Showing papers in "Transactions of The American Institute of Electrical Engineers in 1946"
TL;DR: The thermistor as mentioned in this paper is a new circuit element and control device, the thermistor, or thermally sensitive resistor, is made of solid semiconducting materials whose resistance decreases about four per degree centigrade.
Abstract: A new circuit element and control device, the thermistor, or thermally sensitive resistor, is made of solid semiconducting materials whose resistance decreases about four per cent per degree centigrade. The thermistor presents interesting opportunities to the designer and engineer in many fields of technology for accomplishing tasks more simply, economically, and better than with available devices. Part I discusses the conduction mechanism in semiconductors and the criteria for usefulness of circuit elements made from them. The fundamental physical properties of thermistors, their construction, their static and dynamic characteristics, and general principles of operation are treated. Part II of this paper deals with the applications of thermistors. These include: sensitive thermometers and temperature control elements, simple temperature compensators, ultrahigh frequency power meters, automatic gain controls for transmission systems, voltage regulators, speech volume limiters, compressors and expandors, gas pressure gauges and flow-meters, meters for thermal conductivity determination of liquids, and contactless time delay devices. Thermistors with short time constants have been used as sensitive bolometers, and show promise as simple, compact, audiofrequency oscillators, modulators, and amplifiers.
118 citations
TL;DR: In this article, the voltage gradient in the arc is affected very little by current magnitude, and the increase in apparent gradient due to voltage drop at the electrodes was found to be negligible where the arc length exceeds several feet.
Abstract: Volt-ampere characteristics of 60-cycle arcs in still air with lengths and currents such as occur in power systems have been investigated under laboratory conditions. The arcs varied in peak current from 68 to 21,750 amperes and in length from 1/8 to 48 inches. Typical oscillograms and volt-ampere curves of these tests are presented. The voltage gradient in the arc is affected very little by current magnitude. Through-out the entire range all gradients remained between 21.5 and 50 volts per inch, with 35 per cent of all values in a 5 volt per inch interval having an average value of 34 volts per inch. The increase in apparent gradient due to voltage drop at the electrodes was found to be negligible where the arc length exceeds several feet. The decrease in short-circuit current of a power system through a series arc as compared with that for the same system with a metallic short circuit has been investigated. Data are presented showing the actual reductions observed for various conditions of circuit voltage and impedance.
57 citations
TL;DR: In this article, the authors discuss lethal electric currents and their associated physiological effects, and interprets the data of a previous paper4 in accordance with an original method of analysis found useful by the author in his own investigations of let-go currents.
Abstract: This paper discusses lethal electric currents and their accompanying physiological effects, and interprets the data of a previous paper4 in accordance with an original method of analysis found useful by the author in his own investigations of let-go currents. The present analysis concerns itself with threshold currents likely to produce instantaneous electrocution in one-half per cent of a large groud of normal men. Although the conclusions are derived from tests made on animals, it is believed that the results may be indicative of what might be expected to occur in man. The majority of the work is based on experiments made at 60 cycles with shock durations of 0.03 to 3.0 seconds. Predictions of lethal currents for both direct current and capacitor discharges, while more speculative because of the limited data available, are included because of their importance due to the greatly increased use of direct current and electronic equipment.
46 citations
TL;DR: The mho relay unit was first used 15 years ago as the directional unit for an early-type reactance relay as discussed by the authors, and it can be said that "mho" applied to relays is a new term applied to an old principle.
Abstract: THE mho relay unit was first used 15 years ago as the directional unit for an early-type reactance relay. Thus it can be said that “mho” applied to relays is a new term applied to an old principle. The mathematical justification for the term has been given in a paper1 describing the use of the mho unit in a carrier-current relaying scheme. The mho unit in its present form is a directional impedance unit whose accuracy is comparable with that of the reactance ohm unit used in a distance relay.
24 citations
24 citations
TL;DR: In this paper, a differential analyzer study of the starting characteristics of 2-phase induction motors is presented, and summary curves based upon the conclusions reached are presented in a form useful to motor designers.
Abstract: This paper is the result of a differential analyzer study of the starting characteristics of 2-phase induction motors. The prototype of the motors investigated is the small 2-phase machine commonly used in closed cycle control systems. The performance equations of the induction motor are solved, and summary curves based upon the conclusions reached are presented in a form useful to motor designers. No published data of this type have come to the attention of the authors. It is hoped that the results herein reported can be utilized in the design of better motors for servo applications.
