Showing papers in "Transactions of The American Institute of Electrical Engineers in 1922"

Skin Effect and Proximity Effect in Tubular Conductors

Abstract: The effective a-c. resistance of tubular conductors is required to be predetermined by designers, for radio installations, for large underground cables with non-magnetic cores, and for electric furnace circuits. (See Examples I to IV). For the above purpose, sets of curves are given in this paper. The skin effect ratio for isolated tubes is shown in Fig. 1. For stranded conductors, the resistance must be multiplied also by a ratio for the spirality effect, as is approximately indicated in Fig. 2. When the return conductor is near, a ratio for the proximity effect, as indicated in Fig. 3, is also to be used. A calculation for the proximity effect ratio for thin tubes is made, and the results are compared with tests in Fig. 3. Some of the requirements for future research work on skin effect are discussed. The conclusion is expressed that it seems scarcely worth while providing a non-magnetic core with a 2,000,000 cir. mil, 25-cycle cable in order to reduce the skin effect, but with the other cases considered, the tubular form seems very advantageous.

The Two-Stage Current Transformer

Abstract: This paper presents a brief discussion of the current transformer as used with measuring and controlling apparatus with special reference to the degree of accuracy which can be attained in the ratio and phase angle. A new type of current transformer is then described, in which it is possible to secure much higher accuracy with a given amount of iron and copper in the transformer. In this new device the transformation is effected in stages, the first yielding in the usual way a secondary current which is approximately correct in magnitude and phase, and the second yielding an auxiliary corrective current which, when combined with the first secondary current, gives a resultant current which very closely approximates to the secondary current which would be furnished by an ideal current transformer having no errors. The two currents may easily be combined by having two like windings in the devices operated, one for the main and one for the auxiliary secondary current. The mathematical theory of the two-stage current transformer is developed and applied. Experimental curves are given to compare the performance of the new transformer with that of an ordinary simple current transformer of good average performance. The effect of mutual inductance between the external secondary circuits is discussed, and some of the special advantages of the new transformer are given.

The Petersen Earth Coil

Abstract: Accidental arcing grounds on transmission lines constitute the foremost problem to be solved in the transmission of electrical energy over great distances. There has come into use to a limited extent, arcing ground suppressors. This device consists in principle, of a switch in the station which is automatically closed in parallel with the accidental arc at any point out on the system. The parallel path through the switch shunts the current from the arc and thereby extinguishes the arc. This development is not yet completed. This paper gives the results of some experiments on an entirely different device for suppressing accidental grounds?a device that was first advocated by Prof. W. Petersen of Darmstadt, Germany. The essential part of this new apparatus is a suitable reactor connected between the neutral of the circuit and ground. This reactance is chosen of such a value as to neutralize the capacitance of the circuits when an accidental ground of one phase takes place. Under this acc dental condition the reactor is electrically in parallel with the active capacitances and, by the wellknown fundamental law, the only current that flows to the combination of the inductance and capacitance in parallel is the current necessary to supply the energy loss in the combination. The simplified equivalent conditions are shown in Fig. 4. This energy current can be made very small and it is this relatively small current that passes through the accidental arc to ground.

Prevention of Transient Voltage in Windings

Abstract: This paper relates to windings such as are used in transformers, reactors and the like, with particular reference to the characteristics which determine internal distributions of suddenly impressed voltages or sudden voltage changes, and the resulting internal oscillations. Ordinary lightning arresters, which limit the maximum voltages reaching the winding terminals, but cause rather than prevent the occurrence of sudden voltage changes, certainly give no protection against excessive voltages between turns or between coils. After describing the production of these transient voltages in ordinary windings, and pointing out that the treatment of symptoms by the addition of extra insulation tends to defeat itself by augmenting the cause, this paper explains these phenomena as due to faulty arrangements of inherent capacitance with the inductance of the winding. A fundamental principle is evolved indicating the constitutional remedy, which, if perfectly applied, would give only uniform internal voltage distributions, however abrupt or frequent the voltage changes at the terminals might be. Methods of application are described for the ordinary windings, by supplementing the faulty arrangements of inherent capacitance with auxiliary capacitances or condensers. Methods are given, also, for the construction of windings with the ideal distribution of inherent capacitance called for by the principle. Two alternative statements of the fundatmental principle upon which the ideal distribution of capacitance is based are emphasized in the paper, and the application of the principle is adequately illustrated in the figures, of which Fig.

