Showing papers in "Transactions of The American Institute of Electrical Engineers in 1942"
TL;DR: In this paper, the rate of mechanical deterioration of cellulose insulation is dependent on the conditions of its use and the factors of major importance are the temperature applied and the presence of oxygen and moisture.
Abstract: The rate of mechanical deterioration of cellulose insulation is dependent on the conditions of its use. Those factors of major importance are the temperature applied and the presence of oxygen and moisture. Moisture even in small amounts greatly affects the mechanical stability of the cellulose insulation. In general, the mechanical life of the insulation is reduced by half for each doubling in water content. Deterioration promoted by oxidation is most effective at temperatures below 120 degrees centigrade and is accelerated by the presence of moisture. The rate of deterioration for substantially dry insulation at temperatures above 120 degrees centigrade is dependent upon its previous history. Intermittent exposure to high temperature effects are additive. The ``eight-degree-centigrade rule,'' indicative that the rate of mechanical deterioration is doubled for each eight-degree-centigrade increase from a base temperature of 120 degrees centigrade or higher, applies most closely for practical use when the insulation under study has lost more than 50 per cent of its tensile strength.
51 citations
TL;DR: In this paper, it was recognized that the lightning discharge is not instantaneous and the emphasis was diverted from induced voltages to direct strokes as the agent to be guarded against, which had a profound influence upon the theories of lightning protection.
Abstract: ABOUT the year 1929 it first became appreciated that the lightning discharge is not instantaneous. The recognition of this fact had a profound influence upon the theories of lightning protection, the emphasis being diverted from induced to direct strokes1 as the agent to be guarded against. With the meager information then available the calculations indicated that induced voltages were unimportant when the finite time of discharge was taken into account.2 The more accurate information available today calls for a critical analysis of this subject, which is the purpose of the present paper.
49 citations
TL;DR: In this paper, the authors discussed the shielding characteristics required for transmission lines and extended these investigations to the shielding of substations, and showed that overhead ground wires or vertical masts over substations should be correctly located so as to provide shielding of the structure against direct strokes of lightning.
Abstract: AS compared to transmission lines, it is more important that overhead ground wires or vertical masts over substations be correctly located so as to provide shielding of the structure against direct strokes of lightning. In a previously published paper1 the authors discussed the shielding characteristics required for transmission lines. The present paper extends these investigations to the shielding of substations.
44 citations
TL;DR: In this article, the authors proposed a method to calculate the paths of the eddy currents and the torque in the case of permanent magnet and electromagnet, assuming that the disk is so thin that the skin effect can be neglected.
Abstract: A DEVICE which often occurs in electric machines and instruments consists of a relatively thin conducting disk rotating between the pole pieces of a permanent magnet or electromagnet. The author has received inquiries as to the method of calculating the paths of the eddy currents and the torque in such cases. The following rather simple method, which is quite accurate for a permanent magnet, seems not to be described in the literature. It assumes that the disk is so thin that the skin effect can be neglected. This is true for all frequencies that can be produced mechanically. To facilitate calculation in the special case of circular poles it is also assumed that 2πωabγ=ea is much less than one where ω is the angular frequency of rotation in radians per second, a the pole-piece radius, b the disk thickness, and γ the electric conductivity, all in centimeter-gram-second electromagnetic units. This produces a fractional error of less than ea in the eddy current densities and of less than (ea)2 in the torque. In the case of the electromagnet the situation is complicated by the presence of the permeable pole pieces in the magnetic field of the eddy currents. This may send a large demagnetizing flux through the electromagnet. An approximate solution for this case will be considered.
42 citations
TL;DR: In this article, the authors present a coherent representation of the harmonic problem in induction motors, based on the work of their predecessors, on their own work, and on their experience of experience.
Abstract: ABOUT 40 papers have been written on the asynchronous torques, synchronous cusps at running, synchronous cusps at standstill (dead points), and noise of the induction motor. The subject has been also treated in some textbooks.∗ My aim is to give a coherent representation of the harmonic problem in induction motors. It is based on the work of my predecessors, on my own work, and on my experience.
