Showing papers in "Transactions of The American Institute of Electrical Engineers in 1921"

Carrier Current Telephony and Telegraphy

Abstract: This paper briefly outlines first the history of the development of carrier multiplex telegraphy and telephony. The fundamental principles underlying particularly the newer developments of the art are then discussed. Consideration is likewise given to the propagation characteristics of open wire lines, including those containing intermediate lengths of cable. Commercial types of apparatus and actual installations are then described and a brief statement made as to further applications of the art.

Heat Losses in the Conductors of Alternating-Current Machines

Abstract: The principal object of this paper is to show how hyperbolic functions of complex angles may be applied to the solution of the problem of heat losses in rectangular conductors that are embedded in open slots. A certain knowledge of the functions themselves is presupposed. Inasmuch, however, as they are handled like trigometric functions of real angles?except in regard to the plus and minus signs?it is a simple matter to acquire the requisite technical skill to use them. The hyperbolic function of a complex angle, consisting as it does of a real and an imaginary part, may represent a vector?the real part being the component of the vector along the horizontal, and the imaginary part, component along the vertical. Thus, for example, A sinh (x + j x) represents a vector just as A e j ? A/?, A (cos ? + j sin ?) represent vectors. Considerable experience has shown that the vector method for handling a-c. problems is much superior to the original method in which simple trigonometric functions were used. With this lesson before us, it should require but little contact with the problem at hand to demonstrate the superiority of the vector method, even though it employs the possibly unfamiliar hyperbolic quantities. These hyperbolic vectors have been used for a number of years in the analysis of problems involving a-c. circuits, which have distributed inductance and capacitance, and have proved their usefulness.

Voltage Regulation and Insulation for Large Power Long Distance Transmission Systems

Abstract: Heretofore the distance to which power could be transmitted has been limited. This limitation is now removed by a simple method of loading the line with synchronous condensers, so that the current and voltage may be kept practically in phase. High power factor and hence high efficiency result, and the voltage rises of the system are very much reduced, thus reducing insulation strains. A standard frequency of 60 cycles is advocated for the national system, and 220,000 volts is proposed as standard for extra large-power, long-distance transmission. The system of regulation proposed will result in practically constant voltage at all points of the line at all loads. And power may be taken from or supplied to the line at any point, and the power over sections of the line or over the entire line may be reversed and the constant voltage system maintained. A simple diagram is given, and this shows that for a 60-cycle, 220,000-volt line, the line-charging current supplies the capacity current required for about 0.8 load or 320 amperes load current, and that for larger loads the synchronous condensers supply leading and for smaller loads lagging current. Thus it is seen that the transmission line has largely inherently the currents required for self-regulation, if we correct initially the power factor of the loads to near unity. Every induction motor added to the power system calls for a certain capacity current for correction of power factor to reduce the losses from motor through to the power station.

Transformers for Interconnecting High-Voltage Transmission Systems For Feeding Synchronous Condensers from a Tertiary Winding

Abstract: Owing to the advantages to be realized from the use of the star-star connection in interconnecting high-voltage transmission systems and from the fact that this connection requires the use of an auxiliary winding connected in delta to stabilize the neutral point or to decrease the inductance in the ground connection, a great majority of the transformers designed for interconnecting transmission lines are three-winding transformers. Another type of transformer which would be included in this general class would be that having an auxiliary winding for feeding a synchronous condenser used in controlling the voltage at the receiver end of the line. Many of the alternatives suchl as the choice between self-cooling or water-cooling, or between single-phase units and three-phase units, differ in no way from the same questions on transformers for ordinary service. However, there are a number of important features peculiar to three-winding transformers for these classes of service that complicate the design and operation to an extent that justifies special consideration of these problems. This paper will call attention to these special problems and indicate the way in which the design and performance of transformers for these classes of service are influenced by them.

Hysteresis Effects with Varying Superposed Magnetizing Forces

Abstract: THE hysteresis effects discussed in this paper occur when magnetic fields are produced in iron by electrical circuits carrying simultaneously currents of different frequencies. Investigations have shown that when two currents of different frequencies are so superposed, the losses in the iron corresponding to each frequency may differ greatly from those obtained when each frequency is acting alone in the circuit. These effects are, therefore, particularly important in the electrical communication field because of the practise of transmitting over one circuit currents of different frequencies. Predictions of the behavior of iron-cored inductance coils and transformers in such a circuit may be erroneous if based on measurements of the iron losses which have been made in the usual way with single-frequency test currents.

