Showing papers in "Journal of the Institution of Electrical Engineers in 1940"
TL;DR: In this paper, the authors investigated the causes of the absence of bearing in short-wave Adcock direction-finder signals in the skip zone and found that they are due to momentary irregularities and small clouds in the E region of the ionosphere.
Abstract: It has been known for a long time that signals from strong commercial stations can be received in the skip zone. Early investigations with a short-wave Adcock direction-finder showed that the signals within the skip zone are in general characterized by absence of bearing. The present paper is a complete investigation into the causes of such effects. It was found that they are due to momentary irregularities and small clouds in the E region of the ionosphere. These irregularities produce scattered signals. The investigation, first carried out with the Adcock direction-finder, was later made more definite and accurate by using short impulses from highpower stations. The later investigations entirely confirmed the original deductions. The effects of such scattering on long-distance transmission, direction-finding, etc., are discussed. The phenomenon is considered to be a major factor in practically all transmissions.
24 citations
TL;DR: In this paper, the leakage reactance of transformers is investigated by means of Roth's potential vector method of analysis, where the potential vector is divided into three components: the first component gives rise to the normal reactance as calculated by Kapp's equation; this is termed the “axial reactance; the second component is responsible for additional leakage reaction, and the third, which does not lend itself to easy mathematical treatment, is shown to modify the axial term.
Abstract: This paper investigates the leakage reactance of transformers by means of Roth's potential-vector method of analysis. The potential vector is divided into three components. The first component gives rise to the normal reactance as calculated by Kapp's equation; this is termed the “axial reactance.” The second, which is responsible for additional leakage reactance, is termed the “radial component”. The third, which does not lend itself to easy mathematical treatment, is shown to modify the axial term, giving a closer degree of approximation by its inclusion.In order to enable the total leakage reactance of various winding arrangements to be calculated, three Tables are provided. Thus it is possible to allow for the effects of cooling ducts, tappings, and end-turn reinforcement. In Appendix I a comparison is made between the calculated and tested values of the leakage reactance of two commercial transformers having non-uniform distribution of ampereturns.
10 citations
TL;DR: In this article, the effect of rainfall on earth electrodes has been investigated, both with and without artificial treatment, based on the results of E.R.A. tests which have been in progress for 7 years.
Abstract: Earthing is first considered in relation to the various regulations applicable in Great Britain. These regulations relate to the generation, transmission and use of electricity, and the last item covers use in all types of consumers' premises. Particular attention is given throughout the paper to the peculiar difficulties attendant upon supply in rural areas, where protection is difficult to obtain. The factors affecting the resistance of earth electrodes are their size and shape, and the resistivity of the soil. All these items are dealt with in detail, including an analysis of the effect of rainfall on electrodes, both with and without artificial treatment. This analysis is based on the results of E.R.A. tests which have been in progress for 7 years. Only brief reference is made to the means of avoiding voltage gradients around earth electrodes which are dangerous to cattle, since this has been fully considered elsewhere. Current loading capacity is treated somewhat more fully in view of the important nature of the work and the fact that this is the first occasion on which any such results have been made public. The paper concludes with a section on the design of earth electrodes in which an attempt is made to correlate all the essential features bearing on electrodes, to show them in their true perspective in relation to the whole problem of earthing, and to relate the whole to practical requirements in which the question of cost plays a very important part.
8 citations
TL;DR: In this paper, the causes of wire failure in overhead line conductors subject to the "eddy" vibration due to steady winds ranging from 5 to 25 m.p.h. The theory of eddy vibration is first outlined and tests are detailed dealing with the effect on wire failure of such factors as tension and the design of clamp and conductor.
