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Electrical Engineers, Proceedings of the Institution of

Issue 5 • Date May 1969

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Displaying Results 1 - 25 of 36
  • Wave-propagation analysis of the monolithic-crystal filter

    Page(s): 653 - 660
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    The monolithic-crystal filter has two or more pairs of electrodes on the same piezoelectric plate; mechanical-wave propagation in the regions between electrodes takes place in an evanescent mode. A method of analysis, based on solutions to the wave equation, is first developed in general terms and then applied specifically to AT-cut quartz. Boundary conditions are used to determine resonant frequencies and vibration patterns under short-circuit conditions; from these, the electrical equivalent circuit is developed. Experimental results confirm the validity of the method. The theoretical results presented describe the bandwidth and motional capacitances of 2- and 3-resonator filters as functions of their geometry (electrode width, thickness and spacing). A method of predicting unwanted resonances is developed. A 3-resonator filter, with a centre resonator of different geometry, is considered. Some results relevant to multiple-resonator filters (up to ten) are described. Extension of the theory to overtone-mode devices is also discussed. View full abstract»

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  • Wideband 180° hybrid junctions using phase-corrected asymmetric directional couplers

    Page(s): 661 - 666
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (673 KB)  

    A method is given for the design of 0° (180°) hybrids in TEM-mode transmission lines, the hybrids having a small phase ripple. They consist of optimum asymmetric 3dB couplers cascaded with microwave allpass phase-equaliser networks. The results, which were obtained by optimising the overall phase characteristic using a computer technique, are given in detailed tabular form, and enable hybrids with bandwidths up to at least 12:1 to be designed readily. Experimental results for a 10:1 bandwidth hybrid, having ±8.5° phase deviation from 0°, show good agreement with the theory. View full abstract»

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  • Theoretical performance of the overmoded right-angle corner

    Page(s): 667 - 678
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1148 KB)  

    This potentially important component in overmoded waveguide is examined by a diffraction analysis, and by a cruder mirror analysis. A general symmetry relation for the corner is deduced, and the diffraction analysis, but not the mirror analysis, is shown to satisfy it. Nevertheless, they both give similar numerical values for the scattered modes, though the former indicates somewhat larger values. The diffraction method is beset with difficulties arising near shadow edges from the corners, and although this is overcome in the mutual-illumination part of the analysis, it reappears in the resulting calculation of the radiation into the guide. This part of the solution fails, in any case, for the modes near cut off, and is unusable beyond. A 10in guide with corner mirror is calculated to have a transmission loss of 0.9dB at 4.2GHz, and 0.2dB at 40GHz. Most of the loss appears in the lower-order forward-scattered modes. View full abstract»

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  • Electric-field distribution in the focal region of an offset paraboloid

    Page(s): 679 - 684
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (591 KB)  

    The electric field in the vicinity of the focus of a finite offset-paraboloid reflector, illuminated by a linearly polarised plane wave, is investigated. The paper begins with a general formulation of the reflected field calculation procedure for an arbitrary reflecting surface. The formulation is then specialised to apply to an offset paraboloid. Extensive computed data of the field in the focal region of an offset paraboloid are presented and compared with the field distribution in the focal region of a symmetrical paraboloid. It is shown that the electric-field distribution in the focal region of an offset paraboloid is almost the same as for a symmetrical paraboloid with the equivalent focal length. View full abstract»

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  • Statistics of tropospheric radio-refractive-index soundings taken over a 3-year period in the United Kingdom

    Page(s): 685 - 690
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    The paper discusses the statistical distributions of certain refractive-index parameters which are often used in tropospheric radio-propagation problems. The statistics are derived from three years' results of routine psychrometer soundings made at intervals of 75m, every 6h, to a height of 1200m, by the Meteorological Office at Cardington, Bedfordshire. Parameters discussed are surface refractive index, the lapse in refractive index (lapse rate) measured over the first 75, 150, 500, and 1000m from ground, and the distribution of lapse rates within each height interval of 75m. The distribution of the magnitude and height of occurrence of the largest lapse rates in each sounding, and the associated temperature and humidity changes, are also discussed. The paper also considers seasonal and diurnal variations of these parameters. View full abstract»

