Showing papers in "Transactions of The American Institute of Electrical Engineers in 1915"
TL;DR: In this paper, a series of tests on the impedance of long loops of parallel conductors of different metals, sizes, and cross-sectional forms are presented. But the results of these tests are given of about one hundred series, each covering a range in frequency up to about 5000 cycles per second.
Abstract: The results are given of about one hundred series of tests, each covering a range in frequency up to about 5000 cycles per second, on the impedance of long loops of parallel con-ductors of different metals, sizes, and cross-sectional forms. The measuring apparatus is detailed. The theory of the skin effect in solid rods and in indefinitely wide flat strips is appended in a new and simplified form.
82 citations
53 citations
TL;DR: In this article, an impulse generator from which impulse voltages of any given wave front, length of tail, etc., can be obtained is described. And the strength of air between spheres and needles for impulses of different front, the time in micro-seconds and the voltage required to rupture air between balls and needles on the front of waves rising at various rates.
Abstract: In practise, failures of dielectrics are generally caused by transient voltages. It is, therefore, of great practical importance to determine the various phenomena affecting the strength of dielectrics and means of protecting them when they are subjected to known transient voltages. An impulse generator from which impulse voltages of any given wave front, length of tail, etc., can be obtained is described. Energy is required to rupture gaseous, liquid and solid dielectrics; this introduces a time element. Thus, on account of this time lag, when voltage is applied at a very rapid rate, as by an impulse, spark-over does not occur when the continuously applied breakdown voltage is reached. The voltage ``over-shoots'' or rises above this value during the time rupture is taking place. This excess, or rise, in voltage above the continuously applied breakdown value is greater the greater the rate of application. The time depends upon the nature of the dielectric, the dielectric field, the shape and spacing of the electrodes, initial ionization, etc. The strength of air between spheres and needles for impulses of different front, length of tail, etc., is given, as well as the time in micro-seconds and the voltage required to rupture air between spheres and needles on the front of waves rising at various rates. Transient spark-over and corona voltages for wires, surface spark-over, insulator spark-over, effects of polarity, air density, practical application, etc., are given. Transient spark-over voltage and time are recorded for oil, and various solid dielectrics.
35 citations
TL;DR: In this article, the authors give results and analyses of tests to determine losses in hysteresis loops wherein the magnetism is carried through cycles in which limiting values of flux are different in amount or the mean values of the flux differ from zero.
Abstract: The paper gives results and analyses of tests to determine losses in hysteresis loops wherein the magnetism is carried through cycles in which limiting values of flux are different in amount or the mean values of flux differ from zero. Such variations of magnetism occur in inductor generators, in teeth of induction machines and in materials magnetized from rectifier circuits, etc. The author finds that: 1. The losses in unsymmetrical loops are greater than in symmetrical loops of the same difference of limiting values of flux. 2. For loops of the same difference of limiting values of flux, the losses increase as a definite power of the mean flux density. 3. The increased loss as a power of the mean density is the same for any range of loops or difference of limiting flux values. 4. With any given value of mean density, the increased loss with increased range increases as a definite power of the range, irrespective of the mean value of density selected. The author covers these points in an equation to express the loss in any loop. The general equation is: h = (n + ? Bmy) Bx wherein n and x are the constants of the Steinmetz law, ? is a coefficient depending upon the material, and y a power of the mean density. The present tests satisfied the equation in the form: h = (n + ? Bm1.9) B1.6
25 citations
TL;DR: In this paper, the idea of magnetic reluctance is discussed and the mathematical and experimental methods of determining it are first discussed, and the results of the tests are proved to be more accurate than most of those already published.