Heat Losses in Stranded Armature Conductors

Abstract: In the present paper, which is a continuation of one presented at the last annual convention, the author extends the method of complex hyperbolic functions to the solution of the problem of heat losses in stranded conductors embedded in rectangular slots. In the preceding paper the discussion was confined to solid conductors and to those having an infinite number of strands. In the latter case, the insulation between the strands was assumed to have no appreciable thickness. In the present paper, conductors are considered which have a finite number of strands separated by insulation of appreciable thickness. In the mathematical development which is to follow, free use is made of the results obtained in the first paper.

Key West-Havana Submarine Telephone Cable System

Abstract: The system discussed in this paper includes three single-core continuously loaded submarine cables, each of which provides, in addition to a telephone channel, direct-current and carrier-current duplex telegraph channels. A description is given of the design and construction of the cables, of the method of superposing the various channels on each cable and of the terminal apparatus used for their operation.

Submarine Cable Telegraphy

Abstract: The history of the development of the subject is first outlined, and methods of operation of cables are described. The technical side is introduced with a statement of the various conditions whi h limit operation of cables, and a general method of analysis is developed, based upon an extension of ordinary alternating-current theory. The theory is made use of to analyze the action of cable types and of apparatus which at this time can be regarded as standard. The fundamental theory of the method of analysis, with information on the calculation of transients in electrical circuits, is given in the Appendix.

Heating of Railway Motors in Service and on Test-Floor Runs

Abstract: The rating given to a motor is the manufacturer's guarantee of the motor performance under the conditions given on the name plate. Assuming that this rating is entirely safe, then the successful functioning of the motor depends entirely upon the application engineer's analysis of the particular duty that the motor will be required to perform. Where the required motor output is practically constant the application is simple; however, in many cases the motor load is apt to be anything but constant, consisting of loads of all degrees of magnitude, and in such cases the economically correct application is especially difficult. The past improvements made in the motor design, mechanically and electrically, have resulted in greater importance of the motor-operating temperatures, in fact in the great majority of cases the motor rating is limited only by the motor temperature. It is obvious then that correct motor applications depend to a very great extent upon correct operating temperatures. Ratings such as the continuous, short-time, normal, and dutycycle ratings give the performance of the motors under some particular conditions; however, the duty required of a great number of industrial and railway motors will not agree with any of the above ratings. Thus the application of motors to cranes, hoists, steel mills, and railways must be made with the knowledge of the motor's performance under one or more arbitrary conditions. In general the two ratings which should be known for motor application to such irregular duty are the continuous and a short-time rating.

Exciter Instability

Abstract: 1. The form of equation for exciter voltage and current is the same as the well known equation for the electric circuit containing resistance, inductance and capacity. Hence the same form of oscillations and transients are involved, the only difference being that in the present case the duration of the transients is much longer. 2. Instability may occur when the exciter is operating on the straight part of the saturation curve, if in addition some combination of the following conditions exists: (a) very low residual voltage-say 1 per cent or so. (b) a relatively large voltage drop in the armature. (c) large inductance in the load circuit, as always exists in the alternator field. (d) alternator transient of greater duration than the exciter transient. (e) excessive series field strength. 3. Instability may be classed, for convenience, under two headings: (a) voltage ``creeping,'' and (b) ``double-energy'' transients. The former may be caused by slight speed transients of the exciter; or by temperature transients causing corresponding resistance transients in the shunt field circuit; or by hysteresis effects which may be caused by small undulations in the exciter voltage. The ``double energy'' transients, such as oscillations and reversal of excitation, may be initiated by a shock, such as a short circuit on the alternator, or sudden, relatively large change circuit in constants, for instance a large change in resistance in the shunt field circuit. 4. The exciter can be stabilized against voltage ``creeping,'' (a) by special design to increase the angle ? Fig.