40 citations
TL;DR: In this article, a general method is given to establish equivalent circuits for the determination of the hunting characteristics, such as damping and synchronizing torques, of standard types of electrical machines.
Abstract: A general method is given to establish equivalent circuits for the determination of the hunting characteristics? such as damping and synchronizing torques?of standard types of electrical machines. The method is illustrated by setting up steady-state and hunting equivalent circuits for the salient-pole synchronous machine having amortisseur windings and for the doubly fed single-phase Selsyn with unbalanced windings, special cases of which are the capacitor motor and doubly fed polyphase motor. A companion paper, ``The Doubly Fed Machine,'' contains a detailed study of the characteristics of one of the equivalent circuits as measured on the a-c network analyzer.
30 citations
TL;DR: In this paper, series capacitors of the limited-voltage type in combination with auxiliary equipment are proposed to increase the permissible loadings of long highvoltage a-c transmission lines.
Abstract: This paper presents the results of an analytical and experimental investigation of the use of series capacitors to increase the permissible loadings of long high-voltage a-c transmission lines. Because of limitations imposed by synchronous stability and reactive kilovolt-ampere requirements, conventional lines, when extended to the higher voltages and greater lengths, cannot be loaded to values of power sufficiently high to develop maximum over-all economy. It is shown that, when suitably applied, series capacitors will make possible the desired optimum loadings and will very materially reduce transmission costs. The theoretical possibilities of using series capacitors to compensate the excessive inductive reactance of long lines have received consideration for many years. Practical series capacitors require protective equipment, but shunting of the capacitors in the earlier schemes resulted in a decrease instead of an increase in the transient-stability limits. The authors propose series capacitors of the limited-voltage type in combination with auxiliary equipment which not only protects the insulation but quickly restores the capacitors to the circuit after the faulted conductors are isolated, thus preventing a decrease in system power limit at the time of need. The application requirements of necessary apparatus are also briefly outlined. Results of analytical studies and miniature-system tests in connection with a typical application of series capacitors to one of the major lines of a typical transmission system are included. This work deals with relative transmission costs, transient stability, spontaneous hunting, and the sub-synchronous operation in the induction starting of machines. The conclusion is reached that the proposed series-capacitor scheme appears practicable for long transmission lines.
26 citations
TL;DR: In this paper, the same authors presented the equations for the hunting of a doubly-fed Selsyn machine with a-c excitation on both stator and rotor, and the form of the equations developed possesses the additional novelty of facilitating the setting up of equivalent circuits for hunting on the a-C network analyzer, and allowing the quick determination of damping and synchronizing torques directly by wattmeter readings.
Abstract: SYNCHRONOUS machines, operating with a-c excitation on both stator and rotor are used in many applications, for example, as induction frequency converters, as power and instrument Selsyn drives, and as variable speed power drives. Reference 1 has mentioned particularly the variable speed fan drive, and presented equations for the small oscillations of one such doubly fed machine. Reference 2 has also previously given the equations of hunting of the doubly fed machine (part XIV, section IV) in connection with the general study of oscillations of rotating machines. However, since the present authors have been using in their own work equations which seem to them to be more convenient and simpler in form for calculations, and since it now seems desirable to present not only general equations but also some of the more fundamental and significant performance characteristics of these machines, it is thought that this paper may now be appropriate. The form of the equations developed possesses the additional novelty of facilitating the setting up of equivalent circuits for hunting on the a-c network analyzer, and allowing the quick determination of the damping and synchronizing torques directly by wattmeter readings.
24 citations
TL;DR: In this article, the use of capacitors in banks up to 10,000 kva is being given increased consideration, and several installations having steps in this range have already been made.
Abstract: THE increased kilowatt burden on generation and transmission equipments — occasioned by the existing national emergency — calls for a reduction in the use of these equipments for generating and transmitting reactive kilovolt-amperes. When operating conditions permit the use of either capacitors or synchronous condensers, the relatively shorter production time of capacitors is making them more and more justifiable as a reactive source in the range of kilovolt-ampere ratings where economics might normally dictate a synchronous condenser.1 At the present time the use of capacitors in banks up to 10,000 kva is being given increased consideration, and several installations having steps in this range have already been made.
