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Electrical Engineers, Proceedings of the Institution of

Issue 8 • Date August 1965

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Displaying Results 1 - 25 of 29
  • T.D.M. transmission of programme channels

    Publication Year: 1965 , Page(s): 1483 - 1491
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (809 KB)  

    A programme channel requires greater bandwidth than a normal telephone speech channel. It can be accommodated in a time-division multiplex (t.d.m.) transmission system by using the pulse trains of several speech channels. The paper shows that, when these pulse trains are not equally spaced, distortion components are produced in the output signal. In general, the distortion components are at the channel pulse-repetition frequency and its harmonics, together with upper and lower sideband components. To obtain a sufficiently low distortion level, the permissible departures from equal pulse spacing are only of the order of ±1° or less. Similar distortion is also introduced if the pulses are not identical in height and shape. To obtain sufficiently low distortion level, the differences in height and length of the pulses used for a programme channel may only be of the order of 1%. Although the analysis is made for t.d.m. systems using pulse-amplitude modulation (p.a.m.), its results are shown to be applicable to some systems using other forms of modulation, such as pulse-code modulation (p.c.m.). It is concluded that p.c.m. systems are unsuitable for programme transmission unless the total number of time slots per frame (including synchronising pulses) is an exact multiple of the number of speech channels required to constitute a programme channel. View full abstract»

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  • Aperture distributions, autocorrelation and angular power spectrum for partially illuminated apertures

    Publication Year: 1965 , Page(s): 1492 - 1500
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (554 KB)  

    The relations between the field distribution across an aperture, its autocorrelation function and the angular power spectrum of the radiated field are used to analyse the fields produced by particular aperture distributions. The effect of illuminating only a small part of the total area of a large aperture is considered, and some of the average properties resulting from a randomly distributed illumination are derived. The case of linear arrays with a statistically small number of elements is also considered. The method outlined may also be extended to cylindrical or spherical arrays. View full abstract»

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  • Guided waves on a perfectly conducting infinite cylinder in a magnetoionic medium

    Publication Year: 1965 , Page(s): 1497 - 1500
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The characteristics of the surface waves guided along a perfectly conducting infinite cylinder are investigated for the case in which it is immersed in a magnetoionic medium and oriented so that its axis is parallel to the direction of the magnetostatic field. The surface waves are found to be propagated along the cylinder for frequencies less than the plasma or the gyromagnetic frequency of the electrons, whichever is lower. The phase velocity of the surface waves is always less than the velocity of electromagnetic waves in free space. The dependence of the characteristics of the surface waves on the radius of the cylinder is also examined. View full abstract»

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  • Cathode/heater-insulation failure in oxide-cathode valves

    Publication Year: 1965 , Page(s): 1501 - 1508
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1183 KB)  

    Heater/cathode insulation in indirectly heated valves is considered as a two-part phenomenon: the comparatively slow deterioration during operational conditions followed by a rapid thermal breakdown, which is caused directly by the sudden passage of a large current between heater and cathode. Examination of heater/cathode failures in valves tested under rigidly controlled conditions has indicated some of the laws governing the deterioration of the insulation. The effects of various parameters such as temperature of operation, thickness of insulation and applied potential have been studied, and comparisons have also been made for different heater and cathode materials. The experimental evidence is discussed in an attempt to explain the failure mechanism involved, and the conclusion that electrolysis is the principal factor is supported by the results of a number of experiments carried out with specially designed electrode structures. View full abstract»

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  • Some comments on Linvill's lumped models for semiconductor devices

    Publication Year: 1965 , Page(s): 1509 - 1514
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (594 KB)  

    The Linvill models and the more conventional equivalent circuits can be used to make roughly equally accurate predictions of terminal behaviour of semiconductor devices. An extreme case, the diode storage time, illustrates this point. The principal feature of the Linvill models, not found in other models, is that current is expressed in terms of excess hole and electron densities. Specifically, the distributed current in a semiconductor device is approximated in the Linvill model by a finite number of currents in corresponding current nodes, and each of the nodes is associated with a particular elementary volume. The relation between the hole- and electron-charge density and the current in any elementary volume is represented by elements of a lumped equivalent circuit. When the models are applied to a practical problem, it is not possible to use the very large number of lumped elements which would be needed closely to model the distributed current, and a small number of model elements is used. In such a ?simplified? model, the one-to-one correspondence between model space and device space is obscure, and, furthermore, conditions based on this correspondence are not sufficient to obtain correctly the model element values. Using, in the last analysis, arbitrary configurations, the model elements must be calculated in such a manner that they match some set of terminal characteristics. A further practical drawback is that the lumped elements cannot be measured directly because they are expressible in terms of hole and electron concentrations, themselves not measurable. Without altering the intent of the Linvill approach, both of the above difficulties can be mitigated. One can represent the currents in the device by an alternative set of lumped elements in which the notion of volume is absent. Such elements are not necessarily associated with physical volumes and no contradictions are encountered with the simplified models. The alternative set of elements proposed in th- is paper can, furthermore, often be measured in terms of current and voltage. A last by no means negligible advantage is that a special symbolism is not required. View full abstract»

