Showing papers in "Transactions of The American Institute of Electrical Engineers in 1924"

Certain Factors Affecting Telegraph Speed

Abstract: In considering methods for increasing the speed of telegraph circuits, the engineer is confronted by the problem of transmitting over a circuit the maximum amount of intelligence using a given frequency range, without causing undue interference, either in the circuit being considered or from that circuit to other circuits. In this paper the following two fundamentally important factors in connection with this problem are given principal attention: 1. Signal shaping, i. e., giving signals the best wave shape before impressing them on the transmitting medium so as to be able to send signal elements at maximum speed without undue interference into other circuits. 2. Choice of codes so as to transmit the maximum amount of intelligence with a given number of signal elements. These factors are discussed with the idea of indicating the best methods, as well as to give an idea of what may be expected from these methods. In connection with the choice of codes, consideration is given to the effect of codes differing in the number of ``currentt values'' employed. By this is meant the number of different current values which are employed in a system in forming the different characters.

Experimental Analysis of Stability and Power Limitations

Abstract: A method of determining the power and voltage stability limit of a transmission system taking into account the characteristics of the synchronous condenser and load in conjunction with the characteristics of the line is described. The power limit of a straight 500-mile transmission line is calculated by this method. The power limit is also calculated for the same line with a synchronous condenser at the mid-point which divides the line into two sections. The addition of the synchronous condenser at the mid-point increased the power limit 42 per cent. Tests were made on a 625 kv-a. transmission system operated at 2300 volts to determine experimentally the power and voltage stability limit of a transmission line with a synchronous condenser at the mid-point. The tests check closely with the calculated values. Tests on hunting caused by prime mover pulsations, line characteristics and voltage regulator adjustment were made. It was found that the damper windings on synchronous condensers do not have much effect in reducing hunting, particularly at resonant points. There was practically no difference between the standard high-resistance windings used for starting purposes and low resistance copper damper windings. On a high-resistance and low-reactance transmission line hunting was found to occur at high condenser field excitations. The addition of reactance stabilized the system. On high-voltage transmission lines the reactance is high as compared to resistance and no difficulty from hunting due to line characteristics is to be expected.

Free Convection of Heat in Gases and Liquids-II

Abstract: The present paper is an extension of my earlier work which was found necessary in order to account for the observed convection for both large-and small temperature differences. General expressions are developed, by the method of dimensions, which enable us to calculate the convection from any system of similar bodies when the three undetermined constants K, m, and n have been experimentally determined. The available experinmental data for horizontal and vertical cylinders, spheres and plane surfaces have been analyzed and the results expressed in the form of simple equations.

Power Transmission

Abstract: This paper briefly reviews the development of power transmission, pointing out the power limitations of long distance, high capacity transmission systems. The paper serves as a general introduction to a group of papers, giving the results of analytical and experimental investigations of the power limits and stability of transmission systems. This group of papers which is to be presented at the A. I. E. E. Midwinter Convention includes, in addition to this paper by Mr. Hanker, papers by R. D. Evans and H. K. Sels; R. D. Evans and R. C. Bergvall; and C. L. Fortescue and C. F. Wagner.

Surface Iron Losses With Reference to Laminated Materials

Abstract: Surfaces or pole-face losses are assumed to be governed by ten factors and the influence of each on the resulting losses is considered. After reviewing the work of the previous investigators an account is given of some rather extensive tests recently completed by the writers. These tests cover results obtained on an experimental salient pole machine and an experimental 3-phase induction motor. Data are given for various types and thicknesses of commercial sheet. For a given material and machine the surface losses are assumed to be a function of the air-gap induction, ratio of slot width to single air gap, tooth frequency and slot pitch or width. The laws of variation of surface losses with respect to these variables are deterl mined from experimental results and are shown to be in generat exponential. The relation between hysteresis and eddy-curren losses and the effect of variations in thickness and resistivity of laminations is considered in some detail. Simple methods are given for applying these results to actual design problems which involve plotting the various functions on double log paper, a slide rule being then sufficient for all calculations. The appendix gives a description of a graphical method of separating the various types of core losses which exist in a polyphase induction motor.

