Showing papers in "Journal of the Institution of Electrical Engineers in 1938"
TL;DR: In this paper, the developments in cable practice since the previous rating tables were issued are treated from the aspect of their effect on current rating or carrying capacity, and the basis of the new rating tables is described.
Abstract: The developments in cable practice since the previous rating tables were issued are treated from the aspect of their effect on current rating or carrying capacity, and the basis of the new rating tables is described These tables are given, together with means for calculating the rating of cables installed in any of the usual modes
40 citations
TL;DR: In this article, the rotational hysteresis loss in small disc samples of sheet steel was measured in a simple manner, the loss being determined directly without the inclusion of eddy-current losses.
Abstract: The paper describes how rotational hysteresis loss in small disc samples of sheet steel may be measured in a simple manner a new method, the loss being determined directly without the inclusion of eddy-current losses. The difficulty in the way making measurements on a single disc, due to the magnetic anisotropy of the material, is indicated. The magnetic anisotropy in commercial electrical sheet materials is then briefly discussed, and it is shown how by use of a sample made up of three similar discs the experimental difficulty may be overcome. The observed results on four electrical sheet materials are then given. The loss, plotted against flux density, is seen to fall rapidly towards zero near saturation, as has been found for various ferromagnetics by other investigators, but a sharp increase in loss, hitherto unreported, is shown to occur, for all four materials, at a point near the "knee" of the magnetization curve. A qualitative explanation of this phenomenon and of the general form of the loss curve is given on the basis of the "domain" theory of ferromagnetism.
39 citations
TL;DR: In this paper, an approximate formula for the alternating-current resistance of isolated, hollow, square conductors, including the solid conductor as a special case, was developed theoretically and experimental results were given to show that this formula is correct to within about 2 % at all frequencies.
Abstract: An approximate formula for the alternating-current resistance of isolated, hollow, square conductors, including the solid conductor as a special case, is developed theoretically. Experimental results are given to show that this formula is correct to within about 2 % at all frequencies.Formulae for the proximity effects in single-phase and 3-phase systems are also developed. These formulae are based partly on theoretical development and partly on experimental results. The experimental results cover most of the values likely to be encountered in practice.
10 citations
TL;DR: In this paper, the authors describe the method of assessment of the interference to radio reception from electrical equipment, and determine the level to which such interference must be reduced to permit satisfactory service.
Abstract: The paper describes the method of assessment of the interference to radio reception from electrical equipment, and determines the level to which such interference must be reduced to permit satisfactory service. The methods of achieving this result are described for the various classes of interfering equipment. Although mainly directed towards the protection of broadcast reception, the principles described apply equally to other radio communication services.
10 citations
TL;DR: In this paper, the author describes current practice in street traffic signalling, dealing particularly with vehicle-actuated signals as adapted for use in Great Britain, and the subject is treated from the traffic aspect as well as from the electrical aspect, and details of the performance of certain schemes are given.
Abstract: The author describes current practice in street traffic signalling, dealing particularly with vehicle-actuated signals as adapted for use in Great Britain. Detailed descriptions are confined to the system with which the author is most familiar (the Autoflex vehicle-actuated system). Brief references are, however, made to other systems and to practice in other parts of the world. All parts of the equipment are treated, including signals, controllers, and detectors. The paper is divided into two main portions, the first dealing with generalities and isolated intersections and the second with interlinking of numbers of intersections. The subject is treated from the traffic aspect as well as from the electrical aspect, and details of the performance of certain of the schemes are given.
10 citations
TL;DR: In this article, the authors describe a television broadcasting station recently built by the British Broadcasting Corporation in a part of the Alexandra Palace, London, N.C., and discuss the layout and arrangement of the control room and transmitter equipment installed for the vision and accompanying sound transmissions.
Abstract: This paper describes a television broadcasting station recently built by the British Broadcasting Corporation in a part of the Alexandra Palace, London, N. The development of the television service in this country is traced from the early attempts to promote an experimental service of transmissions on low standards of definition to the establishment of a highdefinitionpublic service. The paper is divided into six parts. Part 1 touches briefly upon the history of television development in this country, and describes in some detail the transmission of low-definition pictures from B. B. C. stations during the years 1929 to 1935. Part 2 deals with the recommendation of the Television Committee that a station for transmitting high-definition television should be established, and it discusses various factors upon which the subsequently appointed Television AdvisoryCommittee based its decisions regarding the choice of the Alexandra Palace site, the operating wavelengths, and standards of definition. Part 3 describes the arrangement of studios and apparatus rooms at the Alexandra Palace station. The problems of studio acoustics, production lighting, and the provision of essential supplies, are also dealt with. Part 4 describes the layout and arrangement of the control room and transmitter equipment installed for the vision and accompanying sound transmissions. Part 5 is concerned with the plant developed to enable current events and other programme items taking place at some distance from the Alexandra Palace to be televised. Some account is given of the use of land lines to carry television signals. Part 6 is a brief consideration of the reception results of signals from the Alexandra Palace since the beginning of the service, and embodies the result of signal-strength surveys made in the vicinity of, and at distances from, the station. Finally, the various types of television receivers and aerials are discussed.
