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Electrical Engineers, Proceedings of the Institution of

Issue 9 • Date September 1969

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Displaying Results 1 - 23 of 23
  • Computer prediction of service areas for v.h.f. mobile radio networks

    Page(s): 1493 - 1500
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (934 KB)  

    The paper describes a computer program written to predict the effective service area of a transmitter in a v.h.f. mobile radio network. The computed results enable field-strength contours to be deduced, and hence provide more useful information than is possible by reference to standard statistical curves. The transmitter siting can be changed, and the field-strength contours recalculated, without the preparation of new geographical data. As a consequence, the efficiencies of a selection of possible transmitter sitings can be readily compared. The accuracy of the program is verified by comparing the computed results with field-strength measurements on a mobile radio installation operating at 86.2 MHz. View full abstract»

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  • Satellite television distribution: service from geostationary satellites to community antennas in multiple-coverage areas

    Page(s): 1501 - 1504
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (575 KB)  

    The first application of satellites for transmitting television to community antennas or for direct broadcasting to the public is likely to be to cover large areas with a single programme. At a later stage, however, it may be concluded that satellites could provide a service similar to that of the existing terrestrial systems, i.e. broadcasting to a large number of small contiguous areas with separate programmes. This presents problems associated with efficient use of the frequency bands which may be available and of the geostationary orbit. The effects of the parameters of the frequency-modulation method assumed, including the interference protection ratios, and of the antenna radiation patterns on these factors, are examined in some detail. From these considerations, an idealised model has been used to obtain generalised expressions, assuming a geometrical arrangement of the coverage areas. Where applicable, these have been used to determine the powers, bandwidths and orbital separations of the satellites serving a typical area such as Europe. It is shown that, for domestic reception via community antennas, four programmes could be provided to each of 30 countries, using eight satellites in 20° of orbital are. A bandwidth allocation of 400MHz at a frequency in the region of 12GHz has been assumed. Direct reception at domestic receivers would require greater satellite transmitter power than community reception, and the orbital are required would be approximately 35°. View full abstract»

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  • Statistical analysis of position fixing in three dimensions

    Page(s): 1505 - 1508
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (493 KB)  

    This paper sets out a statistical analysis of the errors of position inherent in any position-finding system which utilises a number of `position-fixing planes¿ and takes the point of maximum likelihood as the required position in 3-dimensional space. Formulas are given for the mean-square errors associated with the co-ordinates of position and also the covariances of these errors. A simple example is used to illustrate the use of the mean-square-error information, and expressions which give the co-ordinates of the maximum-likelihood point are derived for general application. View full abstract»

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  • Analysis of the multiple-strip H guide

    Page(s): 1509 - 1513
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    A consideration of the field distribution and the characteristics of an H guide, with the dielectric bar sub-divided into an arbitrary number of dielectric strips separated by air layers, is presented. Low-loss wave modes with the magnetic-field components parallel to the boundary surfaces are analysed. Approximate thin-layer equations which indicate methods leading to considerable improvements of the attenuation of the H guide are derived. View full abstract»

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  • Exact analysis of resonant transfer networks

    Page(s): 1514 - 1516
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (318 KB)  

    A state-space approach is used to derive an exact closed-form solution for both the transient and steady-state response of a general resonant transfer network. The usual assumption that the ratio of the switch closure time ¿ to the switching period T, i.e. ¿/T, approaches zero is removed in the analysis. The analysis also gives the time-varying network function of the resonant transfer network in closed form and in Fourier series which in turn yields frequency spectra of the output of the resonant transfer network. The approach is simple and suitable for computer simulation and experiment. View full abstract»

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  • High-voltage nanosecond nonisotropic coupler

    Page(s): 1517 - 1520
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (505 KB)  

    The paper describes the design and analysis of nonisotropic coupled-line couplers capable of measuring fast-risetime pulses travelling on matched transmission lines which are sited at high potentials. The general analysis which is given can be applied to other situations, and the derived theory is in accordance with the experimental results. View full abstract»

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  • Circulating-current pilot-wire differential protection of multiended circuits

    Page(s): 1521 - 1526
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (695 KB)  

