Showing papers in "Transactions of The American Institute of Electrical Engineers in 1929"

Two-reaction theory of synchronous machines generalized method of analysis-part I

Abstract: Starting with the basic assumption of no saturation or hysteresis, and with distribution of armature phase m. m. f. effectively sinusoidal as far as regards phenomena dependent upon rotor position, general formulas are developed for current, voltage, power, and torque under steady and transient load conditions. Special detailed formulas are also developed which permit the determination of current and torque on three-phase short circuit, during starting, and when only small deviations from an average operating angle are involved. In addition, new and more accurate equivalent circuits are developed for synchronous and asynchronous machines operating in parallel, and the domain of validity of such circuits is established. Throughout, the treatment has been generalized to include salient poles and an arbitrary number of rotor circuits. The analysis is thus adapted to machines equipped with field pole collars, or with amortisseur windings of any arbitrary construction. It is proposed to continue the analysis in a subsequent paper.

The Revolving Field Theory of the Capacitor Motor

Abstract: The paper presents an accurate theory of the split phase motor, both as regards starting and running performance. The general equations for an unbalanced two-phase motor are first derived, and the results are then applied to the special case of the capacitor motor. Evidence of the validity of the theory is given in the form of curves, comparing test results with calculations. The principal factors affecting practical capacitor motor design are discussed, and finally the performance characteristics of the motor are compared with those of repulsion-start induction motors. It is concluded that the capacitor motor has important advantages, which will justify its extensive use. The complete derivation of the theory is given in an appendix.

System Stability as a Design Problem

Abstract: Under modern conditions of operation the ability of the component machines of a power system to hold in step during system disturbances has become of major importance in the choice of system layout and machine design. This situation has greatly stimulated activity in the study of the problems involved. This paper reviews the general problem in the light of recent analytical and experimental studies made by the authors. The subject matter of the paper is grouped according to the following headings: Part I reviews the factors affecting stability, including generator short-circuit ratio, voltage regulators, excitation systems, neutral impedance, governors, amortisseurs, intermediate condensers. Part II gives methods of calculating stability, under the following heads: preliminary calculations, idealized case of two machines, general case of two machines, extension to include more than two machines, simplified method of calculating tie lines. The appendixes include an example illustrating the method of calculation in a particular case.

Theory of the Deion Circuit-Breaker

Abstract: Three major features incorporated in the Deion circuit-breaker are discussed. They are: deionization at solid surfaces, the function of the static balancer, and cold electrode arcs.

Effect, of transient voltages on power transformer design — IV

Abstract: When subject to transient voltage excitation, local concentration of voltage takes place in an ordinary transformer in which the capacitance charging current of the coils to ground is supplied through the winding, or the ratio of inductance and capacitance of the various parts throughout the winding is not constant. Calculations and tests of voltage distribution in the winding, caused by the impact of (a) damped high-frequency oscillations, and (b) unidirectional traveling waves, are given. In order to make the analysis clearer, the transformer winding is considered as a network of inductances and capacitances, and this term ``network'' is used throughout the paper. Certain simplified and typical networks are considered. Transformers having one terminal grounded, such as are used in three-phase star connection, particularly in high voltage systems, are frequently built with the insulation graded to other windings and ground, in the order of the normal frequency voltage stress. The danger of such a practise is shown in power transformers which are subject to transient overvoltage, since voltage oscillation in the winding may raise the voltage to ground at intermediate points above the terminal voltage, unless the design of the winding eliminates oscillation. The theoretical and experimental data given show that the distribution and magnitude of voltage stresses existing during recognized standard insulation tests are essentially different from stresses created by transient voltages. This permits the construction of transformers that would satisfactorily pass standard insulation tests but at the same time would not be suitable for average service.

Decibel - The name for the transmission unit

Abstract: In 1923 the “mile of standard cable” was replaced in the Bell System by a new unit for expressing telephone transmission efficiencies and levels. At that time, the generic term “transmission unit” was taken to designate this new unit, since it was considered desirable to defer the adoption of a more distinctive name until this unit had been given further consideration by others who would have use for a unit of this type. This new unit is defined by the statement that two amounts of power differ by one transmission unit when they are in the ratio of 1·1, and any two amounts of power differ by N transmission units when they are in the ratio of 10N(.1). In accordance with this, the number of transmission units corresponding to the ratio of any two powers is ten times the common logarithm of that ratio. [Originally reported in the Bell System Tech. Journal, January, 1929].