Abstract: The development of the idea of magnetic reluctance is sketched, and the mathematical and experimental methods of determining it are first discussed. On the theoretical side it is the theory of complex quantities which leads to numerical results. The electric field of an electric generator is next analyzed and made to depend approximately upon the reluctance of two-dimensional magnetic fields. This study indicates as preferable the one shown in Fig. 6 at the left. The reluctance of these various magnetic fields is determined by experiments made on sheets of high-resistance metal cut in suitable forms, and by mathematical computation. These results are put into charts and formulas convenient for the use of those interested in electrical design. The results of the tests are proved to be more accurate than most of those already published. In particular, present leakage flux calculations are most in error. Of more general interest are the plates of the shape of the magnetic lines of force in the various parts of electrical machinery. In particular, Figs. 42 to 48 include some new results. The flux lines in the corners of transformers and induction motors are there shown, and the exact solution to the much-discussed sine-wave alternator problem is there given. The paper is divided into (I) Introduction, (II) Historical Development, (III) Description of Experiments, (IV) Accuracy of Results, (V) Conclusions. There are two appendices giving some mathematical details, for reference purposes.
21 citations
TL;DR: In this article, the electrical behavior of transformer windings when subjected to steep wave fronts and high-frequency wave trains is discussed, and the dependence of the internal voltages produced, upon the distribution of capacity with the inductance of the winding, is discussed.
Abstract: This paper deals with the electrical behavior of transformer windings when subjected to steep wave fronts and high-frequency wave trains. The dependence of the internal voltages produced, upon the distribution of capacity with the inductance of the winding, is discussed. Practical windings are divided into two general classes, one in which inductance and capacity are practically uniformly distributed, and the other in which the capacity is more or less concentrated at certain points, with relatively concentrated portions of inductance intervening. Neglecting the effects of the high-frequency dielectric losses in the insulation at high frequency, distinct mathematical analysis is given to these two classes of winding to determine the ratios of the internal voltages to the voltage of the external wave or wave train. The resulting internal voltage distributions are plotted for various frequencies, and curves are plotted for the relations of maximum internal voltages to frequency. These curves show that some frequencies are dangerous, while others are not, but it can not be said that one of these types of winding is better than the other from the standpoint of the possibility of excessive internal voltages. The analysis is by no means complete, but an examination is made of the facts and fundamental principles involved which will enable us to insulate for and guard against excessive internal voltages in a more scientific manner.
19 citations
TL;DR: In this article, the authors described results obtained from tests made on pure iron melted in vacuo, to obtain data as to its magnetic and allied properties, and the two best alloys were obtained with about 0.15 per cent and 3.40 per cent silicon, after annealing at 1100 deg.
Abstract: In a paper presented before the Urbana Section, April 16, 1914, the author described results obtained from tests made on pure iron melted in vacuo, to obtain data as to its magnetic and allied properties. The present paper describes further experiments on various alloys of the electrolytic iron melted in vacuo with other elements. The author deals briefly with the iron-boron and iron-carbon alloys, and presents results obtained with the iron-cobalt alloy Fe2Co, but gives in greater detail the data in regard to iron-silicon alloys, from which the most remarkable results were obtained. The two best alloys were obtained with about 0.15 per cent and 3.40 per cent silicon, after annealing at 1100 deg. cent. The values of maximum permeability for both of these alloys are above 50,000, and the values of hysteresis loss for Bmax = 10,000 and 15,000 are about 300 and 1000 ergs per cu. cm. per cycle, respectively. This hysteresis loss is 1/8 and 1/3 of the corresponding loss for commercial silicon steel. While both alloys have similar magnetic properties, the 3.40 per cent silicon alloy has a specific electrical resistance nearly five times that of the 0.15 per cent alloy, making it particularly desirable for use in electromagnetic machinery in places where a low eddy-current loss is a requirement, in addition to high permeability and low hysteresis loss.
18 citations
TL;DR: In this paper, a series of displaced hysteresis loops were investigated to determine the magnitude and, if possible, some of the laws governing the change in hystresis loss due to displacing a loop from its symmetrical position.
Abstract: Most modern revolving electrical apparatus has teeth on the rotor or stator, or both, which are subjected to constantly varying reluctance. This variation of reluctance causes high-frequency changes of flux superimposed on the working flux. The result is a series of displaced hysteresis loops. This investigation was undertaken to determine the magnitude and, if possible, some of the laws governing the change in hysteresis loss due to displacing a loop from its symmetrical position. An account is given of some early tests which, within the limits of induction studied, resulted in certain definite conclusions. It is pointed out that the data from these displaced hysteresis loops limit the applicability of the Steinmetz hysteresis formula to symmetrical loops. Recent tests are then described, giving the details of a new apparatus for obtaining hysteresis loops and showing an improved method of making displaced a-c. watt-loss tests. Numerous loops and curves are included, showing the effect of displacement on the shape and area of the hysteresis loop. No definite laws could be formulated from the data, but some general conclusions are given.