22 citations
TL;DR: In this paper, Hartley's analysis of free oscillations is used to demonstrate the development of negative resistance by what is essentially a modulation process, and applications are then made to the three classes of oscillations listed.
Abstract: Sustained oscillations exhibiting many of the properties of free oscillations are found in saturable reactor circuits under appropriate conditions. The frequencies of such oscillations are classified in relation to that of the driving source as 1. Incommensurable. 2. Subharmonic, and multiples thereof. 3. Harmonic. General properties of the oscillations classified are elucidated by reference to an analysis of R. V. L. Hartley's, dating back to 1917. In part I a comparatively simple form of analysis is used to demonstrate the development of negative resistance by what is essentially a modulation process. Applications are then made to the three classes of oscillations listed. Some of the simplifying assumptions of part I are removed in part II to approximate practical conditions more closey for the evaluation of a specific product, the third subharmonic. Quantities evaluated over wide ranges of the variables involved include the impedance of the non-linear coil to the subharmonic, the subharmonic amplitude, its stability, and the conditions required for starting and maintaining the oscillation. Experimental data are found in general agreement with the results of computation.
21 citations
TL;DR: In this article, a point to emphasize is that further progress in this industry-wide problem can be attained only through continued research and studies directed particularly to the remaining major questions, in this manner it will be possible to pursue in future developments the principles of system-insulation rationalization to their fullest economic possibilities.
Abstract: THE STRIDES achieved since the early thirties in the field of system-insulation rationalization are well known in recent technical literature1–7 and need not be reviewed here. However, a point to emphasize is that further progress in this industry-wide problem can be attained only through continued research and studies directed particularly to the remaining major questions. In this manner it will be possible to pursue in future developments the principles of system-insulation rationalization to their fullest economic possibilities.
19 citations
TL;DR: In this article, an inert gas medium is used to provide an inert medium by which the pressure at the surface of the transformer fluid is kept slightly above atmospheric, and the fluid is not exposed to the moisture and oxygen of the air, as it is with the so-called open-breather or oil-conservator types unless the latter communicate with the outside atmosphere through chemical agents.
Abstract: THE USE of an inert gas in enclosed electric equipment has increased considerably in recent years. In transformers an inert gas is used in the space provided above the transformer fluid to allow for its volumetric expansion with temperature rise. There the function of the gas is to provide an inert medium by which the pressure at the surface of the transformer fluid is kept slightly above atmospheric. Thus the fluid is not exposed to the moisture and oxygen of the air, as it is with the so-called “open-breather” or “oil-conservator” types unless the latter communicate with the outside atmosphere through chemical agents. In gas pressure cables, however, the inert gas is used at pressures up to approximately 15 atmospheres in order that the cables may operate successfully at electric stresses that are higher than otherwise would be possible.1–3
19 citations
TL;DR: The binomial law as discussed by the authors states that if n events have each a probability or rate of occurrence p, then the probabilities that 0, 1, 2, 3, etc., of the n events occur simultaneously, are given by the consecutive terms of the binomial function [p + (1 − p)]n.
Abstract: THE PROBABILITY of simultaneous occurrences of events for which the individual rate of occurrence is known can be determined by the well-known binomial law. This law states that if n events have each a probability or rate of occurrence p, then the probabilities that 0, 1, 2, 3, etc., of the n events occur simultaneously, are given by the consecutive terms of the binomial function [p + (1 − p)]n.
18 citations
TL;DR: The use of geometric mean distance for calculating reactance of parallel conductors is increasing, so much so that the self-geometric mean distance often is tabulated in catalogs of heavy conductors along with other characteristics, such as resistance, current capacity, and weight.
Abstract: THE USE of geometric mean distance for calculating reactance of parallel conductors is increasing, so much so that the self geometric mean distance often is tabulated in catalogs of heavy conductors along with other characteristics, such as resistance, current capacity, and weight.
TL;DR: In this article, it was shown that the electrical loadings of long distance transmission systems may be increased a significant amount by the use of automatically controlled excitation and proper co-ordination of the apparatus characteristics.
Abstract: THE renewed attention now being given to transmission of power from hydroelectric sites located at moderate and long distances from their load areas requires a re-evaluation of some of the factors affecting power system stability. This paper shows that the electrical loadings of long distance transmission systems may be increased a significant amount by the use of automatically controlled excitation and proper co-ordination of the apparatus characteristics.