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  • Video-frequency light modulator having a wide angular aperture

    Page(s): 691 - 698
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1092 KB)  

    This paper discusses the 45° ycut ADP modulator. An investigation of the propagation of light through the crystal shows that there is an inherent limitation in the angular aperture of the simple 2-crystal modulator. The inclusion of a halfwave plate between the crystals to improve the temperature stability also enables large angular apertures to be achieved, provided the crystals are correctly aligned. Results of measurements carried out on experimental modulators are presented and a comparison made with the 45° zcut modulator. View full abstract»

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  • Small-signal, high-frequency equivalent circuit for the metal¿oxide¿semiconductor field-effect transistor

    Page(s): 699 - 702
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (355 KB)  

    The differential equations describing the small-signal sinusoidal operation of the `intrinsic¿ m.o.s.f.e.t. structure are solved using modified Bessel functions of the first kind. Expressions for the small-signal short-circuit admittance parameters are obtained in series form. By retaining appropriate terms in the series, the elements of a convenient equivalent circuit are computed for both the nonpinchoff and the pinchoff cases. Results are compared with those presented by other authors, to show that previous calculations for the nonpinchoff case are incorrect. View full abstract»

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  • Self-starting performance of astable-transistor-multivibrator circuits

    Page(s): 703 - 709
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    Tests are described which have been carried out to investigate the self-starting performance of the simple saturating transistor-astable-multivibrator circuit under different conditions, on connection of the d.c. supply to the circuit. These tests reveal that failure to start is controlled by several complex interacting factors. In general, high-gain transistors are more prone to failure to start than low-gain transistors in any given circuit. A theoretical discussion of the results obtained is included. View full abstract»

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  • Basic nonuniform transmission lines

    Page(s): 710 - 712
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (342 KB)  

    It is shown that for any given nonuniform transmission line (n.u.t.l.) ¿, (which may be a multilayered RC network or a multiwire transmission line), with a per-unit-length series impedance Z(x) and shunt admittance Y(x), there always exists an electrically equivalent `inverse line¿ ¿E, for which ZY is constant. Further, two more electrically equivalent lines may be found for which either Z or Y is constant. Although the study of any n.u.t.l. can be carried out directly, it is often advantageous to do so in terms of its equivalents. At present, the inverse line seems to be very attractive from a constructional point of view. It is also shown that for 2-wire lines, the different classes of n.u.t.l.s (including all their generalisations) known to have hyperbolic solutions are all equivalent to one of the `basic lines`, namely the uniform line, the exponential line, the algebraic line z = z0(l + kx)±2, y = y0(l + kx)±2, the trigonometric line z = z0 cos ±2 (mx + n), y = y0 cos±2 (mx + n), or the hyperbolic line z = z0 cosh±2 (mx + n), y = y0 cosh±2 (mx + n). Thus, the study of networks containing n.u.t.l.s with hyperbolic solutions may be carried out in terms of these basic lines. View full abstract»

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  • Application of linear induction motors to high-speed transport systems

    Page(s): 713 - 724
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2031 KB)  

    The linear motor has been chosen as the method of propulsion for the full-scale prototypes of several high-speed transport systems currently being developed. The paper sets out the problems of the electrical design of such systems, showing its interdependence with the mechanical and thermal designs. Attention is then concentrated on the double-sided flat linear, motor with conducting-sheet secondary, which is thought to offer the greatest advantages for long tracks. Considerations of power supply, thrust and speed control and methods of braking are included. It is shown that a steel plate cannot be used as secondary conductor on economic grounds. The particular requirements of vehicles which are suspended on air cushions are considered throughout the paper and a concluding section discusses the possibility of using electromagnetic current collection for such vehicles. View full abstract»