Magnetic Properties of Compressed Powdered Iron

Abstract: This paper describes a new magnetic material which is peculiarly suited to the construction of cores in small inductance coils and transformers such as are used in a telephone plant. The requirements which were to be met involved a core material which should have a constant permeability, a small hysteresis loss, and a small eddy current loss within the range of magnetizing forces and frequencies which are met in telephonic operation. The material which was developed to meet these requirements is formed by fine grains of powdered iron, insulated and compressed. There is described the circumstances and experiments which led to this development and also the method of commercial production. Tables and curves are given showing the magnetic, electrical, and mechanical properties of the material.

Short-Circuit Current of Induction Motors and Generators

Abstract: There has been a rather prevailing opinion that a sudden short circuit of an induction generator would not cause a serious initial rise in current such as occurs in synchronous generators. This has led to the proposal of the use of such machines as a partial solution of the short-circuit problem on a-c. systems. Theoretical considerations and experimental data given in the paper show that, on the contrary, there is in the induction generator, just as in the synchronous machine, a serious initial rush of current which is limited only by the leakage reactance of the machine. The only difference is that the transient is shorter in the induction machine, and the current dies down of course, to zero instead of to the sustained value which occurs in an excited synchronous generator.

Longitudinal and Transverse Heat Flow in Slot-Wound Armature Coils

Abstract: IT has long been recognized that the heat generated in embedded armature conductors by the I 2 R and eddy current losses in part escapes by transverse flow through the insulation from the copper to the iron (possibly, to a more limited extent, to the air at the ducts) and in part flows longitudinally along the copper to the ends of the coils exposed to the cooling air. The importance of a solution of the combined transverse and longitudinal heat flows has been realized, for upon these the internal copper temperatures must necessarily be dependent. Thus, it has long been known that in a machine of short core length, the iron temperature and temperature at the center of the machine by detector between coil sides could usually be reduced by increasing the volume of air blown upon the ends, but in machines of long lengths (say 50 inches or more), the temperature at the middle could not be so reduced. Again, it has been recognized that as a machine of a given diameter is lengthened, assuming a short core length (say 10 inches for the shortest) the temperatures increased, although the losses per inch of length remained nearly the same.

Electric Propulsion of Ships

Abstract: This paper deals with the electric propulsion of practically all classes of vessels. The several types of electric drive are treated, in general, with special emphasis on Diesel-electric drive, as it is believed that this type of electric drive will be of most general interest, particularly to the inland section of our country, since it is especially applicable to the smaller size vessels, such as are used on rivers and lakes, to vessels in the coastwise trade and to the usual size of ocean freighter. All types of propelling equipment, however, will be referred to for the purpose of comparing the advantages of electric drive with other methods of ship propulsion and to show the natural advantages of each particular system. It is the intent of this paper to provide data valuable in the selection of the proper type of drive for each application, which must necessarily be determined by the character of the vessel and the service it is to render. Each type referred to has a particular field in which it is best suited. The authors desire to give credit to the Westinghouse and General Electric Companies for much of the data and material for cuts included in this paper.

Voltage and Current Harmonics Caused by Corona

Abstract: THE FOLLOWING investigation was made to study the effects of corona in producing voltage and current harmonics in transmission systems. In the early work on corona in 1910 a very complete oscillographic study was made of voltage and current. It was found that the current wave of corona loss very much resembled the excitation current wave of a transformer or iron-core reactor. A typical corona wave is shown in Fig. 1. 1 This wave has a very prominent third harmonic.

An Electromechanical Device for Rapid Schedule Harmonic Analysis of Complex Waves

Abstract: IMPROVEMENT in an art requires perfection of detail. Investigation of the details is often delayed, even though the procedure may be well understood, by the large amount of labor involved in handling cumbersome formulas or mathematical processes. The fundamentals of alternating-current theory are based upon a pure sine wave. More careful analysis considers waves formed of many multiple frequencies, which are found to exist in most practical applications. Thus not only the fundamental sine, but its higher harmonics, must be dealt with. The process of splitting up any known wave into its various components is well understood, but is slow and laborious if more than one or two harmonics are required. In present methods of analysis, it is at once striking how many combinations must be made to obtain the result. In mathematical methods this involves the calculation of a host of sums and products, elementary in form, but laborious in procedure. Methods of selected ordinates require many readings of ordinates from the curve, different sets being required for each harmonic. Graphical methods require a large amount of constructional detail. Machines involve changes of gears or pulleys, and many tracings of the curve.