Abstract: This paper is a resume of available data concerning the causes of and remedies for wire failure in overhead line conductors subject to the "eddy" vibration due to steady winds ranging from 5 to 25 m.p.h. The theory of eddy vibration is first outlined and tests are detailed dealing with the effect on wire failure of such factors as tension and the design of clamp and conductor. Studies of clamp and conductor motions during vibration are also described. It is shown that wire failure is caused mainly by the "nicking" action between wires occasioned by the clamping stresses, and to a lesser degree by the "hammering" between conductor and clamp. The "nicking" weakens the wires locally and thereby prevents full use being made of their fatigue strength. Though it is difficult to reduce the "nicking" action, other data showed that a reduction of wire failure could be obtained by a lowering of the working tension, and that the effects of "hammering" could be reduced by a suitable design of clamp. Geographical factors favourable to vibration are then discussed, and data are set out which indicate that in general light and hollow conductors are more susceptible to vibration than other types. The "non-vibrating" conductor due to Preiswerk is also described. A discussion then follows of the various methods which have been employed in practice to reduce wire failure (i.e. methods of reinforcing the conductor at the clamp against the bending caused by vibration, the use of dampers, festoons, etc.). All.these methods have been more or less successfully employed, and each has its advocate. It appears, however, that wire failure can be reduced by a suitable application of either, though it has not been found possible to make a definite statement concerning their relative costs, which in any case must depend on local conditions. In recent years, however, the tendency has been to employ dampers. The "dancing" of conductors is then disc
7 citations
TL;DR: In this paper, it was shown that the effective leakage inductance of transformers, which in many cases determines transients of restriking voltage, cannot be regarded as a constant, but varies very considerably with time from the start of a transient and with the frequency of the transient.
Abstract: In this paper it is shown that the effective leakage inductance of transformers, which in many cases determines transients of restriking voltage, cannot be regarded as a constant, but varies very considerably with time from the start of the transient and with the frequency of the transient In extreme cases the effect of this phenomenon may be to reduce the rate of rise to 70 %, and the first peak of restriking voltage to 50 %, of the corresponding values calculated using the power-frequency leakage inductance of the transformer It is shown that the laws governing these variations can be calculated with reasonable accuracy from, the dimensions of the transformer In illustration of the importance of this phenomenon in practical cases, the paper describes short-circuit site tests for the measurement of transients of restriking voltage at the medium-voltage busbars of a large substation The work is, however, equally applicable to higher-voltage busbars
7 citations
TL;DR: In this paper, a simplified case of a solenoidal coil of infinite length, placed coaxially in an infinitely long cylindrical screen, is considered, and the shape of the curve of eddy-current distribution in the screen is examined, and it is found that the shape derived from search-coil measurements is very similar to that derived from calculation on the basis of regarding the coil as a flat system.
Abstract: In this paper an effort has been made to determine simple and workable formulae for the changes produced in the characteristics of an air-core coil by placing it in a screening container. The formulae, which have been derived empirically, are based upon the simplified case of a solenoidal coil of infinite length, placed coaxially in an infinitely long cylindrical screen. Another simplification, namely that of regarding the coil-and-screen system as a fiat band of wires placed parallel to a conducting plane, is also mentioned, and from these two simple cases it has been possible to proceed, by application of the results of measurement, to formulae for inductance and resistance change so simple that they almost amount to workshop rules. These formulae are shown to cover all practical cases of finite coils and coaxial screens to an accuracy within 2%. The effects of proximity of ends, small deformations and displacements, and temperature changes, are also examined and estimated. The shape of the curve of eddy-current distribution in the screen is examined, and it is found that the shape of curve derived from search-coil measurements is very similar to that derived from calculation on the basis of regarding the coil as a flat system.
6 citations
TL;DR: The use of synchronous induction motors has steadily increased in the last 15 years, and much information about them is now contained piecemeal in various papers as mentioned in this paper, but no critical account of the various types of secondary circuit and of the ways of exciting them is yet available, however, and in the first part of this paper the author considers these systematically.