15 citations
TL;DR: In this article, the cause and effects of higher harmonic currents in magnetizing currents of transformers were analyzed and the schemes of connecting transformers that are commonly used for polyphase transformation were taken up and the effects of the harmonics on each case pointed out.
Abstract: The purpose of this paper is to show in a concise manner the cause and effects of higher harmonic currents in magnetizing currents of transformers. A hypothetical case is analyzed to show the cause of the harmonics; then the schemes of connecting transformers that are commonly used for polyphase transformation are taken up and the effects of the harmonics on each case pointed out. The author also shows the reason why third-harmonic voltages are not developed in the three-phase ``core type'' transformer when connected star-star.
11 citations
TL;DR: In this article, the effect of the line is to reduce the third harmonic voltage between neutral and line terminals of a star-star connected bank of transformers having grounded neutral on the line side only, and the interrelation of line susceptance from conductor to ground in series with the varying susceptance of the individual transformers may cause the total m. m. f. of one of the transformers to pass through zero at the same instant as the impressed e. f., and thus, give opportunity for a reversal of this transformer due to inertia.
Abstract: 1. Hysteresis, as well as variation of permeability, gives rise to harmonics of considerable magnitude in the exciting current of a transformer; the components from the two sources are in quadrature for each harmonic. 2. There is a fallacy in the idea that the harmonics in the exciting current of a transformer are entirely wattless. 3. For transmission lines of modern lengths, the effect of the line is to reduce the third harmonic voltage between neutral and line terminals of a star-star connected bank of transformers having grounded neutral on the line side only. 4. In transmission with star-star transformer banks having grounded neutral on the line side only, the inter-relation of line susceptance from conductor to ground in series with the varying susceptance of the individual transformers may cause the total m. m. f. of one of the transformers to pass through zero at the same instant as the impressed e. m. f.; and thus, give opportunity for a reversal of this transformer due to inertia, thereby producing a periodically reversing leg and abnormal voltages. 5. In a similar system with high quality line insulation, the effect of atmospheric charges on the line conductors may be to cause the transformers of the bank to assume relations with one leg permanently reversed when energized from the station side; thus, imposing unbalanced voltage conditions on the bank and producing, in two of the units, fundamental frequency components of voltage 264 per cent of normal. 6.
10 citations
TL;DR: In this paper, a new method of measuring power factor and volt-amperes is disclosed, and a method of recognizing power factor in the rate for electric service is discussed.
Abstract: The necessity of recognizing load factor in rate schedules is emphasized. To obtain load factor necessitates the measurement of maximum demand; a new maximum demand meter is described which depends upon heat and heat storage. The theory of such meters is discussed. A new method of measuring power factor and volt-amperes is disclosed and a method of recognizing power factor in the rate for electric service is discussed.
TL;DR: The theory and explanation of the electromagnetic phenomena involved in the sudden sbort circuit of alternators, as given by Berg and Boucherot, is first briefly considered in this article.
Abstract: The theory and explanation of the electromagnetic phenomena involved in the sudden sbort circuit of alternators, as given by Berg and Boucherot, is first briefly considered. It is shown how complex the different resistances and reactances are that enter the equations of sudden short circuits. New methods are developed for the experimental determination of these quantities by simply determining the rise of direct current in the field and armature circuits. (See II) Also new simple methods are given, based on theoretical equations, for the calculation of short circuits directly from oscillographic records. (See IV). Data relating to the short circuit of a 45-kv-a. alternator are given; also an electrical device, designed by the writer and used in most of the tests, for short-circuiting a machine at any given point of the e.m.f. wave, is described. (See III). As a whole, an attempt is made throughout the paper to put calculations of sudden short circuits on a sound rational basis and to test the correctness of the theories given. The paper is divided into the following self-explanatory sections: I?General theory and explat4ation of the electromagnetic phenomena of sudden short circuits of alternators. II?Experimental methods for the determination of alternator constants. III?Sudden short-circuit tests. Three-phase, single-phase, etc. IV?Methods of calculation. V?Determination of armature reactance (impedance). VI?Effect on supply. VII?Critical resume and some conclusions. VIII?Discription of apparatus and list of symbols.
