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Electrical Engineers, Proceedings of the Institution of

Issue 11 • Date November 1975

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Displaying Results 1 - 25 of 35
  • M.T.I. clutter locking when the spectrum is asymmetric

    Page(s): 1169 - 1172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    It is shown that, whatever the shape of the clutter spectrum and whatever the order of a binomially weighted canceller, the output clutter residue is minimised if the local oscillator is locked to null the interpulse phase shift just prior to the final subtraction. In the presence of receiver noise, however, this phase shift will become contaminated. Simply to filter out this phase noise would reduce the ability of the system to adapt to variations in the mean clutter velocity. An alternative approach is to derive the locking signal from a phase detector placed further back along the canceller. The losses in cancellation ratio consequent upon doing this are derived in general terms, and it is shown that the losses are dependent almost entirely upon the shape, and not the scale, of the clutter spectrum. Consideration of two hypothetical and two realistic model spectra possessing considerable asymmetry suggests that, for cancellers of up to the third order, the additional losses are not large. A similar approach is used to derive the losses for a general class of canceller when the locking is effected by nulling the mean interpulse phase shift of the input. View full abstract»

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  • Attenuation in corrugated circular waveguides. Part 1: Theory

    Page(s): 1173 - 1179
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (754 KB)  

    A study of the propagation behaviour of corrugated circular waveguides is described. The phase and attenuation characteristics are obtained using space harmonics in the interior and higher order modes in the slot region of the waveguide. It is found that only the first pair of harmonics and higher modes have a significant effect on the propagation behaviour. The HE11 mode, which is required in antenna applications, is shown to have an attenuation coefficient which is lower than that of any other mode, lower in fact than that of the TE010 mode in a smooth wall circular waveguide of comparable size. An investigation of the fields and currents in the waveguide aids a physical understanding of the phenomenon, which is shown to be only weakly sensitive to the waveguide tolerances. Experimental results to confirm the theory are given in Part 2 of the paper (see p. 1180). View full abstract»

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  • Attenuation in corrugated circular waveguides. Part 2: Experiment

    Page(s): 1180 - 1186
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (700 KB)  

    Measurements of the attenuation characteristics of corrugated circular waveguides in the frequency range 8¿11 GHz are described which support the theory given in Pt. 1 of the paper (see p. 1173). Both cavity techniques and waveguide measurements are deployed, and these lead to attenuation values which are about 40% above the predicted value for an ideal corrugated waveguide. However, it is believed that the discrepancy may be explained by the surface roughness of the metal and other imperfections. The actual measured value of the attenuation of the HE11 mode is just below the theoretical value for the TE010 mode in a comparable smooth-wall waveguide, emphasising the low values being measured. A new method is described for suppressing modes, which is based on the principle of the monomode optical waveguide. View full abstract»

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  • Double-diode trapatt pulse generator with applications to avalanche-diode research

    Page(s): 1187 - 1192
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (940 KB)  

    Improvements in trapatt pulse generators are described. By using two diodes in a push-pull configuration, pulses around 250 ps duration with up to 800 W peak power can be produced with repetition rates around 1 GHz. Measurements of diode breakdown under controlled high-speed voltage pulses from such a generator have been made on X-band trapatt diodes. These measurements show that relaxation-type oscillations can start in resistive circuits and thus support the relaxation oscillation theory for the starting mechanism of trapatt oscillations. They further suggest that high-frequency trapatt devices may have difficulty in operating efficiently at frequencies lower than some particular value determined by the relaxation oscillations. View full abstract»

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  • Computer techniques for solving metal-semiconductor barrier height. Application to Au - CdS thin-film Schottky diodes

    Page(s): 1193 - 1196
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (369 KB)  

    Computer programs are developed for numerical determination of the Schottky-barrier heights from the differential capacitance method, the current/voltage characteristic method under forward bias and the Fowler photocurrent method. The basic theory of these methods is briefly described. As a practical application, the programs have been used to investigate metal-semiconductor contact properties. View full abstract»

