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Electrical Engineers, Proceedings of the Institution of

Issue 8 • Date August 1974

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Displaying Results 1 - 25 of 28
  • Comparisons of category scales employed for opinion rating

    Page(s): 785 - 793
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1328 KB)  

    Comparisons have been made between three category scales that have been used for the laboratory assessment of impaired television pictures. Two of the scales, comprising 5 and 6 grades, respectively, are concerned with assessment of the quality of the picture; the third is a 6-grade scale concerned with assessment of the amount of impairment in the picture. In one group of tests, observers assessed television pictures impaired by an undistorted echo of delay 2 ¿s, and, in another, photographic prints affected by varied amounts of blurring. Various combinations of the scales were used in each group. The 5-grade and 6-grade quality scales gave closely similar results in terms of mean opinion scores, but these results differed from those obtained with the 6-grade impairment scale, which were less critical. Observers preferred the 5-grade quality scale to both of the 6-grade scales. View full abstract»

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  • Numerical comparison of the Green's function and the Waterman and Rayleigh theories of scattering from a cylinder with arbitrary cross-section

    Page(s): 794 - 804
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1236 KB)  

    Until now much has been published of a theoretical nature concerning the validity or invalidity of the Rayleigh and Waterman methods for evaluating the field scattered from isolated perfectly conducting cylinders of arbitrary shape; however, little of conclusive, concrete nature has ensued. In the paper we propose to establish the conditions (if any) under which these methods may be employed with a reasonable degree of confidence in numerical applications. For this purpose, a description is given of one numerical technique appropriate to the Waterman theory, three numerical approaches to the Rayleigh theory and three numerical techniques for the now classical Green's function approach. The numerical results obtained from the latter are compared with those of the Rayleigh and Waterman methods in eighteen test cases covering a variety of cylinder shapes, incident angles and wavelengths. It is shown that the Rayleigh and Waterman methods yield accurate numerical results in all cases in which they lead to satisfactory verification of conservation of energy, and that all attempts fail to extract valid results from the Rayleigh theory in the case of oblique incidence on square and elliptical cylinders. View full abstract»

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  • Approximate method of calculating the radiation pattern of a corner-reflector antenna

    Page(s): 805 - 806
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (214 KB)  

    The known surface currents in a corner reflector having infinite-length sides are used as approximations to the surface currents in a finite corner reflector, to calculate a radiation pattern. It is shown that this approximation results in nearly zero tangential electric field at the surface of the reflectors, so that the assumed surface currents can be expected to be good approximations to actual currents. Experimental and calculated radiation patterns for a particular corner reflector are presented, and show excellent agreement. View full abstract»

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  • Computer-controlled queuing system with switching network

    Page(s): 807 - 812
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    The paper presents a detailed study of a computer-controlled queuing system with a switching network. A generating function for the state probabilities of the system and a necessary and sufficient condition for the existence of statistical equilibrium for the system are derived. Further, a formula for the determination of the waiting-time distribution in the system is obtained by the use of the theory of Markov chains. View full abstract»

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  • Computer peripheral for image data

    Page(s): 813 - 815
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (451 KB)  

    A computer peripheral for the input of grey scale image data is described. Four versatile modes of operation provide flexibility in the collection of data sequentially or at random. A standard t.v. camera with an interlaced raster is used as the image transducer. The composite video signal produced by the camera provides all the information necessary for the peripheral interface circuitry. The peripheral described in the paper enables the collection of four bits of intensity on a 256 × 256 square grid. View full abstract»

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  • Distance-protection comparator with signal-dependent phase-angle criterion

    Page(s): 817 - 825
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1045 KB)  