22 citations
TL;DR: In this paper, the Vi energy flow postulate is shown to be not generally valid, but by adding a simple term it can be made equally valid with other valid energy-flow postulates.
Abstract: The conditions which a valid postulated electric-energy flow must satisfy are given and are stated to be insufficient for its unique determination. The commonly used Vi energy-flow postulate is shown by examples to be not generally valid, but by adding a simple term it can be made equally valid with other valid energy-flow postulates. Various examples are given of the application of this corrected energy-flow postulate. On power systems the engineer commonly limits his use of the uncorrected Vi postulate to applications where the correcting term should have a negligible net effect. Various examples of such use are discussed.
21 citations
TL;DR: In this article, a 1,500-foot section length of non-leaded high-pressure gas-filled cable was installed in a steel pipe without the insulation being adversely affected due to atmospheric exposure or mechanical handling.
Abstract: 1. Nonleaded high-pressure gas-filled cable can be installed in a steel pipe without the insulation being adversely affected due to atmospheric exposure or mechanical handling. 2. No difficulty was encountered in the installation of 1,500-foot section lengths of cable on the commercial line. Based on the relatively low pulling stresses (7,200 pounds maximum), it appears perfectly feasible to install this type cable in lengths up to 2,000 feet. 3. The use of paper, preimpregnated with viscous compound, prevents migration at normal operating temperatures and allows installation on steep grades or in vertical runs without stop joints or other devices. 4. The satisfactory results on this type of cable are due in part to the development and use of a saturant of high viscosity and of excellent electrical properties. 5. The 60-cycle dielectric strength, both short- and long-time, is equivalent to that of oil-filled cable. 6. The impulse strength is at least the equal of oil-filled cable. 7 Power-factor values are approximately constant over a temperature range of 20 to 100 degrees centigrade. 8. The power factor was not affected even after six months at a temperature of 100 degrees centigrade. 9. The radial power-factor curve is flat even at 80 degrees centigrade, where impurities often cause erratic results. 10. Great uniformity of the insulation is indicated by the fact that on long-time voltage tests there are normally numerous partial failures, in addition to the completed failure. 11.
TL;DR: Discussion and authors' closure of paper 42–104 by K. B. McEachron and J. H. Hagenguth.
Abstract: In the search for means for measuring the properties of nataural lightning much can be learned from the evidence left at points struck by lightning. This paper deals principally with such evidence and the process of evaluating the characteristics of the lightning strokes responsible for the evidence. For six years a nickel-plated, 18-inch copper sphere, 878 feet above the ground atop the WSM radiator at Nashville, had been collecting data in the form of holes and pits due to lightning strokes to the sphere. A total of 150 holes of varying sizes were found together with 300 pits. A laboratory setup was made consisting of the high-capacity impulse generator together with a d-c generator so arranged that the known characteristics of lightning with respect to the so-called continuing current could be duplicated. With this equipment holes having the same appearance could be produced in copper sheets, and from the results of the test a calibration curve was produced. At the same time calibration curves were obtained for other metals in addition to copper. From these data an expectancy curve was obtained between coulombs and per cent of holes. The average hole corresponded to 15 coulombs while the maximum size hole corresponded to 240 coulombs. No satisfactory calibration was obtained for the pits, many of which no doubt were the result of high current peaks having a low coulomb content.
TL;DR: In this article, a toroidal coil was used to solve the problem of saturation and provide a linear relationship between secondary voltage and primary current in a bus protection scheme, where coupler secondaries for a given bus are connected in a series loop with the relay.
Abstract: A scheme of bus protection offering advantages in simplicity, speed, and size uses linear couplers (air-core mutual reactances) in place of current transformers. This solves the troublesome problem of saturation and provides a linear relationship between secondary voltage and primary current. The coupler secondaries for a given bus are connected in a series loop with the relay. When the currents entering and leaving the bus are equal, the net induced voltage in the relay loop is zero. For a fault on the bus, however, the net induced voltage, proportional to the fault current, operates the relay. The problems are: 1. To utilize effectively the smaller available energy. 2. To build couplers of sufficiently equal mutual reactance and unaffected by stray fields. A toroidal coil solved the latter problem. Through tests have shown that the performance is strictly linear with respect to primary currnet, practically unaffected by the primary d-c transient, and thus can be calculated accurately and simply.