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  • Large-signal analysis of varactor harmonic generators without idlers

    Publication Year: 1965 , Page(s): 1515 - 1522
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    A large-signal analysis of varactor harmonic generators without idlers is given. The voltage across the varactor is expressed as a Fourier series in the harmonic charges, and, by expressing the input circuit as an impedance, and the output circuit as a voltage generator in series with an impedance, the relevant coefficients of the series are found. It is found expedient to express the circuit in this way in order to determine the coefficients without any approximation. The efficiency is then calculated as a function of input power; it is found that, for maximum efficiency, input and output resistances should be equal and an expression is given to determine their value. Finally, design curves are given for second-, third- and fourth-harmonic generators, from which optimum operating conditions can be found. View full abstract»

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  • New solid-state electronic multiplier-divider

    Publication Year: 1965 , Page(s): 1523 - 1531
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1020 KB)  

    The paper describes a new type of electronic analogue multiplier-divider, in which a voltage-controlled variable-gain element, based on the field-effect transistor, is shared in time between two circuits. In one circuit, the gain is made proportional to the ratio of two input signals; in the other, it acts on a third input signal to provide the output. Sharing is effected at, for example, a frequency of 1 kc/s, by transistor switches, and the system performs 4-quadrant multiplication and 1-quadrant division. Only one, simple a.c., amplifier is required, and high accuracy can be achieved with input signals having full-scale values as low as 5V and 10¿A. View full abstract»

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  • Discussion on ¿Application of electronic sector scanning techniques to height-finding radar systems¿

    Publication Year: 1965 , Page(s): 1532 - 1533
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  • Ladder networks with elements in geometric progression

    Publication Year: 1965 , Page(s): 1533 - 1534
    Cited by:  Papers (1)
    Save to Project icon | PDF file iconPDF (219 KB)  
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  • Influence of parasitic brush currents on the performance of d.c. motors

    Publication Year: 1965 , Page(s): 1535 - 1547
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1597 KB)  

    The brushes in d.c. machines bridge the micas between the commutator segments, and the coils thereby short-circuited may carry parasitic currents. As described in a previous paper on d.c. generators, the short-circuited loops may be represented, for many calculations, by an auxiliary-armature circuit. In the present paper, it is shown, by calculation and test, that the parasitic currents may have marked effects on the speed-regulation properties of motors under linear conditions, and that these effects may partly persist in the nonlinear régime. It is suggested that many anomalies, commonly ascribed in an undefined way to brush effects and armature reaction, are amenable to a stricter treatment in terms of the concepts proposed. View full abstract»

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  • Discussion on ¿Analogue investigation of water cooling of e.h.v. cables¿

    Publication Year: 1965 , Page(s): 1547 - 1548
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  • Transient characteristics of a laboratory universal machine operating as an alternator

    Publication Year: 1965 , Page(s): 1549 - 1556
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (650 KB)  

    The paper describes experimental results obtained from transient tests on a laboratory universal machine, connected to operate as a 3-phase alternator. During these tests, which were carried out in order to measure the parameters, severe harmonic distortion was found in the armature-current waveform under conditions of sudden symmetrical short circuit. This appeared to be mainly second and third harmonic together with a very low-frequency subharmonic. The paper gives an analysis of the machine with computed values of transient current and shows that, with the compromise design used to achieve a measure of generalisation, such harmonics are to be expected. It also shows mathematically that the usual transient d.c. component in the armature current may become a transient, very-low-frequency oscillation, depending on the machine parameters. These effects observed on a `universal machine¿ were also found during tests carried out on a second generalised machine of different design. It was found that damping and field time constant have considerable effect on the transient harmonic distortion in the short-circuit armature current. View full abstract»

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  • Predictor¿corrector methods of numerical integration in digital-computer analyses of power-system transient stability

    Publication Year: 1965 , Page(s): 1557 - 1565
    Cited by:  Papers (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1024 KB)  