Lightning and Other Transients on Transmission Lines

Abstract: A great many uncoordinated researches and observations have been made of lightning on transmission lines both in the field and in the laboratory. It is the purpose of this paper to coordinate this work with a view of determining the various types and order of magnitude of predatory voltages to which transmission lines are subject. No claim is made for exact results. If it were possible to obtain such results, they could apply only to specific cases. A knowledge of the general types of disturbances and their order of magnitude should be of great value in determining the best means of providing against them. Failures of apparatus can be provided against in a number of ways, for instance, by excessive insulation; by less insulation but a design to prevent local high stresses; by prevention of high lightning voltages by placing the line under ground; by greatly limiting the possible voltage by a ground wire; by limiting the time of application of the high voltage by arresters; or by combinations of the above. Obviously, the matter of design and economics is also of importance in considering the problem of protection. The technical part of the discussion will not be limited to cloud lightning, but will cover other disturbances. Recent work of the author with his lightning generator and model transmission lines with and without ground wire will be included.

Theory of Three-Circuit Transformers

Abstract: The characteristics of three-circuit transformers, the literature of which is very meager, are discussed here in considerable detail. The features of the scheme of treatment are as follows: 1. The scope and general aspects of the problems of three-circuit transformers are reviewed. 2. Some peculiar phenomena of considerable theoretical interest are cited. 3. An electrical network equivalent to the magnetically interlinked circuits of a three-circuit transformer is developed, useful in visualizing the problem and in predicting by inspection a number of its characteristics. 4. Two physical interpretations of the equivalent network are given to assist the understanding of its principle and its applications. 5. The case of auto transformers interconnecting three circuits is interpreted so that the formulas developed for three-circuit transformers become universally applicable regardless of the presence or absence of metallic interconnection among the three circuits inside the case. 6. Formulas are developed for the calculation of regulation with various loads in the different windings. 7. Formulas are developed for the division of load between two primary circuits, or two secondary circuits in parallel. 8. Formulas are developed for the equivalent effective impedance for short circuits. 9 The behaviour of a three-circuit transformer operating in parallel with a two-circuit transformer is analyzed so as to determine the flow or distribution of load kv-a. in the network. 10.

The Hysteresis Character of Corona Formation

Abstract: To begin with the hysteresis character of 60-cycle corona formation was indicated by two factors: (1) the value of the crest voltage was of dominating importance in the corona loss-voltage relation and (2) the value of the power lost in coronafrom a high voltage transmission line approximated that given by the product of the voltage in excess of the critical voltage and the line charging current. Diagrams of the cyclic instantaneous voltage-charge relation in corona formation were obtained and revealed the facts that in a given case the charge lags behind the corresponding voltage by an approximately constant amount and that the energy dissipated per cycle is proportional to the product of the crest voltage and the difference between the crests of the voltage and the critical voltage. The corresponding equation for the full corona loss-voltage relation is P = 4f C (E2 - E E 0 ). 60-cycle brushes, coronas and streamers are due to the activities of ions carrying charges largely of the same sign as that of the conductors from which they emanate. The factors that control brush formation are considered. Local corona is due to an incomplete unstable brush pattern. Full corona is correspondingly due to a complete stable brush pattern. In relation hereto critical voltage, crest voltage and irregularity factor are defined.

Theory of D-C. Excited Iron-Core Reactors and Regulators

Abstract: In the usual electrical machinery the magnetic saturation characteristic of iron is a handicap and in a-c. circuits gives rise to such undesirable characteristics as wave dis-tortion and variable reactance, decreasing with increasing load. Furthermore, these characteristics are inherent in the material and can not be controlled by design to suit individual requirements or changing load conditions. Control of these characteristics can however, be accomplished the mean magnetic density in the core be controlled by means of a suitable d-c. excitation, in which event, the saturation characteristics of the iron can be put to some useful applications, (1) APPLICATION AS A FREQUENCY MULTIPLIER The second and third harmonics of magnetization have been utilized in radio to multiply the supply frequency. Using a suf-ficient number of stages, theoretically any desired radio frequency may be obtained from commercial frequencies. However, the efficiency and regulation of the scheme are very poor, and this application has therefore become almost obsolete by the advent of the vacuum tube oscillator and the high-frequency alternator. When used at all, the number of stages would be kept to a minimum. (2) APPLICATION AS A SERIES CURRENT-LIMITING REACTOR The ordinary iron-core reactor is saturated at increasing values of load, and thus having a much lower reactance at short circuit than at normal load, is undesirable as a current-limiting reactor.