Reduction of Sheath Losses in Single-Conductor Cables

Abstract: The use of single-conductor, lead-covered cable for high-voltage, three-phase transmission lines results in sheath losses ranging from 25 to 300 per cent of the conductor losses for cables installed in separate ducts, unless special methods for the reduction of the losses are used. Some of these methods, while practically eliminating sheath losses, cause a-c. sheath potentials which may be injurious. In this connection the authors have developed a new scheme of bonding and a new bonding device, which appear to have marked advantages. This article consists of a general discussion relative to the reduction of sheath losses with special reference to laboratory tests and field work done on 132 miles of single-conductor cable of the Commonwealth Edison Company. The economics of sheath losses and of the methods for their practical elimination are discussed. The theories of sheath losses and induced voltages are outlined and correlated, and new formulas and curves are developed. An analytical and graphical comparison of sheath bonding connections is presented. Investigations are reported on tests regarding the nature and extent of possible corrosion of sheaths caused by a-c. sheath voltages.

Traveling Waves Due to Lightning

Abstract: The purpose of this paper is to describe and analyze the origin and formation of traveling waves on a transmission line induced by lightning discharges, and to investigate their behavior at a transition point where there is an abrupt change of circuit constants. Some of the ground covered is necessarily old and well known, but has been included in the interests of completeness and continuity of treatment. The effect of the rate of cloud discharge and the initial distribution of bound charge on the shape and amplitudes of the traveling waves is brought out. General methods of analysis are formulated and illustrated by practical cases. The assumptions and approximations involved are discussed, and the probable direction of their deviation from fact indicated. Exact and approximate mathematical expressions are derived, and therefrom graphical and tabular methods are outlined. For all of the examples given, line attenuation and distortion are neglected and only the first reflection from a transition point is considered.

Transient analysis of A-C. machinery — II

Abstract: This paper shows how the Heaviside operational methods may be applied to determine the transient currents that are produced in synchronous and induction machines by some sudden alteration of their electric circuits. The observed and computed values of the transient currents have been plotted for a number of cases. There is also a table giving the names of the principal investigators who have written on this subject and the methods of analysis that they have employed.

Theoretical and Field Investigations of Lightning

Abstract: This paper gives a review of some recent developments in the methods of studying lightning phenomena. The Norinder form of cathode ray oscillograph and its application in Tennessee are discussed, together with the information secured. The second part gives the theory of traveling waves along transmission lines. Reflections at open and grounded ends are considered. A mirror scheme of an infinite series of waves on a double infinite line equivalent to actual waves along a finite line is developed. The third part discusses the manner in which surges are actually produced on lines by lightning and the effect of ground resistance on the protection afforded by ground wires, both with respect to induced and direct strokes.

Lightning Studies of Transformers by the Cathode Ray Oscillograph

Abstract: Study of transformers has been under way for some time to coordinate the strength of transformers and transmission line insulation under lightning conditions. This study has taken two forms: first, the transient dielectric strength of the line end of the winding and second, the distribution of transient voltages and therefore the stress caused by them throughout the winding. Theoretical studies and spark-gap tests of transient voltage distribution in transformer windings have been previously published by the Institute. Since then an extensive study of transient voltage phenomena has been made by the cathode ray oscillograph on power transformers connected to a short transmission line and subjected to artificial lightning waves sent along the line. The effects of the transmission line, concentrated inductance, and transformer entrance bushings on traveling waves were studied, as well as the effect of traveling waves of various service conditions in producing internal oscillations in ordinary transformers. The non-resonating transformer was stutdied under similar conditions. A striking agreement between the oscillographic records and theoretical conclusions previously published was found, sufficient to establish beyond any doubt the following conclusions: 1. Very high voltage oscillations occur throughout the entire winding of even a grounded neutral transformer. 2. Points of the winding near the grounded neutral may rise to 95 per cent of the crest voltage of a very short traveling wave (three microseconds long). 3. Entrance bushings have a negligible effect on the shape of the incoming traveling wave. 4.

No-Load Induction Motor Core Losses

Abstract: A detailed method of calculating the no-load core losses of induction motors is presented whereby each loss component is estimated separately. There is included a discussion of extra losses due to imperfection in workmanship. Calculated and test results on a few commercial machines are given as an indication of the reliability of this method.

Bessel Functions for A-C. Problems

Abstract: Tables of Bessel functions of zero and higher orders are given, for use in problems of skin effect and proximity effect in conductors carrying alternating currents. Formulas for deriving numerical values of the functions are given, in the form of series for large and for small values of the argument. The series are complete with their general terms. The application of the tables to the calculation of the skin effect resistance ratio of an isolated tubular conductor is described and an example is given.

