Showing papers in "Transactions of The American Institute of Electrical Engineers in 1917"

Insulation Characteristics of High-Voltage Cables

Abstract: The insulation characteristics of different types of single- and three-conductor cable, determined largely by dielectric energy loss measurements, are discussed in detail. Particular attention is given to paper insulated cable, both new cable and cable that has been in service being considered. Varnished cambric and different grades of rubber insulation, as well as cable compounds are also dealt with briefly.

The Electric Strength of Air.-VII

Abstract: In view of the variation among the values obtained by different observers, this paper aims to make a careful determination of corona-forming voltages for alternating and for positive and negative continuous voltages in the same apparatus and under the same conditions. Within the range of wire diameters used, corona appears at a lower value when the wire is positive than when it is negative, although the two curves converge for increasing diameters. The maximum excess of negative over positive, as observed, was 6.3 per cent. The values with alternating voltage coincide with those of negative continuous voltage. Positive continuous voltage there-fore forms corona at the lowest value. The observations on the negative corona give values higher than any heretofore obtained. Other experiments are described, giving qualitative indications of the correctness of Townsend's theory of ionization by collision.

Regenerative Braking of Electric Vehicles

Abstract: This paper discusses the problems met in applying regenerative control to electric railways. In the introductory section the purposes, advantages, requirements and disadvantages of regenerative control are pointed out, and then the author takes up the description of various systems. In doing this, special attention is paid to those systems which are well adapted to illustrate some fundamental principle, and to those which are of some practical importance. Other systems are, on account of space limitations, mentioned only briefly, or entirely omitted. The three-phase system is discussed under the following heads: regeneration near synchronous and above synchronous speeds; line regulation; practical results and safety of operation; influence upon power factor; regeneration at speeds below synchronism. The phase converter system is next taken up, with a consideration of the requirements of such a system, and practical results attained. Direct-current systems of regenerative control and their problems are exhaustively discussed, under the following heads: series, shunt, and separately excited generator; classification and description of separately excited systems with generators operated by line voltage; inherently constant excitation; excitation varying with the line voltage; excitation varying with the regenerated current; series-parallel control; capacity of exciter and switches; systems with variable armature voltage; miscellaneous direct-current systems; transmission system and substations. The next division of the paper deals with alternating-current commutator motor systems, including those with separately excited generators, armature self-excited generators, excitation varying with the regenerated current, and stator self (load)-excited generators, and the subject of commutation is discussed.

Cooling of Oil-Immersed Transformer Windings after Shut-Down

Abstract: The 1916 A. I. E. E. Rules require that the temperature rise of transformer windings be observed by the resistance method. Since the measurement of resistance usually requires considerable time, there is always a drop in temperature between the instant of shut-down and the time of observing this resistance measurement. There are three general methods of determining the temperature at shut-down. These are: 1. To take a cooling curve and extrapolate back to the instant of shut-down. 2. To use an arbitrary correction. 3. To calculate the rate of cooling. The usual theoretical formula for calculating the cocling of a body is not in a convenient form for practical use. Furthermore, the conditions in a transformer are generally such that it would be difficult to apply. However, it is shown in the paper that the cooling of oil-immersed transformer windings, for a limited time (four or five minutes) after shut-down, is approximately a function of the watts per lb. of copper, and that when it is necessary to make calculations, more accurate results can be obt. ained by this partially empirical method than by attempting to use the theoretical formula. Under ``Conclusions'', the general advantages and disadvantages of each method are given. In the Appendix are developed certain formulas used in the paper.

The Influence of Dielectric Losses on the Rating of High-Tension Underground Cables

Abstract: This paper describes a series of tests made to determine the dielectric losses in various kinds of 13,000-volt cable. These losses were found to increase greatly with the temperature and thus become an important factor in the rating of such cables. A method is developed whereby the influence of these losses on the rating can be approximately calculated for duct lines with uniformly loaded cables.