The Magnetic Properties of the Ternary Alloys Fe-Si-C

Abstract: The variations in the magnetic properties of iron and iron-alloys, even of supposedly constant composition, has been puzzling to the users and investigators of ferro-magnetic materials ever since the introduction of such materials for electrical apparatus. The author started to investigate this problem over ten years ago at the University of Illinois, and has continued it at the Westinghouse Research Laboratory since 1916, concentrating on iron and iron-silicon alloys. While the results obtained do not eliminate 100 per cent of the difficulties, they go a long way in that direction. It has been found that carbon is largely responsible for the variations, because of the fact that amounts so small as previously to be regarded as traces?less than 0.01 per cent?remain dissolved in the iron in the solid state, even after slow cooling, and have a tremendous influence on the magnetic properties. Of much less effect is carbon precipitated as pearlite, free cementite and graphite, the effect being in the order named. If the effect of dissolved carbon be represented by 100, the effect of carbon as pearlite is 16.5, of carbon as Fe 3 C 2.25, and of carbon as graphite nearly nil. The form assumed by carbon?aside from the carbon in solution?depends largely on the silicon content, and can best be explained by referring to Fig. 29.

The Transmission Unit and Telephone Transmission Reference Systems

Abstract: Consideration is given to the method of determining and expressing the transmission efficiencies of telephone circuits and apparatus, and of the desirable qualifications for a unit in which to express these efficiencies. The ``transmission unit'' described in this paper has been selected as being much more suitable for this purpose under present conditions than the ``mile of standard cable'' which has been generally used in the past.

Effects of Time and Frequency on Insulation Test of Transformers

Abstract: Permanently grounded transformers mnust be given the insulation test by inducing the necessary voltage across the windings. The A. I. E. E. Standards specify that the time of induced voltage tests be the same as for high potential test. In certain cases where the transformers are of very large capacity the induced voltage must be made at a frequency several times higher than normal. Since the dielectric strength of most insulating materials decreases with an increase in the frequency, an investigation has been made to determine the proper and fair length of time to make induced voltage test when the frequency is higher than normal. Following are the main points brought out in the investigation, Above a certain voltage, time of voltage application as well as voltage causes failure of insulation. The dielectric strength can be expressed as a function of both time and voltage by an equation on of the form Kv. = A(a + 1-a/?T in which A is the kilovolts necessary to cause failure in one minute ``a'' is a constant representing the ratio of strength for infinite time to the one minute strength and T is time in minutes. The value of ``a'' varies for different materials apparently depending mostly on the dielectric loss.

The Function and Design of Horns for Loud Speakers

Abstract: A discussion of the function of the horn, together with theoretical consideration as to the design of the horn to perform this function in the best way, are given. In the body of the paper, a proof is given to show that the exponential increase in section gives the best results. For this reason, a large part of the appendix is given to the analytical solution of sound propagation in exponential horns. From the results of this work and the well known equations relating first order effects in the telephone receiver, formulas are developed which make possible the design of horns.

Dielectric Field in an Electric Power Cable-II

Abstract: The writer presented a paper in 1919 on the three-conductor cable, giving experimental results for assisting in the calculation of quantities such as capacity, insulation resistance, dielectric loss, temperature rise, etc., and also data on the calculation of stresses at various points in the dielectric. Most of the data were based on cable models composed of metallic electrodes surrounded by conducting electrolyte. In the present paper the old data are amplified both in regard to geometric properties and stresses of three-conductor cables, not only in regard to the range of sizes covered, but especially, inasmuch as the present paper includes cables with sector-shaped conductors. The cable models used are entirely different, being in the form of tinfoil sheets. Curves are given by means of which stresses can be calculated in various important parts of the cross-section of three-conductor cables with either round or sector-shaped conductors.

Harmonics Due to Slot Openings

Abstract: This paper represents a brief graphical-analytical exposition, followed by a mathematical development of the harmonics due to slot openings These were proved to be even and odd multiples of the number of slots plus and minus one. The modifications upon the torque speed curves of these harmonics have been discussed. A simple Fourier analysis underlies the whole phenomena.