Air-Break Magnetic Blow-Outs For Contactors and Circuit Breakers Both A-C. and D-C

Abstract: Magnetic blow-outs have been used in contactors, circuit breakers and controllers for many years for rupturing both a-c. and d-c. power circuits, but their commercial use, particularly on alternating current has been largely confined to relatively low voltages. Oil circuit breakers and switches have been generally used for rupturing high-voltage a-c. power circuits, and their development has reached a high state of perfection. The air break has the advantage of avoiding the possibilities which attend the use of any inflammable material?like oil, with its possible gasification and explosion on heavy short circuits. While there are many different types of magnetic blow-outs this paper deals largely with the ``individual'' type, in which a blow-out coil is connected in series with each pair of current-rupturing contacts, since it is with this type that most of the progress and studies have been made in recent years. Contactors and circuit breakers with the ``individual'' type of blow-out are now used almost exclusively in the main d-c. power circuits of the 1500 and 3000-volt d-c. railway systems. Oil circuit breakers have been tried for this service, but they are rather unsatisfactory because there is no periodic zero point in the current wave at which the oil can form an insulating seal between contacts. The oil under d-c. arc conditions carbonizes rapidly and involves the possible danger from explosive gases. Recently the use of magnetic blow-out contactors on a-c. circuits has been extended to moderately high voltage and capacity. Short-circuit tests on a 6600-volt, 26,700-kv-a.

The Effects of Moisture on the Thermal Conductivity of Soils With a Bibliography on the Heating of Cables

Abstract: It has been appreciated for many years that the presence of moisture in the soil surrounding underground cable was of assistance in dissipating the heat generated within the cable. But little was definitely known, however, of the exact changes in the thermal conductivity of soils caused by the presence of moisture. The following article shows that moisture plays a predominant part. The relative thermal conductivity of various types of perfectly dry soils, such as sand, clay, gravel, etc., covers a range from only one to two, while he addition of moisture increases the range to five times or more that of dry soils. The article also includes a bibliography on the heating of underground cables, giving reference to 59 papers on the subject in English, French and German.

Dielectric Losses and Stresses in Relation to Cable Failures

Abstract: When transmission cables were first operated at potentials exceeding about 7500 volts, it was noted that cable failures occurred in service with loads materially below those which had theretofore been found to be permissible with low-voltage cables, and this reduction in carrying capacity increased with increase of the normal working potential. For example the author has previously reported that No. 0 A. W. G. four conductor cables operating on a four-wire three-phase system with a maximum normal potential of about 4000 volts between phases carry 200 amperes on each of three conductors without damage due to the overheating, whereas a 250,000-cir. mil cable operated at 20,000 volts was found to have excessive burn-outs if the load exceeded 175 amperes per conductor. For a number of years it has been recognized that this reduction in carrying capacity of high-voltage cables was due to the dielectric losses and a number of papers have been presented to the Institute on this subject. A temperature survey of the 20-kv. cable above mentioned showed that nearly all of the burn-outs occurred in a portion of the conduit near the substation, which conduit contained a large nuumber of heavily loaded cables, and in which the temperature was 10 deg. to 15 deg. cent. higher than the rest of the conduit. This portion of the 20-ky. line was replaced over two years ago with cable having a low dielectric loss, since which time no further cable failures have occurred.

Corona in Air Spaces in a Dielectric

Abstract: The consideration of the extreme care necessary in preparing samples of a dielectric for test for electrical properties led to the investigation of the effect of air spaces, purposely formed of definite thickness and location, upon the power factor. This work in a way is an extension of some work done by Clark and Shanklin and Shanklin and Matson several years ago on air spaces in high voltage cables and wrapped armature coils. In their investigation the effect of assumed air spaces of indefinite thickness, extent, pressure and location was shown by plotting effective resistance from the formula RI = E2/W against potential gradient. A characteristic curve was obtained, a sharp inflection point in the curve being interpreted as indicating the starting point of corona. In the work by the writer, various materials were investigated both with air spaces excluded as much as possible, and with air spaces of definite thickness, extent, and location at atmospheric pressure. The results were plotted showing variation of power factor with potential gradient. A definite increase in power factor with potential gradient indicated the starting of corona. The thicker air space with a given thickness of dielectric showed the more abrupt change in power factor, and this took place at a lower potential gradient. By plotting power factor against voltage, a maximum was shown indicating that a saturation of ionization was approached which resulted in a decrease in power factor.

