Showing papers in "Transactions of The American Institute of Electrical Engineers in 1943"

Intrasystem Transmission Losses

Abstract: THIS paper describes a new method of calculating transmission losses within power systems. Reasonable accuracy is obtained with longhand calculation, although the same general scheme with the load-flow determinations carried out on a d-c calculating board would provide greater accuracy with less work. The use of an a-c calculating board with separate tabulations of kilowatt and kilovar flows would be even more advantageous. The method is based on the principle of superimposing the load distribution from each source, determining the current in each line as a sum of the individual load flows (with each in its proper direction), squaring this expression for current, and setting up an equation for losses in terms of megawatt generation at the various plants and of megawatt flows (in or out) at each interchange point. An outward flow of power at an interchange point is considered negative generation.

Effect of Frequency on Let-Go Currents

Abstract: This paper on electric shock covers the subject of sine-wave let-go currents for both men and women and contains an analysis which permits improved accuracy in predicting the response for large groups based on experiments made on a relatively small number of subjects. It should be of especial interest to persons who have had accidents in which they barely escaped ``freezing'' to an electrified conductor and also to those interested in electrical safety. The range of frequencies covered is from 5 to 10,000 cycles and also direct current. The paper is the most comprehensive treatment of the subject yet published as the analysis permits predicting currents of a specified degree of safety for both men and women for this wide frequency range.

The Calculation of Unbalanced Magnetic Pull in Synchronous and Induction Motors

Abstract: Unbalanced magnetic pull may be defined as the net sideways force between the stator and rotor of an electric machine resulting from a difference in the air-gap flux densities on opposite sides of the machine. This difference in flux density is, in general, caused by a difference in the air gaps on the two sides. There is outlined herein a method of calculation of unbalanced pull which takes into account the combined effects of saturation, parallels, and primary reactance. The increased accuracy which this method affords should make possible more accurate predictions of mechanical deflections and critical speeds.

Distribution Factors and Pitch Factors of the Harmonics of a Fractional-Slot Winding

Abstract: The investigation of the fractional-slot windings with respect to their harmonic (differential) leakage, to noise, and so forth, requires the knowledge of the distribution factors of their harmonics. Very valuable work on distribution and pitch factors of fractional-slot windings has been done by J. F. Calvert.1 On the basis of charts he worked out distribution-factor tables covering the actual harmonics up to the 24th. Once the chart of the winding has been set up, a simple formula can be used for computing the distribution factors of the harmonics for any three-phase fractional-slot winding. In the following paper, simple formulas are derived for the distribution factors of the harmonics of fractional-slot windings which make the layout of charts unnecessary. These formulas are similar to those of the integral-slot windings. In deriving them the usual method of attack, namely, the use of charts, had to be abandoned and the vector diagram of the different slots used instead.

Impulse and 60-Cycle Characteristics of Driven Grounds--III Effect of Lead in Ground Installation

Abstract: In laying out grounds for protection against lightning, the inductance of the installation and its relation to the effective resistance of the ground are factors of importance. The lead and ground induction ance becomes particularly significant for rapid current discharges associated with direct strokes when the inductance drop may exceed the resistance drop. Examples show that the voltages developed from steep-front high currents in extensive grounds are considerably greater than where conditions permit shallow grounds. The simple method of analysis for determining the voltage across the ground installation, in which a current is applied to an equivalent circuit, is reasonably correct and practically satisfactory. Ground installations comprising multiple paths to earth are also amenable to simplified calculations. A survey of the terminal conditions in the earth should supplement the simple method of analysis in the more important installations of grounds. In assessing the insulation requirements, these should be considered in relation to the impulse voltages developed, which for ground installations are more complex than the ordinary standard waves.

Effect of Wave Form on Let-Go Currents

Abstract: This paper is a continuation of “Effect of Frequency on Let-Go Currents”2 and concludes studies made to determine let-go currents. This paper extends the analysis to cover various wave shapes and includes a method of determining reasonably safe currents for men, women, and children, for sine waves, direct current, and complex wave forms containing both a-c and d-c components. As in previous papers, conclusions regarding reasonably safe electric currents are based on the criterion that a safe current is the let-go current for 99 1/2 per cent of a large group of healthy subjects.