Power Limitations of Transmission Systems

Abstract: Several independent studies have been made recently to determine the economies of a large, uniform power system. The two studies of more general interest were those conducted by the Department of the Interior, under the direction of W. S. Murray, for the Superpower Zone, and by F. G. Baum for the United States. Both of these investigations are available in published form. During the progress of the Superpower Survey, one of the longest transmission lines proposed was that extending 350 miles from the Niagara Falls Development to New York City. Under emergency conditions on this line, the power limit for the maximum amount of power was approached by two twin-circuit tower lines with three circuits carrying the emergency load. The maximum power limit would have been exceeded if two single-circuit tower lines had been employed, even though the transmission voltages and the total copper cross-section were the same as with the two twin-circuit tower lines. Similarly, several long, high-voltage lines will be required in a nation-wide system, especially through the middle western region as shown by Mr. Baum's report. The tendency to extensive transmission systems has emphasized the necessity of considering the factors which will limit the amount of power that can be transmitted any distance with the highest practical transmission voltage.

Tooth Pulsation in Rotating Machines

Abstract: 1. An experimental method is presented of checking the magnitude of flux pulsations in the teeth of rotating machines where both members are slotted. The method consists in using metallic electrodes shaped like the teeth of a machine and an electrolyte or mercury to represent the air. Voltage is applied between the two members and the current through the tooth under consideration is measured. The magnitude of this current under different conditions is proportional to the magnitude of the flux which would flow under the analogous magnetic conditions. 2. The test results are compared with the pulsation amplitudes as calculated by two methods. The test results are in general slightly lower than the calculated but the agreement is fairly good. 3. It is believed that either of the above-mentioned methods can be used to calculate tooth pulsations without serious errors where saturation effects are not appreciable. These methods should be specially useful in determining which of two or more designs would be subject to the lesser pulsation losses. 4. The effect of saturation in the iron is determined experimentally by making the ratio of the mercury to the electrode resistance small. This ratio corresponds to the magnetic permeabitity. The effect of the tooth resistance on the amplitude of the pulsation is calculated by assuming three resistances in series, namely, the stator and rotor tooth resistances and the air gap resistance. The calculated and test values check reasonably well. 5.

Power Measurements at High Voltages and Low Power Factors

Abstract: A description is given of the apparatus for the measurement of power as low as a fraction of a watt at power factors approaching zero and voltages as high as 175 kv to neutral A standard make of portable wattmeter was used having maximum ranges of 15 watts, 375, 75 and 150 volts and 20 per cent power factor To this wattmeter was adapted a three-megohm water column resistance multiplier In the original form of the wattmeter the origins of certain errors, due to capacitances chiefly, were studied and methods for their elimination were subsequently determined Integrity tests were developed by which the values of error powers were obtained and used as guides in making subsequent adjustments for the reduction of such errors to zero These integrity tests were checked by using the wattmeter for the measurement of known amounts of power Reconnaissance studies were made of the voltage-corona power loss relations for rope laid copper, 091-in, lock wire smooth copper, 091-in and concentric strand aluminum, 1006-in diameter transmission line conductors in rain and fair weather at differing degrees of humidity, temperatures, and barometric pressures, from ``initial'' to ``full'' corona formation This class of studies was extended to corona loss values as offered by a wide variation of the ``surface roughness'' of conductors subjected to high voltages The losses for a single brush were measured and the shielding effect of groups of brushes was studied Losses to single strings of insulators under different conditions were determined

Single-Phase Motor-Torque Pulsations

Abstract: This article gives results of a study of the vibrations of small single-phase induction motors, with a view to determining their causes and eliminating the noise which they produce. The possible sources of such vibrations were analyzed, and an experimental study was made in which the principal cause was definitely determined to be the double-frequency variation of the electromagnetic torque developed by the motor. This variation of torque is fairly obvious when it is considered that the power input to the motor is pulsating and the output is uniform, but it was found that the torque variation at no-load was also very pronounced, a fact which does not seem to have been previously described. A description of the experiments made, a theoretical analysis of the torque variations, and a comparison of test with calculated results are given.