9 citations
TL;DR: This paper presents a somewhat simplified consideration of the processes occurring in the magnetic recording of sound on steel tape, and describes some of the apparatus and methods used in this country in its application to broadcasting.
Abstract: This paper presents a somewhat simplified consideration of the processes occurring in the magnetic recording of sound on steel tape, and describes some of the apparatus and methods used in this country in its application to broadcasting. A brief historical account is given of the early uses of magnetic recording. The essential processes involved are then discussed in a simplified form, and the effects of tthe finite longitudinal spread of the recording field, and of the self-demagnetization of the tape, are considered before the question of background noise is introduced. In the next section certain fundamental experiments are described, followed by a brief account of various possible methods of saturating, recording, and reproducing. Considerations relating to the conditions for the optimum working of any particular arrangement are put forward, with the results of tests of two of those which are now in use. Some details are given concerning the tape itself, after which a recording machine is described. The paper concludes with a short account of the technical and programme service requirements for a recording system for use in connection with broadcasting, and a description of a recording channel at the British Broadcasting Corporation's premises at Maida Vale.
8 citations
TL;DR: In this paper, an instrument of the microphone-amplifier-meter type has been adjusted for measuring the equivalent loudness of noise, which has been shown to give results in excellent agreement with average assessments, by the standard aural technique, of a variety of moderate and loud noises.
Abstract: The present paper relates to an instrument of the microphone-amplifier-meter type, which has been adjusted for measuring the equivalent loudness of noise. Many noisemeters on these lines are available commercially, but the author has not met with any (other than those based on designs supplied to firms by, the National Physical Laboratory) which give results even approximately correct for a series of impulsive sounds. The essential feature of the work now described has been the adjustment of the circuits of the meter so that gives correct results for intermittent and impulsive noises, as well as for continuous tones. The paper describes the principles upon which an empirical adjustment was made, and produces evidence that the meter gives results in excellent agreement with average assessments, by the standard aural technique, of the equivalent loudness of a variety of moderate and loud noises. It is commented that meters which pass certain specification for sound-level meters which has been tentatively proposed recently may give results for impulsive sounds very much below the true values of their equivalent loudness. An important point revealed incidentally was that inconsistencies arise in aural measurements when the loudness of noise is compared. with that of a reference tone heard simultaneously. The difficulties are resolved by adopting technique in which the noise and the reference tone are heard alternately.
8 citations
TL;DR: In this paper, it was shown that the leader stroke always exhibits branching in the direction of propagation; the main stroke follows some of the more important branches but does not develop fresh branches.
Abstract: Study of the mechanism of the electric spark has been mainly confined to the short spark in homogeneous fields, or to the long spark provided by Nature in the form of the lightning flash. Following some early work of the author's on the characteristics of the impulse-voltage spark from a negatively or positively charged point electrode to earth, the author has further studied these discharges with the rotating camera to find the chronological sequence of discharge processes. Discharges preceding the main spark were observed irrespective of the polarity of the high-voltage electrode, the separation in time of the pre-discharge manifestation from the main spark being almost equal to the time-to-sparkover as recorded by the cathode-ray oscillograph. These discharges have been studied in air at atmospheric and lower pressures, and it has been shown that the pre-discharge is a “leader stroke” in the strict sense of the word as applied to the lightning discharge: a “leader” blazes an ionized path from the high-voltage electrode (of either polarity) to earth and is then followed by the return or main stroke of the spark from earth to the high-voltage electrode. Under certain conditions leader strokes have been shown to develop from both electrodes simultaneously. The leader stroke always exhibits branching in the direction of propagation; the main stroke follows some of the more important branches but does not develop fresh branches. The direction of branching of the spark discharge has been shown to furnish the criterion for the direction of propagation of the leader stroke.
7 citations
TL;DR: In this paper, the development of high-power valves is influenced by the standard of reliability demanded by such services as broadcasting, and the principles governing the constructional design of each main part of the valve are outlined; differential expansion frequently appears as a controlling factor.