Transmission Line Design

Abstract: This paper contains a complete mathematical analysis of the forces which determine the location in space of a cable suspended from points of equal elevation, and gives the designer and constructing engineer of a transmission line some useful working formulas based on this analysis. Section A of the paper covers the derivation of the catenary formulas and contains a chart from which any catenary problem may be quickly and accurately solved. Section B contains an analysis of the influences of changes in temperature and cable load, resulting in formulas by the aid of which the magnitude of these influences in regard to changes in position of the cable and changes in stresses at any point of the cable may be accu-rately computed. The formulas derived make it possible to plot a temperature-tension stringing chart to be used by the constructing engineer when stringing the cable at various temperatures. Section C is an investigation of the economic features involved in the proper design of the cable supports. A working formula is derived enabling the designer to determine the most economical span and corresponding height of tower. Solutions of typical design problems are given in each section of the paper demonstrating the use and manipulation of all formulas derived.

An Experimental Method of Obtaining the Solution of Electrostatic Problems with Notes on High-Voltage Bushing Design

Abstract: The electrodynamic method for obtaining the solution of electrostatic and allied problems is developed to a high degree of accuracy. The method is then applied to the study of high-voltage bushings. An experimental high-air-efficiency bushing was built and tested with the result that the arc-over was very materially lower than had been anticipated. A study was then made to ascertain the reason for this large discrepancy, which was found to be due to an unexpectedly large surface effect which varied greatly with different materials. After obtaining the numerical value for the surface effect a reasonably accurate predetermination of the arc-over of structures, in which the stress distribution is known, can be made. In order to determine the desirabilitv of using artificial equipotential surfaces to increase the efficiency of the use of the supporting dielectric, diagrams were taken and a small bushing of this type constructed and tested. A study was then made to find out whether the reduction in diameter of condenser bushings is principally due to equalization of potential or due the greater strength of insulation when barriers are used. As a result of this work, it is believed that the barrier effect greatly predominates. A short discussion follows which shows the difficulties of obtaining a sufficiently exact theory of bushing design to enable us to predetermine the most efficient shape for a practical bushing.

Magnetic Flux Distribution in Annular Steel Laminae

Abstract: The distribution of alternating magnetic flux density in ring laminae is studied experimentally. It is found to differ materially at different radii, not only in root-mean-square magnitude, but also in wave form. The reasons for this distortion are discussed.

Effect of Current Limiting Reactors on Turbo-Generator Systems under Conditions of Short Circuit

Abstract: An account of a cable breakdown near one of the generating stations of the Commonwealth Edison Company's system. The breakdown resulted in a second breakdown on same line within the station, which prevented the oil switch from automatically disconnecting the fault. The system is amply protected by reactors for generators and between bus sections. Their effect on the stability of synchronous apparatus on sections protected by them is very marked. The protection to generating station apparatus was complete. Comparison of maximum stresses encountered in the short circuit as it occurred with what they might have been without reactors present are made, and the conclusion is drawn that without them the damage resulting would have been considerable and the service interruption far more general and serious.

Industrial Research and its Relation to University and Governmental Research

Abstract: 1. Introduction emphasizing the great activity in all branches of research at the present time. 2. A division of research activities into three principal classes, university, governmental and industrial. 3. A statement that the principal function of university research should be to train research men and some suggestions as to the type of training required. 4. A brief statement of the function of governmental research which has to do with such things as the development and conservation of our natural resources, the national defense and the promotion of those things which are for the benefit of the whole people. 5. A brief description of the Research Division of the Westinghouse Electric & Manufacturing Company, its rise and its relation to other departments. 6. A statement of the desirability of co-operation among all agencies engaged in research.

Internal Temperatures of A-C. Generators

Abstract: The paper deals with the internal temperatures of a number of typical large a-c. generators; this temperature being measured by a thermo-couple placed between armature coils in the same slot and in the center of the core. The difference between these measured internal temperatures and the corresponding surface temperatures in the tests given varies from 0 deg. to 35.5 deg. This wide divergence is explained by the aid of the tests and of calculations. A method of calculation for internal temperatures is given which is based on simple heat laws and on data obtained from many tests. By means of the tests and of parallel calculations, the effect on the internal temperature of changes in frequency, core length, thickness and quality of insulation, armature current density and core densities, is explained. The capacity of the end windings to dissipate heat from the center of the core is also discussed. In conclusion, it is stated that although the wide divergence between surface and internal temperatures of different classes of generators is regular and can be justified, yet it is plain that there is no one average figure that can be used for that difference for all classes of a-c. generators.