Abstract: The use of synchronous induction motors has steadily increased in the last 15 years, and much information about them is now contained piecemeal in various papers. No critical account of the various types of secondary circuit and of the ways of exciting them is yet available, however, and in the first part of this paper the author considers these systematically. The characteristics desirable are first elucidated, and each winding is then considered in the light of these characteristics. Their properties are finally summarized in tabular form.The second part of the paper describes experiments by the author on the load reactance of synchronous induction motors. The relation between load and synchronous reactance for a machine with a barrel rotor is established practically, as is also the dependence of both these quantities on the secondary wave form. A correction for “magnetic backlash” is introduced.The third part of the paper deals shortly with parasitic currents in secondary circuits, with oscillograms of these currents.The appendices give mathematical results for secondary wave forms, ratings, starting torques and exciting currents. These results serve as standards with which actual results can be compared.
6 citations
TL;DR: In this article, the authors describe a quantitative investigation into the subject of the noise emitted by transformers, and possible measures for its limitation, as well as permissible noise levels for different situations are discussed and data for residential districts given.
Abstract: The paper describes a quantitative investigation into the subject of the noise emitted by transformers, and possible measures for its limitation. Permissible noise-levels for different situations are discussed and data for residential districts given. The generation of transformer noise is considered. Methods for limiting noise, applicable to a transformer as unit, are discussed, and results obtained with one based on the interception of vibration transmitted from core to tank are given. Methods applicable externally to a transformer are also discussed. The electromagnetic, thermal and economic considerations which arise in the employment of the various methods are discussed and examples are given.
6 citations
TL;DR: Theoretical calculation of the space charge in a thermionic diode having cylindrical symmetry, taking account of the distributed initial velocities of the emitted electrons, is described in this article.
Abstract: Theoretical calculation is made of the space charge in a thermionic diode having cylindrical symmetry, taking account of the distributed initial velocities of the emitted electrons. Curves are given from which the theoretical volt-ampere characteristic can be found. The mathematical method is detailed in Appendices.
4 citations
TL;DR: In this paper, the rates of rise of voltage at the clearance of different types of fault at given points on a network, with the relation between the power-frequency parameters of the various plant units concerned and those effective during the occurrence of the transients of restriking voltage, and with the range of values of rate of rise to be expected at different busbar location.
Abstract: This report deals with the rates of rise of voltage at the clearance of different types of fault at given points on a network, with the relation between the power-frequency parameters of the various plant units concerned and those effective during the occurrence of the transients of restriking voltage, and with the range of values of rates of rise to be expected at different types of busbar location. Rates of rise of voltage under different types of fault condition are first expressed in general terms. These are shown to agree with the values measured under different conditions in particular situations on the network of the Birmingham Corporation, by means of the restriking-voltage indicator. The application of the method of symmetrical components to the calculation of transients of restriking voltage on the clearance of all types of fault is discussed, with particular reference to generators. Rates of rise of voltage in concrete instances on an 11-kV system are given, the values ranging from approximately 200 to 7 000 volts per microsecond: it is considered that the latter figure may well represent an upper limit in British practice at this voltage.
4 citations
TL;DR: In this article, the authors discuss various types of abnormal voltagestresses in transformers, and in particular those due to surge phenomena, and the application of a simple, economical and effective type of shield to commercial transformers is discussed.
Abstract: The paper discusses various types of abnormal voltagestresses in transformers, and in particular those due to surge phenomena. A brief resume of the theory of the effects of surge voltages on transformer windings is given, and a method of determining initial impulse-voltage distribution by means of a calculating board is explained. The principles of electrostatic shielding are considered and the application of a simple, economical and effective type of shield to commercial transformers is discussed. Illustrations of actual transformers fitted with such shields are given, and the efficacy of the shielding is demonstrated by means of cathode-ray oscillograms. An account is given of researches carried out by means of the recurrent-surge oscillograph, and results are compared with those obtained at high voltage, using a continuously evacuated cathode-ray oscillograph. In conclusion, reference is made to the problem of co-ordination of insulation, and the relative merits of various protective measures are briefly discussed. It is shown that a shielded-winding transformer, when properly co-ordinated with line protective devices, possesses a high degree of immunity from breakdown due to lightning or other transient voltages.
TL;DR: In this paper, an approach is made to the more elementary methods, illustrated by examples in order of increasing complexity, and it is indicated that extensions to the Analysis of Variance involving correlation and regression are useful aids in testing and research.