Current Transformer Excitation Under Transit Conditions

Abstract: Tests of circuit breakers, relays, and similar devices in which current transformers have been used to step down the large currents involved to values measurable by the oscillograph, have shown peculiar errors in the records during the transient portion of the current wave. The purpose of this paper is to show that the abnormal excitation of the magnetic circuit of the current transformer required during transient conditions is the cause of these errors, and to point out how the errors may be minimized sufficiently to be negligible. Mathematical expressions are also derived to make it possible to predetermine the ability of a transformer to handle transients correctly and to guide in the design of transformers for this service.

Anomalous Conduction as a Cause of Dielectric Absorption

Abstract: The paper describes a series of experiments on the fundamental electrical properties of a number of waxes and oils, such as are used in composite high-voltage insulation. Particular attention has been directed to dielectric absorption as the origin of dielectric loss and the probable cause of deterioration and short life. The relation of the properties of the constituent parts to the properties of mixtures has been examined, with special reference to purification methods and the influence of small amounts of impurities. The studies have also afforded opportunity to test the validity of certain existing theories of absorption and loss. The method of experiment is the recording of short time absorption curves by means of the string galvanometer. Charge and discharge curves have been traced from a small fraction of a second following the beginning of charge or discharge, these curves having been brought much nearer to their beginnings than any heretofore recorded. It is this region near the beginning of these phenomena, which is most important in its bearing on dielectric loss. The principal results are summarized at the end of the paper, among the most striking being: (a) The extensive evidence that dielectric absorption is purely a conduction phenomenon; (b) The conductivity of dielectrics is highly anomalous in character, sometimes increasing, sometimes decreasing with increases in voltage and temperature. Absorption always follows the conductivity in these changes.

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

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

Power Factor and Dielectric Constant in Viscous Dielectrics

Abstract: This paper gives the results of a study of the peculiar variation with temperature and frequency of the dielectric constant and power factor of rosin, rosin oil, and castor oil. It includes data showing at several frequencies the relation of dielectric constant and power factor to the composition of vulcanized rubber. Electrical double refraction in rosin at different frequencies and temperatures is discussed in relation to its behavior as a dielectric. It is shown that the viscosity is a decisive factor controlling both the electrical and optical behavior. The facts are important in themselves but it is possible to interpret them by a modern physical theory, the Debye1 dipole theory, which it is believed has not hitherto been applied to commercial dielectrics. On this theory the anomalous change of dielectric constant and power factor with temperature and frequency is attributed not to impurities or heterogeneity of structure but to molecules containing electric doublets which try to orient themselves in an electric field. The rotation of the dipole molecules in a viscous medium gives rise to frictional heat loss expressed as power factor, and also to a contribution to the dielectric constant which vanishes when the dipoles are prevented from responding by too great viscosity or too high frequency. For the sake of intelligibility, an outline of the dipole theory is first presented and then the experimental results are discussed on the basis of that theory.

Losses in Armored Single-Conductor Lead-Covered A-C. Cables

Abstract: The losses occurring in single-conductor armored cables whose sheath and armor are bonded and grounded at more than one point are?besides the copper loss and the dielectric loss?the circulating-current losses in the sheath and in the armor, and the additional iron losses in an armor of magnetic material. The circulating-current losses are due to the currents induced in the sheath and armor circuits by the fluxes linking these circuits when these circuits are closed by the bonds or grounding connections. Since the losses obtained in such cables are widely variable, depending on the cable design, both designers and operating engineers desire to know the loss magnitudes obtained in different cases and to have an understanding of the factors tending to give low losses. In this paper the sheath and armor losses have been analyzed for a steel-wire armored cable, a copper-wire armored cable, a steel-tape armored cable, and a cable enclosed in an iron pipe, and have been compared with the losses occurring in a plain lead-covered cable without armor. The data used include test data and calculated values. It is shown that a steel-wire armored 350,000-circular mil single-conductor copper cable with sheath and armor short circuited by low-impedance bonds had a total loss (exclusive of dielectric losses), of 2.8 times the conductor loss, by test in a single-phase 60-cycle circuit at 4 ft. cable spacing, at 260 amperes. The corresponding loss in a similar cable without armor, with lead sheath short circuited, was 2.4 times the conductor loss.

