Showing papers in "Journal of the Institution of Electrical Engineers in 1926"

The magnetic field of the dynamo-electric machine

Abstract: The first portion of the paper is for the most part written around the subject of the reluctance of the magnetic circuit, particularly of the air-gap and teeth. Other matters are, however, referred to, such as that of the shape of the curve of flux traversed by the armature conductors, and that of the flux variation along the pole-face. Much of the analysis was indeed originally developed with other ends in view, such as the determination of harmonics in the e.m.f. wave, of losses in the pole-face and elsewhere, or the investigation of the cause of noises and like incidental effects of the magnetic changes. These are for the most part particular applications of the analysis. The determination of the reluctance of the gap is made to depend on two factors ; one, an equivalent length, which has, in the normal portion of the gap, the same reluctance per unit area as the actual gap ; the other, an equivalent area, made up of the area of the radial projection of the normal gap on the cylindrical surface midway between armature and field, with additions for the fringe effects at the boundaries, and, where necessary, reductions to take account of ducts and band recesses. The magnetization of teeth is also discussed. The second part of the paper deals particularly with slots in which conductors carrying currents are located. The subjects of distributed excitation and of the reaction of the load on the exciting field are here discussed. Finally the reactance of the imbedded conductors is investigated. A number of Appendices deal with details of the calculations.

An instantaneous direct-reading radiogoniometer

Abstract: The paper describes a visual direct-reading radiogoniometer capable of indicating the apparent azimuth of arrival of wave-trains the durations of which need not exceed 0.001 sec. The special properties of the device, which comprises essentially a combination of directional aerials with a cathode-ray oscillograph, are discussed. Amongst these properties is that of giving simultaneous bearings on two or more stations transmitting simultaneously on the same wave-length. A typical installation is described, and specimens of observations on the distribution in azimuth of received atmospheric disturbances are shown. A possible solution of the problem of navigational beacons is suggested.

The propagation of radio waves

Abstract: The paper gives the results obtained from a systematic study of the received intensities of various long-wave transmitting stations at four receiving stations over a period of nearly two years.The weekly averages of the results are studied, and it is shown that they are inconsistent with any law of steady decay. The results also show very marked periodic variations.It is suggested that all the observed effects can most easily be explained on the assumption of an upper refracting layer. This is supported by the results obtained from plotting an intensity distance curve in detail by means of a portable set, and by the study of the systematic changes which take place daily during the sunset period.Various conclusions are drawn from these results, but it is pointed out that considerable further experimental investigation of many of the observed phenomena is necessary.

The cause and elimination of night errors in radio direction-finding

Abstract: The paper describes experiments which have been carried out with a view to obtaining more conclusive evidence as to the causes of the apparent variations in bearings observed under certain conditions on wireless direction-finders. In the course of the experiments the Adcock “four-aerial” direction-finder has been developed, and with its aid it has been shown that the actual deviation in azimuth of wireless waves is practically negligible. These experiments thus constitute a proof that the variable errors observed on closed-coil direction-finders at night are caused by downcoming waves arriving from the upper atmosphere and polarized with the electric force in a horizontal plane. The investigation also indicates the possibility of the Adcock system being developed into a practical direction-finder which is free from night errors, and those errors associated with observations on aircraft transmissions made at a, ground direction-finding station.

The directional recording of atmospherics

Abstract: The paper describes a simple pen-writing instrument for the continuous recording of the apparent direction of arrival of atmospherics, and cites typical samples of the data obtainable from such recorders. The samples chosen show the diurnal variation of intensity of atmospheric disturbance, the diurnal variation of apparent direction of arrival, and the location of apparent sources of atmospherics by a group of recorders.