Wave Form and Amplification of Corona Discharge

Abstract: Corona forms on a round wire or cable when the voltage is raised to such a point that the voltage gradient near the wire is sufficiently high to break down the insulating properties of the air. The larger the wire the higher the voltage to cause corona. The corona is luminous and ionizes the air, giving it electrical conductiuity; thus corona has the effect of giving the conductor a larger diameter; and since a higher voltage is required for corona on a larger wire, a state of equilibrium is reached and corona is an equilibrium phenomenon not necessarily attended by spark-over. Since corona causes conductivity it is a cause of leakage and consequently of loss of power. It also increases temperature and decomposes the air into chemical constituents which are harmful to insulation. Engineers therefore have usually regarded corona as a dangerous phenomenon and one to be avoided by proper design. Transmission lines, for example, for the most part are designed so that their operating voltage is well below that at which corona would be formed on the conductors. Two suggestions have been made to mnake use of the properties of corona. The first is as a protective device for transmission lines. Since the coronais conducting and dissipates energy, it has been proposed to operate transmission lines relatively close to the coronaforming voltage. Whent abnormal rises of voltage due to lightning or other causes occur, corona begins, the air becomes conducting, and the high voltagre relieved.

Philadelphia-Pittsburgh Section of The New York-Chicago Cable

Abstract: Engineering and construction features involved in a complete telephone cable system over 300 miles in length and connecting Philadelphia and Pittsburgh, Pa. are described in the following paper. This cable is designed to operate as an extension of the Boston-Washington underground cable system with which it connects at Philadelphia. It is also designed for operation in connection with the Pittsburgh-Chicago cable now under construction, and other cable projects included in a comprehensive fundamental plan. Beginning with the fundamental factor of public requirements for communication service between cities separated by various distances, there are next considered the methods available to provide this service. Small-gage, quadded, aerial cable, which was decided upon for use in this section after careful economic studies, is described in a general way and the important advantages of the application of loading and telephone repeaters are outlined. The use, in connection with this cable, of the recently developed metallic telegraph system for cables is referred to and some facts are given regarding power plants, test boards and buildings. A few of the many possible combinations of cable and equipment facilities into complet telephone circuits, which will furnish the service required as economically as now possible, are illustrated. The necessity of complete coordination of the many factors involved in a project of this kind is emphasized.

Questions on the Economic Value of the Overhead Grounded Wire

Abstract: Overhead grounded wires have been in extensive use since the construction of the earliest transmission circuits. The fundamental theory of their protective value is based on Faraday's ice-pail experiment. As the resulting law goes, there is no electrostatic field emanating from the inner surface of a charged hollow conductor. The parallel grounded wires do not surround the power wires. Consequently the protection of these grounded wires against induced electric charges by thunderclouds, is only partial?usually of the order of 25 to 40 per cent. It might be erroneously inferred that several decades of use of the overhead grounded wire had established by practise its value. The several factors involved in its use do not lend themselves easily to experimental observations. For example, power lines extend over hundreds of mile while any particular induced charge is localized at some point in these vast distances. Taking into account the broef period of a lightning stroke. the unwilling observer stands a small chance of being near the point of discharge. Furthermore, thunder-clouds differ from one another. Still further, at the instant the lightning bolt takes place the distance from the thunder-cloud to the power wires varies quite indefinitely. In fact, there is a long list of difficulties involved in experimental observation of the effect of cloud lightning on power wires. As a result, except for a few small-scale experiments performed in the laboratory, knowledge of the subject is confined almost entirely to theoretical analyses.