    A general analysis is made of symmetrical multiended pilot-wire circuits terminated by impedances in parallel with the current sources. The fundamental-frequency-transmission characteristics of the pilot circuits are accounted for, and compensation for pilot phase shift is applied by a suitable choice of parallel impedance. A range of alternative amplitude-comparator relay characteristics is presented graphically on the basis of the complex ratio of the relaying current at any relay location to the phasor sum of relaying currents at the remaining terminations. A method is described by which the insertion of a simple network at the electrical centre of a system of symmetrical pilot circuits permits the application to multiterminal lines of schemes of protection requiring the correct termination of the pilot circuit in its characteristic impedance. View full abstract»

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  • Twenty years of electricity distribution under public control

    Page(s): 1527 - 1543
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2398 KB)  

    The paper forms a broad survey and appraisal of progress in the public distribution of electricity in Great Britain since the industry was nationalised in 1948. A statistical analysis of the principal growth features including sales, finance and persons employed is presented. Some assessment of the progress made and the present state of development is derived from international comparisons, by considering the relative growth of public supply and private generation, and by comparing the production and use of electrical energy with other fuels, i.e. coal, gas and oil. The comparative performance of individual UK area boards is assessed on selected criteria. The statistics are presented in diagrammatic form for each of the two decades since 1948 to give some indication of trends. The authors describe the UK electricity-supply organisation, with brief references to the negotiating and consultative machinery. Changes in the pattern of area-board administration are noted, with particular reference to the evolution of district management units. The paper also deals with technical changes and progress. Reference is made to the standardisation of systems and of the underlying principles and practice of system planning, and some of the more important changes in design of distribution switchgear, transformers, cables, overhead lines and metering equipment. Improvements in constructional techniques and in operation and maintenance of the systems are also noted. A Section on research and development traces the expansion of these activities, and lists a few of the more important projects undertaken. View full abstract»

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  • External thermal resistance of air-installed power cables

    Page(s): 1547 - 1552
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (603 KB)  

    Calculations of the external thermal resistance of power cables installed in free air have so far been based on the heat-emission coefficient h, introduced by Whitehead and Hutchings in the form of empirical curves derived from experimental work. This paper gives new formulas for h for the most important cases of cables installed in air. View full abstract»

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  • Multiconductor transmission lines. Theory of natural modes and fourier integral applied to transient analysis

    Page(s): 1553 - 1563
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1134 KB)  

    In this paper, a theoretical formulation of a method of multiconductor transient analysis is developed. The method combines the use of the modified Fourier transform and the steady-state theory of natural modes. The virtues of this particular formulation are that the frequency dependence of parameters can be taken into account irrespective of the complexity of the expressions defining their steady-state values. The paper discusses the problem of the first pole to close when a power line is being energised from a source of infinite capacity. The argument is further extended to cover simultaneous pole closure of a circuit breaker. The mathematical representation of the source-side network is covered and two alternative methods of simulation of a multiconductor-source infeed are presented. Both methods are shown to retain the distributed-parameter nature of a source infeed, or a group of such infeeds, while achieving a reduction in the computation time that would otherwise be required to meet the needs of a fairly accurate form of representation. The numerical results of a series of digital-computer studies are presented. These illustrate various cases of practical important and highlight specific aspects of the behaviour of multiconductor systems. View full abstract»

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  • Thermal rating of transformers. Introduction of multiflow principle

    Page(s): 1564 - 1570
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (798 KB)  

    The thermal rating of power transformers has hitherto been based on the average temperature rise of the windings as determined from the increase in resistance, because that has been the best practical measurement. Unfortunately, for a given and guaranteed temperature rise by resistance, the hottest-spot temperature can vary over quite a wide range depending on individual design characteristics. The introduction of the multiflow principle allows the hottest-spot temperature to be determined from measurements made during a single temperature-rise test. Using this method, it is suggested that the temperature rise by resistance should be abandoned as a standard guarantee, and replaced by the hottest-spot temperature, this being the fundamental basis of the true thermal rating. The designer will then have wider latitude in choosing his parameters, and freedom to exploit more intensive cooling systems such as increased oil circultation and directed flow. The resulting reductions in both winding- and oil-heat-exchanger capacities are substantial. As a broad comparison with existing practice, the principle of multiflow in forced-oil-cooled transformers permits an increase in the average winding-temperature rise from the present international guaranteed limit of 65°C to 75°C, or more, without any increase in the hottest-spot temperature. View full abstract»