TL;DR: In this paper, it was shown that loss of field in a large generator may cause serious voltage disturbance to the system and a need for some suitable protection method that will initiate disconnection of the troubled machine is indicated.
Abstract: THOUGH electrical circuits from generator armature windings outward to utilization apparatus have received much attention from a protective viewpoint in the past 20 years, relatively little attention has been given to generator field-winding protection. Calculations show that loss of field in a large generator may cause serious voltage disturbance to the system. A need for some suitable protection method that will initiate disconnection of the troubled machine is indicated.
TL;DR: In this article, the authors show that during the period of the war the need for obtaining maximum transformer overload capacity is very great, particularly under rare emergency conditions, and that the amount of overload is limited by the hottest spot in the transformer winding.
Abstract: The paper points out that during the period of the war the need for obtaining maximum transformer overload capacity is very great, particularly under rare emergency conditions. From a thermal standpoint, the amount of overload is limited by the hottest spot in the transformer winding. To obtain accurate data 1. On the actual hot-spot temperatures under rated load conditions 2. On the increase of the hot spot with load under both ultimate moderate overload and heavy short-time overload conditions approximately 50 heat runs were made on several power transformers of different ratings, representing a wide variety of design conditions. The results of the tests are given in the paper. The subject of how heavy overloads affect the life of transformers, is discussed and temperature limits somewhat higher than those given in the American Standards, Guides for Operation of Transformers, are suggested. Calculated short-time overloads are given to show the effect of transformer characteristics on overload values.
TL;DR: In this paper, a closed solution for the variation of flux and electromotive force is given, valid for any sudden change of load, including short-circuit current formation or capacitive superexcitation.
Abstract: By reducing to the same parameter with saturation the voltage-current equations for stator, rotor, and magnetic circuits of synchronous machines, a differential equation in time for the main-pole flux and the induced electromotive force is derived, a relation easy to evaluate graphically. The difference of current between the magnetic characteristic of the machine and the electric characteristic of the stator circuit determines the rate of change of the electromotive force from which all the other slow-transient magnitudes can be derived. For constant excitation voltage, a closed solution for the variation of flux and electromotive force is given, valid for any sudden change of load, including short-circuit current formation or capacitive superexcitation. The combined effect of damper circuits and rotor leakage causes a superposed rapid-transient variation manifested by an additional current peak at sudden short circuits and by a rapid initial voltage rise at sudden interruptions of the circuit. The method of solution is in principle independent of the distribution of the saturation on rotor and stator, as well as of the character of loading of the machine, be it by constant or variable impedance, by symmetrical or unbalanced currents, by active or reactive power. The common subdivision into transient and sub-transient phenomena is not identical with the separation into slowand rapid-transient effects, the physical significance of which is derived in this paper.
TL;DR: In this paper, the results of a study of current-transformer transient performance that has been made on the differential analyzer with the effects of transformer saturation more accurately considered are presented.
Abstract: THE factors involving current-transformer performance that affect the operation of protective equipment have recently received considerable attention.1–3 The fact that the transient performance may be greatly different from the steady-state performance has been recognized, but little quantitative data on transient performance have been published. Data from oscillograph records of tests and from approximate analytical methods have definitely indicated the magnitudes of the expected steady-state errors and at the same time conveyed the thought that the transient errors would be very much larger. This paper presents some of the results of a study of current-transformer transient performance that has been made on the differential analyzer with the effects of transformer saturation more accurately considered.
TL;DR: In this article, short approximate methods for the solution of several types of intangible problems which require load-curve analyses are described, such as peak loads, losses, and required capacities of equipment.
