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1887

Proceedings of the Institution of Electrical Engineers

Volume 119, Issue 2, February 1972

Volumes & issues:

Volume 119, Issue 2

February 1972

Accurate measurement of the electrical length of long coaxial radio-frequency cables
Acoustic-surface-wave amplitude and phase measurements using laser probes
IEE Western Electronics & Control Section: Chairman's address. Recent developments in radiocommunication
New method of interference rejection in fast analogue-digital convertors
  • Author(s): D. Velašević
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 127 –132
  • DOI:  10.1049/piee.1972.0023
  • Type: Article
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  • p. 127 –132 (6)
    A new method of solving the problem of interference rejection in high-speed analogue-digital (a.d.) convertors is given. The measurement speed obtained in such a way in multichannel data-acquisition systems is much higher (up to two orders of magnitude) than that obtained with filters and integrating a.d. convertors which have the same rejection of line frequency. Different solutions of interference rejection, based on the same method, are presented. A time interval of only 20 ms is required to achieve line-frequency suppression higher than 50 dB, so that the fast a.d. convertors could replace the integrating ones. The method proposed is especially suitable for application in online computer systems.
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Design of asynchronous multilevel sequential circuits
Second-order-difference integrator. Design base for realising high-resolution digital differential analysers
Distortion effects in a switching-diode modulator with tuned terminations
  • Author(s): A.M. Yousif  and  J.G. Gardiner
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 143 –148
  • DOI:  10.1049/piee.1972.0026
  • Type: Article
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  • p. 143 –148 (6)
    Analysis previously developed for the prediction of distortion outputs in broadband switching-diode mixers and modulators handling multifrequency inputs is modified to include the effects produced by tuning both source and load terminations. The compensation theorem is invoked to replace the sideband tuned circuits by equivalent generators. An important consequence of tuning the modulator terminations is shown to be the appearance of distortion products absent from the output spectra of the broadband-terminated circuits. Good agreement is demonstrated between theoretical predictions and the measured outputs from typical series and shunt modulators operating at high frequency.
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Power regulation by means of a switched capacitor
Synthesis of a network containing a cascade of commensurate transmission lines and lumped elements
  • Author(s): M. Uruski  and  M.S. Piekarski
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 153 –159
  • DOI:  10.1049/piee.1972.0028
  • Type: Article
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  • p. 153 –159 (7)
    Simple necessary and sufficient conditions are presented under which a 2-variable admittance function may be realised as a cascade of commensurate lossless transmission lines with several lumped shunt capacitors located at specified positions at the junctions of adjacent lines and terminated in a positive resistance. Two types of networks are considered. The first consists of equal-delay transmission lines, the second contains not necessarily equal-delay but commensurate-delay transmission lines. The main results are obtained on the basis of Trudi's theory of bigradient arrays.
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V.L.F. propagation parameters derived from observations of sunrise and sunset phenomena
Erratum: Theory of cylindrical antennas with arbitrary impedance loading
SNAP: symbolic-network-analysis program
Radio-frequency defocusing of electron beams
  • Author(s): B. Minakovic
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 161 –165
  • DOI:  10.1049/piee.1972.0032
  • Type: Article
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  • p. 161 –165 (5)
    At medium relativistic velocities and high r.f. power levels, the defocusing of an electron beam is mainly due to r.f. radial forces, the space charge usually being negligible. Under these conditions, there is no opposing force preventing an electron from crossing the beam axis or coming close to it. In either case, severe scalloping or defocusing is produced. It is shown that the absence of space charge may be compensated for by allowing some axial magnetic flux to cross the cathode. Also, a partially shielded cathode is essential to avoid defocusing due to the phase oscillations or variation in the beam radius at the injection plane.
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IEE Sheffield Sub-Centre: Chairman's address. Development of telephone transmission
IEE Worcestershire Sub-Centre: Chairman's address. Electronic components—past, present and future
Optimal scheduling of hydrothermal systems
IEE West Wales Sub-Centre: Chairman's address. Progress in the uses of electricity in the oil industry
Results of stability tests on an underexcited 120 MW generator
  • Author(s): G. Shackshaft  and  R. Neilson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 175 –188
  • DOI:  10.1049/piee.1972.0037
  • Type: Article
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  • p. 175 –188 (14)
    The paper is primarily a factual account of stability tests carried out by the Central Electricity Generating Board on a 120 MW turbogenerator at Northfleet power station. The tests were carried out with the test generator operating at leading power factors, and the generator was connected to the main body of the system by a high-impedance transmission link to simulate the situation in which a large coastal power station might be required to operate on the CEGB's system. The results of 2-phase-to-earth-fault and 3-phase-fault tests are presented, one of which resulted in instability of the test generator followed by automatic resynchronisation. The perform ance of the auxiliary system during the fault tests is shown, as also is the behaviour of the turbine and governor. Since the tests were done at leading power factors, particular attention is given to the generator parameters in the quadrature axis. Special tests were done to investigate these parameters, and the results of these tests are also given in the paper.
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Development of power supply and supervisory equipment for British Railways 50 Hz a.c. electrification