Temperature Rise of Stationary Electrical Apparatus as Influenced by Radiation, Convection and Altitude

Abstract: Part I of the paper takes up first the division of losses by radiation and convection from tall vertical planes. It is shown that the loss by convection from tall planes can be expressed by the formula W c = 0.0014 A ?5/4 in which W c is the watts, A the square inches of surface and?the temperature rise in degrees centigrade. It is then shown that the division of losses from a black plane is, for temperature rises up to 100 deg. cent., approximately 45 per cent convection and 55 per cent radiation. Based upon this division, a simple formula is given for determining the ratio of losses for an irregular surface where the greater part of the loss is by convection. The effect of various colors on the temperature rise of transformerse having both plain and corrugated tanks is discussed. In Part II it is shown that altitude does not affect radiation. The general average of the results obtained by various investigators shows that convection varies as the square root of the air density. Based on this, it is shown that for a constant loss by convection the temperature rise increases about 4.6 per cent for each 1000 meters increase in altitude. For transformers where a part of the loss is by radiation (unaffected by air density) the effect is reduced by the ratio of the convection loss to the total loss.

Some Theoretical Considerations of Power Transmission

Abstract: The following points are developed in the paper: 1. A proof of the circle diagram maintaining therein the idea of the angle between the generator and receiver voltages. 2. It is shown how the characteristics of the synchronous condenser limit the maximum power that can be transmitted over a line. 3. The effect of character of load on stability. 4. Comparison of 500-mile straightaway line with 500-mile line with condenser at mid-point.

Short Circuits of Alternating-Current Generators

Abstract: In this paper, the author presents a physical conception and simple non-mathematical analysis of the short-circuit phenomena of alternating-current generators. Formulas are developed for the maximum instantaneous values of the armature and field short-circuit currents delivered by both single and polyphase generators, which are equipped with and without damper windings. A similar analysis covering the rate of decay and the sustained values of the short-circuit currents will be presented in the near future.

An Electrical Frequency Analyzer

Abstract: An apparatus has been developed by means of which it is possible to measure and obtain a permanent record of the frequency components of an electric current wave. The device has two frequency ranges: 20 to 1250 cycles and 80 to 5000 cycles; the amount of power required does not in general exceed 500 microwatts; and the time necessary for making a record is about 5 minutes. An attachment is provided which permits of the making of simultaneous harmonic analyses of two complex waves in the same length of time. In principle, the process consists in feeding the complex wave to be analyzed into a selective network, the essential feature of which is a sharply tuned circuit whose frequency of tuning is controlled by varying the capacitance in small steps with a pneumatic apparatus similar to that in a player piano. A maximum of response of the circuit occurs at each frequency of tuning which coincides with a component of the complex wave. An automatic photographic recorder of the response to each frequency of tuning is provided by means of which the frequency and magnitude of each component of the complex wave may be obtained. For convenience of operation, an automatic control apparatus is provided, so that it is only necessary to connect the complex source or sources to be analyzed and press a starting button. The completed record of the analysis is delivered after the machine has passed through the entire range off frequencies.

The Limitations of Output of a Power System Involving Long Transmission Lines

Abstract: The conditions of stability of a system are discussed and it is pointed out that while the various transmission line diagrams as used at present implicitly assume the terminal voltage at the two ends to be constant the degree of voltage regulation as determined by load conditions is an important factor in the determination of the limit of output. A type of combined diagram is proposed whereby this factor and other characteristics of the load may be included. The effect of the inherent regulation of synchronous condensers is taken up particularly with respect to compound transmission lines. A numerical example of a 300-mile line is considered and various characteristic curvesaredrawn. The relation between the maximum output and the capacity of condensers installed at the mid-point shows the benefit obtained by increasing the condenser capacity?within certain economic limits. Mathematical analyses are presented to cover a number of different conditions.

High-Voltage Impregnated Paper Cables

Abstract: A limit of carrying capacity was reached in high voltage cables due to high dielectric losses, and in order to overcome this limitation, science had to be called upon to introduce measurements and tests to control this quality. The exact experience gained in the development of these tests by scientific men working in cooperation with the men of practical experience enabled the cable industry to attack the next limitation that confronted it, namely, dielectric strength. The industry has already made considerable progress, and the present problem is the complete elimination of occluded air and vapor from the insulation. Air films have been regarded as causes of low dielectric strength, due to ionization of the air and consequent formation of hot spots. It is advanced, herein, that a more useful conception of the danger of air films, is that they promote internal surface leakage. It has also been generally believed that air films can be detected by the slope of the voltage power-factor characteristic. It is contended herein that such is not the case. It is pointed out that the foundation for future developments has been laid by the equipment and organization of American cable manufacturing plants for accurate quality control by continual testing of raw and process materials.