The Electric Hammer

Abstract: The power hammer has been in use for a long time and there are now on the market many types of power-operated hammers which may be roughly classed according to the nature of the power as follows: Pneumatic, steam, motor and pulley; cam or crank, and electropneumatic drives. The pneumatic drive includes all riveting hammers; the steam drive includes practically all forge hammers, some drop hammers, pile drivers and steam drills; the motor and pulley drive class, includes the greater part of drop hammers; the electro-pnuematic drive includes only small forge hammers. The pneumatic hammer, due to its lightness, holds the field of hand-operated riveting hammers and it is hardly possible that any other means will ever surpass air for driving hand-operated riveting hammers; the steam hammer holds its own in very large forging and drop hammers and it is doubtful whether any other kind of hammer can remove it from that place. The field for very large forging or drop hammers is however rather limited; they are used only in very large plants in which all sorts of power prevail. There is an immense field, however, for medium and small forging and drop hammers which are used to produce all the small automobile and other similar parts as well as name plates, jewelry apparel, etc. It is this field which the electric hammer is supposed to cover. The present methods of driving these hammers are cumbersome, complicated, costly and very unsafe for the workman.

Printing Telegraph Systems Applied to Message Traffic Handling

Abstract: Ever since the building of the first practical automatic telegraph instruments by Vail in America in 1837, and Wheatstone in England in 1841, an ever-increasing amount of the world's high-speed communication has been carried on by the printing telegraph. While these early machines were built primarily for the use of the European Government Telegraphs or the large American telegraph companies, the developments of the last few years have produced an instrument which is a practical working tool for the service of modern commercial and industrial enterprises. This paper discusses some of the economic principles which determine the applicability of the automatic printing telegraph to present-day communication problems. Examples are given of the application of this type of apparatus to modern business conditions and the fundamental fact is demonstrated that whenever speed is essential in communication, consideration should be given to the automatic printing telegraph. The discussion is limited to those forms of light traffic load printing telegraph systems which have been developed particularly for linking together the departments of the factory, the terminal points of the railroad, the branches of the banking, the brokerage or the selling organization or the units of any other large corporation. A description is then given of the principle of operation of three such systems, somewhat in detail, as there is very little literature on the subject.

On the Minimum Stress Theory of Cable Breakdowns

Abstract: For the rational and economical design of electric cables, it is important to know the relation be-between the dimensions of the cable and its breakdown strength. Many different theories have been proposed in the past, such as the maximum stress theory, the average stress theory, Russell's theory, and Osborne's theory, all of them conflicting. Recently a new theory has been proposed by Fernie that the minimum stress, namely that at the sheath of a cable is the limit. It is the purpose of this paper to discuss Fernie's theory and data, inasmuch as it is so diametrically opposed to some of the earlier theories. It seems quite plausible that insulating materials have a specific breakdown stress. Fernie having discovered, as he states, that the minimum stresses were constant in his tests, feels forced to abandon this idea and attempts to explain his results in terms of a limiting value of stress at the sheath, namely the minimum value. An analysis of his test results, however, does not seem to justify him inasmuch as, although his minimum stresses were much more constant than the maximum stresses, they were by no means constant, and in fact, it could be claimed with almost equal justice that his test results vindicated the average stress theory. Since, however, Fernie's experimental minimumn stresses present a certain degree of constancy, this phenomenon (which remains to be proved) is investigated further.

Effects of the Composite Structure of Impregnated Paper Insulation on its Electric Properties

Abstract: The effect of composite structure upon the electric properties of dielectrics has been observed and theorized upon by various people, as mentioned in the Introduction. The present paper attempts to show a quantitative expression of power-factor and dielectric loss in terms of the resistivities and specific capacities of the elements of the insulation. It also shows the electrical function of the paper in impregnated paper insulation, and cites experiments which indicate that the electric failure of such insulation is due to ionic motion in the oil; the obvious deduction being that the voltage rating of cables should depend upon the degree to which ionic motion in the oil can be restrained.