    Contemporary methods of providing specially shaped relay characteristics, i.e. other than the familiar circular and straight-line types, are assessed, particularly from the point of view of relay performance and complexity. A new method of shaping is established in which the phase-angle criterion of the block-average type of comparator is a function of the primary system quantities and is therefore continuously variable between well defined limits around the characteristic boundary. This method of shaping affords precise design, which is confirmed by comparisons of experimental and theoretical results. The applications described are limited to providing a characteristic with optimum fault coverage but which has increased immunity from extreme balanced system conditions such as heavy loads and power swings. Further applications, to provide characteristics that will accommodate high fault resistances, will be considered in a later paper. View full abstract»

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  • New mathematical model for current transformers

    Page(s): 826 - 828
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (298 KB)  

    For the complete transient analysis of any protective scheme, knowledge of the dynamic behaviour of the current transformer (c.t.) is necessary. Thus, an accurate model to represent the current transformer requires careful consideration. In this paper, a new mathematical model to simulate the exciting circuit is reported. Some of the earlier models used have been discussed, and the advantages of the new model over these have been pointed out. View full abstract»

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  • Fail-safe earth-fault-detection device for battery supplies

    Page(s): 829 - 830
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (282 KB)  

    An electronic method for detecting an earth fault on a fully insulated battery system that fails to safety in the event of supply, component or connection failure, is described. The particular application to battery-driven coal-mine locomotives is discussed, and a device recently built and tested by the authors for this purpose is described in detail. The device is such that intrinsic safety for methane-air mixtures may be achieved, if desired, with flameproof enclosure of a minimal number of components, and in normal operation even a zeroresistance fault to earth on the battery, to which it is connected, cannot cause ignition of hydrogen-oxygen gas mixtures. View full abstract»

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  • Applications of a synchronous-machine circuit model

    Page(s): 831 - 832
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (241 KB)  

    A circuit model of a synchronous machine offers ease of formulation of the state equations and eliminates the need to invert the inductance matrix at every step during a digital simulation. The effects of fast-acting excitation control on the stability of a system are studied as an example and an exact analysis of a system containing two synchronous machines connected through a short transmission line is also given. View full abstract»

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  • Unified control for synchronous-machine stabilisation

    Page(s): 833 - 839
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (545 KB)  

    This paper describes the theory and procedure for the design of a unified control to improve the stability of a synchronous machine whenever a major disturbance occurs. Using a nonlinear state-space model in directphase quantities, a direct-optimisation technique has been used to derive the unified controls that are effective for the most common types of balanced and unbalanced faults. Practical considerations such as the relative frequency of occurrence of various faults are taken into account. It is shown that the unified controls give an improved system performance over that obtained with the use of conventional controls. View full abstract»

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  • Transformer multiflow hottest-spot rating: proposed standard specification

    Page(s): 840 - 844
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (601 KB)  

    The present practice in thermal rating is reviewed with recognition of its defects and limitations, of which the most serious is its inability to relate the standard rating with the hottest-spot temperature (h.s.t.). Modern improvements in cooling reduce the h.s.t., but are circumscribed by these limitations. The multiflow principle allows the h.s.t. to be determined for each individual winding from the present standard temperature-rise test measurements. It is anomalous that forced-oil cooling¿a standard rating for many years-has never been defined. It is quite legitimate to install such a small oil pump that the term has no real significance. The proposed international recognition of directed flow is neither justified nor desirable. Increased and directed flow are alternatives, and must both be recognised. In natural cooling, small distribution transformers are underrated and large ones are overrated. The h.s.t. multiflow rating removes all these anomalies, and leads to a draft revision of the present UK national standard rating for both natural and forced cooling. The proposed new rating can be determined as simply as the present standard rating but with the full benefit of the hottest-spot temperature limit controlling the thermal life of the insulation, and hence of the transformer itself. This benefit applies not only to the guaranteed rating but is available also for other service loading conditions of concern to the user. These sometimes bear little relation to the standard, but widen the practical field of application View full abstract»

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  • Effects of mechanical and aerodynamic damping on the galloping of overhead lines