Abstract: In the Introduction the authors discuss how the development of high-power valves is influenced by the standard of reliability demanded by such services as broadcasting. The principles governing the constructional design of each main part of the valve are outlined; differential expansion frequently appears as a controlling factor.The glass-work is of lead-potash-soda glass, the anodes of thick copper tubing; for glass-to-metal seals nickel-iron alloy is preferred, but copper is sometimes used. Insulating members have been eliminated from the active part of the valve. Grids are not cross-braced, grid seals include a large ring section let into the bulb, and there is an 8-lead multiple seal for pentodes. Cathode seals for 1000 amperes are described; these support the whole cathode system, the evolution of which into a freehanging multiple construction is outlined. Heat transfer between anode and cooling liquid is discussed, and also forced-air cooling.Modern evacuation technique proves to be governed by two effects; the lower readings of grid current in the “ gas test” are shown to be due to photo-electric electron emission caused by X-rays from the anode and not directly to gas, and the clean-up capability of the valve is found to be very large. The method is described for determining the operating filament voltage for a standard emission by extrapolation to full emission from a reduced-emission test. Examination of the statistics of emission-test data shows that former variations are to be ascribed to variable thermal emissivity and not to variable dimensions.Methods are given for extrapolating low-power space-current readings into the operating region, with allowance for division between anode and grid, and the “tail” of the anode-current characteristic is discussed. The control of the secondary-emission component of the grid current and the effect of the magnetic field of the filament are described. An account is given of later experiments and of recent experience with flash-arc breakdowns (Rocky Point effect). Recommendations are made for switching-on filaments and anode potential in operation, and for purity of cooling water. Curves are shown of the distribution of evaporation wastage in various types of filament. Typical valve-life data from normal operation are illustrated by survivor curves for constant voltage and for constant emission during life, and a Table is given showing the recent performance of the largest valves at three stations. A table of ratings for the various types of valve covered by the paper is also included.
7 citations
TL;DR: In this paper, the minimum impulse flashover characteristics of gaps between spheres ranging in diameters from 125 mm to 1000 mm have been determined with the aid of the highvoltage cathode-ray oscillograph and the resistor voltage-divider.
Abstract: The technique of measuring impulse voltages with the aid of the high-voltage cathode-ray oscillograph and the resistor voltage-divider is discussed, and applied to the determination of the minimum impulse flashover characteristics of gaps between spheres ranging in diameters from 125 mm. to 1000 mm. Flashover measurements on sphere-gaps have also been made at power frequencies and compared with the corresponding figures for impulse voltages. The results of some previous workers are considered, and compared with those obtained by the authors.
TL;DR: In this paper, the authors proposed a circuit for a grid-controlled phase-advancer with auxiliary valves and a capacitor, where the capacitor is connected, through the auxiliary valves, in parallel with each of the principal valves in turn, and extinguishes them.
Abstract: By connecting a charged capacitor between the anode and the cathode of a grid-controlled valve it is possible to break off the current through the valve. The paper deals with circuits for grid-controlled phase-advancers based on this principle. Into the circuit of a conventional grid-controlled rectifier are introduced auxiliary valves and a capacitor. The capacitor is connected, through the auxiliary valves, in parallel with each of the principal valves in turn, and extinguishes them. The effect of this is to make the current lead the voltage. There are (a) double-step circuits with two groups of valves and a capacitor which extinguishes in turn the valves of the first and of the second group; and (b) multistep circuits with N groups of valves and N capacitors changing their charge in a periodic fashion. The paper includes formulae and diagrams for the computation of the rated-output factors of the extinguishing capacitor and the smoothing reactor respectively. Experimental results and oscillograms are given which confirm theoretical conclusions. A grid-controlled phase-advancer can be utilized to improve the power factor of an a.c. main, instead of rotary machines or static capacitors.
TL;DR: In this paper, it was shown that the noise in a space-charge-limited valve is best expressed as a thermal noise, and that a small correction must be applied to the valve slope resistance to give the value of resistance effective as a noise source.
Abstract: From a consideration of the physical phenomena involved in thermionic conduction and in thermal or Johnson noise, it is deduced that the noise in a space-charge-limited valve is best expressed as a thermal noise, and it is shown that a small correction must be applied to the valve slope resistance to give the value of resistance effective as a noise source. The theoretical temperature of this resistance is then shown to be approximately half the cathode temperature. In a temperature-limited valve, both the resistance and the temperature of the conducting path are indeterminate. The ?pure shot noise? formulae are applicable to this case, and represent the maximum noise which can result from the passage of a given current through the system. It is incorrect, however, to state that in space-charge-limited conditions ?pure shot noise? is smoothed out, while thermal noise in the internal resistance of the valve appears as an additional factor; shot noise and thermal noise in the valve's internal-resistance are essentially the same phenomenon, but are modified by the differing conditions of electron transit. Nyquist's expression for thermal-agitation noise is derived from the atomic mechanism in the case of a metallic conductor.
