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1887

Proceedings of the Institution of Electrical Engineers

Volume 124, Issue 2, February 1977

Volumes & issues:

Volume 124, Issue 2

February 1977

Test-point condensation in the diagnosis of digital circuits
Mobile radio propagation in British cities at frequencies in the v.h.f. and u.h.f. bands
  • Author(s): K. Allsebrook  and  J.D. Parsons
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 95 –102
  • DOI:  10.1049/piee.1977.0016
  • Type: Article
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  • p. 95 –102 (8)
    Measurements of the received signal envelope magnitude have been made in three British cities at frequencies of 85.875, 167.2 and 441.025 MHz. In all cases unmodulated carrier waves were radiated from aerials atop tall buildings, or prominent terrain features, and detected using a vehicle-mounted receiver. These measurements have provided the basis for an analysis of the factors affecting the transmission loss in urban/suburban areas which, in turn, has enabled a propagation prediction model to be constructed. Close agreement between measured and predicted path losses has been found for the various terrains investigated. The statistical prediction errors produced by the proposed model for the three British cities analysed are shown to be similar in magnitude to those obtained using an extrapolation of the Okumura method. Because the proposed model is much less complex and procedurally simpler, it is recommended for use, in the first instance, in British cities.
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Signal transfer and degradation in surface-channel charge-coupled devices
  • Author(s): R.M. Barsan
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 103 –108
  • DOI:  10.1049/piee.1977.0017
  • Type: Article
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  • p. 103 –108 (6)
    The properties of surface-channel charge-coupled shift registers are analysed taking into account all four mechanisms involved in the transfer of charge, namely thermal diffusion, charge gradient-induced drift, fringing-field drift, and interface state trapping. A nonlinear equation for the simulation of the signal transfer and degradation in charge-coupled shift registers in the presence of interface states is derived. It is shown that under some realistic assumptions, the nonlinear properties of both 2-phase and 3-phase devices are governed by the same equation. The theoretical results are used to investigate, by computer simulation, the input/output properties of digital registers. Among the discussed results, special emphasis is placed on worst case output signals. Small-signal and large-signal degradation parameters are also discussed and numerical results are presented.
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Effects of field-dependent mobility on transfer efficiency in m.o.s. b.b.d. analogue delay lines
Amplitude fluctuation of underwater signals and its effect on the bit-error probability of underwater data-transmission systems
  • Author(s): R.S. Andrews  and  L.F. Turner
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 115 –119
  • DOI:  10.1049/piee.1977.0019
  • Type: Article
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  • p. 115 –119 (5)
    Two models are proposed for the probability density function (p.d.f.) of the amplitude fluctuations that arise when short-duration sound pulses are transmitted under shallow-water conditions. The models are derived for the conditions in which the prevailing surface-wind directions are parallel and perpendicular to the line of transmission. The probability density functions obtained from the models are compared with experimentally measured p.d.f.s and are found to be in excellent agreement. The models are then used to predict the bit-error probability in a binary underwater amplitude-shift-keyed (a.s.k) data-transmission system and the results are compared with experimentally measured error probabilities. It is found that the measured error probabilities lie between the values computed using the p.d.f. models and it is conjectured that the proposed models provide approximate upper and lower bounds to the average error probability in a.s.k. underwater data-transmission systems. Finally, the p.d.f. models are used to compute new receiver-operating-characteristic (r.o.c.) curves.
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Erratum: Survey of measurements of attenuation by rain and other hydrometeors
Analysis of fields and inductances in air-cored and iron-cored synchronous machines
  • Author(s): A. Hughes  and  T.J.E. Miller
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 121 –126
  • DOI:  10.1049/piee.1977.0021
  • Type: Article
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  • p. 121 –126 (6)
    A consequence of the projected trend in turbine-generator design towards large airgaps, airgap windings without slots, and superconducting windings, is a progressive change in the nature of the machine from ‘iron-cored’ to ‘air-cored’. A general analysis of fields and winding inductances that is applicable to all configurations is presented. The underlying unity of the various types is brought out, and particular attention is given to a comparison of the conventional design and the fully air-cored (superconducting) machine. In a companion paper the comparative design and performance analysis of air-cored and iron-cored synchronous machines is discussed.
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Comparative design and performance analysis of air-cored and iron-cored synchronous machines
  • Author(s): T.J.E. Miller  and  A. Hughes