Switching Overvoltage Hazard Eliminated in High-Voltage Oil Circuit Breakers

Abstract: High-voltage transmission lines, when de-energized by conventional oil circuit breakers, are often subjected to high-voltage surges which present a real hazard to terminal equipment. The mechanism of surge generation is initiated by circuit-breaker restriking phenomena which are encouraged by the interruption of the large leading currents required to charge moderate and high-voltage lines. By interposing suitable resistors across the interrupting elements during the opening stroke of the breaker, the switching overvoltages may be either eliminated by preventing restriking or so reduced in magnitude in the event of restriking that the system is relieved of their hazard. The development of this achievement is presented chronologically: 1. Theoretical considerations 2. Transient-analyzer studies 3. Power-laboratory switching tests 4. Actual field tests on the 220-kv lines of Southern California Edison Company Ltd. at Boulder power plant

Self-Excited Oscillations of Capacitor-Compensated Long-Distance Transmission Systems

Abstract: THE transmission of electric power over long distances has been the subject of considerable study,1 and it has been concluded that an effective way of increasing the permissible straightaway transmission distance is by means of series-capacitor compensation of part of the transmission-line inductive reactance. The introduction of longer lines together with capacitor compensation brings up several technical problems which must be considered if proper operation is to be assured. Studies of transient stability and switching times following faults and of abnormal overvoltages which may result from interaction of line capacitance and transformer exciting impedance at no load are presented in references 2 and 3 respectively. This paper presents the results of a study of hunting and self-excitation during normal operation as affected by line and machine characteristics.

Dielectric-Recovery Characteristics of Large Air Gaps

Abstract: In contrast to power arcs in air, for which the dielectric-recovery voltage decreases with increasing arc current, arcs in air produced by surge currents of several hundred microseconds' duration possess dielectric-recovery characteristics that vary only slightly with current magnitude and wave shape. Even when the discharge current is prolonged at low magnitude for as long as a thousand microseconds, the rate of dielectric recovery is little affected. For this condition at times when current as high as one ampere is flowing, the transient voltage required to convert to a high current arc is quite high. The mechanism for such a discharge is different than for the breakdown of virgin air, and the initial arc drop is sufficiently high to record its transient character. It is about ten times the steady-state value at the time the crest current is reached and drops about 50 per cent in the first 20 microseconds. Photographic studies show that even at short-time intervals successive discharges do not follow exactly the path blazed by the initial discharge but occur in an air column of low dielectric strength expanding radially with time. It is indicated that the high arc temperatures diffusing in this region can be the principal factor determining the rate of recovery after the first 1,000 microseconds. A comparison is made with the mechanism of natural lightning particularly from recent data obtained on the low-magnitude portions of stroke currents between successive components.

The Effect of Corona on Coupling Factors Between Ground Wires and Phase Conductors

Abstract: Measurements of coupling factors between ground wires and phase conductors, as a function of ground-wire voltage, have been made for a sufficient number of cases to determine them for any of the standard transmission-line configurations. It was found that the effect of corona can be expressed in terms of an effective corona ground-wire radius to be used in the conventional coupling-factor equations. Curves are also presented for the quick determination of coupling factors for all standard line configurations. A photographic study of the visual characteristics of surge corona was made for a comparison with the effective radius and with 60-cycle corona. Actual measurements were made for potentials up to about 2,000 kv, but the data were extrapolated to 6,000 kv with what is considered to be reasonably good accuracy. Coupling factors for positive polarity were found to be considerably higher than those for negative polarity and both higher than values previously calculated from purely theoretical considerations. For a potential of 1,000 kv the actual coupling is 1.2 to 1.5 and 1.4 to 1.8 times as great, for negative and positive polarity respectively, as the values obtained by assuming no corona. At 2,000 kv the corresponding figures are 1.4 to 2 and 1.6 to 2.7 respectively, and at 4,000 kv 1.7 to 2.9 and 2 to 4. Ground-wire size was found to be unimportant above about 200 kv and, therefore, need not be considered.

The Effect of Current-Transformer Residual Magnetism on Balanced-Current or Differential Relays

Abstract: High-speed current-balance relaying has been subject to occasional false tripping that has not been explained satisfactorily. Field and factory tests now show that this is probably due to differences in residual fluxes in the current-transformer cores. The limiting value of these fluxes can be calculated approximately, and they can be measured with portable instruments connected to the secondary winding. They may cause a deficiency in secondary current, especially during the first half-cycle of fault current, which will cause current-balance or differential-overcurrent relays to operate falsely. This false operation can be avoided by the addition of a short inherent or external time delay with relays having a high dropout, or by the use of special current transformers.