Abstract: This paper was originally written merely as an elementary introduction to a discussion on the application to industrial problems of modern statistical methods. In view, however, of the alteration in the arrangements for meetings minor changes have been made, but the paper should still be read as an introduction to a general discussion on the subject.The authors have had in mind particularly the scrutiny of test data obtained in the course of the development of new manufacturing procedures and in the control of established ones.Having first dealt with the fundamental conception of variability and the basic effect of chance on the magnitudes of test values, an approach is made to the more elementary methods, illustrated by examples in order of increasing complexity. At the end of the paper it is indicated that extensions to the Analysis of Variance involving correlation and regression are useful aids in testing and research. The authors emphasize that the efficient use of the statistical tool can come only by practice, and that in no sense can it be substituted for sound technical knowledge, with which in all problems it must be combined.
TL;DR: In this article, the authors show the important part played by storage batteries in present-day electrical engineering practice, and survey many of the applications in detail as regards design, purpose, latest improvements and practice.
Abstract: The object of this paper is to show the important part played by storage batteries in present-day electrical engineering practice. Many of the applications are surveyed in detail as regards design, purpose, latest improvements and practice, and actual results obtained in service. Contrary to general anticipation that the national grid would lead to a greatly reduced demand for storage batteries, the grid has given rise, directly and indirectly, to numerous new applications for batteries. Although the review deals entirely with lead-acid batteries, it is not intended to belittle the importance of other types or to ignore the fact that these types too may be of great practical value in many applications.
TL;DR: In this article, it was shown that the propagation of horizontally and vertically polarized waves is identical over a range of transmitter and receiver heights which are small compared with the distance between transmitter and receivers but not small compared to the wavelength.
Abstract: The paper describes the results of an experimental investigation of the characteristics within optical range of the propagation over land of radiation having wavelengths of 2 and 3 metres. It is shown both theoretically and experimentally that for such conditions the propagation of horizontally and vertically polarized waves is identical over a range of transmitter and receiver heights which are small compared with the distance between transmitter and receiver but not small compared with the wavelength. In these circumstances, for a receiver at height hR metres the field strength in volts per metre at a distance d metres from a half-wavelength radiator at a heighthT metres is given bye = 90√PhThR/λd2in which P is the power (watts) radiated at a wavelength λ metres). Continuous observations of field strength showed that within optical range of the transmitter the fading was less than ±3 db.
TL;DR: The nature of the drying process in paper, at two temperatures and various ambient pressures, has been investigated in this article, at high vacua, and which is sufficiently sensitive to measure the electrical changes due to a water content of the order of 0-05 % of the weight of cellulose present.
Abstract: The nature of the drying process in paper, at two temperatures and various ambient pressures, has been investigated Apparatus has been developed, and is described, which permits the drying process to be investigated at high vacua, and which is sufficiently sensitive to measure the electrical changes due to a water content of the order of 0-05 % of the weight of cellulose present A number of theoretical conclusions has been derived from the experimental data, and these are summarized at the end of the paper
TL;DR: In this article, it was shown that the field at the receiver is equal in most practical cases to the vector addition of two fields, one that given by the ray theory, and the other corresponding to the Sommerfeld surface wave, having a magnitude dependent on the electrical properties of the reflector and the distance between transmitter and receiver but independent of the heights of transmitter and receiving aerials.
Abstract: The paper contains curves from which the reflection coefficient at the earth's surface for radio waves of any state polarization can be determined for angles of incidence greater than 80°. It is pointed out that the ray theory, on which reflection from a reflector is assumed to be equal to the radiation from an image of the transmitting aerial in the reflecting surface, is not applicable at grazing incidence unless the heights the transmitting and receiving aerials are comparable with the wavelength. From an analysis given by Norton, however, it is deduced that, when the ray theory does not apply, the field at the receiver is equal in most practical cases to the vector addition of two fields, one that given by the ray theory, and the other, which corresponds to the Sommerfeld surface wave, having a magnitude dependent on the electrical properties of the reflector and the distance between transmitter and receiver but independent of the heights of transmitter and receiver. The ratio of the magnitudes of the surface wave to image fields is much less for horizontally than for vertically polarized waves, so that the ray theory is applicable over a wider range of angles of incidence for horizontally than for vertically polarized waves.