Some Problems in Dielectric-Loss Measurements

Abstract: The measurement of dielectric loss in high-voltage cables presents many problems that are not obvious until such measurements have actually been attempted and the results checked and analyzed. Some of these problems are not simple, and their solution is obtained only after considerable effort and research. This paper presents some of the problems that the authors have encountered in this type of work, together with the methods used for their solution. The bridge method, which is used for the measurement of dielectric loss, is described in some detail. Details of the auxiliary equipment, such as galvanometer, amplifiers, air condenser, shielding, and special methods of bringing the shielding to the proper potential are also given. If accurate results are to be had in dielectric loss measurements, the entire bridge, including cable, air condenser, and leads, must be properly shielded and the capacitance between leads and shielding should be made small. Errors of large magnitude may be introduced in the results if these precautions are not taken. It is entirely insufficient to shield the bridge and ground the shielding directly. At times shielding cables may increase the measured losses. In measuring the capacitance of the air condenser, all stray capacitance to its guard rings and to surroundings must be eliminated. The paper gives a method of accomplishing this. The voltage across the voltmeter coil of a high-voltage transformer is frequently taken as a measure of the voltage across its secondary.

A New Type of Hot Cathode Oscillograph and its Application to the Automatic. Recording of Lightning and Switching Surges

Abstract: This paper presents a new general purpose type of hot cathode oscillograph, which employs a new electrostatic method of focusing the beam. This oscillograph will operate at any beam potential from 500 to 20,000 volts or more, and at any gas pressure below 30 microns. High photographic sensitivity at medium voltages is attained by the use of a high intensity beam. A portable form of the oscillograph for recording lightning surges on transmission lines is described, together with circuits by means of which the lightning surge automatically starts the beam in from ? to ? microseconds after the surge voltage begins to rise from zero. This oscillograph was put into operation on one of the 140-kv. transmission lines of the Consumers Power Company of Jackson, Michigan, on August 27, 1928.

Totalizing of Electric System Loads

Abstract: The importance of measuring an electric system load at any distance from that load is emphasized. The use of thermal wattmeters in conjunction with thermal couples is suggested. Time of response of such devices is discussed; temperatures attained are also discussed. Characteristics of circuits for transmitting the thermal e. m. f. from the load to the point of measurement are discussed in detail. A list of users together with data pertaining to the measurement-transmitting circuits is given.

Study of Noises in Electrical Apparatus

Abstract: The objections to unnecessary noises in electrical apparatus are becoming so insistent that the manufacturers are making every effort to reduce them. In order to attack the problem intelligently it is first necessary to determine the amplitude and frequency of the components of the complex sounds. The first requirement then is a simple portable sound analyzer. Descriptions are given of two resonance types which have been developed. There is included also a short discussion of the laws of sound variation and sound units. Finally there are discussed various applications of the sound analyzer to the study of noises in gears, motors, generators, induction regulators, loud speakers, vacuum sweepers, and the like.

Progress in High-Tension Underground Cable Research and Development

Abstract: This paper deals primarily with the ``solid'' type paper insulated high-tension cable, the development field still ahead being extensive. A review is given of the progress made during the past four years. The research and development work which made this progress possible is outlined, only the more important features being considered. Particular attention is given to void formation both in the factory and in the field, and methods of arriving at some understanding of this are demonstrated. The conclusion is drawn that void formation under service conditions is inherent in paper insulated ``solid'' cables. Methods of reducing the size and duration of voids, and increasing their pressure, thereby reducing the possibility of ionization deterioration, are carefully considered. Oil reservoir feed at the joints is of great value in this respect. This is dealt with in detail. Research data on ionization and other characteristics of finished cable and cable materials are presented.

Impulse Flashover of Insulators

Abstract: For the most part this paper is a discussion of the mechanism of insulator flashover. The breakdown of air between electrodes, with particular consideration of the effect of various factors upon the flashover characteristics of insulator strings equipped with arcing rings, is discussed. It is shown that critical dimensions and spacings of arcing rings exist for a given insulator string. If the arcing rings are designed to lie on the safe side of this critical point, cascading flashovers will not occur. If the arcing ring dimensions are below the critical values, cascading may or may not occur depending upon the nature of the applied voltage wave. Data from tests, which determined the limiting physical dimensions of arcing rings that will prevent cascading under all types of impressed voltages, are presented.

The Fundamental Theory of the Capacitor Motor

Abstract: A fundamental theory of the motor and capacitor is given partly by the algebraic method and partly by graphical method. The variables in the design of a complete capacitor motor unit for any desired performance are discussed. A few examples of unbalanced phases and performance are given. The suitability for various classes of service is discussed briefly.