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  • Transverse edge effect in sheet-rotor induction motors

    Page(s): 725 - 731
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (831 KB)  

    A 2-dimensional-field analysis is presented for the problem of the sheet-rotor induction motor with finite width. Account is taken of the redistribution of the air-gap flux under the action of currents which flow in the active portion of the sheet in the direction of motion. The performance is shown to depend on three dimensionless parameters which are functions of the design data and the slip. It is seen that, for certain motors, the flux redistribution can affect the performance considerably. Measurements of force and flux density made on a linear motor, although showing reasonable agreement with the analysis, suggest that it would be desirable to take into account also, at least for those motors in which severe transverse redistribution occurs, the neglected secondary leakage fluxes that exist in the end regions and within the air gap. View full abstract»

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  • Effect of parameter changes on the performance of shaded-pole motors

    Page(s): 732 - 736
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    Using a method of analysis previously published by the authors, computed results are presented of changes of some of the performance characteristics of a shaded-pole motor due to varying its major design features, namely, the number of main-winding turns, the total-pole arc, the shaded-pole arc, the shading-ring conductance, and the resistance and skew of the rotor cage. Such results enable the choice of a preliminary design which is not far removed from the optimum design, and therefore allow the latter to be obtained with a minimum of trial computation. View full abstract»

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  • Stray losses of polyphase cage-induction motors with particular reference to the condition of imperfect rotor-bar¿iron insulation

    Page(s): 737 - 751
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1812 KB)  

    The paper presents an analysis of stray losses in polyphase cage-induction motors, under linear and saturation magnetisation conditions, with particular attention being given to the effects of circumferential currents flowing in the rotor as a consequence of imperfect bar-iron insulation. Such effects are included in a modified equivalent circuit of the motor, and are expressed in terms of factors readily determined from a set of normalised curves, not previously available. For example, the consequent reduction in the effective skew of the rotor bars can be determined, and thus a more correct evaluation obtained for those factors and losses dependent upon the resultant skew. Also, a simple graphical method is given for determining the effective increase of the air gap due to main-flux saturation, which assists in demonstrating that favourable agreement between the predicted and experimental torque/slip characteristics can be obtained with some reduction of the empiricism employed hitherto. View full abstract»

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  • Variable-characteristic synchronous machines

    Page(s): 752 - 762
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (912 KB)  

    The paper deals with the operation of a standard cylindrical-rotor synchronous machine with several novel forms of excitation control. It shows how, by using a nonlinear function of load-angle control, the machine can be made to develop characteristics normally associated with a salient-pole machine, and how a very wide range of the effective ratio of direct-axis to quadrature-axis synchronous reactances can be produced. Alternative control functions, designed to produce a machine with infinite stiffness, or with tangential forms of power/load-angle characteristics, are also described. Possible applications in large power systems, local generating plant and synchronous motor control are discussed. View full abstract»

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  • Development of an electronically commutated motor with laminated brushes

    Page(s): 763 - 768
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (699 KB)  

    Recent developments in switching by means of thyristors offer possibilities for commutating motors electronically. The method proposed uses a laminated form of brush, and is applicable to existing motors or d.c. generators. Trial equipment was tested over a wide range of speeds in a d.c. motor, and with high current densities in a 200kW d.c. generator, with promising results. View full abstract»

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  • Improvement of alternator stability by controlled quadrature excitation

    Page(s): 771 - 780
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1175 KB)  

