: In this article, the authors present the problems encountered in the development of electrical systems for amplifying the voices of public speakers and music; and describe the equipment as brought to a commercial state and now in use in the United States and various other countries.
Abstract: THIS paper aims to present the problems encountered in the development of electrical systems for amplifying the voices of public speakers and music; and to describe the equipment as brought to a commercial state and now in use in the United States and various other countries.
TL;DR: In this article, a regenerative system consisting of a 100-cycle tuning fork, of low decrement, maintained in vibration by a vacuum tube amplifier is described, and the absolute value of the frequency of the alternating current delivered by this generator is determined by counting the number of cycles executed in an accurately known time.
Abstract: The need for increased accuracy in the measurement of any frequency between one and several million cycles per second is first considered. A brief discussion of general types of frequency standards leads to the reasons for choosing a continuously operating generator of alternating current. The generator developed is, in effect, a regenerative system comprising a 100-cycle tuning fork, of low decrement, maintained in vibration by a vacuum tube amplifier. The absolute value of the frequency of the alternating current delivered by this generator is determined by counting the number of cycles executed in an accurately known time. A small synchronous motor is used for making this count. Recording apparatus for comparing the rate of the fork with various time indicators is described. Data are given showing the effect upon the frequency of such external conditions as temperature, potential of power supply, circuit constants of the amplifier and vacuum tubes. This information is obtained either by comparisons with a constant frequency or by determinations of the absolute value of the frequency. The ratio of the rate of the fork to the rate of a carefully maintained clock has been found to be constant to within six parts in 1,000,000 over considerable periods of time. For measuring the frequency of any alternating current used in electrical communication in terms of the known frequency there has been developed a decade arrangement of harmonic producers and a special modulator-rectifier circuit for combining known harmonics of the base and comparing other frequencies with them.
TL;DR: In this paper, a discussion of general considerations of neutral grounding is divided into two parts, that of overhead line systems and underground cable systems, and the general conclusion is that, on either overhead or underground transmission systems, high-voltage strains are more to be feared than high-current strains and that resistance to limit ground current, if used at all, should be of very low value.
Abstract: In the early days of power transmission, there was no consistent practise in respect to operating with neutral isolated or with neutral grounded. The rapid growth of transmission systems with their extensive networks soon began to show disastrous results from arcing grounds on isolated neutral systems and now most power transmissson networks have their neutrals grounded in some manner. The discussion of general considerations of neutral grounding is divided into two parts, that of overhead line systems and underground cable systems. He brings out the fact that while most overhead systems are grounded there is some difference in practise as to the extent to which they are grounded, that is as to whether they are grounded solidly or through resistance. Prevailing practise tends toward little or no resistance. Attention is called to different possible methods of grounding a system and shows by diagrams the flow of short-circuit current with the different methods. Underground cable systems are consistently operated with neutral grounded but general practise tends toward the use of resistance in neutral. General considerations as to protection from the voltage strains due to arcing grounds on cable systems are similar to overhead line systems and the author analyzes briefly the character of cable breakdowns and general effect of such breakdowns with a view to determining the importance of the extent to which a cable system should be grounded. The conclusion in regard to cable systems indicates about the same limitations as those found for overhead systems and no very good reasons are found for a distinctive difference in practise. The paper considers the use of grounding resistors of different types and gives some cast figures to show the effect of time and current in the design of metallic resistors. The general conclusion arrived at is that, on either overhead or underground transmission systems, high-voltage strains are more to be feared than high-current strains and that resistance to limit ground current, if used at all, should be of very low value.
TL;DR: In this paper, the Petersen Earth Coil was installed between the neutral and ground of a 120-mile, 44,000-volt, 3-phase, star-connected, 60-cycle system.
Abstract: This paper is a report on the Alabama Power Company's operating experience with a Petersen Earth Coil installed between the neutral and ground of a 120-mile, 44,000-volt, 3-phase, star-connected, 60-cycle system. A Petersen coil is essentially an inductive reactance of such value as to maintain resonance with the capacitance of the system to ground at the fundamental system frequency. With a ground on one wire the current through the fault is reduced to such a low value as to prevent maintenance of an arc. Therefore, on the assumption that the majority of phase-to-ground short circuits start as insulator flashovers, the installation of such a device as a Petersen coil which would snuff out flashover arcs should considerably reduce the number of interruptions to the line. By means of proper relaying, cases of trouble outside of the operating sphere of the Petersen coil, such as phase-to-phase short circuits and solid grounds have also been successfully taken care of. Previous to the installation of this coil numerous interruptions to service were experienced on this system during lightning storms, which are unusually severe in the territory covered by these lines. This system, therefore, offers an ideal location for a trial installation of the coil. Since the installation of the coil the number and duration of interruptions due to lightning flashovers have been reduced by 88.5 per cent and 94 per cent respectively. Several doubtful actions, however, have occurred during switching operations, indicating the presence of unusual phenomena. By proper relaying it is hoped to prevent the recurrence of such action. Further tests are also contemplated to investigate the unusual phenomena accompanying certain operating conditions.