Underground Alternating Current Network Distribution for Central Station Systems

Abstract: 1. Certain experimental arrangements for an underground alternating current distribution system are covered in the paper. 2. Low costs and characteristics satisfactory for general utilization of alternating current are contrasted with difficulty of obtaining reliability. The advantage of adopting system characteristics which will make each service suitable for lighting, appliances, and motors is indicated. There is described experience with a combined light and power network on one set of mains. Effect of voltage variation on incandescent lamp illumination is discussed. An appendix covers tests on this subject. 3. Reliability in service of standard distribution materials is considered. Tests on cables are described which indicate that for underground distribution conditions, low-voltage cables will eliminate arcing faults while high-voltage cables will not do so. An appendix of arcing tests is attached. 4. Certain factors are discussed relative to size of mains and location of transformers necessary to make the low voltage network clear its own faults. 5. There is a description of an experimental system consisting of several radial high-voltage feeders, the distribution transformers of all these being connected on the low-voltage side to a common low-voltage cable network. 6. The reactance of the transformer circuits is almost three times that of standard distribution transformers. 7. The only protective devices used are automatic circuit breakers installed in the low-voltage cables between the distribution transformers and the network.

The guided and radiated energy in wire transmission

Abstract: THE object of this paper is to give a brief preliminary account, without mathematical details, of the results of a mathematical investigation of wave propagation along wires. This investigation had its inception in the problem of radiation from transmission lines, which was discussed by the writer some time ago.1 It was found that, in order to completely and directly account for radiation phenomena, it was necessary to recognize the incomplete and approximate character of the usual engineering transmission theory, discard the special assumptions underlying it, and develop the theory ab initio from Maxwell's equations. Theoretically interesting and instructive deductions followed from this study, which are believed to justify the present preliminary discussion, which the writer hopes to supplement with a paper dealing with the mathematical theory.

Insulation Tests of Transformers as Influenced by Time and Frequency

Abstract: Many transformers are now being designed for service with one end of the high-voltage winding solidly grounded. These transformers require an overpotential test by induced voltage of either 2.73 or 8.46 times their normal line voltage above ground plus 1000 volts. These tests must be made at more than normal frequency, to avoid too high a flux density in the core, and also to reduce the power required for excitation. It has long been known that the breakdown voltage of solid materials was affected by the length of time of application of voltage. Likewise the frequency of the applied voltage is shown to affect the breakdown voltage for solid insulations, increase in the frequency resulting in a decreased breakdown voltage. The voltage required for creepage failure is shown to be relatively unaffected by frequency. From the results of the tests made it is concluded that induced voltage tests on transformers with graded insulation at higher than normal frequencies should not have the test voltage reduced, but should have the duration of the test shortened to make the severity of the test comparable to the test at 60 cycles on normally insulated transformers.

Current-Limiting Reactors Their Design, Installation and Operation

Abstract: The essential features in the design, installation and operation of current-limiting reactors are pointed out. The application of reactors to different circuits is not treated because a number of good papers dealing with this subject has been presented at Institute meetings. Design.-A current-limiting reactor should have low reactance at low currents and high reactance at high currents. Such a reactor has been developed and is known as the ``saturated core'' reactor. It has not been used as yet for current-limiting protection to any extent. A reactor having an iron core and only an a-c. winding gives a drooping voltage-ampere characteristic and, therefore is not suitable for current-limiting protection. Reactors with air cores have straight line volt-ampere characteristics and, therefore, are well adapted for this protection. Since the only function of current-limiting reactors is to limit the current during short circuits to safe values, they should be capable of performing this function when other apparatus is being destroyed, due to excessive current. For this reason, heat resisting materials should be used for holding and insulating the conductor of a reactor. A useful formula is given for determining short-circuit temperature rises. A current-limiting reactor functions as such only when there are short circuits on the system. Short circuits are almost sure to be preceded or accompanied by voltage disturbances of abnormal value. Therefore, the insulation factor of safety in a reactor should be relatively high.