TL;DR: In this article, the application of the transient analyzer to the solution of servomechanism problems by the electrical-mechanical analogy method is described, together with the fundamental concepts by which the systems can be defined in terms of dimensionless parameters.
Abstract: This paper describes the application of the transient analyzer to the solution of servomechanism problems by the electrical-mechanical analogy method. The analogies for angular position servomechanisms are developed in detail together with the fundamental concepts by which the systems can be defined in terms of dimension-less parameters. This permits the results to be given in dimensionless form suitable for general application. Typical solutions of representative systems are given in the form of transient response curves. These show the response characteristics for suddenly applied constant velocity and sinusoidal motion. Also shown are the effects of varying the controlling parameters of the system including the stiffness constant, one, two, and three time delays, and methods of producing system stability including negative RC feed-back and anticipatory control. A method is developed for setting up the analogy for a specific system on the transient analyzer by a suitable change in time and impedance bases.
TL;DR: In this paper, the authors presented formulas for the armature current, field current, and torque of d-c machines on short-circuit conditions, in which the two windings are not, in effect, in quadrature with one another and are mutually inductive.
Abstract: This paper presents formulas, in terms of easily evaluated coefficients, for the armature current, field current, and torque of d-c machines on short circuit. The method of the paper makes it unnecessary to calculate the mutual inductance between the armature and field windings. Heretofore, this mutual inductance (between the two windings which normally are in quadrature with each other) has made it exceedingly difficult to calculate current and torque on short circuit. Under short-circuit conditions, the armature and field windings are not, in effect, in quadrature with one another and are mutually inductive partly because of saturation of the flux path at one side of the poles and partly because of commutation phenomena. These circumstances create difficulties uniquely overcome in the paper. A basic feature of the paper is the expression for the relation between flux, armature amperes, and field amperes. Calculations cannot be made without establishing this relationship (plotted for a specific case in Figure 9) and a simple expression for it has not been presented before to the author's knowledge. Another important feature, also believed to be new, is the development of an expression for the resistance to current flow created by the reactance voltage of the alternating current in the armature winding. A third feature is a formula for estimating the time constant of the armature circuit using an average coefficient of inductance. The results are applied to several machines and the calculated performance compared with test data. In most cases, particularly with large machines having bar windings, approximate calculations can be made without need of manufacturer's data.
TL;DR: In this article, Schuck et al. presented a fundamental interpretation of observed performance characteristics of high interrupting-capacity power fuses of the current-limiting type and verified their results by a study of test performance.
Abstract: THIS PAPER is part of an analytical study conducted for the purpose of establishing a sound fundamental interpretation of observed performance characteristics of high interrupting-capacity power fuses of the current-limiting type. Some of the more important conclusions, which have been verified by a study of test performance, are presented and discussed in the foregoing part of this paper by C. L. Schuck. In another sense this paper is an application of the analytical methods developed in the two papers on “Geometry of Arc Interruption.”15,16 This application to fuse performance is particularly fitting since the interval from the inception of a short circuit until the arc voltage of the fuse is introduced, may be predetermined quite accurately from the melting characteristics of the fuse. Conductor heating and energy equations are presented for the first time which include all the essential variables to predetermine the arc energy to be developed by the interrupter for various magnitudes of arc voltage, degrees of circuit asymmetry, and melting times of the fuse.
TL;DR: In this article, the authors describe a servomechanism as a device which acts with power on the difference, or error, between a desired quantity and an actual quantity, and it acts in such a way as, 1. To make the error approximate zero in the steady state.
Abstract: AN excellent way to describe a servomechanism is to picture it as a device which acts with power on the difference, or error, between a desired quantity and an actual quantity. It acts in such a way as, 1. To make the error approximate zero in the steady state. 2. To limit peak errors and the error-time integral when the output quantity is following a typical random input quantity. 3. To recover from sudden disturbances with adequate speed of response and degree of stability.
TL;DR: In this article, the main results of a study of the various phenomena which take place during the interruption of currents in high vacuum are given, and the experimental results obtained lead to a theory of the basic mechanism affecting switching.
Abstract: The main results of a study of the various phenomena which take place during the interruption of currents in high vacuum are given. The experimental results obtained lead to a theory of the basic mechanism affecting switching in high vacuum. With a proper design of the switch, a constant working pressure can be obtained which represents an equilibrium between gases and vapors evolving from the electrodes and a pumping action based on the sputtering of cathode material. A detailed study is made of the factors determining the loss of electrode material because of switching. The most essential design features of a vacuum switch are discussed briefly.