TL;DR: In this article, the relative phases of short-circuit currents and voltages at different points of the system during short circuits are calculated using a-c. test and d-c test.
Abstract: No means has yet been discovered whereby the abnormal rise of current occurring during short circuits is avoided. Protection against its destructive effects remains, therefore, a subject of major importance. Among the problems requiring short-circuit current determinations, the following are the chief ones: (1) Selection of oil circuit breakers of the required interrupting capacity. (2). Determination of the size of current-limiting reactors. (3) Determination of relay settings in relay systems depending on selective action from over-current and directional relays. (4) Calculation of mechanical stresses in the structural elements of apparatus subject to short-circuit electromagnetic forces. Each of these problems requires the knowledge of the magnitude of short-circuit currents; relay problems frequently require, in addition, the relative phases of currents and voltages at different points of the system during short circuits; in item (4) above the wave-form of the short-circuit current sometimes has to be considered. The available information on the latter subjects, i. e. on phase relations and on wave form during short circuits is relatively meager, probably because it has been required in special cases only. Nevertheless, the demands for these data are increasing — on account of both the tendency towards increased sensitiveness of protective devices and the rapid increase in the magnitude of the short-circuit currents to be handled — and it will be worth while, therefore, if this added information is obtained. This paper is confined to the problems of the determination of the magnitude of short-circuit currents. The magnitude of short-circuit currents depends on a multiplicity of factors which have been enumerated and dealt with in other publications.1 When the impedances of all the circuit elements affected by the short-circuit are known together with the current-time decrement characteristics of all machinery capable of supplying current to the short circuit,2 the problem of short-circuit-current determination resolves itself into one of current division in a given network of electrical conductors under given electromotive forces. In the following paper, the comparative merits of three methods — calculation, a-c. test, and d-c. test — of determining short-circuit currents in networks are briefly discussed. Two d-c. experimental methods applicable to the “short-circuit calculating table” are analyzed in detail. The accuracy of its results, by both methods, is obtained for a variety of circuit conditions. The proper field of use of the short-circuit calculating table, and the best method of its application are determined.
TL;DR: A neutral grounding reactor (Petersen Coil) has been in operation on the system of the Alabama Power Company since October 12, 1921 as mentioned in this paper, which is the first of these devices in this country, although there are perhaps several hundred of them in operation in Europe.
Abstract: A neutral grounding reactor (Petersen Coil) has been in operation on the system of the Alabama Power Company since October 12, 1921. This is the first of these devices in this country, although there are perhaps several hundred of them in operation in Europe. The present paper discusses the tests made shortly after installation of this reactor. A companion paper by Messrs. J. M. Oliver and W. W. Eberhardt, discusses the operation of the reactor for a period of about a year. It is believed that this device has a somewhat limited use in this country on account of the prevalence and popularity of the solidly grounded neutral. Nevertheless, there are certain installations favorable to the use of the reactor and it is partly the purpose of the present paper to outline the field of this device as well as to show how its rating may be determined for a particular system.
TL;DR: In this article, the authors present a three-phase miniature a-c circuit for the analysis of power transmission systems, which includes synchronous machines, transformers, adjustable resistors, reactors, and condensers.