    Operation of a synchronous generator at leading power factor has been severely limited in the past because of stability considerations. A regulator, acting on a normal direct-axis field winding, can only extend the range of stability when the generator is loaded, and has no effect under unloaded conditions. An additional winding on the quadrature axis, provided with a suitable control, can, however, ensure stable operation at any leading-power-factor load, within the heating limit of the generator. The most effective control uses a closed loop actuated by a signal derived from the load angle. The theoretical treatment in the paper consists of two parts. First, some general results are deduced from simplified equations, particularly relating to the limitations of a direct-axis regulator and the benefit of using an angle signal with the quadrature regulator. More complete computations are then made to obtain stability-limit curves for many alternative schemes. The work is concerned with the steady-state stability of a l-machine system, in which a generator is connected to an infinite bus through a reactance. Experiments to confirm the theoretical results were carried out on the micromachine equipment at Imperial College. The alternatives studied included simple proportionate regulators and more elaborate schemes using first- and second derivative elements, and the angle signal was taken alternatively from the infinite bus and the generator terminals. Good agreement was obtained with the corresponding computations. View full abstract»

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  • Importance of winding and permeance harmonics in the prediction of reluctance-motor performance

    Page(s): 781 - 787
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (586 KB)  

    Extending earlier analyses by Lawrenson and Gupta on single-speed machines and by Lawrenson, Gupta and Vamaraju on multispeed machines, generalised performance equations for single-and multispeed operation of reluctance machines are given, and their validity is supported by experimental results. The equations are used to investigate the effects of permeance and m.m.f. harmonics on machine performance, and both are shown to be of considerable practical significance. For accurate computation, it is found necessary to consider at least 40 permeance harmonics with a segmented rotor and at least 80 m.m.f. harmonics for multispeed operation of both salient-pole and segmented machines. View full abstract»

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  • Surge transfer through transformer-generator units

    Page(s): 788 - 800
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1823 KB)  

    The paper describes a study of the transfer of lightning surge voltages through transformers, between high-voltage overhead transmission-lines and directly connected generators. As such, it covers similar ground to the companion paper by E. L. White, which deals more fully with the theoretical aspects of the subject, and also reports simulated on-site surge tests on three transformer-generator units connected to systems of 132?400kV. The present paper has a rather more practical bias, and presents the results of tests on seven transformers connected to generators (two assembled on site in power stations), and on further transformers, 13 in all, connected to impedance networks simulating the appropriate generators. Transformers with 18?600MVA ratings, for connection to 33kV up to 400kV overhead-line systems, are covered here. Simulation of each phase of the generators, both by resistors (representing the winding surge impedances), and by parallel LC circuits, was studied; the comparisons made between the amplitudes and waveforms of the transferred surges reaching the ?generator? terminals, and those measured on the actual machines, showed that the LC network in all cases gave much the best approximation to the real-machine conditions. A basis for calculation of the transferred voltage transient, in amplitude and waveshape, has been developed and is given in an Appendix. It is shown that the relevant LC parameters can readily be calculated from known machine-design parameters, of which the most important is the unsaturated sub-transient reactance. Calculated results, obtained by computer, are given for all cases investigated experimentally. The present work forms a continuation of an earlier study, in which the theoretical basis for calculation of the surge transfer was first proposed; both the theoretical and the experimental aspects of that investigation have been considerably extended. The mechanisms of electromagnetic and capacitive surge transfer are discussed, b- oth in order to explain the effects of transformer and machine parameters, and to interpret discrepancies between theoretical and experimentally determined surge transfer. Conclusions are drawn on the practical importance of surge transfer to generators, the practicability of calculating these transients, and also on appropriate methods for separately impulse-testing generator transformers. View full abstract»

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  • Thyristor control of a multiload system with d.c. supply

    Page(s): 801 - 810
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1312 KB)  

    A thyristor control system has been developed for several loads energised from a common d.c. supply. All load-controlling thyristors are turned off at regular intervals by an interruptor unit interposed between the supply and the loads. Loads can be controlled, either in an `on-off¿ mode or using mark/space regulating techniques. Several configurations are considered. One is chosen to control 110V auxiliary loads on a diesel-electric locomotive, particularly when the generator field and separately excited traction-motor fields are so energised. Techniques for overcharging the interruptor capacitor to a controlled voltage are presented, including an optimisation of the circuit design. Experimental results on a 1/20 scale model compare favourably with design predictions. View full abstract»