TL;DR: In this article, the theoretical transmission equations for both continuous and damped waves are discussed and the empirical formulas for the latter are given, and an empirical formula for the calculation of probable sending radius with such waves is proposed.
Abstract: Ability to predetermine the probable normal daylight sending radius of high-powered radiotelegraphic stati ons is of prime importance in their design. The theoretical transmission equations for both continuous and damped waves are discussed and the empirical formulas for the latter are given. Experiments with continuous waves over a period of six months between San Francisco and Honolulu, a distance of 2100 nautical miles (3880 km.), are described, and an empirical formula for the calculation of probable sending radius with such waves is proposed. This is checked by experiments between Tuckerton, N. J., and Honolulu, 4330 nautical miles (8000 km.). Curves giving the energy received at Honolulu from San Francisco under both day and night conditions are shown, and the effects of changes in wave length upon transmission efficiency are discussed. Evidence strengthening theories of the reflection, refraction and interference of Hertzian waves in long-distance transmissions, and experimental data showing interference bands not over 18 miles in width, are given. The great value of easy and rapid changes in wave length, especially at night, is apparent from the curves. Final conclusions drawn from a comparison of the empirical transmission formulas for continuous and for damped waves are that the transmission efficiency of continuous waves is somewhat higher than that of damped waves on wave lengths of approximately 3000 m. or above, and that this advantage increases with the wave length.
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TL;DR: In this article, a graphical method of representing the flow of energy is described and pictures are drawn showing the functions of generators, motors, transformers, transmission lines and other parts of an electric distributing system in terms of the flow energy through them.
Abstract: A new graphical method of representing the flow of energy is described and pictures are drawn showing the functions of generators, motors, transformers, transmission lines and other parts of an electric distributing system in terms of the flow of energy through them. The method is based on using two ribbons; one to represent the flow of energy proper, and the other (not used for direct currents) representing the magnetizing power. It is shown that various phenomena of alternating-current transmission are determined by the widths and directions of the two ribbons. The principal elements of the picture (generators, synchronous motors, induction motors, etc.) are taken up one by one and in simple combinations, each case being illustrated by typical figures.
TL;DR: In this article, the authors considered the relation between the maximum.volts per bar and flashing conditions, both from test and general experience, and the effects of the negative coefficient of the contact resistance.
Abstract: In direct-current machines, there are a number of apparently distinct limitations, such as sparking at brushes, flashing at the commutator, burning and blackening of the commutator face, picking up of copper, etc., which, in reality, are very intimately related to each other. The principal object of the paper is to bring out such relationships and to show that all these actions are special cases of well-known phenomena. The theory of commutation is considered only in its relation to the e.m.fs. generated in the coils short-circuited by the brush; and the limiting e.m.fs. per commutator bar and per brush are shown to be fixed principally by brush contact resistance. The effects of the negative coefficient of the contact resistance are also referred to briefly. Flashing due to various causes is next taken up, and the relations between the maximum .volts per bar and flashing conditions is indicated, both from test and general experience. Flashing due to various other causes, such as interrupting the circuit, etc., is also considered. Burning and blackening of commutators, high mica, picking up of copper, etc., are treated in detail, and these actions are shown to be very closely related to the commutation limits derived in the earlier part of the paper. Noise, vibration, etc., are also considered as limitations in design of d-c. apparatus. In approaching the ultimate design, these limitations become increasingly prominent. Flickering of voltage and winking of lights are two well-known actions in direct-current practise.
TL;DR: Thomas A. Watson as discussed by the authors gave an address at the annual meeting of the AIEE in New York on May 18, 1915, upon the occasion of the presentation of the Edison Medal to Alexander Graham Bell.
Abstract: Thomas A. Watson (F '15), who assisted in the development of the telephone and who died December 14, 1934, delivered this address at the annual meeting of the AIEE in New York on May 18, 1915, upon the occasion of the presentation of the Edison Medal to Alexander Graham Bell. The address is given here as it originally was published in AIEE PROCEEDINGS, volume 34, number 8, August 1915, pages 1503–13.