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  • Error detectors using signal distortion

    Page(s): 1197 - 1202
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    A synchronous serial data-transmission system has recently been proposed for use over channels that introduce severe signal distortion. The serial stream of data elements at the transmitter output is arranged into separate groups, with sufficient time gaps between adjacent groups to ensure that these do not overlap at the receiver. The received signal has many of the properties of a linear error-detecting or error-correcting block code. Although the signal lacks some of the simplicity and elegance of conventional linear block codes, it can nevertheless be used very simply and effectively to recognise the presence of errors in the detected data signal. The paper describes four different error detectors and three different signal detectors with which these may be used. The performances of the four error detectors are studied by computer simulation and their potential merits are assessed. View full abstract»

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  • Study of overheads in packet-switched data networks

    Page(s): 1203 - 1206
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    An analytical formulation for determining the optimum packet size is presented. The mathematical model developed takes into consideration the message statistics, acknowledgment delays, channel-error characteristics, delays due to retransmission, packet header and the overheads due to blank padding of last packet etc. Network operational overheads have been considered to be functions of packet size. The system analysed is a half-duplex network operating in a stop-and-wait strategy for error detection and correction. The theoretical formulations lead to a 3rd-order algebraic equation having one and only one positive real root ¿ which signifies the optimum packet size. Furthermore, these studies indicate that a packet size can be determined that minimises the network operational overheads; while the overheads due to blank padding increase more or less linearly with packet size. View full abstract»

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  • Symbol generator for a graphical-display system

    Page(s): 1207 - 1210
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    A symbol generator producing vector-drawn characters has been designed for use in a graphical display. Since the storage medium is a random-access memory, user-dependent symbols may be drawn in addition to a full alphanumeric-character set, thus reducing the display-file size and access rate. It is also capable of generating sequences of fixed instructions for special purposes, thereby reducing the load on the driving computer. It is shown that these additional facilities are provided at a very small extra cost over the pure alphanumeric generator. View full abstract»

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  • Computer-controlled queues in series

    Page(s): 1211 - 1212
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (271 KB)  

    The paper presents an investigation of a computer-controlled queuing system with N queues in series and Mi, 1 ¿ i ¿ N, servers of negative exponential service-time distribution serving the ith queue. A generating function for stationary-stateprobabilities of necessary and sufficient conditions for the existence of statistical equilibrium for, and a formula for thedetermination of, the waiting-time distribution in the system are obtained. View full abstract»

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  • Multiserver computer-controlled queuing system with nonpre-emptive priorities

    Page(s): 1212 - 1213
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (259 KB)  

    The paper presents an investigation of a computer-controlled queuing system with nonpre-emptive priorities. A generating function for stationary-state probabilities of, the necessary and sufficient condition for the existence of statistical equilibrium for, and a formula for the determination of the waiting-time distribution in the system are obtained. View full abstract»

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  • Switching overvoltages in short crossbonded cable systems using the Fourier transform

    Page(s): 1217 - 1221
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (545 KB)  

    A mathematical model of a single major section of a crossbonded cable system is developed, and an outline of the Fourier-transform method of determining transient-voltage waveforms in the system is presented. Crossbonded cables are analysed in terms of the parameters of the constituent homogeneous sections. These parameters are compounded by using a rotation matrix at each crossbonding point. Conductor-voltage and sheath-voltage waveforms are calculated at various points along typical systems comprising one and two major sections, respectively. View full abstract»

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  • Foyers pumped-storage project

    Page(s): 1222 - 1234
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2347 KB)  

    The Foyers pumped-storage scheme is the second in the United Kingdom to use reversible pump turbines and the first shaft-type station. The paper shows how the requirements of the power system and the characteristics of the site influenced the design parameters and describes the various engineering and costing studies which were undertaken in arriving at the final design. The station is constructed in a geologically faulted zone, and this influenced the design and choice of construction methods for the civil-engineering aspects. Novel mechanical and electrical features, aimed at improving performance, reliability and access for maintenance, were incorporated in the generating plant as a result of experience on earlier pumped-storage plant. The paper also describes briefly the principal features in the construction of the scheme and early operational experience. View full abstract»