The Rugby radio station of the British Post Office

Abstract: This paper gives a general description of the Post Office high-power radio station erected at Hillmorton near Rugby. The introduction sets out the requirements which the design had to meet. The paper is divided broadly into three sections:- Power Plant, High-frequency Generating Valve Plant, and Masts and Aerials. The first section deals with the selection and type of power plant employed for converting the e.h.t. alternating-current supply to suitable e.h.t. direct-current and l.t. direct-current and l.t. alternating-current supplies for use on the various parts of the installation, and the precautions necessary in dealing with a wireless load of the magnitude involved. The method of providing lighting for the masts for warning aircraft of obstruction is given. The high-frequency generating-valve plant section deals with the design of valve generating plant suitable for full-power transmission or subdivision into two transmitters for use with larger and smaller portions of the whole aerial, and gives the methods adopted for maintaining constant frequency, successive amplification and freedom from harmonics. This Section includes:-The e.h.t. direct-current supply; the general scheme of circuits; the filament supply; the excitation unit; consideration in regard to the size of power unit; the power unit; the paralleling of valves in a power unit; the paralleling of power units; safety devices and control circuit; the control table; types of coupled circuits; the design of inductances for high power; relative positions of amplifiers and aerial circuit; method of keying and shape of signal. The masts and aerials section includes: a brief general description of the 820-ft. masts; the method of insulating the masts and the stays; the method of staying the masts; tensions on the stays, etc.; the method of applying test load to top of masts; the aerial system; aerial insulation; aerial spreaders; earth system; curves of aerial resistance; voltage on aerial, etc. The final section gives the general results obtained to date, and a brief description of the experimental telephony installation.

The effect produced on the permeance of a laminated pole-core by the insertion of a solid steel fixing-piece

Abstract: The object of the paper is to discuss the effect produced on the permeance of a laminated pole-core which has been perforated with an axial circular hole into which a solid steel fixing-piece or plug is inserted to receive the holts which attach the core to the yoke. The theory of a core in which the plug fits perfectly in the hole is first examined, and curves for the permeance calculation are prepared. The theory is then extended to apply to a plug which fits loosely in the hole, the influence of imperfect fit being shown by a numerical example. The application of the theory in practical cases is shown, in general, to be satisfactory. In the extreme example of pole-coies used in water-wheel generators, where numerous secondary matters have to be considered, the discrepancy between theory and practice is explained. The utility of the theory in calculating the permeance of transformer limbs consisting of laminae clamped together by insulated bolts is shown, and uses in certain problems of current conduction, e.g. in a perforated busbar, are suggested.

Recent improvements in the insulation of electrical machinery

Abstract: The paper constitutes a review indicating the more recent developments in the manufacture and use of insulating materials. A survey of the prominent characteristics of such materials is followed by a summary of process improvements. In handling this subject the authors put forward a strong plea for standardization of nomenclature and of test methods for determining essential properties of insulating materials. The paper is accompanied by eight appendixes, which include examples of standardizing of material terminology and a considerable amount of data obtained by test methods as adopted by the E.R.A.

The performance of amplifiers

Abstract: The paper describes the researches which have been carried out at the National Physical Laboratory for the Radio Research Board. A standard method of testing the amplification and input impedance of an amplifier is described, and the theory of the load introduced by the amplifier as well as by reaction is shown to agree with the observed results.Some preliminary experiments on distortion are described, output wave-forms from audio-frequency amplifiers being analysed.

Dielectric problems in high-voltage cables

Abstract: The paper deals with several important problems of particular theoretical and practical interest at the present time in connection with the design, manufacture, and operation of high-voltage impregnated-paper cables. In the first place, the phenomenon of dielectric absorption is discussed as a question of fundamental importance and as a basis for a proper understanding of dielectric losses. It is shown how dielectric resistance must be carefully defined in order to be of any value as a characteristic of cable quality, or in analytical discussion, and the results of experiments are given to show that whilst the usually accepted absorption expression departs from the truth, it can be used within limits. Experimental work on absorption in different dielectrics and on the effect of moisture and temperature on the constants is also described. The dependence of alternating dielectric losses on direct-current characteristics is discussed, and the author suggests a conception of the former in which they can be explained as I2R losses, without retaining the difficulties of a dielectric hysteresis. Several new points are brought to light and supported by experimental evidence in a discussion of the relationship between d.c. and a.c. losses. The nature of the ?V? curve connecting dielectric power-factor and temperature is investigated, and an explanation of the ?V? curve is suggested based on the I2R theory of losses. The paper also discusses the rise of power factor with voltage, the important effect of time on the breakdown strength, and the bearing which this has on the effect of surges in a system. In conclusion, some suggestions are made on the nature of breakdown and the assessment of cable quality.