TL;DR: In this article, the authors present an apparatus for measuring mutual inductance, self-inductance, and alternating-current resistance of current transformers, which is used for calibrating the transformers.
Abstract: Reasons are given for the selection of mutual inductances as a means for calibrating current transformers, the most important of which is the wide use to which they may be put besides the calibration of current transformers The design and manufacture of the apparatus are described, reasons being given for the choice of the form of the secondary coil of the mutual inductance, which is a uniformly wound ring, and of the material used for the core, namely, marble The formula used in calculating the values of mutual inductance is given and its limitations stated Variations in physical dimensions are given and errors in calculated value discussed The method of calibrating the mutual inductances is described, which illustrates also one method of using the apparatus for measuring mutual inductance The method of measuring ratios and phase displacements by means of the apparatus, and the merits of various instruments for obtaining a balance, are described and discussed An artificial method of loading the transformers under test is proposed Its advantages are pointed out The use of the apparatus for measuring mutual inductance, self-inductance and alternating-current resistance is described In conclusion it is stated that the apparatus has been satisfactory, and has given little difficulty in manufacture
TL;DR: In this paper, the authors used the quadratic law to calculate the loss of the Corona loss curve on a number of experimental and practical lines by different investigators and plotted the calculated loss curves for comparison.
Abstract: Corona loss curves made on a number of experimental and practical lines by different investigators have been corrected and plotted. The loss has been calculated by the quadratic law for each case under the same conditions as to spacing, conductor diameter, altitude, etc., and plotted for comparison. It is of interest to note that the measured values were made in various parts of the country. The time period covers a number of years and the altitude varies from sea level to 10,000 ft. An exact check of calculated and measured losses cannot be expected, as the exact conditions of conductor surface, the wave shape, etc. are not always known. Such losses are also difficult to measure, especially on practical lines where the voltage range is quite small and there is a large number of corrections to make. The check is as close as the accuracy of the measurements permits. The variations from the calculated values are in most cases due to the fact that practical measurements have been made on the unstable part of the curve below the visual critical voltage value. The losses at this part of the curve are fully discussed.
TL;DR: In this paper, the effects of short-circuit conditions on a transmission system under short-cycle conditions were investigated. But the authors focused on the effect of placing a busbar between generator terminals and the bus from which power is taken.
Abstract: The following features of a transmission system under short-circuit conditions are discussed: 1. Mechanical forces between the phases of three-conductor, three-phase cables when carrying short-circuit current; also the forces between busbars are investigated. 2. The heating of the conductors of the cable from the instant of short circuit to a time 0.8 seconds later is traced analytically, during the transient state of the current, and typical computed heating curves are presented. 3. The effectiveness of the method of placing reactors between generator terminals and the bus from which power is taken, and additional reactors between generators and an auxiliary synchronizing bus, is analyzed. 4. This scheme is compared with the present well-recognized schemes of feeder and busbar reactors.
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TL;DR: In this paper, the authors present a brief explanatory discussion of some of the arc phenomena in oil circuit breakers and describe the present tendencies in oil breaker construction and practise, and present a proposed method for rating breakers.
Abstract: The purpose of the paper is to present a brief explanatory discussion of some of the arc phenomena in oil circuit breakers and to describe the present tendencies in oil breaker construction and practise A proposed method for rating breakers and specifying is included
TL;DR: In this paper, a method of testing the phase angle of current transformers by comparing readings obtained on a wattmeter whose current circuit is first connected to receive a part of the primary current and then connected to the secondary circuit; the potential circuit is supplied from the primary voltage, and capacity or inductance is used to give the effect of a low power factor in the wattmeter.