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  • Bridge rectifiers with double and multiple supply

    Page(s): 811 - 821
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (896 KB)  

    The paper presents a new type of bridge rectifier with more than one 3-phase supply, suitable particularly for higher direct voltages. A generalised method of analysis for such multisupply bridges is derived, and detailed characteristics of various double-supply bridge rectifiers are given. View full abstract»

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  • External thermal resistance of two buried cables. Restricted application of superposition

    Page(s): 822 - 826
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    New formulas are derived for the external thermal resistance of one of two equally loaded identical cables laid direct in the ground at the same depth. The formulas are based on a restricted application of the principle of superposition, and remain valid when the cables are close or touching. Two assumptions made are that the depth of the buried cables is much greater than the cable radius, and that the cable surfaces are isothermal at a common temperature. The former assumption is justified as the cable depth is generally equal to at least ten times the cable radius. The latter assumption is recognised to be an approximation, but the present approach may prove to be more acceptable than alternative techniques. Comparison is made with previously published formulas. View full abstract»

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  • Electroheated fluidised beds

    Page(s): 827 - 833
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (698 KB)  

    Use of electroheated fluidised beds is a fast-growing branch of electroheating, but this growth has been hampered because the models available hitherto were incomplete, in that they ignored flow and mode dependence and were unnecessarily complicated for the engineer concerned with practical industrial processes. A class of conducting fluidised beds, representing common chemical, metallurgical and industrial processes, has been studied. New models are developed which are complete and are much easier to manipulate for studies of existing or proposed beds with their control systems, and which can readily be determined from a simple test series. They have been found to represent these beds with an accuracy sufficient for many practical studies. The presentation is intended for the professional engineer concerned with the application and control of these beds in industrial processes. View full abstract»

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  • Effects of internal discharges on prospective life and overvoltage-withstand behaviour of e.h.v. oil-impregnated paper bushings

    Page(s): 834 - 846
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1761 KB)  

    The paper gives the results of an experimental laboratory investigation of model bushings, with the object of predicting the behaviour of full-scale e.h.v. oil-impregnated paper bushings operating at a radial a.c. stress of 3kV r.m.s./mm. One of the aims was to determine whether discharges of up to 5pC in full-scale bushings might damage the insulation during prolonged periods in service, and so reduce the prospective life. Frequency-accelerated life tests were made on over 90 model bushings, some of which were constructed according to accepted manufacturing methods, whilst others contained defects of various kinds. It was found that, while the initial-discharge magnitude is a good indication of air trapped in the windings in a region of high electric stress, it is not a good guide to the prospective life of the bushings. The most critical factor is the ability of the oil to dissolve any trapped gas. If the trapped gas dissolves, bushings working at a stress of 3kV r.m.s./mm will have a low discharge level and a long life, provided they have no constructional defects. If not, the discharge magnitude may fall at first, but will then rise steadily until breakdown occurs after 12?20 years. A further aim of the investigation was to determine the extent to which either permanent damage or temporary impairment of the dielectric properties could be caused by overvoltages in the range 7?16kV r.m.s./mm, applied for periods of 1?50min. The effects of impulse stresses up to 19kV peak/mm were also studied. It was found that a sensitivity of about 0.1pC would be required to detect the discharge resulting from the gas generated during a normal overvoltage test on a well made 400kV bushing, but that much larger quantities of gas produced in this way would dissolve in the oil within a few days, and the bushing would then return to a discharge-free condition, without apparent physical damage. Where a quantity of air was trapped in the winding during manufacture, it was shown that a - discharge level of 30pC at working voltage in a 400kV bushing having a moisture content not greater than 1% would not involve a risk of degradation by a single overvoltage test having a duration of 1 min at a stress of 14kV r.m.s./mm. 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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