The Effect of High Currents on Disconnecting Switches With Special Reference to the Mechanical Stresses Resulting

Abstract: In the early days of the electrical industry, disconnecting switches adequately performed their functions without the use of locking devices, except perhaps in a few isolated cases, where the blades opened downward, and some mechanism was provided to hold the blade in against the action of gravity (when subjected to jars, vibration, etc.). The generating capacity of central stations at this time was relatively small. Hence, the short-circuit currents obtaining were relatively low, and the forces resulting were insufficient to overcome the friction and other resistance offered by the blade and to cause opening. With the increase in generating capacity came a formidable increase in the short-circuit currents, to such an extent that it was no uncommon for a disconnecting switch to open, causing considerable damage, with consequent demoralization of operation. The result was that there were attempts made to attach locks to switches already installed, and to design new switches of which the lock was an integral part. Many of these locks were found to be inadequate, as opening occurred in many instances. In an attempt to prevent the possible recurrence of such unfortunate incidents the tests described in the following paper were planned; it was hoped thereby to improve the class of service rendered the public and safe-guard the lives of our employees.

The Action and Effect of Moisture in a Dielectric Field

Abstract: In studying the subject of dielectric loss in electric cables the author has become convinced that the moisture content of the dielectric is the dominant factor determining the a-c resistance Evershead's explanation of the action of moisture in a fibrous dielectric seems plausible but leads to the conclusion that moisture causes a decrease of a-c resistance with increasing voltage, whereas the experience of the author is that with a fairly well dried dielectric a-c resistance is independent of voltage, and that decreasing the moisture content still further gives higher and higher a-c resistance, with no limit in sight It seems obvious, therefore, that Evershead has not fully covered the subject In order to get a picture of the action of moisture in a dielectric field the author has assumed a simply hypothetical case and tried to follow it to its logical conclusions He assumed a pure dielectric of a homogeneous and plastic nature between parallel electrodes and subject to electric stress He then mentally placed a very small globule of conducting moisture in the dielectric and watched the action Under constant potential stress the moisture elongated into a thread-like filament until it bridged the dielectric But under alternating stress the moisture globule, if sufficiently small stretched out only a short distance and then no further, no matter how high the voltage This showed how the a-c resistance could be independent of the voltage and yet depend upon moisture

Magnetic Flux Distribution in Transformers

Abstract: It is customary when discussing magnetic leakage in the transformer to consider the primary and secondary windings as having a counter e. m. f. induced by a flux surrounding the coil and having the core for a part of its path. This leakage flux is frequently represented by closed lines. Since the main flux is also represented by closed lines in the core, apparently two fluxes are to be found in the core under a given coil, namely, the leakage flux and the main flux. The main flux is the flux found in the core at a point not under either the primary or secondary winding, and has been commonly considered as being the flux which causes the secondary induced voltage. If the leakage fluxes have a separate existence, i. e., if they are to be represented by closed lines, then the flux along the edges of the core would consist largely of leakage lines while that to be found in the middle portion of the core would be the main flux. Since these fluxes are out of phase with one another it should be possible to identify them if they are present as separate fluxes. Using a simple test core-type transformer, provided with belt exploring coils under both the primary and secondary windings, data concerning the magnitudes and phase positions of the fluxes in different sections of the core were secured. The results show that leakage fluxes do not exist as separate fluxes in the core.

Rating of Cables in Relation to Voltage Bibliography on Dielectrics

Abstract: This bibliography was prepared at the request of the Subcommittee on Wires and Cables of the Standards Committee of the Institute of Radio Engineers (IRE), and is intended specifically to be a continuation of that published by E.H. Rayner in Journal of the Institution of Electrical Engineers, (England) 1912, volume 49, p. 53, who describes his bibliography as follows: The references given are to articles in periodical literature only. With few exceptions they deal with the physics of dielectrics from the point of view of energy loss and electric strength.

Potential Gradient In Cables Discussion of the Logarithmic Formula, Its Modification and Effect of Internal Heat