Transient Conditions in Asynchronous Induction Machines and their Relation to Control Problems

Abstract: This paper discusses a number of transient conditions existing in asynchronous machines immediately after certain changes in the circuit connections are made. The advisability of considering these conditions in connection with the control layout for the purpose of eliminating bad effects caused thereby, is pointed out. The principal subjects considered are undesirable peak currents, which may be caused by the damping effect of the short-circuited rotor windings and the over-voltages, which are obtained with certain control arrangements.

Oscillating-Current Circuits by the Method of Generalized Angular Velocities

Abstract: The oscillating-current circuit differs from the alternating-current circuit in that the sinusoids involved are damped. In the same way that alternating-current theorems are obtained by generalizing direct-current theorems, it is possible to obtain oscillating-current theorems by still further generalization. This involves a generalized angular velocity and a generalized impedance which are complex quantities. Kirchoff's law may be thus generalized; and yields a simple method of determining the generalized angular velocities, and thus the frequencies and decrements, of free oscillation. Since, in an oscillating-current circuit, there is no impressed voltage, the initial voltage present in the circuit must be used in determining the amplitudes of oscillation. This results in the introduction of a ``threshold impedance'' for use in determining the amplitudes, which is obtained by a single differentiation from the generalized impedance. Further direct-current rules may also be readily generalized for convenient use in the solution of oscillating-current circuits. A simple example is given to show the method of procedure. The discharge of a leaky condenser through a reactor furnishes a second example which better illustrates the convenience of the method for numerical computations. As a third example the oscillation of a three-section artificial cable under particular terminal conditions is chosen. The algebraical portion of this example is given in an appendix. A list of symbols used will be found at the end of the paper.

The Insulator Situation

Abstract: This paper gives a resume of the insulator situation as it exists at the present time and shows the gradual increase in requirements that have been held essential to a successful insulator. A statement of the apparent causes of the very rapid deterioration of insulators, even when stored and subject to no electric stress is given, and the conditions necessary to the production of an insulator that will reduce this deterioration cost are discussed. Microphotographs showing the structure of the porcelain from several insulators are given. Interesting flows and defects common to porcelain insulators are shown. Three means are given for improving the insulator situation, one of which is the use of fused quartz as an insulator material, the laboratory feasibility of which has been shown. Investigations as to the commercial manufacture of quartz insulators are under way.

Relays for High-Tension Lines

Abstract: The author considers the following arrangements desirable: For radial feeders not in parallel?inverse-time-limit overload relays, with selective ground relays. Radial feeders in parallel?reverse-power relays in combination with reverse-time-element relays, or the balanced system. Single lines in tandem?definite and inverse-time-limit relays with progressively longer time settings near the generating station. Two or more parallel lines in tandem?inverse-time-limit relays at the points where the power leaves the station or substation, and overload relays in combination with reverse-power relays at the points where the power enters the substation; also, the balanced system preferable, when possible. Single line ring systems?inverse-time-limit relays, combined with reverse-energy relays, or, preferably, the balanced system. Parallel line ring systems?inverse-time-limit relays on the outgoing feeders at the generating stations, and a balanced interconnected combination of reverse-energy and inverse-time-limit relays at the receiving ends of the supply feeders. Tie lines?some balanced arrangement. Generator relays seldom used, but arrangements are suggested. Transformers?differential relays. Special grounding relays for extra high-tension cable feeders. Appendices A, B, C describe connections of reverse-power relays, relay testing and a special installation.

Industrial Research with Some Notes Concerning its Scope in the Bell Telephone System

Abstract: The interrelation of industrial and ``pure scence'' research and the restrictions which must be imposed to insure mutual existence. A brief outline of the scope and progress of industrial research in the Bell Telephone System.