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 127 –132
  • DOI:  10.1049/piee.1977.0022
  • Type: Article
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  • p. 127 –132 (6)
    A consequence of the projected trend in turbine-generator design towards larger airgaps, airgap windings without slots, and superconducting windings, is a progressive change in the nature of the machine from ‘iron-cored’ to ‘air-cored’.A simple analysis is presented which enables the main design and performance paramaters of both types of machine to be calculated and compared. A design philosophy for air-cored machines is outlined, and a number of favourable and adverse design features are revealed. In a companion paper the analysis of fields and inductances in air-cored and iron-cored synchronous machines is discussed.
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Laplace analysis and computer simulation of transient current in power transmission lines
  • Author(s): D. Khuong Tran
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 133 –136
  • DOI:  10.1049/piee.1977.0023
  • Type: Article
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  • p. 133 –136 (4)
    A systematic Laplace method is presented for the determination of transient-current propagation in a single transmission line. Earth distortion and skin effects are considered in the analysis. The method permits a quick and accurate evaluation of these currents without using numerical-integration techniques. From the theoretical study, an efficient method of digital simulation is also derived for a simpler current evaluation in computers. Both analytical and simulation expressions are in terms of line and earth parameters, which enables an easy computation of transient current propagation in different transmission lines to be carried out. Results are in good agreement with those obtained by other investigations. Part 1 of the paper deals with a basic single line which would represent either an a.c. or a d.c. scheme. Part 2 of the paper deals with polyphase systems with lossy earth returns (see p. 137).
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Laplace analysis and computer simulation of transient current in power transmission lines Pt, 2-Polyphase systems with lossy earth return
  • Author(s): D. Khuong Tran  and  Due Phi
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 137 –140
  • DOI:  10.1049/piee.1977.0024
  • Type: Article
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  • p. 137 –140 (4)
    In this study, an operational Laplace method is presented for analysing current propagation in 3-phase lines. Basic results obtained in Part 1(see p. 133)are systematically extended to polyphase-line investigations. Modified operational Laplace impedances are used and results can be carried out by a direct use of Laplace transforms and matrix theory. An efficient simulation method is also presented, which permits an easier computation of current surges in computers. Earth distortion and skin effects of conductors are included in the study. Analytical and simulation expressions are in terms of line and earth parameters. Therefore they make easy numerical computations of currents of different lines. Other advantages mentioned in Part 1 of the paper are also found in Part 2 of the paper, e.g. no numerical integration is needed.
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Distance protection performance during simultaneous faults
  • Author(s): V. Cook
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 141 –146
  • DOI:  10.1049/piee.1977.0025
  • Type: Article
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  • p. 141 –146 (6)
    The paper considers the performance of both unswitched and switched distance protection schemes using polarised-mho relays on systems subjected to simultaneous faults. The disturbances considered are flashoverfaults to earth, cross-country earth faults and open-conductor plus earth faults on a double-circuit 132 kV transmission system. Consideration is also given to protection performance for double earth faults separatedby a star-delta transformer. Differences in protection philosophies of British and Continental relay manufacturers are highlighted and a comparison is given for switched schemes employing overcurrent starter units.
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On-site investigation of electrohydraulic governors for water turbines
  • Author(s): G.W. Bryce ; P.W. Agnew ; T.R. Foord ; D.J. Winning ; A.G. Marshal
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 147 –153
  • DOI:  10.1049/piee.1977.0026
  • Type: Article
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  • p. 147 –153 (7)
    Hydroelectric generating sets controlled by conventional, mechanical, temporary-droop governors respond rather slowly to changes in system frequency and do not, therefore, realise their full potential as spinning reserves. Because of this, the electrohydraulic governor system described in this paper was developed for on-site evaluation of control strategies on a 32.5 MW set at Sloy power station, and to complement earlier work on a hybrid simulation of the plant. It is arranged so that it can be used as an alternative to the mechanical governor, and changeover from one to the other can be effected in a few minutes. Frequency-response test data are presented. Also shown are the results of a series of system-splitting tests in each of which a substantial area of West Scotland was supplied by the Sloy set when isolated from the Grid system. An electronic double-derivative governor is shown to improve greatly the response of the generator to frequency changes while at the same time preserving operational stability