The Effect of Heat on Paper Insulation

Abstract: A discussion is given in detail of the mechanical properties of paper especially as influenced by drying, heating, and impregnating. Tests for measuring the changes due to these causes are discussed and it is shown that tensile tests are unsatisfactory for this purpose. A measurement of tearing resistance is found to be satisfactory and two machines for this purpose are described. Measurements are given of rate of deterioration of paper at different temperatures. The relation of these data to allowable operating temperature is considered. No discussion is given of the various causes including heating due to dielectric losses which affect the limiting temperature of high-voltage, cables. The rapid increase of deterioration with temperature is shown. Emphasis is placed on the importance of not exceeding intended temperatures through lack of knowledge of conditions.

Permissible Operating Temperatures of Impregnated Paper Insulation in Which Dielectric Stress is Low

Abstract: The writer reviews the effect of temperature on insulating materials, abstracting from the 1913 Steinmetz and Lamme report, and the 1905 British Engineering Standards Committee tests Then he gives surveys of low-tension cables in large distributing systems, and special tests on cables including sheath cracking, high temperature tests, effect of bending on cables heated at high temperatures, distillation of cable compounds, ambient temperatures in subway ducts as affected by thermal conductivity of concrete, amount of moisture in soil, different arrangements of ducts and load factors at which the cables are operated From this review, conclusions are derived that the permissible operating temperatures are to be a function of the load factors at which the cables operate The writer recommends 105 deg cent, 95 deg cent and 90 deg cent for load factors of 33 per cent, 50 per cent, and over 66 per cent, respectively

Notes on the Effect of Heat on Impregnated Paper from Cable Insulation

Abstract: THE tests outlined below were made to determine at what temperature marked deterioration in the paper of impregnated paper cable took place. There are many shots well off the target in these results, although the average were determined from something over six hundred readings. Anyone who is familiar with the manufacture of paper and with the handling of it, knows the wide variation which occurs in different parts of the same sheet. The maximum tensile strength in a series of tests is frequently twice the minimum.

The Maximum Safe Operating Temperature of Low-Voltage Paper-Insulated Cables

Abstract: The Standards of the Institute state that for low-voltage cables the maximum safe operating temperature is 85 deg. cent. Experiments show that continuous operation of 100 deg. cent. for less than a month, seriously impairs the mechanical condition of impregnated paper. A standard of permissible mechanical condition should, therefore, be established, if such high temperatures are to be allowed. Operation at higher temperatures than allowed by the present Standards is, however, in the nature of a gamble and it is questionable whether the Standards should take cognizance of it.

Voltage and Power Factor Control of 66,000-Volt Transmission Lines Connecting Two Generating Stations

Abstract: The problem which confronted The Philadelphia Electric Company of providing for the control of voltage and power factor of the two 66,000-volt transmission lines connecting its Schuylkill and Chester generating stations is presented in this paper. It is required that the control of voltage and power factor of the transmission lines referred to permit of the transfer of energy in either direction, at suitable power factor, up to the rated kv-a. capacity of the lines, with the generating stations operating at approximately equal bus voltages. The situation is considerably complicated by the necessity for supplying energy to several industrial substations, connected to these lines near the midpoint, which under certain operating conditions are supplied from one of the two lines. Another important factor in the selection of regulating equipment is the severe short-circuit effects possible in a system of which the ultimate capacity of the present three generating stations will be approximately 500,000 kv-a. The comparison made to determine upon the most satisfactory type of regulating equipment and the reasons for the selection of three-phase induction regulators are given. Data on the performance characteristics of the lines, with the induction regulators are included. In the discussion of this problem of voltage and power factor control, certain conclusions of a more or less fundamental character are brought out.

High-Current Tests on High-Tension Switchgear

Abstract: The article describes a series of tests on oil circuit breakers and disconnecting switches to determine their strength at brush contacts and supports in withstanding the mechanical stresses engendered by the magnetic flux due to the flow of large currents of the order of 100,000 amperes, as may exist at times of short circuits on large systems. Other tests were made on current transformers and potential transformer fuses. For the first time, a synchronized motion picture machine and an oscillograph, were coupled to reproduce the coincident actions of the apparatus tested, and the variations of voltage and current in the circuit. The tests proved that practically all the circuit breakers then on the market had the brush contact placed in the wrong position, creating arcing before the operating mechanism had sufficient time to perform its function. The tests emphasized the importance of strong locks for disconnecting switches. Only single-turn primary-type current transformers and potential transformer fuses with resistance in series, were found adequate to give the service requirements.