Protective Relaying for Long Transmission Lines

Abstract: UP to a certain length of transmission line, conventional distance relays will readily distinguish internal faults, for which the line should be opened, and external faults, load conditions, and power swings, for which the line should not be opened. This distinction is based on the magnitude of the impedance or reactance of the line as it appears to the relay. This impedance will be referred to hereafter as the input impedance and is determined by the current and voltage existing at the relay location.

Performance Requirements for Relays on Unusually Long Transmission Lines

Abstract: Analysis of fundamental bases of relaying made as part of the engineering for the 270-mile 154-kv interconnection between systems of Nebraska Power Company and Kansas Gas and Electric Company reveals that, of current, phase angle, impedance, and impedance angle, none alone offers satisfactory discrimination among open-circuit, short-circuit, and load conditions. Combination of input-impedance magnitude Z and impedance angle ψ = tan−1 X/R is studied by means of “impedance circle diagrams” of the interconnecting circuit. On these diagrams is charted the dynamic behavior of the interconnected systems during faults and surges of synchronizing power. The desirable areas of trip and no trip are mapped, and general specifications for the performance of relay systems are presented in terms of impedance magnitude and angle, Z ∠ ψ. Thereby full advantage can be taken of all possible synchronizing power inherently available over the interconnection and at the same time faults and approach of out-of-step condition can be recognized properly.

Application of Carrier to Power Lines

Abstract: DURING the 20 years or so that have elapsed since power-line carrier was first introduced on a commercial basis, enormous advances have been made in the communication arts. In the somewhat specialized branch of power-line carrier, advances in technique and apparatus design have not been as highly publicized as those in some other branches of the art; nevertheless, they have kept pace with the field, with the result that power-line carrier is today one of the most useful and versatile tools available to the power-utility engineer. There are now over 1,300 terminals of power-line carrier in operation in the United States. These terminals provide channels for telephone circuits, pilot relaying, telemetering, load-control, supervisory, and other remote-control functions over transmission lines of all voltages, totaling over 40,000 channel-miles. The last several years have seen a rapid increase in the number of terminals and in channel-miles, and there is every indication that this rate of growth will continue to increase for some time. With very few exceptions, every new transmission line of any importance is now engineered to include power-line carrier for one or more functions. Many large integrated systems1 have already made such extensive use of carrier circuits that the problem of channel space and frequency assignment is rapidly becoming of major importance.

Insulation Testing of Electric Windings

Abstract: THE paper describes a new method for the testing of insulation of windings, the advantages of which are adequate stressing of turn and conductor insulation and certain detection of defects. The new tester consists of a repeating-type surge generator, cathode-ray oscillograph, and synchronously driven switching equipment. The surge generator provides a succession of voltage waves of controlled shape adjusted to give the necessary turn and conductor insulation stresses. The cathode-ray oscillograph is timed to give a stationary image of the repeating surge on the screen. By virtue of the special method of surge application and oscillograph connection, the waves on the screen indicate turn or conductor-insulation defects quickly and certainly.

Pole-Face Loss in Solid-Rotor Turbine Generators

Abstract: ONE of the primary problems which confront the designer of electrical machinery is the predetermination of losses. This is peculiarly true for the designer of high-speed turbine-driven generators; the losses must be kept low, not only to increase the efficiency but also to keep the size of the apparatus to a minimum.

Steady-State and Transient-Stability Analysis of Series Capacitors in Long Transmission Lines

Abstract: IN long-distance large-block power transmission, where is reactance compensation applicable? The complete answer to this question involves the weighing of compensated line performance against its costs, tempered with engineering judgment. This paper presents the results of an analysis made to determine basic performance data of compensated lines under steady-state and transient conditions. The data presented therefore allow the question to be partly answered and, it is believed, to a sufficient degree to permit certain general conclusions to be drawn. The system designer is thus provided with the fundamentally necessary data permitting him to proceed with an economic analysis for his particular case, where the cost factors are available. It is felt that in this field lies the value of these data. The costs of the various factors for a particular case can be weighed with the performance obtained by the same factors. The best design must necessarily be one where per cent line compensation, number of parallel circuits, generator short-circuit ratio, and number of intermediate switching stations are all used to their optimum degree for a given reliability of service. The number of factors which may be varied obviously depends upon whether compensation is to be used for increasing the power limits of a system already in operation or to be used as a factor in the design of a projected system.