TL;DR: It is proposed to give in this paper a description of the system in this country and its immediate connections to the Continental and Empire networks, with some reference to the American system as an indication of the general differences between American and European practice.
Abstract: Any form of transport calls for a communication and signalling system, and by its nature civil air transport has to rely on radio-telegraphy and radio-telephony for the majority of the services it requires, and is peculiarly dependent on navigational help by radio. As a result an extensive communication system has been built up to provide these services throughout the world, a system which is closely interconnected internationally and which provides a service for the aircraft of any country operating on the various routes. It is proposed to give in this paper a description of the system in this country and its immediate connections to the Continental and Empire networks, with some reference to the American system as an indication of the general differences between American and European practice. The paper is divided into the following Sections:? (1) The growth of the communication system. (2) Technical considerations and requirements of groundstation equipment. (3) Aircraft radio equipment and installation. (4) The Atlantic and Empire routes to the East. (5) A brief outline of the communication system in the U.S.A. (6) Future developments.
TL;DR: In this article, it was shown that in all types of magnetron valves, oscillations are possible for which the ratio of the product of wavelength and anode voltage to magnetic field has a series of discrete values given by the series K : K/2: K/3... K/n in which K is a function of the anode diameter.
Abstract: The paper describes an experimental investigation of the oscillations produced by magnetrons. It is shown that in all types of magnetron valves, oscillations are possible for which the ratio of the product of wavelength and anode voltage to magnetic field has a series of discrete values given by the series K : K/2: K/3 ... K/n in which K is a function of the anode diameter. Oscillations at frequencies corresponding to values of n up to 7 have been observed. In a full-anode magnetron all the oscillation intensities are small. For a 2-segment-anode magnetron the amplitude of the oscillation of lowest frequency (n = 1) is pronounced; in a 4-segment-anode magnetron oscillations at the frequency corresponding to n = 2 are predominant, and so on. These oscillations all belong to the class known as resonance oscillations. It is shown that there is no clear distinction between resonance and electronic oscillations at very short wavelengths, and it is suggested in the paper that they are essentially of the same nature.
TL;DR: In this article, the single-and double-dipole compensated loop direction-finder is described and reference is made to several patents which embody applications of these principles, and a brief account is given of the theoretical and practical work carried out at Slough on the Single-Dipole system.
Abstract: The principle of both the single-dipole and double-dipole compensated loop direction-finder is described and reference is made to several patents which embody applications of these principles. A brief account is given of the theoretical and practical work carried out at Slough on the single-dipole system. It is shown that this system can in certain circumstances be made to have a considerably higher pick-up factor for a given overall area than the Adcock direction-finder but that it is limited to use on ground of good conductivity. The double-dipole system, on the other hand, is independent of ground conductivity but has no superiority over the “H” type of Adcock system as regards pick-up factor.
TL;DR: In this paper, the effect of frequency on the depth of penetration of eddy currents in steel is examined, and consideration is given to the relation between the degree of penetration and the shape of the surface being treated.
Abstract: There has recently been a great increase in the use of highfrequency currents for heat treatment of metals, in such processes as surface hardening, cementation and alloying, welding, hot machining, and zonal tempering. The paper deals chiefly with surface hardening.After giving an account of the advantages of the process and an estimate of the power requirements, the authors deal with the design of the heating coil in relation to the shape of the specimen, and describe a “model” method whereby the distribution of the electromagnetic field in the system may be investigated.Curves are plotted from the authors' experimental results to show the distribution of temperature and current density over the specimen, and the variation of the power absorbed, during the heating period.The effect of frequency upon the depth of penetration of eddy currents in steel is examined, and consideration is given to the relation between the depth of penetration and the shape of the surface being treated.The paper concludes with a statement of the results which have been obtained from the application of the high-frequency method to the hardening of tools and gears.
