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Electrical Engineers, Proceedings of the Institution of

Issue 5 • Date May 1972

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Displaying Results 1 - 25 of 28
  • Carrier wave in n type gallium arsenide under crossed d.c. electric and magnetic fields

    Page(s): 505 - 511
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (777 KB)  

    Assuming that current-density/electric-field curves are provided and that the Hall mobility does not change appreciably with the electric field, the small-signal tensor conductivity of n-GaAs in the presence of d.c. electric and magnetic fields is derived. Using this tensor conductivity, carrier-wave equations are solved for a long slab of n-GaAs sandwiched between dielectrics. It is found that wave vectors are generally skewed against the direction of the direct current. The gain factor of the propagation coefficient is found to be controllable by the magnetic field, especially when the slab is thin and the d.c. electric field is near the threshold value. View full abstract»

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  • Pseudorandomly dithered quantisation of speech samples in p.c.m. transmission systems

    Page(s): 512 - 518
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (889 KB)  

    The paper reports on an investigation of the application of variable-level quantisation in p.c.m.-type speech-transmission systems. Variable-level (dithered) quantisation systems are compared with normal fixed-level quantisation systems. The systems are compared using intelligibility tests and subjective-appreciation tests, and a statistical analysis of the results is given. The analysis indicates that, in general, normal quantisation is superior to dithered quantisation. View full abstract»

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  • Analysis of hollow elliptical waveguides by polygon approximation

    Page(s): 519 - 522
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Numerical results for elliptical waveguides are usually obtained from the appropriate Mathieu and associated Mathieu functions, but these are expensive to compute, because of slow convergence, and difficult to tabulate. It is shown that results for the cutoff wavelengths can be obtained using simple new formulas relating the ellipse (or circle) to an inscribed polygon. Cutoff wavelengths for the polygon can then be obtained efficiently using an available computer program. In this way, by applying boundary perturbation theory, the accuracy for cutoff wavelength from the original program has been increased by a factor of up to 104. Besides using an extrapolation technique, special advantage is taken of the elliptical shape which allows an `area correction¿ to be applied to the approximating polygonal results. View full abstract»

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  • Characteristics of dielectric-tube-loaded coaxial cables

    Page(s): 523 - 528
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (553 KB)  

    A study of the complete mode spectrum of the dielectric-tube-loaded coaxial cable reveals that only the low-loss slow-wave TM01 mode has no lower cutoff frequency. Mode designations are shown to be consistent with those previously adopted for dielectric waveguides. A numerical optimisation procedure is applied to an accurate perturbation analysis of the dominant mode to determine optimum dielectric-tube radial dimensions for minimum loss. Attenuation reductions as high as 75% of the unloaded values are attainable in certain overmoded cases. For the optimum conditions, the cable is well equalised, and the propagation characteristics are relatively insensitive to small variations in the dimensions of the tube. View full abstract»

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  • Microwave model of an instrument-landing-system glidepath

    Page(s): 529 - 536
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1132 KB)  

    A 1/30th scale model of the international standard instrument-landing-system glidepath is described. Interference effects on the linearity of the path in space are investigated, and a theoretical analysis is applied which confirms the integrity of the model operation. The effects due to aircraft taxying in typical airport regions have been measured using accurate scale models of common civil aircraft. Typical results are presented. View full abstract»

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  • Solution to the approximation problem for a class of 2-variable resonant ladder networks

    Page(s): 537 - 540
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    By using the results on explicit formulas for element values in 1-variable ladder networks dependent on one or two auxiliary parameters, and by using appropriate frequency transformations, certain generalisations may be made to 2-variable networks. For the solution to the approximation problem, which results in an elliptic function or Cheby¿shev response, nonreciprocal 2-variable networks result, but for the matched inverse-Cheby¿shev-response case, a simple 2-variable ladder network is obtained. This case is treated in detail, and typical responses for networks containing lumped and commensurate distributed elements are presented, with a specific example on a waveguide bandstop filter. View full abstract»

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  • Production of transient-current waves with long time constants for test purposes