Permissible Operating Temperatures of Impregnated Paper Insulation in Which the Dielectric Stress is Low

Abstract: FOR a number of years the standard low-tension direct-current feeder cable in Chicago was 1,000,-000-cir. mil two-conductor concentric paper-insulated cable with three pressure wires laid up with the outer conductor. Apparently there has been the greatest tendency to overload this particular size of cable more than any other as, with both single and concentric cables in service, it was difficult to make a proper distinction between the carrying capacity of the two kinds of cables. About ten years ago we had two cases in which the cables of this kind were called upon to carry loads somewhat larger than had been customary, and steadily throughout the day instead of a short peak in the evening. The two customers in these cases, in different portions of the city, were both manufacturing customers with an eight-hour load, and on account of some increase in business they increased their load on short notice when no cable was available for another feeder to their premises. In each case, the cable has to be ordered from the factory so that this unusual load was carried by these cables for some three or four months. In the first case of this kind we were so disturbed about the temperature that we made a rather extended series of temperature measurements, using one of the pressure wires imbedded in the outer conductor as a resistance, and determining the temperature by the rise in resistance. This, of course, would give us the temperature of the outer conductor which would be probably 8 or 10 deg. lower than the inner conductor. The temperature measured in this manner was slightly above 100 deg. cent., and as there was some doubt regarding the accuracy of the determination made in this manner, it was checked by cutting a small hole in the lead sheath of the cable and in the outer insulation, and measuring the temperature of the outer copper with a thermometer. The temperature taken in this way checked very closely with the temperature as determined by the rise in resistance of one of the pressure wires. The insulation removed in this manner was carefully preserved and compared with the insulation in a piece of new cable, and it was impossible, by careful examination, to discover any appreciable difference.

Regulation of Frequency for Measurement Purposes

Abstract: IT happens very often that it is desirable or necessary to transmit a quantitative indication to a more or less remote point. For instance, in a modern power system with its various sources of power, the load despatcher may wish to know the amount of power generated in a station perhaps several miles away, so that he may be able to better distribute his load. In addition, it may be desirable to regulate automatically the distribution of power as well as limit the amount that is received from a distant point. In this connection the problem may not be simply that of limiting the indicated power but of measuring and limiting the integrated demand over a definite time period. Of a different nature is the problem of recording at widely distributed points various operations in an industrial plant so that the results can be compared on the basis of the exact time of occurrence.

Modern Production of Suspension Insulators

Abstract: This paper pictures the progress made during the past few years in the production of electrical porcelain. The information covers: First: The engineering and works organization. Second: The manufacture. Third: Design and test.

Some Phases of Railroad Telegraph and Telephone Engineering

Abstract: Statement of size of N. Y. C. Lines telegraph and telephone plant and variety of engineering problems involved. Telephones used almost exclusively for train dispatching, not so general for message work, but growing. Automatic telephones used. Extensive local and long distance lines and switchboards. Telegraph system reaches all stations. Pole line is basis of plant, increasing in strength to meet safely the loads to which subjected. Railroad employs wire chiefs. Problems include electric protection, inductive interference, electrolysis, transmission, traffic, necessitating continual experiment and investigation. Telegraph answer-back used with selectors. Phantom telephone circuits used. Single wires for railroad telegraph obsolete, all wires used in simultaneous telegraphy and telephony. Extra high impedance telephone used for train dispatching. Iron wire joints welded. Battery consumption data; unit type switchboards designed, supplant dry battery for main selector ringing battery; chemical rectifier also used. Oscillograms of single-line telegraph current waves, when line insulation varies. Railroad long-distance lines can be loaded. Telephone selector current waves given. Gill local bell selectors used with repeat coil signaling to obtain low-resistance simplex. Duplex telegraph used on about 10,000 miles of circuit on N. Y. C. Lines. Polar duplex is approximate three-wire circuit. Self-balancing duplex designed especially adaptable at unattended repeater stations; oscillograms illustrating results in better balance of duplexes. No. 5-U retard coil of standard bridging duplexes and quads is auto-transformer as well as retard coil; is useful as retard, detrimental otherwise. Polar relay armature of differential duplex and quadruplex has more force than in bridging.