TL;DR: In this paper, the authors describe means for producing and viewing recurrent surges suitable for use in analysing the transient behaviour of power engineering circuits, and in particular a recurrent-surge oscillograph having an especially fast time-base.
Abstract: It is the purpose of this paper to describe means for producing and viewing recurrent surges suitable for use in analysing the transient behaviour of power engineering circuits, and in particular a recurrent-surge oscillograph having an especially fast time-base. Methods of applying such analytical instruments will be described, with special reference to the problems of current suppression by switch action.
TL;DR: In this article, a method for the calibration of short-wave field strength measuring sets by radiation using a loop transmitter in the horizontal plane is described, and the advantages ensuing from the use of horizontally polarized waves for this purpose may be summarized as follows: (a) the heights of transmitter and receiver may be reduced practically to any extent, so that high masts are no longer required.
Abstract: The paper describes a method for the calibration of shortwave field-strength measuring sets by radiation using a loop transmitter in the horizontal plane. It is shown experimentally that in the case of vertically polarized waves of the simple ray theory does not apply unless the transmitter and receiver are both elevated to considerable heights above the ground. With horizontally polarized radiation, however, the simple ray theory holds on short waves for practically all heights of transmitter and receiver. This distinction between the propagation characteristics of the two types of radiation suggests the use of horizontally polarized waves for fieldstrength calibrations on short waves. The advantages ensuing from the use of horizontally polarized waves for this purpose may be summarized as follows:- (a) The heights of transmitter and receiver may be reduced practically to any extent, so that high masts are no longer required. (b) For low heights of transmitter and receiver the reflection coefficient of the ground is sensibly unity for all types of the earth's surface, so that little error can be introduced in the analysis due to wrong assumptions as to the electrical properties of the ground. The analysis of the results is considerably simplified when the reflection coefficient of the ground is approximately unity. (d) With no masts at the transmitter or receiver it is an easy matter to take an attenuation run, so that the calibration is not dependent on one observation. (a) It is particularly suitable for the calibration of receivers incorporating rectilinear antennae, as there is no error in calibration due to varying height of the aerial above ground.
TL;DR: In this article, the power factor of cellulose acetate has been investigated over the temperature range 25° C to 90° C, using alternating voltages at frequencies covering the range 50 to 4000 cycles per second, and also direct voltage.
Abstract: The possibilities of cellulose acetate as a dielectric have received attention recently from several investigators, at home and abroad. This material has been under consideration by the Electrical Research Association for the past two years, not only from the point of view of its industrial applications, but as a medium for the investigation of fundamental phenomena. The policy of the Electrical Research Association in regard to protracted researches of this nature is to release as much information as possible in the form of interim reports, rather than waiting until the final conclusions are available. The report which follows is one of a series on dielectric phenomena which, for convenience, are related to materials or groups of materials widely used in industry. Other reports in this series relate to ebonite, paper, and varnished cloth. The dielectric properties of cellulose acetate have been studied over the temperature range 25° C. to 90° C, using alternating voltages at frequencies covering the range 50 to 4000 cycles per second, and also direct voltage. Preliminary tests showed that the power factor of commercial cellulose acetate may vary from 2 percent to about 15 percent. The detailed investigation was confined to samples of low power factor. The material was found to absorb water from the atmosphere, and its power factor was reduced by drying. Samples which were dried at a temperature of 90° C. were regarded as completely dry, and such samples were used for most of the measurements. Other samples dried at 25° C. possessed a slightly higher power factor and therefore presumably contained traces of water. Measurements were made also on these samples in order to find out the effect of the water. Measurements of permittivity and power factor were made by means of the Schering bridge fitted with a Wagner earth connection. Mercury electrodes were used. It was found that as long as the voltage gradient does not
TL;DR: In this paper, the reflection coefficient of the ground can be determined for any angle of incidence or any value of dielectric constant and conductivity of that surface, by two interpolations.
Abstract: Curves are given from which, by two interpolations, the reflection coefficient of the ground can be determined for any angle of incidence or any value of dielectric constant and conductivity of that surface. Curves are given for the two cases in which the electric vector of the incident radiation is polarized in and perpendicular to the plane of incidence respectively, so that the reflection coefficient can also be determined for any state of polarization.