    Page(s): 541 - 547
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (790 KB)  

    A development in laboratory bench-testing facilities for protective schemes is described. Test benches used at present contain linear inductors which have high X/R ratios so that offset transients associated with power systems may be simulated. However, owing to losses in the test network, these transients cannot be satisfactorily reproduced at large currents. It is shown here that by replacing the make switch in the conventional test bench with two inverse-parallel-connected thyristors, fired at carefully chosen intervals, it is possible to simulate transients on any system with acceptable accuracy. Details of the proposed test circuits are given, and both computed and experimentally obtained results are included to illustrate the negligible nature of the errors introduced. A method using the equipment for fusegear testing is also described. View full abstract»

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  • Remote measurement of phase angle

    Page(s): 548 - 556
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1401 KB)  

    A system is described for the measurement of the phase angle between two voltages separated from each other, and from the point where the results are to be displayed, by a distance of several miles. A correction for the transmission delay of the measurement signals is automatically made, and an accurate knowledge of the transmission-path characteristics is not required. At power frequencies, the measurement accuracy is within a small fraction of one degree. View full abstract»

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  • Minimisation of reactive-power installation in a power system

    Page(s): 557 - 563
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (729 KB)  

    Reactive-power installations at suitable points become necessary in most modern high-voltage networks, to prevent excessive voltage drops at load busbars. In the paper, the minimisation of the total required reactive-power installation is formulated as a nonlinear-programming problem. Based on certain specific features of this problem, a new solution technique, which results in a considerable reduction of computational effort, as compared with general optimisation techniques, is developed. An additional feature of this technique is that it can be used in conjunction with any standard a.c. load-flow program. The technique is applied to a typical network to bring out the advantages of this approach. An extension of this technique for cases where the voltage restrictions have to be satisfied for two or more loading conditions is also presented. View full abstract»

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  • Improvement of current-transformer transient performance

    Page(s): 564 - 568
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    The simplest way of improving protective-current-transformer performance during transients is to make the transformer's magnetising inductance relatively low. This method may diminish transient errors but always increases steady-state errors. If the maximum acceptable transient error is defined, the primary current that may be transformed during the transient within the error limits depends on the transformer's magnetising inductance. For certain values of the magnetising inductance, this current reaches its maximum. It enables an optimisation of the protective current transformer to be made by adjusting both the core cross-section and the airgap length to achieve the desired level of transient accuracy. View full abstract»

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  • Method of determining power-frequency current distribution in cylindrical conductors

    Page(s): 569 - 574
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (718 KB)  

    An approximate, but accurate and conceptually simple, computer-oriented method for determining the distribution of alternating current in cylindrical conductors is presented in the paper. Although general in principle, the method particularly lends itself to the analysis of power-frequency current distribution, i.e. to cases in which the skin effect is not extremely pronounced. The integral equation for current density is solved approximately, by assuming the current density to be in the form of a finite double power series, with unknown complex coefficients, and determining these coefficients by stipulating the integral equation to hold at a sufficient number of points inside the conductor. The numerical results obtained by the present method are in excellent agreement with the available theoretical solution (circular conductors) and with the existing experimental results (rectangular and thin strip conductors). View full abstract»

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  • Calculation of the external thermal resistance of buried cables through conformal transformation

    Page(s): 575 - 586
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1322 KB)  

    The calculation of the outside thermal resistance of a buried cable system related to uniform, nonuniform and temperature-dependent resistivity of soil can be made, if a suitable transformation of the thermal field is automatically drawn and the resistance is computed on the transformed field. A suitable conformal transformation is analysed giving rise to maps of the transformed field. On the maps, the calculation of resistances involves simple operations even when the soil is nonuniform and of temperature-dependent resistivity, provided some approximations are introduced. The errors incurred by such approximations are slight and can be checked, when necessary, by direct computation of the thermal field. The calculation of resistances on the maps can also be carried out by means of automatic design programs. View full abstract»

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  • Analysis of asymmetrical faults in synchronous generators by d-q-0 frame of reference