TL;DR: In this paper, a preliminary investigation of radio direction-finding on wavelengths between 2 m and 3 m was carried out with the aid of instruments fitted with rotating aerial systems similar to those used in earlier work in the band 6 m. to 10 m.
Abstract: This paper describes a preliminary investigation of radio direction-finding on wavelengths between 2 m. and 3 m. (100 to 150 Mc./s.) with the aid of instruments fitted with rotating aerial systems similar to those used in earlier work in the band 6 m. to 10 m. (30 to 50 Mc./s.). The sensitivities of the loop and Adcock direction-finders used are such that bearings with a swing of ±5° can be obtained with field strengths of 20 and 40 μV per metre respectively. The reciprocal error of the instruments has been reduced to 1°, and the polarization error can be kept below 5° for angles of incidence and polarization to the vertical of 60°, although readjustment of the compensation arrangement is required to maintain this over an appreciable wave-band. The two direction-finders have been operated at various distances up to 30 miles from an experimental transmitter developing 100 watts on a wavelength of 3 m., and the average errors varied from about 10° at 1 mile to 3.5° at 20 miles with a vertical transmitting aerial. These errors are somewhat larger than the corresponding values found for the longer-wave band of m. to 10 m. (30 to 50 Mc./s.). When an attempt was made to use a direction-finder inside a wooden hut, the observations were found to be subject to an octantal error 2° to 5° amplitude, the value increasing as the wavelength was reduced. This error was found to be due to reflection effects from the walls of the hut, and experiments made with various wooden boards showed that it depended upon the nature of the wood and direction of the grain. A synthetic material with no grain direction was found to have only a small effect.
TL;DR: In this paper, a brief account of the manufacture of such materials, followed by a discussion of their mechanical and electrical properties is given, and the differences in values obtained on test samples and those which may be realized practically are emphasized.
Abstract: During the past few years, ceramic materials with properties especially suited to working at radio frequencies have been developed. The present paper contains a brief account of the manufacture of such materials, followed by a discussion of their mechanical and electrical properties. It is pointed out that many of the discrepancies in previously published data may be explained by the difficulties of the measurements and by the variation of some of the quantities to be measured with factors not always sufficiently controlled or specified. The differences in values obtained on test samples and those which may be realized practically are emphasized. The paper concludes with a brief account of the application of ceramic materials in the radio industry.
TL;DR: In this article, the effects of various forms of contacts on the frictional characteristics of circuit-breakers are described, and the design steps necessary to prevent a change of friction affecting the reliable performance of circuit breakers in service are considered.
Abstract: The paper covers some of the mechanical requirements of electrical circuit-breakers. Methods to be applied in the design stage to meet these requirements, and to guard against imperfections which may arise during manufacture, are suggested. The effects of various forms of contacts on the frictional characteristics of circuit-breakers are described, and the design steps necessary to prevent a change of friction affecting the reliable performance of circuit-breakers in service are considered.A series of practical routine tests is put forward which should ensure that the calculated design factors are complied with, and which should also lead to an improved standard of workmanship.Emphasis is laid on the importance of accuracy in workmanship and the necessity for careful calculations to comply with rigid standards.The paper concludes with illustrations and information relative to suitable apparatus and shop fixtures considered essential in. carrying out the prescribed routine tests.
TL;DR: In this paper, a method for grading overload inverse-time relays, with definite minimum time, on an 11-kV system is discussed with special reference to the reduction of tripping times throughout, especially at the source of supply.
Abstract: Methods of grading overload inverse-time relays, with definite minimum time, on an 11-kV system are discussed with special reference to the reduction of tripping times throughout, especially at the source of supply. A method is developed which attains this object and allows a large number of relays to be used in series. A system of recording network short-circuit calculations and emergency relay settings is also discussed.
TL;DR: The problem of measuring torque in induction motors is discussed, and methods of measurement are described based on the analysis of motion-picture records.
Abstract: The problem of measuring torque in induction motors is discussed, and methods of measurement are described based on the analysis of motion-picture records.