Abstract: If the dielectric of a single-conductor concentric cable is homogeneous, the voltage gradient at any diameter x is given by d v/d x = 0.868 V/x log 10 /D/d where d v/d x is the voltage gradient or dielectric stress, V the voltage between conductor and sheath, D the diameter over the dielectric and d the diameter over the conductor. A complete discussion of the above formula is followed by considerable experimental data and curves accumulated from many breakdown tests. Results of tests on cables with large ratios of dielectric diameter to conductor diameter are included and a modification of the above theoretical formula is discussed. The modified formula is checked by tests on a special cable which was constructed for this purpose. A new relation between the rupturing gradient at the surface of the conductor and the ratio D/d is suggested and curvnes of experimental data given. Breakdown tests on three-conductor cables are included and the calculated rupturing stresses compared with those for single-conductor ductor cables. Special cables were constructed so that measurements could be made of voltages between layers of insulation. From data obtained from these tests, curves are given showing the change in potential gradient as the internal heat of the cable is increased. Curves are given showing the effect of a change of temperature on the dielectric strenrenth, the stresses and the factor of safety of cables. A complete description is given of the low-capacitance electrostatic voltmeter used in the temperature-potential-gradient tests.

Tests on General Electric Oil Circuit Breakers at Baltimore

Abstract: DURING the year 1920 an invitation was received by the General Electric Company from the Consolidated Gas Electric Light and Power Company of Baltimore, Maryland and the Pennsylvania Water and Power Company to submit oil circuit breakers for test on their system in Baltimore. The object of the test was to develop a breaker which would satisfactorily handle a short circuit on the 13,200-volt, 25-cycle system as it then existed, and show an apparent factor of safety at that load (20,000 to 25,000 r. m. s. amperes) which would be fairly conclusive to them that the breaker would also handle a short circuit on the system of at least 40,000 amperes. r. m. s. when the generating capacity had been increased by a proposed new generating station.

A Graphic Method for the Exact Solution of Transmission Lines

Abstract: There seems to be a popular superstition among engineers that the voltage and current relations at different points in a transmission line are peculiar and are not governed by Ohms law. This idea is not true. A transmission line is governed by Ohms law just as is any other alternating-current circuit containing resistance inductance and capacity. The only difference from an ordinary circuit is that in a transmission line we must make a correction for the effect of distributed constants. If we change the current flowing through a line by an amount I, there will be a voltage change eq-ual to I Z between the two ends of the line. The Z in this case, however, is corrected for the distributed constants of the line. The hyperbolic formula which are so widely coming into use, since Doctor Kennelly has given us tables of complex hyperbolic functions, are merely short methods of determining this Z as well as certain other constants which we must use. If we start wth a certain voltage Eg at the generator; on open circuit, we will have a slightly higher voltage at the receiver, due to the line capacity drawing a leading current through the inductance. As we load the line with a lagging current this voltage rise is counteracted by the impedance drop. In a similar manner the generator current is equal to the vector sum of the charging current, and the load current which has been multiplied by a constant.

Electrical Characteristics of Transmission Systems

Abstract: In making the electrical calculations for a long transmission line, it is desirable to include the effect of the step-up and step-down transformers and to make a direct calculation for the complete system, without any trial and error procedure. A miethod for doing this is described for constant-voltage lines, since long, high-power lines, especially those of 220,000 volts, usually require to be operated at constant voltage by means of synchronous condensers. The necessity of using the hyperbolic theory in calculating such lines is pointed out.

Three Thousand Tests on the Dielectric Strength of Oil

Abstract: Three thousand successive disruptive strength tests are herewith shown. These were made in six groups with 500 tests in each group under constant conditions of test. Three groups of tests were taken of standard insulating oil with three different shapes of the electrostatic field; small sphere gap, large sphere gap, and sphere-needle gap. One group of tests was made with commercial and another with chemically pure benzol. The last group was made with air as a dielectric. A brief review of results and conclusions follows. In measuring the voltage by a single sphere gap, set in air with reasonable care, the maximum error of test does not exceed 4 per cent and the average error is 1 per cent. In the average of six successive tests the maximum error decreases from 4 per cent to 2.9 per cent and the average error decreases from 1 per cent to 0.6 of 1 per cent. In contrast to air, the behavior of oil is very erratic. Successive observations of its disruptive voltage, made under most carefully controlled conditions, differed by a percentage many times greater than the accuracy of the test,?the minimum value was as low as 49 per cent of the maximum. This inconstancy of the disruptive strength of oil appears inherent to the material. Little of the variation is dependent on the shape and size of the electrostatic field. Much of the variation is due probably to the complex chemical and physical nature of the oil.