Parallel Operation of Airplane Alternators

Abstract: The increase in airplane electrical loads has made necessary an increase in the distribution voltage to avoid excessive copper weight. Difficulties in the use of higher d-c voltages are mentioned, and past experience with a 400-cycle three-phase system is outlined. In the light of this experience and of new developments in progress, requirements are outlinied for a larger 400-cycle system with multiple generating units operating in parallel.

Thermal Rating of Overhead Line Wire

Abstract: THE major problems in rating overhead wires according to thermal limits are 1 How materials lose their strength 2 How hot wires become when various currents are passed through them

Design Relationships for D-C Generators for Use in Aircraft

Abstract: The paper sets forth the different operating conditions met with in aircraft generators as compared with standard types of industrial generators. It discusses certain features inherent in applications to aircraft, such as reliability and light weight. Certain requirements in both electrical and mechanical design are imposed by the fact that a plane is flying through varying altitudes resulting in changing atmospheric conditions, such as rarefication, low temperature, and ionization. Other unusual conditions are created from the motion of the plane setting up accelerating forces on the generator, as well as mechanical forces caused by engine vibrations. Because of important features such as commutation, voltage regulation, cooling, driving means, and light weight, special and unusual methods must be employed. In solving these problems the most perfect methods known in the art of building d-c machines must be resorted to, and the paper lays particular stress on the use of compensation.

Staged Fault Tests of Relaying and Stability on Kansas-Nebraska 270-Mile 154-Kv Interconnection

Abstract: Results and conclusions are presented from 22 staged fault tests made on a 154-kv transmission line and terminal systems to check the characteristics of new long-line relays, discussed in companion papers,1,2 which were designed to differentiate between faults and high power swings. Observed power swings and relay performance are compared with theoretical aspects and predictions. Data on the transientstability limit of the interconnection, together with observations made during the tests, are also presented. Measured values of line constants and short and open-circuit impedances are given, together with results of attenuation tests at carrier frequencies. Manner of initiating the faults, scheduling of power flows, and organizing personnel are briefly discussed.

Theory of rectifier-D-C motor drive

Abstract: THE use of rectifiers for furnishing power to d-c motors is becoming more common, particularly for variable-voltage drives. The theory applying to drives such as those incorporating the Ward Leonard system is quite inadequate for use with a rectifier-d-c motor drive. This paper is an introduction to the theory involved when operating a d-c shunt-wound motor from a rectifier. It is hoped that further thought and discussion of this new and vital subject will be stimulated.

Formulas for Calculating Short-Circuit Forces Between Conductors of Structural Shape

Abstract: THE mechanical forces acting on busbar supports during short circuit are determined both by the magnitudes of the mutual electromagnetic forces exerted among the bus conductors and by the elastic properties of the supporting structure: its motional resistance, natural frequencies, and physical nature and arrangement. Comprehensive mathematical studies,∗∗ substantiated by experimental data, of the individual and collective effects of these factors and general methods for calculating the magnitudes involved have been advanced by Schurig and Sayre,1 Dahlgren,2,3 and Pilcher.4 In shorter articles based on the work of the first-named Schurig, Fricke and Sayre,5 Tanberg,6 Specht,7 Edson,8 and others9 have presented certain charts, nonograms, and short cuts that facilitate the numerical labor incident to actual calculation.

Safe Ratings for Overhead Line Conductors

Abstract: Many factors must be considered in establishing safe ratings for overhead copper line conductors. Most important is the low-temperature annealing and loss of strength of the hard-drawn copper itself. Others are the effect of atmospheric conditions and line location relative to structures and topographical features tending to obstruct the wind. The actual construction details of the line, such as ground clearances, conductor splices, and connectors are pertinent, as are the policies of the personnel responsible for maintaining the line. This paper attempts to show how these factors can be evaluated to establish operating ratings, indicating how readily available data can be utilized, pointing out the lack of completely satisfactory data on other points. Procedure is stressed rather than results, as the influence of local conditions upon many of the factors precludes publication of ratings which are entirely safe to apply without careful investigation of the effect upon the particular copper conductors to which they are to be applied.