The Protective Equipment on the System of the Commonwealth Edison Company

Abstract: The use of protective devices is based primarily on the desire to maintain a high continuity of service rather than to protect apparatus. The tendency in the development of large systems is toward interconnection, and to make this practicable, satisfactory relays are necessary. The paper describes briefly the system of the Commonwealth Edison Company of Chicago with special reference to the protective devices installed thereon. Generators are equipped with balanced relays, lines with induction-type inverse-time-element relays, some of them of the uni-directional type, and balanced relays, while substation apparatus has the usual equipment of overload relays, speed-limit devices, etc., and outgoing feeders the instantaneous type of relays. The arrangement of these relays is shown and some of the settings described.

Corona and Rectification in Hydrogen

Abstract: The results of an investigation of the corona discharge between co-axial cylinders in an atmosphere of hydrogen are given in this paper. Both direct and alternating electromotive forces were used. The characteristic behavior of the corona is given by means of curves, photographs and oscillograms. The corona discharge in hydrogen was found to differ from that in air in the following particulars: The discharge from a negative wire was found to differ widely from a positive wire in the magnitude of the voltage necessary to start the discharge in the shape of the volt-ampere characteristic and also in the stability of the discharge. Corona in hydrogen between concentric cylinders is shown to be a practicable method for rectifying high potential alternating currents. The apparent evidence of ionization, potential gradients at the surface of the tube and the general character of the visual phenomena are discussed. A brief statement of conclusions is given.

Reactors in Hydroelectric Stations

Abstract: The advantages and limitations in the use of current limiting reactors in hydroelectric stations are not so well recognized or understood as they are in steam turbine stations, but it is now coming to be realized that their use may be quite as justifiable and necessary in the former as in the latter. The two beneficial results of reactance, protection and localization, are distinct; the former being associated with the square, and the latter with the first power of the reactance. Of two detrimental results of reactance, or limitations to its use, one, that of voltage drop, is well understood but the other, the reduction of synchronous stability is not so well understood. The installation of reactance usually results in a decrease in the stability of synchronism. Such stability may be expressed in terms of the angular phase displacement between two groups, due to a sudden load disturbance. Practically, complete instability or asynchronism occurs in a large station when the phase angle exceeds 90 deg. The asynchronizing effect of a sudden load change is approximately twice that of a gradual change of the same magnitude. The origination of a power surge by sudden loss of load and the accompanying hunting oscillation is described. Increased reactance increases the amplitude of both the power surge and the phase-angle oscillation and also increases the period.

Performance of Polyphase Induction Motors, under Unbalanced Secondary Conditions

Abstract: Continuous operation of the wound-rotor induction motor, when the external resistances in the secondary phases are not equal, is shown to be feasible. The effect upon power factor and heating is discussed. Curves showing the performance of poly-phase motors with single-phase secondary are presented. The practical advantages of using unbalanced secondary connections are pointed out.

Present Practise in the Design and Manufacture of High-Tension Insulators

Abstract: As considerable time or a severe condition is necessary to show up serious insulator defects, the favorable line conditions on the earlier lines permitted the use of inferior material and designs. The apparently satisfactory operation of inferior insulators together with the large production necessary did much to retard improvement in the insulators, for improvement was practically impossible unless same could be accomplished without materially increasing the cost. The desire to increase production and improve the material necessitated radical changes in the manufacture and equipment, so that the well equipped plant today is far different from the ordinary pottery which it resembled a few years ago. The rapid development in the transmission field has materially changed conditions, and rendered much apparatus obsolete, the early insulator being no exception. As causes of losses have become evident, means have been found to eliminate the serious effects of same. The recognition of the increased value of reliability together with the study of operating conditions has materially changed the insulator situation, so that the material going to the scrap pile today is more suitable for line work than the best product a few years ago. The loss from porosity has been reduced to a negligible quantity by improved firing methods and a closer selection. To prevent the serious cracking loss noticeable on old insulators, has been the most difficult problem. To prevent trouble on old lines, it may be necessary to give the insulators a temperature, as well as an electrical test.

Economical Combination of Water Power and Steam Plants and a Convenient Method of Solution

Abstract: A determination of the respective economic limits in steam and water power plant developments. Formulas are derived for determining total annual costs of each type of plant and the most economical combination. Certain general conclusions are reached as follows: Practically all water power plants should be developed beyond minimum power available and hence in combination with a steam plant. The economic limit depends largely on the value of money, fuel, labor, the increasing efficiency of steam turbines and the location of the enterprise.