    Single-step methods of numerical integration, such as the Runge-Kutta routine, have been widely used in the application of digital computers to the analysis of transient stability in synchronous power systems, but no previous paper appears to have described the alternative integration methods, which are based on prediction and correction, although they are being increasingly used in other scientific applications of digital computers. The purpose of the present account is therefore to document a comprehensive series of experiments which incorporate several different predictor-corrector methods, the primary aim of which has been to discover the feasibility of using longer step lengths than are possible with single-step methods, thereby reducing the total computing time expended in analysis. The experiments indicate that the length of step interval is influenced, in addition to the precise technique of integration, by the essential basis of step-by-step analysis, in which the solutions of algebraic equations always lie one step behind those of differential equations. A method of auxiliary prediction of nonintegrable variables is developed to promote a closer realisation of their required simultaneous solution, and the substantial increase in step length which then becomes possible is demonstrated. View full abstract»

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  • Discussion on ¿Resistive earthing of electrical distribution systems in ships and similar installations¿

    Publication Year: 1965 , Page(s): 1566 - 1568
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  • Discussion on "Mercury-arc valves for high-voltage d.c. transmission"

    Publication Year: 1965 , Page(s): 1569 - 1574
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  • Calculation of field factor for a vertical sphere gap, taking account of surrounding earthed surfaces

    Publication Year: 1965 , Page(s): 1575 - 1582
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (790 KB)  

    Using a digital computer, field factor has been calculated for spherical electrodes by the image-charge method, taking account of adjacent plane or spherical boundary surfaces. The method has been applied to a vertical asymmetric sphere gap represented by a pair of spheres above an infinite earth plane or a pair of spheres within an enclosing earthed sphere. Graphs are presented showing the percentage increase in field factor above the value applicable to isolated spheres, for different positions of the boundary surface; these graphs enable values of field factor to be deduced, for the geometries represented, with an accuracy better than 0.1%. For the standard sphere gap of BS3581 and IEC52,2 varying the position of the infinite earth plane over the full permitted range leads to changes of up to 0.4% (±0.2%) in field factor, for a gap spacing of one sphere radius. When the clearance from the sphere gap to additional earthed surfaces, representing the walls and ceilings of a laboratory, is varied from the minimum value permitted to about five times this value, with the earth plane as close to the sphere gap as allowed, the field factor falls by 0.5%. View full abstract»

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  • Induction-field calculations and their application to measurements of conductivity distributions in cylindrical plasmas

    Publication Year: 1965 , Page(s): 1583 - 1588
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (658 KB)  

    The problem of determining conductivity distributions from measurements on magnetic loops (induction coils) is examined. Maxwell's equations are written for a cylindrically symmetric system allowing for radial variations in conductivity, and solved numerically for specific types of distribution similar to those found in plasma experiments. Methods are described by which the field impedance (E/H) at the boundary of the medium can be found and used to characterise the distribution. View full abstract»

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  • Eddy-current modes in linear solid-iron bars

    Publication Year: 1965 , Page(s): 1589 - 1594
    Cited by:  Papers (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (675 KB)  

    The solution of Maxwell's equations to find the magnetic-field decay in a long rectangular iron bar of constant permeability is a classical problem in electromagnetic theory, with a well known solution. The converse problem of establishing the field when a voltage is applied to a winding on the bar is much more difficult, and has not been satisfactorily solved. Re-examination shows that the orthogonality of terms in the classical series solution leads to an exact circuit representation of the solid iron, composed of an infinite number of network loops. The explicit solution is found to be readily available by numerical methods using a digital computer, since the networks may be described by rapidly converging infinite series. Computed results are compared with answers obtained analytically by considering only a very few of the network loops. In determining time constants, accuracies of the order of within 1% are shown to be achievable, using a simple network analysis without the use of computing machines. Formulas for calculating the necessary network-component values, together with some sample computer results, are given. View full abstract»

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  • Existing theories of operation of induction meters

    Publication Year: 1965 , Page(s): 1595 - 1600
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (794 KB)  

    The two theories dealing with the operation of induction meters are reviewed. Their final expressions for the torque acting on the rotor, in terms of the power, voltage, load current and speeds of revolution, are found to be the same. However, despite this coincidence, the two theories are both considered to be admissible. The existing proofs of the erroneousness of the travelling-field theory tend to lead indirectly to the conclusion that only the transformer or eddy-current theory is valid. Furthermore, the measured distributions of the magnetic flux density along the air gaps of the electromagnets in the meter are analysed for agreement with the travelling-field theory. The conclusion reached is that, although the travelling-field theory fails to give a full description of the phenomena which determine the operation of the meter, it still deserves to be retained beside the transformer, or eddy-current, theory. View full abstract»

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  • Silicone insulation for class C transformers

    Publication Year: 1965 , Page(s): 1601 - 1606
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (954 KB)  