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  • Analysis and operation of an invertor-fed variable-speed induction motor

    Page(s): 1571 - 1580
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1028 KB)  

    The paper attempts to make a time-domain analysis of an induction motor supplied by an invertor. In the steady-state analysis, the mathematics can be reduced to a two-point boundary-value problem, a solution of which is given. A novel running mode of the induction motor, called the constant-slip operation, is proposed and analysed by this method. In the transient analysis, results of starting and regenerative braking are given. View full abstract»

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  • Application of an online computer to an acetic-acid process

    Page(s): 1585 - 1588
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (685 KB)  

    The paper discusses the application of an Elliott Arch 9000 computer to the BP Chemicals (UK) Ltd. acetic-acid process operated at Kingston upon Hull, England. The computer was used as a tool to assist in a detailed study of the process. The main objective of the work was to develop a process model of the plant for control purposes. The role of the computer was twofold: (a) to collect plant-performance data for offline development of the model (b) to provide direct digital control of certain key control loops important to the study. The project was a combined exercise with Elliott Process Automation, involved a total of 28 (graduate) man years and incurred a total cost of £260000. A breakdown of these figures is presented. The difficulties of organising and administering such an extensive project are also discussed. Reference is made to the important role of process models in relation to the many control levels in a company hierarchy. View full abstract»

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  • Model adaptive switching controller

    Page(s): 1589 - 1594
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (735 KB)  

    This paper is concerned with the solution of the actuation and identification problem in a particular model adaptive control system and with the structure of a suitable decision computer for the generation of a suboptimal bang-bang switching function. The control strategy is one of feed-forward prediction, where emphasis is placed on minimising the time required for process identification and actuation. A new type of fast-actuating or adaptive mechanism based on photoelectric principles is proposed for adjusting the parameters of the plant model, which is formulated in electronic-analogue terms. View full abstract»

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  • Stability of nonlinear-feedback systems with hysteretic controllers

    Page(s): 1595 - 1598
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (405 KB)  

    The paper presents a simple method for deriving frequency-domain-stability criteria for nonlinear-feedback systems which have hysteretic controllers. It is shown that the problem can be resolved by using known results on the stability of multidimensional systems if the hysteresis characteristic is modelled properly. A possible approach to the modelling problem is discussed. This leads to a representation of the hysteresis function in the form f (x, sgn x¿), where sgn x¿ stands for the signum function of the derivative of the input signal. Three different cases of hysteresis are considered in the paper. Numerical examples of each of these are presented, together with experimental data. View full abstract»

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  • Theory of feedback shift registers with invertors

    Page(s): 1599 - 1605
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (575 KB)  

    The existing theory of linear sequential circuits is extended to include linear circuits modified by the addition of invertors. Essentially, these contralinear circuits are analysed by embedding them in higher-order linear circuits. It is shown that a general contralinear sequential circuit is equivalent to a collection of contralinear feedback shift registers, each containing, at most, one invertor. The feedback shift register containing a single invertor in its feedback path is considered in some detail. View full abstract»

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  • Imposition of sinusoidal flux by feedback for analogue and digital computation of the field distribution in a.c.-magnetised ferromagnetic laminas

    Page(s): 1613 - 1620
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (896 KB)  

    The paper gives a method of imposing a sinusoidal flux when computing the electromagnetic Maxwellian field distribution in a lamina which is considered to be plane, and infinite in two directions. The static hysteresis loop has been modelled by a polygonal line. The method has been developed on an analogue computer, and then adapted for digital computation. This avoids the need for iterative computing, and maintains the stability and the convergence achieved with the analogue computation; it also avoids difficulties common to analogue function generators. Both analogue and digital computers need, at the most, one quarter of a period to start computing the steady-state field distribution, and the complete solution is obtained in a single computer run, extended to three quarters of a period only. Agreement between the computed and the measured magnetisation current is poor; it is thought that the main divergence results from the disagreement between the assumed and the actual behaviour of the material. Recognisable, but relatively insignificant, errors result from modelling the hysteresis loop by a polygonal line, and from limitation of the number of steps into which the width of the lamina has been divided. 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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