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Electrical Engineers, Proceedings of the Institution of

Issue 4 • Date April 1967

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Displaying Results 1 - 20 of 20
  • New features of wave propagation not subject to cutoff between two parallel guiding surfaces

    Page(s): 421 - 427
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (737 KB)  

    Wave propagation not subject to cutoff between two parallel guiding surfaces is generally described in terms of the so-called TEM mode. Although this is recognised to be an over simplification, it is nevertheless very close to the truth in many cases when bare copper conductors are used to form the guiding surfaces. However, at high frequencies, such surfaces, having very nearly equal resistive and reactive components which are not entirely insignificant, tend to require the support of a hybrid TEM-dual-surface-wave mode, and this can be readily accentuated by deliberately enhancing the surface reactances. Investigation shows that the accompanying redistribution of power flow over the cross-section of the guide can, in appropriate circumstances, lead to a very significant reduction of the attenuation suffered by the wave. The technique is applicable both to striplines and to coaxial cables. View full abstract»

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  • U.H.F. tunnel-diode amplifier

    Page(s): 428 - 434
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (893 KB)  

    The paper is mainly devoted to a detailed account of the design of the reflection amplifiers for use in a tunnel-diode repeater described in a companion paper. The amplifiers are constructed in stripline, incorporating transmission lines of variable characteristic impedance. Thus tunnel diodes of widely differing characteristics can be accommodated in a single amplifier; yet the tuning procedure is particularly simple. Results are also given for a circulator-coupled amplifier formed from the reflection amplifier and a 4-port circulator. View full abstract»

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  • Short-hop radio-relay systems using tunnel-diode repeaters

    Page(s): 435 - 442
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1166 KB)  

    The first part of the paper considers the properties and design requirements of short-hop radio-relay systems; in particular, systems using nondemodulating, nonfrequency-changing repeaters. It is concluded that a system of close-spaced low-power repeaters, mounted on the towers of the high-voltage transmission network, is technically and economically feasible and would be efficient in utilisation of the frequency spectrum. The second part of the paper describes the design of a 2-way u.h.f. tunnel-diode repeater and its performance in the laboratory and in a short experimental link. The u.h.f. repeater was developed to test the practicability of tunnel-diode repeaters for the short-hop system already considered, but, because of the relatively low aerial gain available at u.h.f., its application is restricted to overcoming obstacle loss between two u.h.f. radio terminals. It is finally concluded that tunnel-diode repeaters are feasible for short-hop systems and could find an immediate application in reducing propagation loss over short but difficult radio paths. View full abstract»

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  • Transverse equivalent networks for slotted inhomogeneous circular waveguides

    Page(s): 445 - 456
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1418 KB)  

    Transverse equivalent networks are determined for a circular waveguide of infinite extent possessing a narrow longitudinal slot in the waveguide wall. The waveguide contains a dielectric rod of circular cross-section located on the waveguide axis. It is shown that, provided that the ratio rod-radius/waveguide-radius does not approach unity too closely, a simple transverse representation is permissible. Azimuthally dependent hybrid fields in the waveguide are represented by a combination of radial-line modes of pure Htype and pure Etype. The discontinuity presented by the slot to each mode is determined for n = 0 and n = 1 azimuthally dependent fields, and, in the latter case, two angular positions of the slot are considered. The slot susceptances are evaluated by obtaining the solution of an integral equation for the aperture electric field, subject to quasistatic and small-aperture approximations. The slot conductances are obtained using a variational expression into which the aperture field is inserted. View full abstract»

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  • Propagation behaviour of slotted inhomogeneous circular waveguides

    Page(s): 457 - 464
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1028 KB)  

    By employing an approximate transverse-equivalent-network representation, the propagation behaviour of a slotted circular waveguide containing an axial dielectric rod is investigated. The complex transverseresonance equation is solved for E and Htype modes possessing an azimuthal dependence of zero and unity. The behaviour of both fast-wave and slow-wave regions is considered, and it is shown that, whereas the E mode propagation coefficient is a continuous function of frequency when the normalised phase-change coefficient passes through unity, the H mode propagation coefficient is discontinuous. The theoretical results for the slotted cylinder also demonstrate the form of the transition between the slow-wave behaviour of completely closed and completely open dielectric-rod structures. Theoretical phase-change coefficients in the fast-wave region are compared with those previously obtained from measurements of leaky-wave radiation patterns. Although good agreement is obtained, it is concluded that the perturbation caused by the introduction of a slot can be quite large in certain cases. A method is proposed whereby the perturbation might be reduced for modes with an azimuthal dependence of unity. it is suggested that the technique could prove useful in determining the fast-wave propagation characteristics of those asymmetric inhomogeneous-waveguide structures that are unamenable to analysis. View full abstract»