Electricity in mines: a short survey

Abstract: The paper provides a general review of the present position of electricity in mines, with particular reference to coal mines. Dealing with the safety aspect, it is claimed that the special requirements of colliery work have been amply met by manufacturers of electrical apparatus. It is further claimed that Great Britain has established a lead over other countries in respect of the design of mining electric plant. The question of public versus private supply is discussed, and the author states that, in his opinion, supply from an outside source is overwhelmingly the correct policy wherever two rival estimates show an equal, or nearly equal, financial result. Some general statistics are given and the conclusion is ultimately drawn that one-half the motive power of the mines of Great Britain still remains non-electric. Finally, some important directions in which the use of electricity in mines is likely to increase are mentioned.

The attenuation of wireless waves due to the resistance of the earth

Abstract: The paper calls attention to the present condition of knowledge on the subject of the attenuation of wireless waves travelling over the earth's surface, due to energy absorption by the earth itself. The theories put forward on this problem by Sommerfeld and Zenneck are briefly outlined, and it is shown that the latter has taken account only of a special case of the more general theory of Sommerfeld. The results deduced from this theory have been worked out for some typical practical cases of both short- and long wave transmission, but, owing to the complete lack of experimental evidence, no practical test of the theory has yet been made. In view of the importance of a knowledge of ground absorption in connection with the complete study of the propagation of wireless waves of all lengths over the earth's surface, it is highly desirable that a systematic experimental investigation should be carried out in the near future.

Problems in connection with two parallel electrified cylindrical conductors

Abstract: Electrostatic problems in connection with two unequal parallel cylinders, and with single-core cables when the axes of the cores are parallel but not coincident with the axes of the outer cylinders, are considered. The solutions are given by formulae the numerical value of which can be readily evaluated. Novel relations are given connecting the capacity between any two cylinders with the capacities between two equal cylinders and with the capacities of cylindrical condensers.

Power factor and tariff

Abstract: The great amount of attention now being given to the question of poor power factor suggests that tariffs such as are commonly used to-day are unsuitable in present circumstances. The paper contends that a wattless component of current, despite its having no energy content, involves the supply undertaking in extra running costs, and that therefore a charge should be levied for supplying it. A three-part tariff is proposed, embracing a periodic charge per kVA of maximum demand, a charge per kWh of energy, and a charge per kVA-hour of lagging wattless component. The additional running costs caused by wattless component are briefly touched on, and it is suggested that in a station with an average power factor of 0.7 the charge per kVA-hour of wattless component should be about one-ninth of the charge per kWh of energy. The question of metering the three-part tariff is discussed, and a method is shown whereby, with balanced load, a three-phase wattmeter may be ?biased? to record the total energy consumption, plus or minus any desired fraction of the kVA-hours of lagging or leading wattless component.