    Asbestos and glass-fibre insulation, impregnated with silicone resins, is now widely used in the construction of dry-type transformers rated as class C in BS 171: 1959, and operating at a maximum winding temperature of 200°C. Applications range from mining transformers to packaged substations, wherever oil is prohibited because of fire hazard. It is noted that the costs of class C air-cooled transformers are usually about 50% higher than for oil-cooled transformers of equivalent rating, so that these units are only selected where other factors justify this price differential. The insulation components are described, with some notes on their thermal-aging performance. Though present designs are mostly restricted to voltages of 11kV or below, it is considered that the use of fluorinated-hydrocarbon gases for cooling may lead to further developments at much higher voltages, e.g. for indoor-generator transformers. View full abstract»

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  • Silicone rubbers. Their present place in electrical insulation

    Publication Year: 1965 , Page(s): 1607 - 1613
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (927 KB)  

    Silicone rubbers are introduced in terms of their chemical composition and physical properties, with a description of different types and the methods by which they are processed. Applications described include cables, insulating sleeving and tapes, while a later Section deals with the important and versatile cold-curing rubbers, which are widely used for potting and encapsulating purposes. Recent developments are then indicated, with special mention of rubbers with improved physical properties. View full abstract»

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  • Dielectric losses in polymer films formed by a discharge

    Publication Year: 1965 , Page(s): 1614 - 1616
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    A continuous process is described which has been used to produce thin (¿1¿m) polymer films from styrene vapour subjected to an a.c. glow discharge. Dielectric losses in such films were investigated, including the effects of various gases present during polymerisation. View full abstract»

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  • Assessment of the possible use of polythene/gas dielectrics in h.v. cables

    Publication Year: 1965 , Page(s): 1617 - 1624
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (940 KB)  

    From the point of view of its electrical and mechanical properties and its ready availability in thin tape form, polythene is one of the most promising dielectrics for possible application in h.v. cable construction. To predict the behaviour of the polythene/gas dielectric system, having a lapped-tape construction, experiments were carried out on thin-walled models in nitrogen and several electronegative gases. The effects on impulse strength of a number of variables, a.c. life tests, and factors affecting the discharge-inception stress were investigated. In addition, the gas-pressurisation time was determined. Optimum electric strength, consistent with good mechanical performance, was obtained with tapes of 3 mil thickness. It was concluded that a composite polythene-tape/gas dielectric system has many advantages to recommend it for full-scale h.v. cable development. View full abstract»

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  • Performance of synthetic insulating materials under polluted conditions

    Publication Year: 1965 , Page(s): 1625 - 1632
    Cited by:  Papers (37)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (898 KB)  

    Both the dust/fog and IEC methods have been used to investigate the resistance to surface tracking and erosion of a range of synthetic insulating materials under polluted conditions. The relative merits of these test methods are discussed, and reasons given for preferring the dust/fog test. Consideration is also given to methods of accelerating the dust/fog erosion test. Results of such tests have been considered from a theoretical aspect, and a relationship between chemical structure and resistance to surface tracking is proposed. Using this approach, it was deduced that the alicyclic epoxy resins would be superior to the conventional bisphenol-based resins; this has been confirmed by dust/fog tests. Tracking resistance can also be increased by use of fillers, and this is illustrated for silica and alumina trihydrate in some epoxy casting systems. The application of track- and erosion-resistant materials to service use is considered, with special reference to casting resins. It is shown that the use of fillers to improve track resistance may cause deterioration in other electrical and mechanical properties of the material. View full abstract»

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  • Higher-melting-point polyolefines as flexible dielectrics

    Publication Year: 1965 , Page(s): 1633 - 1644
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1487 KB)  

    High-density polyethylenes can offer an advantage of 20degC, and polypropylenes an advantage of 55 degC, in the upper temperature limit, over the currently used low-density-polyethylene insulation. None of the 16 high-density polyethylenes examined, however, combines good mechanical properties with the desirable dielectric characteristics at high temperatures. Many are relatively tough when prepared by quenching the melt but embrittle on subsequent exposure to 100° C; the majority have low impact strength and inadequate resistance to thermal cracking. The commercial polymers with the best mechanical performance have relatively poor dielectric properties. Commercial polypropylenes are all very brittle, and, if cooled slowly from melt, crystallise with visible voids between spherulites. With few exceptions their loss tangent is high at high temperatures and mains frequency. One type of modified polypropylene, made in America, shows a moderate improvement in mechanical properties coupled with excellent dielectric characteristics. Another type, made in Britain, shows outstandingly good mechanical properties, which include high impact strength and high extensibility, even after slow cooling from melt. View full abstract»

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Aims & Scope

The Proceedings of the Institution of Electrical Engineers was published by the IET between 1963 and 1979.

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