Abstract: A method of testing the phase angle of current transformers by comparing readings obtained on a wattmeter whose current circuit is first connected to receive a part of the primary current (the remainder of the primary current passing in shunt through resistance) and then connected to the secondary circuit; the potential circuit is supplied from the primary voltage, and capacity or inductance is used to give the effect of a low power factor in the wattmeter. Corrections are applied for the error of phase of the part of the primary current which passes through the wattmeter, and separately for the error of phase in the primary caused by the fact that the primary current is not exactly in phase with the voltage used to supply the wattmeter. A second method of connection is suggested which avoids the latter correction, and other methods including the use of a three-phase circuit are discussed. Results of tests are given, and also check obtained by the use of an a-c. potentiometer. The method requires only portable instruments.
TL;DR: In this paper, the results of three series of tests, made on the first 3750-kv-a. generator installed at Niagara Falls, to determine internal copper temperatures are given, and the operating history of the generator is given, showing that it has been in operation for twenty years with no interruption to operation due to any effect of temperature on the winding.
Abstract: The paper gives the results of three series of tests, made on the first 3750-kv-a. generator installed at Niagara Falls, to determine internal copper temperatures. The object of the tests was to obtain data to assist in the determination of the safe maximum temperature of built-up mica-and-cambric (or mica-and-paper) insulation. The present Institute Standardization Rules recommend the conservative limit of 125 deg, because of the lack of convincing data justifying the general adoption of a higher limit. In the third series of tests, temperatures of the copper conductors were obtained at the usual operating loads by installing special conductor bars having thermocouples in actual contact with the copper at its hottest part. The operating history of the generator is given, showing that it has been in operation for twenty years with no interruption to operation due to any effect of temperature on the insulation of the winding. The summary of service and tevmperature results given in Tables VIII and IX shows that the generator has operated for a time equivalent to nearly seven years without shut-down at temperatures ranging from 120 deg. to 285 deg., for a time equivalent to nearly three years operation without shut-down at temperatures ranging from 145 deg. to 285 deg., and for a time equivalent to fifteen months operation without shutdown at temperatures from 175 deg. to 285 deg. An examination made in 1914 showed the insulation to be in good condition?with the mica unchanged and with the conductors tight in the slots.
TL;DR: In this article, the theory of ionization in gases is outlined in non-technical language and the law of corona-forming intensity E = 32 + 13.4/?d is explained.
Abstract: (1) Some of the simpler fundamental experiments on the electrical conductivity of the air are described. (2) The theory of ionization in gases is outlined in non-technical language. (3) Townsend's proof that the law of corona-forming intensity E = 32 + 13.4/?d is in accord with the theory of ionization tion by collision, is explained.
TL;DR: In this article, a general expression for form factor is derived in terms of the relative amplitudes and phase positions of its harmonic components; curves are drawn showing the variation of form factor with the amplitude and phase of the third harmonic.
Abstract: Form factor is significant in the study of transformer losses; as is well known, hysteresis loss is small when the form factor is large, and vice versa. Every wave shape has a definite value of form factor; but the converse is not true, for a particular value of form factor does not indicate a particular wave shape. A wave may contain a third harmonic equal to seventy five per cent of the fundamental and still have the same form factor as a true sine wave. Form factor, therefore, has no general significance as an indicator of wave form or wave distortion. A general expression for form factor is derived in terms of the relative amplitudes and phase positions of its harmonic components; curves are drawn showing the variation of form factor with the amplitude and phase of the third harmonic. Various wave forms are shown, very unlike in appearance, having the same form factor.
TL;DR: The technical and financial progress made by the Research Corporation since its organization in 1912 is given, and several plants are described in this article, with reproductions from photographs of installations in various stages of operation.
Abstract: The technical and financial progress made by the Research Corporation since its organization in 1912 is given, and several plants are described. Voltages, electrode spacings, power consumption, etc., are given for several installations. Mention is made of a number of improvements in the electrical apparatus and means for its control. Progress has been made towards standardization of apparatus for this work. The paper is illustrated with reproductions from photographs of installations in various stages of operation. Curves and charts show the peculiar character of the circuit, the method of obtaining data to be used in designing precipitators and of conducting tests. Alternating current of 250,000 volts has been rectified and used for precipitating particles from gases. Fumes have been separated into fractions by means of temperature control and the electric processes. A selected bibliography is included. The statement is made that within three years' time the original capital of $10,100 has been paid back to the stockholders, and that a fund of over $150,000 has been accumulated from the corporation's work, to be used for scientific research.