High-power fusible cut-outs

Abstract: The subject of high-power fusible cut-outs is one entitled to the greatest respect, but it has undoubtedly been neglected in the past. The author has endeavoured to tackle the subject from a logical point of view in the present paper, and, in view of its fundamental importance, the problem of rupturing capacity has been selected as that to which attention is primarily confined.The paper includes a consideration of the factors influencing the rupturing capacity of a cut-out, and a description of an extensive series of tests carried out on various types of cut-outs, including many of those most widely used to-day. A selection is given from the records of tests on fundamental forms of elementary construction, on plain cut-outs and on various commercial forms, and this shows clearly the inadequacy of such cut-outs for high-power work. Certain recently developed forms of cartridge cut-outs which operated satisfactorily are referred to and their sphere of usefulness is indicated. A description is given of an ironclad oilimmersed cut-out, which appears from the tests to satisfy nearly all requirements for high-power work. A new design of cut-out for small-current high-pressure services is also described.An attempt has been made, by carrying out actual rupturing-capacity tests, to indicate how far the various types of cut-outs can be safely employed, and a chart has been drawn up to show a comparison between the rupturing capacities of these types.A striking feature made apparent by the tests is that there are remarkably few efficient cut-outs available. This is all the more to be regretted when it is realized that a fusible cut-out can be made into a most accurate and efficient device—consistency of calibration and consistency of rupturing performance being possible to a high degree of excellence.

Theory of overlapping joints

Abstract: Melsom and Booth have investigated experimentally the theory of overlapping joints, dividing the resistance of the joint into two parts: one representing the resistance due to the contact, and the other that due to the stream lines of the current at the joint. In the present paper the latter part is obtained theoretically in terms of elliptic functions. The result is expanded and leads to a very simple formula, with which the experimental results of Melsom and Booth are found to agree.

The generation of very intense magnetic fields

Abstract: The paper describes a method for generating magnetic fields of the order of magnitude of 1 million gauss, and for impressing such fields on a specimen of magnetic material at regular intervals, with a view to ascertaining whether any disturbance of the electronic orbits could be obtained of sufficient magnitude to produce a marked effect on the magnetization curve of the specimen.An account is given of the means used for measuring the magnitude and frequency of the heavy transient currents to which the intense magnetic fields are due.The influence of the dimensions of the solenoid through which the transient currents flow is considered as determining the intensity of the magnetic field produced.A comparison is given of the calculated and measured values of the transient currents for three different solenoids. It is found that, whilst the calculated values agree well with the measured values for solenoids with a relatively small number of turns of thick wire, there is an appreciable discrepancy in the case of a solenoid with a large number of turns of thin wire. An attempt is made to explain this discrepancy as due to the condenser effect of the contact E.M.F. between the copper wire and the oil-soaked cotton insulation which is in contact with the wire.

Low-frequency intervalve transformers

Abstract: The theoretical expression for the voltage amplification of a valve followed by a transformer is developed in its simplest possible terms, and various particular cases are considered. The importance of low leakage inductance for the uniform amplification of the higher frequencies is emphasized. A practical verification of the theory is provided by actual measurements of the vector amplification ratio and comparisons with the theoretical equations, and graphical methods are given whereby the constants of a transformer can be deduced from these measurements and the amplification ratio extrapolated to frequencies beyond the range of convenient measurement. A practical design of transformer is described in which low leakage inductance and self-capacity are ensured by a sectionalized and spaced construction, and a curve of amplification of this transformer is given. Various questions relating to intervalve transformers are briefly considered, and circuits are described for increasing the amplification of low frequencies and the effective stepup ratio of the transformer. The use of low-frequency reaction for correcting distortion is described and is illustrated by measurements.

The power losses in magnetic sheet material at high flux densities

Abstract: From an examination of the results of a number of investigators it is shown that while there is general agreement as to the validity of Steinmetz's expression ηB x , where x is a constant index, for the hysteresis loss at flux densities up to about 10 000 C.G.S. units, there are considerable divergences between the results of different experimenters at flux densities above that value, particularly in tests on sheet material. Some find Steinmetz's law to apply closely up to the highest flux densities at which tests could be carried out, whilst others record more rapid variations of hysteresis loss with B in the region of B = 10 000-16 000. The extent of the departure from Steinmetz's law also varies considerably, some observers finding a maximum exponent of approximately 2.0 and others obtaining values as high as 3.2. In the paper a series of tests, both by a.c. and ballistic methods, on a wide range of sheet materials is described. The results of this appear to confirm the increase in the exponent of B in the expression for the hysteresis loss at values of B between 10 000 and 15 000. They also show comparatively little difference between the various specimens of sheet material tested. The construction of a new Lloyd square for tests at still higher flux densities, and a further, more detailed, series of tests, both a.c. and ballistic, on a representative specimen of each type of material, making use of this square, are then described. These tests were carried up to B = 17 000 or 18 000 and, while confirming and extending the previous results of increased exponents of B for values up to 16 000, they indicate a rapid decrease in the exponent at the highest values of B employed.