    Page(s): 587 - 595
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (685 KB)  

    The paper describes the development of a mathematical model in the d-q-0 frame of reference for the analysis of unbalanced operation of synchronous machines. The equations for faults between two phases and between one line and the generator neutral are described. The solution of the equations of the model by digital computer is presented. Initially, the model neglects nonlinearities and subtransients in the synchronous generator. The validity of the method of analysis developed is examined by comparing the computed results with the test results for a 7 MW generator and a 50 MW generator. View full abstract»

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  • IEE Conference Publication 82 (International medium-voltage-earthing practices)

    Save to Project icon | PDF file iconPDF (170 KB)  
    Freely Available from IEEE
  • IEE Conference Publication 83ߝPt. 1 (Metalclad switchgear)

    Save to Project icon | PDF file iconPDF (170 KB)  
    Freely Available from IEEE
  • Measurement of inductance coefficients of saturated synchronous machines

    Page(s): 597 - 602
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    In order to employ a coupled-circuit approach for the accurate prediction of the performance of a synchronous machine, it is necessary to know the winding-inductance variations with the machine currents. The paper describes simple techniques by which these variations can be determined in terms of a resultant direct-axis or equivalent field current, and which thereby enable the complete nonlinear inductance matrix of the machine to be specified in these terms. Some of the inductance variations are derived by correct interpretation of results obtained from conventional ballistic techniques. The remainder are associated with the inaccessible damper windings, and these are derived from the results of a proposed new set of tests. The techniques described were used to obtain the parameters of a 15 kVA alternator, and the results obtained are presented in the paper. View full abstract»

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  • Optimal control of linear time-invariant systems with polynomial-type measurable disturbances

    Page(s): 605 - 611
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (630 KB)  

    The optimal control of a linear time-invariant multivariable system with an integral quadratic index of performance and with measurable polynomial-type disturbances occurring in both the output and state derivative is considered in the paper. It is shown that the optimal control consists of a feedback controller and a feedforward controller. The feedback controller is the same feedback controller obtained when no disturbances are present, and an explicit expression is given for the feedforward controller. Some numerical examples are included to illustrate this optimal-control result. View full abstract»

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  • Estimation of transfer function of continuous system from sampled data

    Page(s): 612 - 614
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (421 KB)  

    The problem of the estimation of the transfer function of a continuous system based on the observation of sampled input and output data is considered. The paper deals mainly with the online determination of the continuous-system transfer function from a linear discrete model obtained from the data. A number of different digital-analogue transformations are considered, and a comparison is made of their suitability for online identification. It is suggested that the bilinear z transformation is the most suitable for a large number of practical situations. View full abstract»

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  • Relationship between Box-Jenkins-Åström control and Kalman linear regulator

    Page(s): 615 - 620
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (691 KB)  

    The Box-Jenkins-Åström minimum-variance control law for univariate linear stochastic systems is summarised. A minimum-expected-quadratic-loss feedback control law for the same system is derived using state-space theory. Subject to conditions sufficient for the control laws to exist, both theories are shown to give the same result in the 1-step-ahead (unit-delay) case. The more general case is discussed. View full abstract»

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  • Real-matrix solutions for the linear optimal regulator

    Page(s): 621 - 624
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (467 KB)  

    Algebraic expressions, containing only real matrices, are derived for the solution of the multivariable-optimal-linear-regulator problem for a constant plant and quadratic performance index. They enable both the time-varying-or constant-feedback gains and the plant state and input variables to be computed at any required instant without the need to integrate the differential equations. View full abstract»

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  • Regions of transient stability for power systems involving saliency using the Popov criterion

    Page(s): 625 - 628
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The Popov criterion has previously been applied to power systems involving round-rotor machines. Here the method is exploited to obtain regions of transient stability for a single-machine system taking into account the effects of saliency. The generalised Popov criterion, which applies to systems with more than one nonlinearity, is used. The resulting regions of stability are shown to approximate closely the exact regions, and those previously obtained using the method of Zubov. 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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