Abstract: The use of so-called “artificial lines” — i.e. miniature models of electric circuits — for experimental laboratory studies of transmission-line phenomena is well known. The miniature models are commonly made so as to represent, in true proportion, the electrical constants of a real line. Thus there are artificial telephone lines, artificial submarine cables, artificial long-distance power-transmission lines, etc. A miniature line is a true model of a real line to the extent that the miniature circuit has, for any desired degree of approximation, the same electrical behavior as the full-size circuit. Such laboratory models frequently permit — far more conveniently than the full-size circuit — the study of actual circuit phenomena in a practical and efficient manner. When their limitations are properly understood, miniature circuits may be of great value to transmission-line and operating engineers. Miniature electric circuits may for the present purpose be divided into two general classes: (1) Miniature circuits intended for the study of problems on long lines, such as lines having continuously distributed circuit constants. (2) Miniature circuits for the solution of problems involving complete system networks, inclusive of generating-station and substation apparatus. The following paper deals with a three-phase miniature a-c. system of the network type. The circuit includes synchronous machines, transformers, adjustable resistors, reactors, and condensers, for complete representation of generating stations, substations, lines and loads. The circuit connections are variable, so that any system having not more than the available number of circuit elements may be represented for the correct experimental solution of low-frequency problems. This miniature system has so far given about three years of service in the experimental analysis of transmission system behavior, for existing systems and for systems to be constructed. The problems solved have been within the realms of both the designing and the operating engineers, and have been applied to power systems in this country as well as abroad. One of the by-products of the miniature system is the confirmation and extension of the theory of transmission-line phenomena. Several prominent engineers have expressed the belief, and made the prediction, that after a few years of proper use of the miniature system, the theory and calculation of the present transmission problems will have been so well established that experimental solutions will no longer be necessary. In this paper are given (1) a brief discussion of some of the present problems calling for solutions by the miniature experimental method, (2) a full description of the miniature equipment, (3) an outline of the operating procedure in the solution of problems, and (4) an example illustrating the application of the miniature equipment.
TL;DR: In this paper, the similarities and contrasts of power transmission and telephone phone transmission over long distances are pointed out, and the problems of telephone transmission on open-wire lines are illustrated by a discussion of the methods by which the overall efficiency of the transcontinental telephone circuit has been greatly improved.
Abstract: In this paper are pointed out some of the similarities and contrasts of power transmission and telephone phone transmission over long distances. The problems of telephone transmission on open-wire lines are illustrated by a discussion of the methods by which the over-all efficiency of the transcontinental telephone circuit has been greatly improved. A brief discussion is given of recent important developments in telephone transmission through cables over long distances. An outline is given of the results obtained in the commercial application of carrier telephone and telegraph systems. Finally, a demonstration talk between Havana, Cuba, and Avalon on Catalina Island off the Pacific coast, is described as an illustration of what can be done with the commercial telephone system in its present stage of development.
TL;DR: In this article, a series of tests on a number of 6600-voltage mica folium armature bars made up with different degrees of mica content was described and the variations of the dielectric losses with voltage and with temperature were studied.
Abstract: It has been suggested frequently that the failure of high-voltage armature bars might be due to deterioration caused by gaseous ionization in entrapped air spaces. In an earlier paper a series of tests on a number of 6600-voltage mica folium armature bars made up with different degrees of mica content was described. The variations of the dielectric losses with voltage and with temperature were studied and by means of the application of pressure it was shown to what extent losses due to internal ionization were present. The influence of these ionization losses on the life of the bars was also studied. The tests of the foregoing paper are continued in the present paper, extending to a wider range of type of armature insulation. The general results are as follows: 1. The absolute values of loss due to internal ionization in well constructed armature bars are small compared with dielectric losses of other types. 2. The losses due to internal ionization do, however, cause a progressive deterioration of the insulation. This is shown by a gradual increase in the loss and power factor of the insulation. S. It is indicated that the principal function of mica in this type of insulation is in the reduction of the conductivity of the insulation and the withstanding of the action of internal ionization. The indications are that full mica folium content can be safely reduced only by use of the best grade of mica folium and the best conditions of application without variation.
TL;DR: In this paper, the authors pointed out that the existing methods of measuring power when applied to unbalanced three-phase systems are not equitable for symmetrical polyphase machinery and proposed a method to measure the positive phase sequence power output and charge the user for the amount of unbalance.