TL;DR: In this article, it was shown that stalling a synchronous machine with the field voltage applied can result in pulsating torques greater than those obtained by inadvertent synchronizing 180° out of phase.
Abstract: ASYNCHRONOUS operation of synchronous machines has been the subject of numerous articles in the technical literature, for example, the articles of Fechheimer,1 Hay and Mowdawalla,2 Putman,3 Park,4 Linville,5 Lauder6. The fact that articles on this subject continue to be of primary interest to design and operating engineers is attributable to the importance of satisfactory operation at asynchronous speeds. It is only through a precise knowledge of the conditions present in asynchronous operation that machines can be designed for and operated through these asynchronous periods satisfactorily. As examples of the extreme conditions which can arise during asynchronous operation, it should be noted that stalling a synchronous machine with the field voltage applied can result in pulsating torques greater than those obtained by inadvertent synchronizing 180° out of phase;6 or that the currents in the damper bars on the trailing half of a pole can be considerably greater than the currents in the corresponding bars on the leading half of the pole, and the resulting unequal heating will influence the design of the damper winding to a considerable degree. Because of the importance of these and similar phenomena, the problem of asynchronous operation must be studied continuously until a complete, easily visualized, and easily applied solution is obtained.
TL;DR: In this paper, the authors simplify the equations from Doherty and Nickle's classic paper on "Synchronous Machines" by eliminating the terms having to do with field current and arranging them in the form of a simple calculation sheet.
Abstract: IN 1926, Messrs. Doherty and Nickle presented their classic paper on “Synchronous Machines” giving a complete and thorough analysis. Since many fractional horsepower engineers have occasion to design small reluctance motors (synchronous motors without field excitation) and these engineers in general have no need of becoming thoroughly familiar with the great and extensive field of synchronous motor theory, it has seemed advisable to simplify the equations from this famous paper by eliminating the terms having to do with field current and to arrange them in the form of a simple calculation sheet. It also has been found possible by the use of calculated curves to arrange a simple method of calculating the synchronous pull-out torque.
TL;DR: The need for more adequate discrimination by means of distance relays, between fault conditions and power swings has been heightened in recent years by the construction of longer transmission lines and by the transmission of larger amounts of energy over existing lines as discussed by the authors.
Abstract: THE NEED for more adequate discrimination by means of distance relays, between fault conditions and power swings has been heightened in recent years by the construction of longer transmission lines and by the transmission of larger amounts of energy over existing lines.
TL;DR: This paper considers engineering problems in the application of compandors and describes the circuit principles involved in the equipment.
Abstract: Prior to the war a compandor was developed for general use on telephone circuits of the Bell System. This equipment provides power range compression at the transmitting end and power range expansion at the receiving end of a telephone channel. The resulting crosstalk and noise reductions of about 25 decibels are large enough to make useful circuits out of channels which otherwise would be unworkable. This paper considers engineering problems in the application of compandors and describes the circuit principles involved in the equipment.
TL;DR: In this paper, the advantages of the frequency response approach to the analysis of automatic control systems, as contrasted to the analytic solution of transient responses, are discussed. And the equivalence of information available from the two approaches is demonstrated.
Abstract: This paper illustrates the advantages of the frequency response approach to the analysis of automatic control systems, as contrasted to the analytic solution of transient responses. At the same time the equivalence of information available from the two approaches is demonstrated. A numerical example is given based upon a torque amplifier using a motor-generator type control.
TL;DR: In this paper, a series of tests on two sizes (AN-16 and AN-8) of insulated aircraft wires and cables were made to determine their permissible short-time current-carrying capacities.
Abstract: This paper gives the results of a series of tests on two sizes (AN-16 and AN-8) of insulated aircraft wires and cables, which were made to determine their permissible short-time current-carrying capacities. The times under consideration ranged from 0.01 to 1,000 seconds. A description is given of a very simple but adequate electrical test together with an accompanying insulation test to determine what are considered permissible transient temperatures. Tentative recommendations of short-time current-carrying capacity for aircraft cable sizes AN-22 to AN-00 are made.
TL;DR: Information relative to d-c short-circuit currents has been limited to theoretical analyses based on formal solution of the differential equations of current flow and the machine inductance and resistance values.