    Page(s): 845 - 848
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    This paper examines theoretically the effects that mechanical and aerodynamic (drag) dampers can have on the amplitudes of the bulk galloping oscillations of overhead lines. The oscillation amplitudes are calculated using an energy-balance method and the results are presented in a way that allows the two types of damper to be compared. It is shown that, for lines with small vertical phase spacings, mechanical dampers should be more effective in reducing oscillation amplitudes. For lines with larger vertical phase spacings, aerodynamic dampers should be better, provided that a sufficiently large fraction of the span length can be fitted with dampers. View full abstract»

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  • Modified form of Newton's method for faster load-flow solutions

    Page(s): 849 - 853
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (573 KB)  

    A modified form of Newton's method for load flow is introduced in this paper. The results tabulated, for eight different power systems, indicate a consistent advantage in using this modification over the standard Newton method. The comparisons are made on systems that include several for which load-flow results were previously published by other authors. View full abstract»

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  • Linear prediction model of speech production with applications to deaf speech training

    Page(s): 865 - 873
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    The linear prediction model of speech production is reviewed and its various formulations are related. Algorithms are presented for efficient fixed-point analysis and synthesis, together with their execution times, on a small computer. The properties of the model are discussed, and the acoustic-tube analogue is developed. This forms the basis of a system currently being used for deaf speech training. The system is described, and results and experience gained from the initial evaluation period are discussed. View full abstract»

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  • Pole assignment by means of unrestricted-rank output feedback

    Page(s): 874 - 878
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    The problem of pole assignment in linear, multivariable systems using an unconstrained-rank feedback matrix is considered. The effect of output feedback of unspecified rank on the characteristic polynomial of a multivariable system is first studied. The results are then used to derive a recursive algorithm for pole assignment without any restrictions on the rank of the output feedback matrix used. The method is based on the pseudoinverse concept for obtaining least-squares solutions of sets of linear equations, and is computationally efficient. View full abstract»

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  • Suboptimal control of linear systems via simplified models of Chidambara

    Page(s): 879 - 882
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (334 KB)  

    A method is developed for using simplified models, developed by Chidambara, for deriving suboptimal controllers to the original higher-order systems. An equivalent performance criterion has been developed, which is to be used in conjunction with the simplified models to derive the suboptimal controllers. The method developed is also useful when some of the state variables are not accessible for measurement and feedback. A numerical example is included to illustrate the procedure. View full abstract»

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  • Synthesis of a class of nonlinear systems in multidimensional frequency domain

    Page(s): 883 - 885
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    The paper presents a method of synthesis for a class of nonlinear systems characterised by Volterra functional series. A canonic form is introduced that permits the system kernels to be realised by a finite number of multipliers and 1st-and 2nd-order linear systems. The method of synthesis is illustrated by synthesising the Volterra kernel of a ring-multiplier circuit. View full abstract»

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  • Three-stage near-optimum design of nonlinear-control processes

    Page(s): 886 - 892
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (705 KB)  

    A systematic near-optimum design technique for the control of nonlinear-control processes is presented. The method consists of three stages. In the first stage, called `subprocess decoupling¿, coupling is neglected between two or more subsystems, thus reducing the process to a set of weakly coupled subprocesses. The second stage is to represent each subprocess by `slow¿, `basic¿ and `fast¿ models, and is called `time-scale decoupling¿. The third stage eliminates slow and fast variables, and obtains a near-optimum control for the basic subsystem. The method is applied to a coiler process common in continuous rolling mills. View full abstract»

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  • Online computer control of an evaporation process

    Page(s): 893 - 898
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (827 KB)  

    The paper describes the application of single-input/single-output discrete linear-control theory to control the evaporation of various dielectric material in a vacuum chamber. The process is modelled using a recursive least-squares method and a controller is designed from the model. Process nonlinearity is shown to inhibit the performance of linear feedback control. A compensation is introduced to overcome this difficulty, and an effective final control design is achieved. 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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