Abstract: The object of this paper is to point out that the existing methods of measuring power when applied to unbalanced three-phase systems are not equitable for symmetrical polyphase machinery. On the other hand, unsymmetrical loads on polyphase systems are not sufficiently penalized for the trouble which they create in the system. It is first of all shown that a symmetrical generator cannot deliver power except through the balanced components of current. The unbalanced currents are capable of resolution into two balanced systems of currents, one of which is of the same phase sequence as the generator e. m. f., and the other component is of reversed or negative phase sequence. The generator cannot deliver power through the medium of this latter component of the currents, because the instantaneous product of the generated voltage and these currents in the three phases is always zero. However, the volt-ampere product per phase is of great significance, because it is a measure of the effect of the current unbalance on the system. The generator therefore delivers power only through the medium of the positive phase sequence currents. Any power that appears in the system through the negative phase sequence currents is positive phase sequence power which has been supplied by the generator and degraded through unbalanced loads and fed back to the system in the form of negative phase sequence power. This power is always additional loss in all rotating machines on the system, and with the present method of charging, the consumer having symmetrical machines is charged with this additional power, which serves him no useful purpose but reduces the output of his machine and decreases his load power factor. In the paper it is proposed that the positive phase sequence power output only be measured, and the power charges be made on the basis of this measurement. It is further proposed that the unbalanced k-va., which is the product of the positive sequence voltage and the negative sequence current be measured either by means of a negative sequence ammeter, indicating or recording, or a k-va. meter, and a charge made for the amount of unbalance. The user of symmetrical polyphase rotating machinery should then be given a lower rate, based on the estimated cost of unbalance, and the consumer having unbalanced loads should be charged directly for the amount of unbalance he creates, or else should have his positive phase sequence power rate increased, based upon the estimated cost of unbalance. It is pointed out that the unbalanced kv-a. is a factor of the same order of importance as reactive kv-a. and in any system subject to unbalanced conditions this factor should be considered and the unbalanced factor, as well as the power factor, should be measured. The unbalanced factor is the ratio of the negative phase sequence kv-a. and the positive phase sequence kv-a., the former being obtained by taking the product of the positive phase sequence voltage and the negative phase sequence current. Devices for measuring these quantities are being developed and the outfit for making these measurements will be no more complicated than the present existing measurement devices. In fact the tendency is towards greater simplicity. In presenting this subject the author has no intention of suggesting how rates should be made, but merely wishes to point out what factors enter into the question of equitable rates when the polyphase system is subject to unbalance.
TL;DR: In this paper, the dielectric strength ratio of liquid and non-homogeneous insulations of homogeneous and nonhomogeneous structure was determined and compared with direct and alternating voltages over a range of temperature, thickness and rate of voltage application.
Abstract: High-Voltage insulation testing has been and is usually still done by alternating voltages. High direct voltage was made available for testing purposes by the development of the kenotron tube. When used for testing insulation direct voltage has several advantages over alternating voltage. (1) the power necessary is often much less with direct voltage than with alternating voltage. In apparatus of high electrostatic capacity, such as long high-voltage cables, the size of the alternating-voltage testing transformer becomes excessive, thousands of kilovolt-amperes being necessary. Direct voltages are therefore preferable as they necessitate only a few kilowatts. (2) Excess direct voltage is less likely to permanently damage the insulation than excess alternating voltage. (3) If direct voltage is used conductivity tests can be made and the action of the material on the application of the voltage more thoroughly studied. As the use of high direct voltage for testing purposes is found to be increasing, it is important to determine the relation between the insulation stress produced by direct and that produced by alternating voltages. Little is definitely known of what is called the “dielectric strength ratio of insulation” which is the ratio of the direct disruptive voltage to the crest value of the alternating disruptive voltage. In general, this ratio might be expected to be unity. While such is the case with air some engineers have claimed, however, that some solid insulations stand a higher direct than alternating voltage. Therefore, a very extensive set of investigations was made, with direct and with alternating voltages, on liquid and solid insulations of homogeneous and non-homogeneous structure, over a range of temperature, thickness and rate of voltage application. Their dielectric strength ratios were determined and are given and discussed in the paper. It was found that the dielectric strength ratio may be greater than unity, and sometimes very much so, that is, that the material may stand higher and sometimes very much higher direct voltages than alternating voltages, but also that the ratio with other materials may be less than unity, that is, the material may stand higher alternating than direct voltages. Ratios less than unity were given by oils, petrolatum, powdered glass, etc., that is, they stood higher alternating than direct voltage, though the difference rarely exceeded 10 per cent. Ratios above unity were given by paper, cloth, solid glass and mica, etc., indicating a greater strength for direct than for alternating voltages. The dielectric strength ratio of some materials, such as laminated paper, was found to vary with the condition and in general increase with decreasing temperature, decreasing thickness and increasing rapidity of voltage application. Some materials, such as petrolatum impregnated cable paper, gave a very high ratio, some times exceeding two, while the component materials did not differ much from unity, petrolatum being a little below and air-dry paper a little above unity. It is believed that the observation of the dielectric strength ratio and its changes with the condition of test, will give us a powerful tool for the investigation of insulation, and assist in solving the problem of understanding the mechanism of the breakdown of insulation in an electric field.
TL;DR: A new relay for automatically sectionalizing transmission lines, similar to existing relays in many respects, but equipped with ``brains'' so that it can determine the location of the trouble and govern its operation accordingly.