Abstract: KNOWLEDGE of the short-circuit characteristics of d-c machines is an essential factor in the design of d-c electric systems having a large low-voltage machine capacity concentrated in a small area. This information is particularly important in the design of systems such as those encountered aboard ship where circuit breakers, fuses, relays, and other protective equipment must be so applied and co-ordinated as to provide a high degree of reliability and service continuity. Available information relative to d-c short-circuit currents has been limited to theoretical analyses based on formal solution of the differential equations of current flow and the machine inductance and resistance values. As a tool in the routine design of d-c systems, this information has not been adequate, particularly when estimates must be made of the effect of fault resistance, choice of machine construction, and so forth.
TL;DR: In this paper, the authors outline system characteristics encountered when series-capacitor compensation is used, with a view toward solving the problems arising therefrom, and no attempt will be made to reexamine the relative cost of transmission with and without series compensation.
Abstract: SERIES capacitors have been recognized for some time as a means of increasing the amount of power transmitted over a long transmission line and as a means of increasing the distance that alternating-current power can be transmitted economically.1 The basic concept of neutralizing any portion of the series inductive reactance of a long transmission system by means of series capacitors is theoretically sound. The practical application of series capacitors for such service introduces several new and interesting problems of system design and operation, which while capable of solution will require the attention of engineers of both the equipment manufacturers and the operating companies. It is the objective of this paper to outline system characteristics encountered when series-capacitor compensation is used, with a view toward solving the problems arising therefrom. No attempt will be made to reexamine the relative cost of transmission with and without series compensation. In fact, the cost of the compensated system will be influenced to a certain degree by the methods used to solve the problems arising through use of series compensation.
TL;DR: In this paper, an 8-channel microwave relay system is described, which uses radio frequencies approaching 5,000 megacycles, where the waves are concentrated into a sharp beam and do not travel along the earth much beyond seeing distances.
Abstract: An 8-channel microwave relay system is described. Known to the Army and Navy as AN/TRC-6, the system uses radio frequencies approaching 5,000 megacycles. At these frequencies, there is a complete absence of static and most man-made interference. The waves are concentrated into a sharp beam and do not travel along the earth much beyond seeing distances. Other systems using the same frequencies can be operated in the near vicinity. The transmitter power is only one four-millionth as great as would be required with nondirectional antennas. The distance between sets is limited but by using intermediate repeaters communications are extended readily to longer distances. Short pulses of microwave power carry the intelligence of the eight messages utilizing pulse position modulation to modulate the pulses and time division to multiplex the channels. The eight message circuits which each AN/TRC-6 system provides are high-grade telephone circuits and can be used for signaling, dialing, facsimile, picture transmission, or multichannel voice frequency telegraph. Two-way voice transmission over radio links totaling 1,600 miles, and one-way over 3,200 miles have been accomplished successfully in demonstrations.
TL;DR: In this paper, the authors demonstrate that the attainment of good service reliability of most electric power cables has become substantially more a function of the characteristics of the sheath than of the insulation.
Abstract: OPERATING EXPERIENCES have demonstrated that the attainment of good service reliability of most electric power cables has become substantially more a function of the characteristics of the sheath than of the insulation. Modern underground installations of impregnated-paper-insulated, lead-covered power cable include 1. Solid-type cable with (a). Compound-filled joints without reservoirs. (b). Oil-filled joints with reservoirs. 2. Oil-filled cable operated at 10- to 15-pound gauge pressure. 3. Gas-filled (or pressure) cable operated at (a). Low pressure (10- to 15-pound gauge). (b). Medium pressure (24- to 40-pound gauge). (c). High pressure (150- to 300-pound gauge).
TL;DR: In this article, a small resistance and capacitance circuit connected between cathode and anode of each tube delays the voltage rise the few microseconds necessary to eliminate gas cleanup, which results in short tube life because of residual ions attracted at high velocity to the negatively charged anode with consequent gas cleanup.
Abstract: In certain common rectifier and inverter circuits, gas-filled rectifier tubes supplying highly inductive loads with firing delayed by grid control, are subjected to the application of high rates of rise of initial inverse voltage. This phenomenon results in short tube life because of the sputtering of anode material by the impact of residual ions attracted at high velocity to the negatively charged anode with consequent gas cleanup. The paper describes a method of slowing down or cushioning this rate of rise of initial inverse voltage. A small resistance and capacitance circuit connected between cathode and anode of each tube delays the voltage rise the few microseconds necessary to eliminate gas cleanup. Life test data and practical applications are cited.