New methods of improving the synchronizing torque and weight efficiency of self-excited synchronous induction motors

Abstract: Polyphase self-excited synchronous induction motors, including the latest types, are analysed with special reference to weight efficiency, conversion efficiency, and configuration of synchronizing torque. It is shown that the weight efficiency of such machines is low compared with that of polyphase asynchronous motors, because the secondary must be designed to carry polyphase load currents as well as unidirectional load and exciting currents. The alternating currents must be carried in a polyphase winding, the unidirectional currents in a single-phase winding. Although the latter may be a part of the former, it nevertheless follows that it is practically impossible to make the maximum synchronous torque of a given frame equal to the maximum asynchronous torque of the same frame. It is further pointed out that, even with a unidirectional and pulsating synchronizing torque, such motors do not run asynchronously with a sufficiently uniform peripheral speed of the revolving member to permit of the general utilization of their asynchronous overload capacity. To overcome these drawbacks the author has conceived the idea of providing self-excited synchronous induction motors with a constant synchronizing torque, to run the machines synchronously from no load to a little beyond full load, and to run them asynchronously for all higher loads. The manner in which a constant synchronizing torque is produced is explained in detail and it is shown how the somewhat conflicting requirements of synchronizing torque and acceptable compounding characteristic are harmonized. Several embodiments of the resulting new motors are described, their synchronous performance being analysed by means of the circle diagram.

An all-electric house

Abstract: The scarcity of precise and detailed information on the several domestic applications of electricity encouraged the author to write a succinct account of the arrangements adopted in a 10-roomed house designed and built in Glasgow for all-electric working. In this house neither coal nor gas is used. The sections dealt with are:-(1) Layout of house.(2) Distribution board.(3) Wiring.(4) Bells.(5) Lighting.(6) Clothes-washing and drying.(7) Cooking.(8) Hot water.(9) Ventilation.(10) Heating.(11) Running costs.(12) Conclusions.The total cost of 16 584 units used in one year's working was £43 8s. The consumption and costs are analysed for the several services.In an Appendix, the results of a 4-roomed all-electric flat are given. The consumption for one year was 4 656 units and the total cost of energy was £14 18s.

Frequency variations in thermionic generators

Abstract: The paper is divided into six parts, as follows:-In Part I, the variations of frequency which occur in mechanical oscillating systems with pendulum control are referred to. Unless the driving impulses are given at the moment the pendulum is vertical, the frequency of the oscillations varies from the true oscillation frequency of the pendulum. When the pendulum is near the limit of its swing an impulse directed inwards makes the clock go fast, whilst an impulse directed outwards makes the clock go slow. Such an effect is “reversible” because the clock goes fast or slow according to the direction in which the impulse is applied. Another type of variation is connected with the amplitude of the swing, and makes its appearance unless the amplitude is infinitesimal. Increase of amplitude always makes the clock go slow, and the effect is therefore “irreversible.”In Part II, the phase relationships of currents and potentials in a thermionic generator arc examined, and it is shown that the frequency of the oscillations is affected by the nature of the coupling between the grid and anode circuits. Equations are obtained which give the difference between the frequency of the oscillations generated and the resonant frequency of the tuned circuits. These equations show that the variations of frequency connected with the method of coupling are analogous to the reversible variations existing in the pendulum-controlled clock. With normal coupling the thermionic generator goes slow, with reversed coupling it goes fast, and with resistance coupling the variation disappears.In Part III, three “irreversible” variations of frequency are discussed, namely:-(i) A variation connected with a change in the effective inductance of the circuit, which occurs when the oscillation is free instead of forced;(ii) A variation connected with a change in the resonant frequency of a damped circuit, which occurs when the oscillation is free instead of forced; and(iii) A variation associated with the presence of harmonics in the E.M.F. generated by the valve.In Part IV, certain points in the design of thermionic generators employing resistance coupling are discussed.In Part V, the design of thermionic generators using reversed coupling is discussed, and some interesting points affecting the design of untuned circuits are described.In Part VI, the experimental results obtained with various types of circuit are given, and are explained in terms of the theoretical variations discussed in Parts II and III.The characteristics of various types of constant-frequency generator are then compared. It is pointed out that frequency variations associated with changes in the voltage of supply can be reduced below 1 part in 20,000, or 1 part in 50,000, according to circumstances..