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  • Calculation of switching transients with particular reference to line energisation

    Page(s): 465 - 477
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1714 KB)  

    The calculation of transient overvoltages due to circuit-breaker operations in power systems has always been of importance, but in the past attention has been focused on the restriking voltage transient occurring when a circuit breaker opens, since this intimately affects the duty and hence the design of the circuit breaker. More recently, owing to the rise in system operating voltage and to a desire to reduce capital costs by a reduction in system insulation level, the transient voltages arising when long transmission lines are energised and re-energised and the means for reducing these transient voltages have become of considerable importance. Although a number of methods for calculating switching transients exist, some are more accurate than others. The use of the most accurate methods, however, may not always be justified, owing to system-data limitations and the larger computation costs involved. The authors believe that the methods they have adopted and which are described, although not the most accurate, are well suited to the system data which are normally available at the present time. The paper outlines first a method based on a lumped-parameter representation of the system, and secondly a method based on a lattice-diagram solution of the transmission-line wave equations. Some of the facilities available with this second method are described, including the representation of lumped inductive and capacitive elements and transmission-line attenuation and distortion. After the results obtained using these methods have been compared, the effects of source inductance, line-connected shunt reactors and trapped-charge voltages on the transient voltages produced by the energisation of long lines are considered. Other effects which may modify these voltages are those of corona loss and reduced trapped-charge voltage, caused by the discharging effect of equipment connected to the line, e.g. shunt reactors and circuit-breaker-opening resistors. If the inclusion of the- se factors does not reduce the overvoltages sufficiently to enable the desired system insulation level to be obtained, the use of circuit-breaker-closing resistors or point-on-wave switching of the circuit breaker can be considered. View full abstract»

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  • Calculation of switching phenomena in power systems

    Page(s): 478 - 486
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (958 KB)  

    A method of computing switching overvoltages based on the numerical inversion of the modified Fourier transform is discussed. Several applications are made to practical studies of varying degrees of complexity. The results of a 3-phase switching problem are shown to be in agreement with those obtained by other workers using analogue simulation. The method allows more complete representation of the problem than was previously possible. Indeed, during the course of the work, the type of data necessary to permit an even closer representation became apparent, and attention is drawn to the desirability of recording this on future site tests. View full abstract»

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  • Factors affecting the design of electrical accessories

    Page(s): 487 - 502
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3190 KB)  

    The definition contained in the 14th edition of the IEE Wiring Regulations has been extended to include a wider range of electrical accessory, such as would be used for lighting, heating or power requirements in a domestic or similar type of wiring installation. No attempt has been made to cover the complete range of electrical accessories, such as those used for an industrial installation or the larger type of commercial or specialised wiring installation. The first part of the paper is devoted to a brief survey of electrical accessories that have been in use for wiring installations over the past 80 years. This is followed by a more detailed approach, dealing with accessories for specific purposes, having regard to the development of the use of electricity for performing everyday tasks. Apart from the basic design requirements to satisfy an appropriate British Standard, the factors primarily considered are those which are of interest to the user or installer of the accessory. These include safety in operation, adequate protection and enclosure of wiring connections, facility for making such connections, and general external appearance. The paper concludes with some suggestions for possible future design considerations, some of which may materially affect long-accepted practice in the use of electrical accessories. View full abstract»

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  • Induction-motor reswitching transients

    Page(s): 503 - 509
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (841 KB)  

    The transient behaviour of an induction motor when disconnected from the supply and reswitched to the same or to a different supply before the complete decay of rotor currents is investigated. A digital-computer program is described for calculating the internal voltage generated by the decaying rotor currents and the transient torques and currents produced on reswitching. Experimental measurements of the transients experienced by a 7 5hp motor following reconnection to the same supply, plugging and dynamic braking are compared with computed results. Tests were made both at rated and at reduced supply voltage, and better agreement between theory and measurement is obtained at the lower voltage. View full abstract»