Lightning Surges Transferred From One Circuit to Another Through Transformers

Abstract: IT is generally recognized that through the medium of transformers surges can be transferred from circuits exposed to lightning to circuits considered otherwise nonexposed. The latter may connect to rotating machines or to industrial apparatus of inherently low-impulse insulation level. On these seemingly nonexposed circuits may be found apparatus of old design which as a rule are even more vulnerable to surges. In these problems the question is to determine 1. The extent apparatus may be endangered. 2. Whether the relative risk incurred weighed against the importance of the installation and the cost of damage, warrants protective equipment.

Operation of Nonsalient-Pole-Type Generators Supplying a Rectifier Load

Abstract: IT has been recognized that the presence of harmonic currents in the supply circuit are a source of additional heating in the generators supplying a rectifier load, particularly where a six-phase rectifier is the total load. Robert Pohl has presented papers on this subject, and from his work has concluded that an appreciable reduction in the rating of turbine generators is required when the rectifiers are connected for 6-phase and 12-phase operation.1,2 Experience in this country with turbine generators operating with rectifier loads indicated that the reduction factors presented by Doctor Pohl were too large, so a test program was carried out to determine the practical limits of such loads. The test results and experience both indicate that for 12-phase operation and above, the effect on the supply system is very small and in most cases may be neglected.

Equivalent Circuits for Oscillating Systems and the Riemann-Christoffel Curvature Tensor

Abstract: Many electromechanical systems that are being studied in connection with the war effort have so many degrees of freedom that it is totally impractical to analyze their performance by direct calculation. It is, therefore, increasingly important to develop equivalent circuits for these multiple oscillating systems, that can be put on the a-c calculating board and so solved by direct reading of instruments. In this paper it is shown that a necessary (though not sufficient) condition for the existence of a physical model, corresponding to a given set of equations, is that the set should be a tensor equation. This follows from the fact that only quantities that are tensors can be measured by instruments. The conclusion is therefore reached that only equations that are in tensor form can be set up on the a-c calculating board. The principle is illustrated by setting up equivalent circuits with the aid of tensorial hunting equations for the determination of the steady-state, hunting, and self-excitation performance of two interconnected instrument-Selsyns, of two salient-pole synchronous machines, and of a capacitor-compensated transmission line connected to a salient-pole synchronous machine. A companion paper, ``Self-Excited Oscillations of Capacitor-Compensated Long-Distance Transmission Systems''12 contains the results of an extended study made on the a-c network analyzer with the aid of one of the equivalent circuits developed here.

Temperature Limits and Measurements for Rating of D-C Machines

Abstract: Existing industrial practice for determining the temperature rise of d-c machines is based on measurements with thermometers, placed on exposed or accessible surfaces of the machine. Tests using resistance measurements with improvements in technique have disclosed the existence of considerably higher internal temperatures than those indicated by thermometers, especially for short-time rated machines. Experience has indicated, nevertheless, that such machines have entirely satisfactory service records. Greater accuracy and consistency are possible with the resistance method, with proper measurement techniques, and it affords a truer indication of winding temperatures. This paper, therefore, suggests that the resistance method should be more generally used and should ultimately be recognized in the Standards as is now the case for railway motors. With this in view, detailed recommendations for resistance-measurement technique are presented. Correlation of the temperature rises determined by the resistance method with those measured by the thermometer method is necessary if resistance methods are to supplant the now standard thermometer methods. This paper shows the relation existing between temperature rises measured by thermometer and those measured by resistance on variously ventilated and insulated machines. Values for temperature limits measured by resistance for continuous and short-time rated class-A and class-B insulated d-c machines are presented. These are consistent with the recently published AIEE Standard 1A “Report on General Principles for Rating of Electrical Apparatus for Short-time, Intermittent or Varying Duty.” The information presented in this paper is intended to apply primarily to low-voltage (approximately 600 volts maximum) d-c machines with form-wound armature coils and conventional types of field coils.

Skin Effect in Bimetallic Conductors

Abstract: Mathematical expressions for a-c impedance and current distribution are derived for bimetallic conductors with circular symmetry. The results are illustrated by application to a copper-covered steel conductor in the frequency range up to 160 kilocycles. Measurements of the a-c resistance in the same frequency range provide a check on the theoretical results. The studies made on the copper-covered steel conductor indicate that its resistance is substantially that of its tubular copper portion alone and, for all but the lowest frequencies, may be taken from the simpler formulas and curves already available for tubes.