TL;DR: In this paper, the behaviour of a transient on a finite distortionless line can be described in terms of two travelling-wave systems propagated in opposite directions along the line, and the voltages in these two waves satisfy two ordinary differential equations depending on the terminal conditions, involving a relation between the voltage at two times differing by the time of travel of a wave from one end of the line to the other and back.
Abstract: The behaviour of a transient on a finite distortionless line can be described in terms of two travelling-wave systems propagated in opposite directions along the line The voltages in these two waves satisfy two ordinary differential equations depending on the terminal conditions, and involving a relation between the voltage at two times differing by the time of travel of a wave from one end of the line to the other and back Equations of this type can be handled mechanically by means of the differential analyser, using a special form of input table, and the use of the differential analyser does not require that the terminal impedances should have linear characteristicsThe application of the differential analyser to a line with a capacitance at one end and a non-linear resistance (lightning arrester) at the other is discussed in some detail as an example, and specimens of machine solutions, both with a linear and with a non-linear resistance at the far end, are given and discussed, and compared with oscillograms taken on an actual line
TL;DR: In this article, the authors discuss the problems of collective control on modern supply networks, examine various alternative methods, and explain how, by the aid of superimposed high-frequency signals, any distribution network may be used as a signalling system which will enable a supply undertaking to exercise remote control of consumer circuits from its own power station.
Abstract: It is the author's purpose in this paper to discuss the problems of collective control on modern supply networks, to examine various alternative methods, and to explain how, by the aid of superimposed high-frequency signals, any distribution network may be used as a signalling system which will enable a supply undertaking to exercise remote control of consumer circuits from its own power station. He concludes that recent developments in this field have placed in the hands of the supply industry a powerful weapon with which to attack the economical development of heating loads, as well as providing an elegant solution to commonplace difficulties of street-lighting control, to which the supply industry has become accustomed but not reconciled. The special application of superimposed control in war time for the extinction of public lighting and for the dissemination of warning signals is not discussed in great detail, as such problems are of political rather than technical interest. As to terminology, control systems using superimposed signals are variously referred to as ?carrier control,? ?phantom circuit control,? and ?ripple control? systems. Of the three, the author prefers ?ripple control,? since it' avoids confusion with terms more properly applicable inother fields, yet gives a correct picture of the method itself.
TL;DR: In this paper, the Petersen coil is used to prevent interruptions of supply under certain types of fault conditions in underground networks, where even on underground networks it is regarded as indispensable by many supply authorities.
Abstract: The object of this paper is to stimulate interest in a piece of apparatus which, until comparatively recently, was practically unknown in this country. Its efficacy in preventing interruptions of supply under certain types of fault conditions has been for many years fully appreciated on the Continent, where even on underground networks it is regarded as indispensable by many supply authorities. Although the principles involved are briefly referred to for the benefit of those who are not familiar with the publications available dealing with the fundamental theory, the matter is dealt with from an operating rather than a theoretical point of view by drawing attention to a number of problems, many of them peculiar to this country, which arise when a Petersen coil is to be applied on a system originally intended to operate with the neutral solidly earthed; by suggesting convenient ways to obtain the information required by the makers for a coil or coils to suit any particular network; by dealing with a number of cases in which special measures are necessary; by explaining the means of tuning the coil to suit changing network conditions; by giving results obtained from coils in operation; and by comparing these results with those of solid or resistance earthing.
TL;DR: In this paper, the authors present a calibration of the sphere spark gap at 50 cycles of a range of sphere spark-gaps at voltages up to 1 million volts with one sphere earthed.
Abstract: Since the issue of B.S.S. 358 in 1929 on the "Measurement of Voltage with Sphere-Gaps," a number of calibrations of the sphere spark-gap have been put forward in Germany and the United States, but these differ appreciably amongst themselves and, moreover, are usually restricted to voltages of the order of 500 kV(eff.) and to spheres of 75 cm. diameter or less. The present paper is still another contribution to the literature on the subject, its justification being that it contains calibrations for larger spheres and at higher voltages than have hitherto been obtainable in this country. After a brief review of existing information the calibration at 50 cycles (a.c.) of a range of sphere spark-gaps is discussed in detail; methods of absolute measurement of high voltages are described, and calibrations are put forward for spheres up to 200 cm. diameter at voltages up to 1 million volts (effective) with one sphere earthed. These calibrations are based on a method of voltage measurement which is believed to be unique. Some attention has been directed towards the determination of the polarity of the high-voltage electrode when breakdown occurs, in view of the obvious importance of this feature in its relation to the breakdown of asymmetrical gaps under direct and impulsive voltages. A new type of polarity indicator is described. A correlation was observed between the noise of the spark and the polarity of the high-voltage electrode at breakdown. The effect of irradiation of the gap with radium and by other means is described.