Abstract: This paper describes short approximate methods for the solution of several types of intangible problems which require load-curve analyses. Laborious effort may be expended in compiling results from a group of curves without greater precision than is believed possible to obtain from the use of one or a few synthetic curves which combine the characteristics under investigation, and permit the determination of such items as peak loads, losses, and required capacities of equipment.
TL;DR: In this paper, the results of an analytical study of tie-line power control are presented as a logical development of the general subject of power system control, and the general requirements of supplementary control are given in the companion paper.
Abstract: THE object of this paper is to present the results of an analytical study of tie-line power control. This study was made as a logical development of the general subject of power system control. Previous work1,2 has indicated the general requirements of the prime-mover speed governors and the desirability of supplementary control to insure proper load division, frequency, and time. The general requirements of supplementary controls are given in the companion paper3 by Crary and McClure. In most cases these controls are satisfactorily obtained as rather slow corrective adjustments to the speed-governor mechanisms, but for certain types of load a more active tie-line load controller, which will tend to suppress transient load swings also, may be required. An example of this is a rapidly varying load, such as a strip mill supplied from local generation as well as from a tie to a larger power system, in which it may be desirable to keep the load variations off the tie line as much as possible.
TL;DR: In this article, the problem of protecting pilot-wire circuits, briefly discussing the sources of disturbing voltages, describes two types of neutralizing transformers, and illustrates how they are used to distribute the disturbing voltage most favorably throughout the pilot wire circuit.
Abstract: THIS paper reviews the problem of protecting pilot-wire circuits, briefly discusses the sources of disturbing voltages, describes two types of neutralizing transformers, and illustrates how they are used to distribute the disturbing voltage most favorably throughout the pilot-wire circuit. The recent increase in use of high-speed pilot-wire relays for the protection of important power circuits has accentuated the need of better understanding of the pilot-wire protection problem. Therefore, a review of this general subject and a description of a new type of neutralizing transformer with mathematical formulas to determine its effectiveness, is considered timely.
TL;DR: In this article, the authors correlate experience with theory and provide a basis for determining the proper characteristics of speed governors and their supplementary control and their effect on the performance of the speed governors.
Abstract: THE development of interconnected systems has required improvements in the manual and automatic control of load, frequency, and time. The speed governors of the prime movers have always provided the medium for supplementary control of frequency, load, and time. Experience with various types of control devices and the factors influencing their functioning have been discussed frequently in the technical literature. Recently the problem has been given renewed attention1–5 with an effort to correlate experience with theory and to provide a basis for determining the proper characteristics of governors2 and their supplementary control.
TL;DR: In this paper, the first occurrence of gaseous ionization within the test specimen was detected by using a thyratron in the grounded lead of the sample with suitable connection to a rapid circuit breaker in the primary.
Abstract: STUDIES of the causes and mechanism of the failure of impregnated-paper insulation are commonly obscured by the burning due to the final complete breakdown. In a number of years of study of the more accessible properties of impregnated paper and their relation to stability and breakdown, constant attention has been given to the restriction of this burning and a nearer view of the beginnings of failure. Simple fuses and even rapid circuit breakers in the primary circuit of the testing transformer are of no avail. Some improvement is obtained by the use of a thyratron in the grounded lead of the sample with suitable connection to a rapid circuit breaker in the primary. But by far the best results, and indeed very complete success, have been reached by a method for detecting the first occurrence of gaseous ionization within the test specimen. This method is a development of the pioneer work of Paine1 and the subsequent applications of Arman and Starr and of Whitehead and Shaw,2 using resonance methods for following the oscillations which arise in the ionization of gas spaces in the insulation wall. New features which have been added are increased sensitivity, improved balancing of the Schering bridge for the frequency of maximum oscillations, the use of greater amplification, and a sensitive recording instrument for registering the first occurrence of internal ionization. The complete setup, as described in this paper, is called the “ionization recorder.” With this instrument it is possible to detect the beginnings of failure in a completely impregnated specimen initially free of gas spaces or voids, often to within one layer of the impregnated structure, and also to follow its growth, with interruption at any desired stage on the way to complete breakdown. So far, the instrument has been applied only to the study of the influence of paper density on dielectric strength and stability, and the comparative behavior of two types of paper and two types of oil. From the results it will be seen that a very intimate picture of breakdown and its causes is presented.