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Probabilistic techniques in a.c. load-flow analysis
  • Author(s): R.N. Allan  and  M.R.G Al-Shakarchi
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 154 –160
  • DOI:  10.1049/piee.1977.0027
  • Type: Article
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  • p. 154 –160 (7)
    The paper describes how the previously published formulations for an a.c. probabilistic load-flow analysis can be extended to ensure precise computation of expected values, and how these may be used to obtain more precise values of standard deviations and probability-density curves than was possible thereto. Both of the present formulations linearise the problem around the precise expected value, and one of them accounts for the coupling effect between active and reactive powers. It is shown that this coupling effect may have a significant impact on some of the voltages and reactive powers, but little effect on angles and active powers. A typical system is analysed and discussed to illustrate the increased depth of information that can be gained from these improved techniques.
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Estimation of the states during refining in electric-arc-furnace steelmaking
  • Author(s): F.M. Boland  and  H. Nicholson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 161 –166
  • DOI:  10.1049/piee.1977.0028
  • Type: Article
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  • p. 161 –166 (6)
    The commercial incentives to obtain improved control of the steelmaking process in the electric-arc furnace are presented, and the progress made in applying computer control is reviewed. The development of a mathematical model of the refining process is shown to be restricted by the complex metallurgical nature of the process and the deficiency of existing plant instrumentation. The ability of a mathematical model, evolved from theoretical considerations, to simulate, accurately, a limited class of operating practice is demonstrated. A compromise between complexity and implied certainty of the model is obtained by a reduction in the dimension of the model state vector, and by the introduction of a white-Gaussian-noise process to account for the effect of the ignored states and the hypotheses on which the model is developed. Techniques developed recently for obtaining noisecorrupted measurements of the carbon content and temperature of the process are investigated, and the statistics of the uncertainty of these measurements is determined. The implementation of the extended Kalman filter for online state estimation is considered, and the operation of the filter under varied conditions of uncertainty is discussed. A technique for controlling divergence of the filter algorithm is presented, and the results of simulations indicate that estimates of the states can be obtained to the accuracy required for the design of a refining control strategy.
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Optimal return difference matrix
Improvement and prediction of open-loop starting/stopping rates of stepping motors
Digital point-on-wave switch for investigating motor starting characteristics
Effect of corona on the density of ionisation in a high–voltage laboratory
  • Author(s): N.L. Allen ; T.E. Allibone ; D. Dring
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 174 –178
  • DOI:  10.1049/piee.1977.0032
  • Type: Article
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  • p. 174 –178 (5)
    Ion densities in a closed laboratory due to d.c. corona from an impulse-voltage generator and its charging set have been measured by means of a Gerdien-type aspirator. By comparison with natural ionisation, the densities of ions of the same polarity as the generator charging voltage were increased by two orders of magnitude, but ions of opposite sign were greatly reduced in density. Use of a filtering aspirator yielded information on the densities of ‘large’ ions which were shown to be an important part of the total ionisation occurring under natural and corona conditions. The significance of the results for impulse-voltage testing is briefly discussed.
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Computation of axial and radial development of discharges between plane parallel electrodes
Optical studies of prebreakdown events in liquid dielectrics
  • Author(s): P.B. McGrath  and  J.K. Nelson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 2, p. 183 –187
  • DOI:  10.1049/piee.1977.0034
  • Type: Article
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  • p. 183 –187 (5)
    A combination of time-resolved Schlieren and scattered-light optical techniques has been used to examine the prebreakdown events in dielectric liquids. When a negative high-voltage pulse is applied to the point of a nonuniform gap, a disturbance, associated with discrete shock waves, propagates outwards from the point. For the opposite polarity, the disturbance moves at supersonic velocity, and is characteristically different in appearance and self luminosity. In both cases, the disturbance is identified as a region of closely packed microbubbles which ultimately fragments into isolated bubbles if breakdown does not intervene. The events recorded are explained in terms of cavitation nucleated by transient cavity collapse, and the polarity differences are attributed to field emission. The mechanism is further supported by experimental findings using prestressing techniques.
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Unbalanced a.c. bridges for the measurement of dielectric loss

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