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  • Canals as cable routes

    Page(s): 510 - 518
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1306 KB)  

    An investigation into laying cables in canals showed the thermal resistivity of the silt to be as high as 118 cmdegC/W. This high value led to the investigation of the laying of cables on posts in free water. The possibilities of uncontrolled silting and algae growth suggested a more conservative approach by laying cables in troughs on the towpaths. This method, using different filling mediums, was thoroughly examined experimentally, and found to be so satisfactory as to allow two 275 kV, 760 MVA circuits to be installed in a 4ft 6in-wide trough without water cooling. Savings in the overall contract cost are expected using this technique, which, it is believed, may be extended to areas around substations and alongside motorways or railways. An analysis is presented which takes account of the increase in temperature of the ground surface where cables are laid at shallow depths. View full abstract»

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  • Thermal aspects of changes in the environment of underground cables

    Page(s): 519 - 524
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (899 KB)  

    The thermal field established by a trench containing three closely spaced single-core cables in horizontal formation, bedding sand, concrete slabs and backfill has been determined by the use of an electrolytic tank, and the effects of variation in the backfill thermal resistivity obtained for bedding-sand and soil resistivities of 150 and 120cmdegC/W, respectively. The effective thermal resistances from the cable outer surface to the ambient surroundings are compared with those obtained by the analytical method of Schmill, which applies to only two different resistivities, backfill and soil. The effect of changes in the bedding-sand resistivity are summarised in a simple equivalent thermal circuit. Using this, the cable-surface-temperature-rise/cable-loss curves are obtained for sand-resistivity/temperature relationships which are assumed to represent the moisture-migration process; this applies for moisture migration in the bedding sand alone. It is seen that the temperature dependence of the resistivity of the material immediately around the cables is decisive when determining thermal runaway. The cable-surface temperatures are determined with artificial cooling using external water pipes, and include the effects of coolant-temperature rise and bedding sand. It is shown that the thermal time constants obtained for a particular environment and cooling scheme may be approximately adjusted to represent others, provided that the burial depth is the same. The changes in conductor temperature with an interruption in coolant supply are shown. View full abstract»

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  • Proposed method for economic load scheduling

    Page(s): 525 - 531
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (842 KB)  

    In the last two decades, economic load scheduling for multiplant power systems has received much attention, with the result that computers have been put `on line¿ to issue instructions to the various plants to adjust their outputs at regular intervals to secure economical operation in accordance with system requirements. The suggestion presented in this paper is an improvement on the existing method for digital computation, and results in a reduction of computing time of approximately 50 to 70% when the economic load scheduling is based on total generated power, and 40 to 60% when it is based on total load; the method proposed uses exact penalty factors and loss-formula coefficients, and takes the total generation or load requirements directly as input. An illustrative example is included. View full abstract»

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  • Impedance of long solenoids with nonferrous tubular cores

    Page(s): 533 - 536
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (490 KB)  

    To assist in the practical application of nondestructive eddy-current test methods, theoretical solutions have been derived for the normalised impedance of long solenoids encircling nonferrous metallic tubular conductors. Calculated values are presented in tabular form for a range of tube dimensions and test frequencies of practical interest. View full abstract»

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  • Effect of electronegative gases on prebreakdown conduction-current pulses in transformer oil

    Page(s): 538 - 540
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (374 KB)  

    Results are given of the effect on prebreakdown conduction-current pulses of dissolving air, oxygen (O2) and sulphur hexafluoride (SF6 in transformer oil. The pulses were recorded during the experiments on magnetic tape and subsequently subjected to statistical analysis. It was found that during the stress-conditioning pulses of different magnitudes behaved differently. Air or O2 in solution in the oil resulted in a pronounced quenching effect on the pulses. A similar effect was observed with SF6 in solution, but after a breakdown a drastic change in the behaviour of the pulses was noticed. View full abstract»

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  • Transformation of linear constant system equations

    Page(s): 541 - 544
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    With the equations of a linear constant system is associated a matrix from which the equations can be reconstructed. Transformations of the matrix correspond to transformations of the equations which leave certain properties (order of the system, transfer functions, etc.) unchanged. The mathematical results are used to give a new and simpler way of realising a transfer-function matrix, and to develop some other results of practical significance. 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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