TL;DR: In this article, the general problem of voltage regulation under load is reviewed and the principal technical and operating characteristics of existing voltage-regulators are summarized and a recent development is described which in principle involes an isolated and short-circuited coil moving up and down the leg of a laminated iron core over fixed coils.
Abstract: The general problem of voltage regulation under load is reviewed and the principal technical and operating characteristics of existing voltage-regulators are summarized. The problem has not been found easy of solution, as the more simple devices are restricted in scope and have other technical limitations, whilst apparatus of more general application is relatively expensive and complicated. A recent developmentis described which in principle involes an isolated and short-circuited coil moving up and down the leg of a laminated iron core over fixed coils. Smooth voltage variation over any desired range is obtained without switches, contacts, flexible leads, or windings in slots. After a discussion of the new regulator, the special features and application of regulators are considered under the separate headings of voltage control (a) in transmission and distribution circuits, and (b) for industrial and laboratory purposes.
TL;DR: In this article, a representation of thermionic fiuchiations is proposed analogous to that adopted for thermal fluctuations, and a general formula applicable to certain classes of networks containing thermionic valves is deduced.
Abstract: This paper is concerned with the fluctuations generated in networks with non-uniform temperature distribution, Experiments are described which verify a formula relating to thermal fluctuations deduced in an earlier paper. The simplified representation adopted in that paper is fully substantiated: the fluctuations are shown to be independent of the temperature of reactive circuit elements.Coexistent thermal and thermionic fluctuations are then discussed. They are assumed to be mutually independent, and experiments are described which verify this hypothesis. A representation of thermionic fiuchiations is proposed analogous to that adopted for thermal fluctuations, and a general formula applicable to certain classes of networks containing thermionic valves is deduced.This formula is applied in a concluding section to a wideband photocell amplifier. Various practical recommendations are made which yield improved signal/noise ratios.
TL;DR: In this paper, the authors present a perspective of the safeguards that have an economic utility in a supply system to ensure an uninterrupted supply of electricity to consumers, classified broadly under the headings of general, routine, protective, and ultimate.
Abstract: The paper is intended to present a perspective of the safeguards that have an economic utility in a supply system to ensure an uninterrupted supply of electricity to consumers. The safeguards are classified broadly under the headings of general, routine, protective, and ultimate. Although the most consistent application of general and routine safeguards can never completely eliminate the risk of faults, the appropriate blending of these with protective safeguards, which isolate faults automatically in their initial stages, should prevent any fault from developing into a breakdown of the major order, such as to involve the functioning of ultimate safeguards.After a general discussion of the application of protective safeguards to supply systems according to whether they include cables or overhead conductors (which, owing to differing conditions, have to be dealt with differently), there follows a survey of protective safeguards available for use with various components of a supply system against short-circuits transient faults, and excess voltages. These include feeder and busbarzone protective systems; methods of reducing unnecessary outages of overhead lines; and rapid operation of circuit breakers. Particulars are given of high-speed small-oilvolume circuit breakers developed on the lines of utilizing in improved ways well-tried principles and components, and of an automatic reclosing 132-kV oil circuit-breaker with an arc duration of one cycle at full rating.It is claimed that, when a fault has developed in a component of a supply system provided with protective safeguards such as automatic instantaneous protection and fast-acting circuit breakers, the result is a switching operation with very little if any damage of the faulty component, and, depending upon the system layout, an outage with either no interruption or only a slight interruption of supply. If, however, a fault develops in an unprotected component of a supply system, the sustained feeding of power into it may lead to severe breakdown and fire, with risk of serious interruption of supply.The authors suggest that, if the supply industry is of the opinion that it is detrimental to have such interruptions of supply as have occurred in the past (for example, because of outages from transient faults on overhead lines or because of outages due to fires resulting from sustained arcing on unprotected apparatus), and that such interruptions are an uneconomic risk for the future, one of the first steps to be taken is a consideration of safeguards adequate to prevent them.
TL;DR: In this paper, the lateral deviations of short-wave signals received at Slough from various shortwave transmitters over a period of several months are investigated. But the results obtained show that the variations in bearings which arise from instrumental causes do not exceed about 2°, and are usually of the order of 1°.