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  • Maximin algorithms for interactive synthesis of electricity-supply networks

    Page(s): 1235 - 1240
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1008 KB)  

    The paper presents two network-synthesis algorithms based on a maximin principle. Each algorithm attempts to produce minimum-cost outline designs, in accordance with a mathematical model of the network-design problem, which contain a maximum degree of security in terms of the mathematical constraints. The application of these algorithms, using an interactive computer display system, is described and a philosophy for interactive synthesis is advanced. Interaction times are sufficiently short to allow experimentation with a realistic size network that will produce a family of outline designs within a flat-topped range of near-optimal solutions. The algorithms are illustrated by their application to two networks containing seven and seventeen nodes, respectively. Although the algorithms have quite different starting points, the final designs they produce are very similar in appearance and cost. Both methods underline the advantages of a family of solutions and the use of an interactive display. View full abstract»

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  • Optimum allocation of spinning reserve by quadratic programming

    Page(s): 1241 - 1246
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (747 KB)  

    Quadratic programming offers attractive advantages as an optimisation technique in power-system optimumdispatch problems. A quadratic cost function can be minimised, subject to constraints linearised through sensitivity coefficients. If, however, there is a spinning-reserve requirement, the spinning-reserve characteristics of the individual generators cannot be effectively linearised through the sensitivity coefficients. To solve this problem, a technique known as quadratic-approximation programming is used. Limits on the transmission-line current are also incorporated in the algorithm. It is shown that the minimum-cost dispatch problem, subject to a specified spinning reserve and the maximum-spinning-reserve problem, can be easily solved with moderate computing-time requirements. View full abstract»

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  • Calculation of wind loadings on components of overhead lines

    Page(s): 1247 - 1252
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (978 KB)  

    The paper describes a procedure for the calculation of wind forces on components of overhead lines. The nature of the terrain in which the line is situated affects the properties of the atmospheric wind incident on the line. The effects of these changes in wind properties on the loading on the components of the line are discussed. Although the method is based on a statistical approach, the calculation procedure has been considerably simplified by presenting the results in terms of coefficients which depend on the type of terrain and the parameters of the line. These coefficients are presented in graphical form. Whenever possible, the effects of parameters which are of secondary importance have been simplified. View full abstract»

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  • Developments in UK cable-installation techniques to take account of environmental thermal resistivities

    Page(s): 1253 - 1259
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1087 KB)  

    Accounts are given of the authoritative and novel recommendations concerning the current ratings of distribution cables which were promulgated by the ERA in 1969, and of the manner in which long-established rating and installation practices for transmission cables were transformed during the period 1962¿1968. The second of those two accounts is preceded by a description of the evolution, composition and characteristics of the special backfills introduced during that period, provision of which is now obligatory for all buried CEGB transmission circuits. Attention is drawn to the dearth of information on the extent to which the latest ERA recommendations are being implemented; it is suggested that consideration should now be given to the possibility of wider application of some techniques now peculiar to one or other of the two main fields. View full abstract»

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  • Model for radio interference produced by corona pulses on a. c. lines

    Page(s): 1260 - 1264
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    A model is proposed for radio interference produced by pulsed corona on a.c. lines. This model uses pulse shapes which agree with experimental observations, and it incroporates the timing information forced on the corona by a sinusoidally varying voltage. For applied voltages ranging from the onset Voltage to a level just below the spark voltage, predictions are given of the mean corona current and the spectral density. The effect of the alternating line voltage on the spectral density is indicated through an example. View full abstract»

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  • Predetermination of generated voltage in heteropolar inductor alternators