The frequency characteristics of telephone systems and audio-frequency apparatus, and their measurement

Abstract: The value is demonstrated of the frequency/amplitude characteristics of telephone systems or apparatus in determining the transmission efficiency, including volume and articulation efficiency. The audio-frequency ranges of importance for speech and music are then considered.Methods are described for the direct and indirect production of constant acoustic output over the audio range, and the calibration of acoustic measuring instruments is dealt with.The next section of the paper deals with the production of electrical energy of constant value over the required frequency range, and a description is given of a special form of oscillator, together with associated apparatus for the direct recording of frequency characteristics.The concluding part of the paper gives frequency characteristics of each part of the apparatus used in a telephone connection, and also of audio-frequency amplifiers and loudspeakers. For the purely electrical portions of the circuit, current or voltage characteristics are given, whilst for apparatus such as transmitters and receivers the characteristics are given in terms of acoustic pressures on the diaphragm. The characteristics of some commercial types of granular transmitters are first given, then under the heading of receivers will be found the characteristics of both the Bell pattern and some typical loud-speakers of the horn and hornless types. Particulars are given of apparatus designed to measure diaphragm motion, some results obtained by an aural balancing method being included.In the section dealing with lines will be found characteristics for unloaded open wires and cables and for loaded cables. An impedance/frequency characteristic is also given and its application to fault location illustrated.Some notes on telephone line repeater characteristics are included, and the next section deals with exchange cord circuits and subscriber's instrument characteristics.Under audio-frequency amplifiers some typical intervalve transformers of the type used for broadcast reception are characterized, and an extension is given of the theory of this type of transformer covering the effects of resistance and capacity loads.

Interference between circuits in continuously loaded telephone cables

Abstract: This paper is concerned with the interference between circuits in homogeneous cables, and its reduction. The line is replaced by its equivalent network, and, in the case of a four-wire group as used in superimposed circuits, the network consists of six members. The relations between the induced and inducing currents and voltages are established, and a quantitative definition of interference is given. The effects of unbalances in the line constants are discussed, and the influence of distance and frequency is investigated. An account is given of methods of measurement and of the means of reducing interference in cables, and a method developed by the author for dealing with the difficulties introduced by the distributed inductance in continuous loading is described.

Circuit constants in transmission-line calculations

Abstract: In this paper the use of ?circuit constants? for the calcualtion of transmission-line problems is dealt with in an elemetary way, in the hope that many who perhaps would not have the time or patience to follow the original papers of Messrs Evans and Sels may be encouraged to use their very powerful and useful methods To avoid having to refer to textbooks for the elements of complex algebra, a few notes on its use have been included The formulae for calculating the constants of series and parallel circuits are developed; and the determination of the particular values of the constants for transmission lines, and for transformers, is dealt with in detail Following this, methods for dealing with more complex cases of lines supplying more than one substation, and branching lines, are dealt with An actual example of an existing transmission line is worked out in detail