Abstract: The paper gives an account of some systematic measurements of the lateral deviations of wireless waves received at Slough from various short-wave transmitters over a period of several months. The measurements were made by means of a spaced-aerial direction-finder of the four fixed-loop type, and the first part of the paper is devoted to a description of the apparatus, together with an account of its performance in respect of instrumental accuracy, pick-up factor, and other characteristics. The second part of the paper describes the measurements themselves, which were made photographically from a cathoderay oscillographic goniometer. Some of the observations were made on pulse transmissions from Nauen (? = 30 m.) and Dorchester (? = 37.3 m.), and the remainder on continuouswave transmissions from Zeesen (? = 31.4 m.), Prague (? = 44.6 m.), and various American stations. The results obtained show that the variations in bearings which arise from instrumental causes do not exceed about 2°, and are usually of the order of 1°. The records demonstrate that lateral deviation occurs for the above cases to an extent which depends on the range and type of the reflected waves observed. Deviations of 10° to 20° were recorded from the more distant stations, while in the case of Dorchester, distant 160 kilometres, the deviations were as much as 50° on occasions. From a study of these observations it is concluded that the effective points of reflection at the ionosphere may be as much as 50?100 km. out of the great-circle path.
TL;DR: In this paper, the authors show that an excellent picture can be transmitted with from 2? to 6 millilumens per cm? on the mosaic of the standard iconoscope.
Abstract: Field tests have shown the present standard iconoscope to be a very satisfactory television pick-up device. However, from a theoretical point of view the efficiency of the iconoscope as a storage system is rather low. The principal factors responsible for the low efficiency are lack of collecting field for photo-electrons, and losses caused by the redistribution of secondary electrons produced by the beam. Limits to the sensitivity of the standard iconoscope are set by the ratio of picture signal to amplifier and couplingresistor ?noise.? Experimental and theoretical determinations indicate that an excellent picture can be transmitted with from 2? to 6 millilumens per cm? on the mosaic. Two methods are considered by which the sensitivity may be increased. The first is by the use of secondary-emission signal-multipliers and a low-capacitance mosaic, while the second makes use of secondary-emission image intensification. The sensitivity limits for the two cases are calculated.
TL;DR: In this paper, an examination of the phenomena occurring during the operation of electrical contacts, with particular reference to the destructive effects produced on the contact points is made, and suggestions are made which should help to reduce the wear of contact points to a minimum.
Abstract: An examination has been made of the phenomena occurring during the operation of electrical contacts, with particular reference to the destructive effects produced on the contact points. Four main stages in the break of a current have been observed, of which the resistance rise, the arc, and the spark, are well known; intermediate between the resistance rise and the arc is a stage in which the gap between the contact points is bridged by a drop of molten metal; this latter is of great practical importance since it is of almost universal occurrence, causes well-marked transference of contact material, and, as the potential difference between the contact points is then only about 2 volts, it cannot be suppressed by modifications of the interrupted circuit. The voltage-current-length characteristics of the molten bridge between electrodes of platinumiridium (25 per cent Ir) have been determined and are found to be of a similar form to those for an ordinary arc, i.e. voltage inversely proportional to current and directly proportional to length. The reason for such characteristics is not known. The conditions of voltage and current necessary for the formation of the different stages are described, and the effects produced by typical simple circuits are dealt with. Suggestions are made which should help to reduce the wear of contact points to a minimum.
TL;DR: In this article, it was shown that for a given total length of conductor the optimum shape of a rectangular frame aerial, with respect to induced e.m. f., is square, and that a square frame with side equal to half a wavelength appears to have useful practical characteristics in respect of sensitivity and symmetry, both for field-strength measurement and direction-finding.
Abstract: The paper contains an analysis of the behaviour of frame aerials consisting of a single turn of conductor. It is assumed that the behaviour of such systems, including the mutual interactions of the various elements, can, to a useful degree of approximation, be represented by the differential equations of classical transmission-line theory. Formulae are obtained for the effective induced e. m. f. and the effective impedance (at the tuning point) of frame aerials the dimensions of which are not small compared with the wavelength, both for symmetrical and asymmetrical systems of tuning. It is found that in the case of symmetrically tuned systems the output voltages across the two equal halves of the tuning impedance will not in general be quite equal.It is shown that the “resonance factor” of a frame aerial (i.e. the ratio of output voltage to induced e. m. f.) can be determined by the usual method of reactance-variation at a constant frequency, in spite of the non-uniformity of the current distribution along the length of the conductor, but that the same process carried out by variation of frequency will not, in general, be valid.It is shown that for a given total length of conductor the optimum shape of a rectangular frame aerial, with respect to induced e. m. f., is square. In particular, a square frame with side equal to half a wavelength appears, to have useful practical characteristics in respect of sensitivity and symmetry, both for field-strength measurement and direction-finding.The method of applying the formulae to circular loops by a process of integration is given and illustrated by particular cases. It is found that in the case of small closed aerials the magnitude of the induced e. m. f. is not very sensitive to shape.