TL;DR: In this article, the authors proposed a method to calculate the temperatures within windings, and to know safe operating temperatures, which would enable operators to obtain the most from available equipment or to install equipment which would provide reasonable overload capacity in case of emergency.
Abstract: IN recent years operators have wanted to know how much overload a transformer would carry for a given length of time without exceeding a safe temperature. This knowledge would enable them to obtain the most from available equipment or to install equipment which would provide reasonable overload capacity in case of emergency. In order to do this, it is necessary to be able to calculate the temperatures within windings, and to know safe operating temperatures.
TL;DR: In this paper, the transient recovery voltage and its characteristic are assumed a more important place in the design and application of circuit breakers with the growth and increasing capacity of power systems.
Abstract: WHILE there have been a number of papers on recovery voltage and its effect on the operation of circuit-interrupting devices, and although the transient recovery voltage and its characteristic are assuming a more important place in the design and application of circuit breakers with the growth and increasing capacity of power systems, there has not been available to the average power-company engineer a convenient method for determining this characteristic. The present paper offers such a method and also tabulates capacitance data for the more important circuit elements.
TL;DR: The existence of transient recoveryvoltage phenomena in connection with the interruption of short circuits by circuit breakers has been recognized for a number of years, and from time to time measurements and calculations have been made on actual field circuits as discussed by the authors.
Abstract: THE existence of transient recovery-voltage phenomena in connection with the interruption of short circuits by circuit breakers has been recognized for a number of years, and from time to time measurements and calculations have been made on actual field circuits.2,5 However, while these more or less isolated and scattered instances have provided some valuable information, they have not afforded a comprehensive picture of transient-recovery voltage conditions existing in the field.
TL;DR: In this paper, temperature-aging data were presented on class-A-insulated fractional-horsepower motor stators, determined at 200, 160, and 135 degrees centigrade.
Abstract: Temperature-aging data are presented on class-A-insulated fractional-horsepower motor stators, determined at 200, 160, and 135 degrees centigrade. Of particular interest is the relative aging time to failure at the different temperatures and the resultant temperature-aging curve. This curve shows a slope of 10 to 15 degrees centigrade increase in temperature to halve the aging time to failure in the temperature range covered, 135 to 200 degrees centigrade.
TL;DR: In this article, a two-tone carrier-current telegraph system is described, which employs true frequency modulation to derive the advantages of polar current signalling, with the same spectrum efficiency as conventional amplitude systems, and secures at the same time freedom from attenuation change in the transmission medium and greater immunity to extraneous disturbing currents.
Abstract: Voice-frequency carrier-current telegraph systems used in this country and abroad have until now employed amplitude modulation, analogous to single current signalling in d-c telegraphy. A variety of so-called two-tone telegraph systems has been tried out by various workers, but none of these was adopted on a commercial scale because all required the employment of at least double the frequency spectrum space ordinarily assigned for amplitude modulation. The system described employs true frequency modulation to derive the advantages of polar current signalling, with the same spectrum efficiency as conventional amplitude systems, and secures at the same time freedom from attenuation change in the transmission medium and greater immunity to extraneous disturbing currents.
TL;DR: In this paper, the electric strength of nitrogen, dichlorodifluoromethane (Freon F-12), and mixtures of these gases were investigated for 60-cycle applied voltage.
Abstract: Results are given of an investigation of the electric strength of nitrogen, of dichlorodifluoromethane (Freon F-12), and of mixtures of these gases. Sparking voltages are presented as measured between spherical electrodes of brass and aluminum and between pointed electrodes of brass, at various spacings, and in gas at pressures ranging from one to several atmospheres. All measurements are for 60-cycle applied voltage. Dichlorodifluoromethane is found to withstand much higher voltages than either air or nitrogen; this advantage is more marked between points than between spheres, which suggests its use in certain types of insulation applications. A small percentage of dichlorodifluoromethane gas in nitrogen produces an anomalously large rise in the electric strength of the gas, indicating practical advantages of such mixtures.