    Page(s): 1265 - 1272
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    When the slotted surfaces of the stator and rotor of a heteropolar inductor alternator occupy different relative positions during rotation, several airgap configurations are obtained depending on the stator/rotor slot ratio and the toothwidth/slot-pitch ratios in both stator and rotor. These configurations are classified in seven basic positions and are analysed by conformal mapping to give expressions for specific permeance at different instants of travel of the rotor. The results are used to determine the steady-state flux linkages and induced voltages in the a.c. phase coils. A simpler analysis of the airgap permeance is also given neglecting fringing of flux and classifying the airgap configurations into four basic positions. This leads to analytical expressions for the generated voltage. Two inductor alternators were constructed with different slot ratios and coil pitches, and the oscillograms of their generated voltages are compared with predicted waveforms. View full abstract»

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  • Analytical methods for invertor-fed induction motors

    Page(s): 1273 - 1274
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (205 KB)  

    Invertor voltage waveforms for variable-frequency inductionmotor drives are frequently of a discontinuous form. One approach to steady-state analysis is to approximate periodic waveforms by a truncated Fourier series. As a less restrictive alternative, suitable for those commonly occurring cases where the piece-wise continuous sections can be described either as constant or portions of sine waves, relatively simple matrix methods yielding `exact¿ solutions are developed. These provide solutions for waveforms of all winding currents and torque, both for steady state and certain transients such as voltage disturbance types. For illustration, some computed and experimental results are compared. View full abstract»

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  • Effect of mechanical contact force on withstand voltage of copper-bismuth and CLR vacuum interrupters

    Page(s): 1275 - 1278
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (525 KB)  

    The d.c. breakdown voltages of two commercial vacuum interrupters, having different electrode materials, is measured prior to and following axial compression of the contacts in a hydraulic press. In one switch, the contacts are fabricated of copper-bismuth alloy and the other of a propriety material known as CLR. It has been found that the compression of the contacts results in reducing the withstand direct voltage (deconditioning) of the open contacts in both interrupters. After a few compression cycles, the deconditioning effect diminishes and almost disappears for the Cu-Bi contacts. The CLR switch shows some tendency to cold welding of the contacts. However, the welds are easily broken and after a few compression cycles the deconditioning is smaller compared with, for example, the deconditioning due to high current arcing. The d.c. and a.c. breakdown voltages of vacuum gaps can be made to have almost the same values after spark conditioning of both electrodes with alternating voltage. View full abstract»

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  • New sinusoidal pulsewidth-modulated invertor

    Page(s): 1279 - 1285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (878 KB)  

    Sinusoidal p.w.m. invertors depend intrinsically for their operation on quite complex modulation processes. An in-depth study of these modulation processes is presented and the sources of possible operational problems are identified. These problems are shown to be manifest in low-frequency harmonic distortion and the possible existence of subharmonics at noninteger frequency ratios, particularly at low-frequency ratios. These problems restrict the viable invertor-output frequency range. A new method of control is presented which overcomes these problems and allows the possibility of low-frequency-ratio operation, resulting in significantly wider invertor-output frequency ranges. An analytic comparison of both the existing and new methods of control is presented, using a 3-dimensional modulation-model approach. The results of this analysis provide the system designer with generalised frequency-spectra characteristics for any particular frequency ratio and modulation depth by direct inspection. View full abstract»

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  • Prediction of performance of synchronous-generator/transformer/ bridge-convertor installations

    Page(s): 1286 - 1288
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (261 KB)  

    The paper outlines a technique for the digital-computer analysis of synchronous-generator/transformer/bridge-convertor installations. The solution is based on Kron's method of tensor analysis of networks, and is shown to produce results in close agreement with experimental measurements. View full abstract»

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  • Generalised short-circuit characteristics for h.r.c. fuses

    Page(s): 1289 - 1294
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (539 KB)  

    The short-circuit performance of fuses is analysed using simple models to represent prearcing and arcing behaviour. The analysis is developed for both d.c. and a.c. source-circuit conditions, and the resulting equations are normalised by the introduction of a unified per-unit system. From these normalised equations a comprehensive set of generalised fuse characteristics has been prepared. These characteristics can be used for many purposes in fuse design, testing and application, and some examples of their use are given. 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.

Full Aims & Scope