TL;DR: In this article, the authors present a survey of the field in which their activities meet, including dielectrics and the factors which represent their value to the electrical engineer, with some general conclusions as to lines of research which may be expected to yield results profitable to both industrial chemist and electrical engineer.
Abstract: The paper is submitted to a joint meeting of plastics chemists and electrical engineersas a contribution to a general survey of the field in which their activities meet. It consists of the following parts:- (i) A brief discussion of dielectrics and the factors which represent their value to the electrical engineer. (ii) A discussion of the essential nature of plasticity, and of the characteristics which the chemist has to produce when synthesizing plastics for the moulding industry. (iii) An experimental investigation of the properties of synthetic resins of the bakelite type, and the way in which their electrical properties may be affected by chemical and physical factors. (iv) A brief discussion of the various synthetic plastics now available, and of such of their properties as are of importance in electrical practice, with some general conclusions as to lines of research which may be expected to yield results profitable to both the industrial chemist and the electrical engineer.
TL;DR: The paper gives a quantitative analysis which shows how asymmetry, either of phase or of magnitude, between two sideband components, created by any given modulation component, is related to harmonic distortion; and it is shown that this distortion is proportional, over a large range of values, to depth of modulation.
Abstract: The major factor which hampers the progress of broadcasting is the lack of a sufficient number of channels in which to contain the increasing number of transmissions. In the present state of the art few, except local, stations can be received without interference from other broadcasting stations on frequency-contiguous channels Unless the upper frequencies of modulation of the wanted station are severely attenuated and unless, therefore, reproduction is lacking in intelligibility and naturalness. This inter-station interference can be eradicated or minimized, and quality improved as regards “top” reproduction, if all or part of one sideband of the transmitted spectrum is cut away. The cutting-away operation on the side-band, however, produces harmonic distortion in the received signals. It is the object of the asymmetricsideband system of transmission to cut away part of one sideband without introducing audible harmonic distortion.The paper gives a quantitative analysis which shows how asymmetry, either of phase or of magnitude, between two sideband components, created by any given modulation component, is related to harmonic distortion; and it is shown that this distortion is proportional, over a large range of values, to depth of modulation. The nature of the sound spectrum is such that the intensities in the upper register are much less than those in the lower middle register. Since the degree of asymmetry between counterpart sideband components is a measure of the attenuation of the cut-away sideband, this attenuation can be increased as the modulation frequency is made greater. This is tantamount to saying that, as the sideband frequency becomes more and more removed from the carrier frequency, it may be more and more attenuated while the distortion can be made to remain constant and small. Thus in asymmetric technique the outer parts of one sideband may be removed without the introduction of audible distortion.Curves are derived, based upon the evaluation of expressions given in the quantitative analysis, which show the required attenuation-constant of niters which cut away part of one sideband but produce no more than a constant distortion. It is proved that phase asymmetry between counterpart sidebands may give rise to more serious distortions than are created by magnitude asymmetry acting alone, and a network is described which keeps phase asymmetry to a minimum and yet gives a close approximation to the required attenuation.Accounts are given of practical tests wherein the quality of reproduction obtainable from an asymmetric transmitter is compared with that given by orthodox modulation. While it is true that a highly trained ear may, on rare occasions, be able to detect some slight differences between the two types of reproduction, when they are directly compared, the general public would be quite incapable of so doing, even if they possessed receiving apparatus so free from distortion itself as to give them an opportunity to do so. It is pointed out that it is better to face the occasional minute deteriorations in quality given by the asymmetric system than to suffer from the continuous hissing and splitting sounds brought about by existing inter-station interference.In the latter part of the paper an analysis is given which shows that the asymmetric system has three possible applications to space broadcasting as it is practised to-day, namely (1) It could be used to allow carrier difference frequencies of the order of 11–12 kc. without introducing any sideband overlap interference. (2) It could be applied to existing conditions, where carrier difference frequencies are of the order of 9 kc, and would reduce inter-station interference to the order of one-tenth its present value. (3) If existing interferences are considered to be tolerable, then carrier difference frequencies can be reduced to 6 kc. without increasing interference above its existing values; this implies that 11/2; times the number of stations workingin Europe to-day on exclusive waves could be accommodated in the existing waveband.It is suggested, finally, that a policy could be adopted such that the introduction of the asymmetric system would encourage receiver development along lines wherein, by an augmentation of only the carrier component at the detector, all distortion due to the use of an asymmetric spectrum would be eliminated. Thus an evolution might be envisaged which led to the introduction of the ideal carrier and single-sideband type of transmission when all receivers were adapted to reduce the resulting distortion to a tolerable amount.