Abstract: This paper describes a new relay for automatically sectionalizing transmission lines, similar to existing relays in many respects, but equipped with ``brains'' so that it can determine the location of the trouble and govern its operation accordingly. For dead short circuit its time of operation is proportional to the distance from the short circuit so that when it is used the circuit breaker nearest to the trouble always trips out first. When applied to any system it is adjusted to fit the particular length of line which it controls and no change in this setting need ever be made due to operating conditions on the remainder of the system. Its discrimination is obtained by a time limit which varies directly as the voltage and inversely as the current existing during the trouble. It has the incidental advantage that since the circit breaker nearest to the trouble is opened first, the final breaker to open is the one having the longer section of line in series with it to limit the current and therefore decrease the duty required of the circuit breaker.
TL;DR: In this paper, it was shown that a third-class conductor can be considered as a combination of a negative resistance with a source of power, and as such is capable of transforming the low machine frequency into a high oscillation frequency of alternating currents, and their presence in an electric system thereby may produce cumulative oscillations.
Abstract: In high-voltage power circuits, such as transmission lines and the high-voltage coils of large power transformers, not infrequently disturbances are observed of a frequency differing from, and usually very much higher than that of the power supply, and differing from the typical transient of energy readjustment, in that they do not gradually die out, but increase in intensity until either destruction occurs, or they finally limit themselves. Such cumulative oscillations or arcing grounds derive their energy from the machine power of the system, and so constitute a frequency transformation, of which the mechanism has been little understood. Physically they may be derived from the typical condenser discharge by the conception of a negative resistance, in combination with a source of power, which supplies the energy given out by the negative resistance. Attention is drawn to a class of conductors — to which arcs and gas discharges belong — the so-called “third-class conductors,” in which the voltage decreases with increase of current, and it is shown that these conductors can be considered as a combination of a negative resistance with a source of power, and as such are capable of transforming the low machine frequency into a high oscillation frequency of alternating currents, and their presence in an electric system thereby may produce cumulative oscillations. The general equations are then derived of a system comprising a third-class conductor shunted by an inductive circuit containing capacity, and supplied with voltage over an inductive circuit from an alternating low-frequency source, and it is shown that in such a system currents and voltages of two distinct frequencies may continuously exist, of which the one is the machine frequency, the other a high oscillation frequency. It is further shown that the voltage of the latter is limited only by the resistance of the oscillating circuit, and in low-resistance circuits may build up to very high values. Furthermore, the high oscillation frequency is essentially limited to the circuit shunting the third-class conductor and but little of it enters the supply circuit, while the supply frequency enters the shunt circuit to a limited extent only, and both frequencies are superimposed in the third-class conductor as the frequency converter.
TL;DR: The problem of operating many of the present day transformers designed and built to function in sizes and under conditions unheard of only a few years ago, is now of prime importance to the larger power companies.
Abstract: The problem of operating many of the present day transformers designed and built to function in sizes and under conditions unheard of only a few years ago, is now of prime importance to many of the larger power companies. A statement of one type of the operating troubles encountered in the larger sizes is discussed in this paper and data taken as far as practicable under operating conditions is given. From experience so far gained it is thought that both the autotransformer and the grounded neutral system are here to stay and such problems as they present merit considerable investigation under actual working conditions. The present paper presents rather than solves one type of trouble encountered.
TL;DR: In this paper, a theoretical analysis of the problem is given, and it is shown that if any motion is permitted, thus allowing the factors of mass and resilience to become active, then the maximum stress may be significantly increased above that for no motion.
Abstract: The mechanical stress in the supporting members of any structure or apparatus under steady state is determined by the dimensions of the member and the magnitude of the resultant applied force. Under accelerated motion, however, an additional factor enters, namely, the reaction of the mass; and if the supporting members in this case are resilient, thta is, spring-like, then this becomes still another factor which enters the problem of determining the mechanical stress produccd by a given impressed force. The determination of the stress in the holding device (bolts, etc.) of reactors under short-circuit condition is just such a problem. If any motion whatever is permitted under this condition, the factors of mass and resilience are active. This paper gives a theoretical analysis of the problem, and shows that if any motion is permitted, thus allowing the factors of mass and resilience to become active, then the maximum stress may be significantly increased above that for no motion. Illustrative calculations lations show that this increase in practical cases my be of the order of 25 per cent. On the other hand, if motion of the reactors is prevented by sufficient initial bolt tension, or otherwise, then the maximum stress in the holding device obviously need be only as great as that corresponding to the maximum instantaneous peak of the electromagnetic force.