  • Author(s): A.H. Cole ; H. Roper ; F. Whittaker
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 189 –199
  • DOI:  10.1049/piee.1972.0038
  • Type: Article
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  • p. 189 –199 (11)
    Cost considerations have been a major factor in the developments which have taken place in BR's 50 Hz a.c. electrification since 1960. The first efforts towards cost reduction were directed towards the more economical application of established techniques and included the elimination of brick buildings to house ancillary equipment and the use of switchgear in a steel housing with bare overhead connections to the contact system. Subsequently, the development of the vacuum interrupter was seen to offer prospects for still greater economy in switchgear, and a design of great simplicity has been developed in which the vacuum-interrupter circuit breakers and all ancillaries are housed in one modular enclosure. 144 vacuum-interrupter 25 kV single-pole single-phase circuit breakers are now on order. Advantage has been taken of developments in solid-state devices to develop faster protection for track feeders and to apply a supervisory system of the continuously scanning type in which the wear and tear associated with electromagnetic devices is minimal. The basic principles are given. It continues to be necessary to suppress inductive interference at source and established methods are used. The harmonics generated by the rectifiers on the motive-power units are a matter affecting the power-supply network, and information is given concerning the magnitude of these. A table of costs applicable to the beginning, the middle and the end of the period shows that they have been held down in spite of inflation.
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System design for 50 Hz a.c. electrification
  • Author(s): E. Claxton  and  B. Sandham
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 200 –208
  • DOI:  10.1049/piee.1972.0039
  • Type: Article
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  • p. 200 –208 (9)
    System design, as its name implies, is the design of the electrification system for a particular route or area, and is not directly concerned with equipment design. The paper describes the steps by which the result is achieved, principally train performance, system loading, choice of electricity supplies, correlation with other undertakings and maintenance considerations, as well as the machine aids employed to ease the task of calculation and develop ment. The more precise design of equipment which has evolved over the years requires a more accurate design of the system as the margins are not now available to the same extent to cover unexpected events;further, increas ing economic pressures demand ever keener capital and operating costs. It is indicated how the design leads to the essential report. Reference is also made to likely future developments and procedures which should result in cheaper electrification.
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Behaviour of h.v. d.c. links under unbalanced-a.c.-fault conditions
Steady-state stability of parallel h.v. a.c.-d.c. power-transmission systems
  • Author(s): D.B. Goudie
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 216 –224
  • DOI:  10.1049/piee.1972.0041
  • Type: Article
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  • p. 216 –224 (9)
    A number of authors have shown that appropriate utilisation of the fast controllability of the power flow in d.c. transmission link can significantly damp oscillations in associated a.c. networks. The improved damping has been interpreted to mean that stability will be improved over the whole range of system operation. The results of this study show that the effect on system stability of a d.c.-link reference-current controller depends largely on the system operating point, and a control system which improves stability at one operating point may have a detrimental effect at other system operating conditions. A system consisting of a single machine, feeding over a parallel a.c.-d.c. transmission link into an infinite busbar, is investigated using a mathematical model of the d.c. link which is consistent with the accepted steady-state model of an a.c. system. The effects of various regulators on the stability limits are given.
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Effects of environment on transient thermal performance of underground cables
  • Author(s): B.M. Weedy
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 225 –230
  • DOI:  10.1049/piee.1972.0042
  • Type: Article
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  • p. 225 –230 (6)
    Two forms of cable installation are considered, direct burial and integral cooling. Existing methods for the calculation of transient temperatures in directly buried underground cables with changes in load assume a homogeneous environment of soil. In the present work, the effects of trench backfills of different thermal resistivities from the existing soil are investigated using a numerical method and a computer. The relative effects of the backfill and the soil on the transient temperatures are discussed. For times of up to 100 h after the application of a step function of the load current, the effective thermal resistivity of the cable environment approximates to that of the backfill. Using this value, established analytical techniques to represent the soil may be applied with reasonable accuracy. For times greater than this, the soil becomes increasingly important, and the full 2-dimensional heat-flow approach is necessary. Temperatures in integrally cooled cables are readily calculable, but if, owing to a fault in the cooling system, the water flow ceases, new thermal models must be developed to facilitate the calculation of the subsequent cable-temperature rises. By means of practical experimentation, an approximate but simple representation for this condition, using a thermal network, is obtained, and is used in conjunction with the cable thermal network to compute conductor temperatures.
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Erratum: Sensitivity analysis of d.w.r. synchronous generator
IEE Southern Centre Western Area: Chairman's address. Asynchronous or induction generator
Synchronising performance of reluctance motors
Applications of linear induction motors in industry
Magnetic permeance of identical double slotting
Comparison of alternative skew-effect parameters of cage induction motors
Line calculations for major road-lighting schemes
Erratum: Magnetic permeance of identical double slotting. Deductions from analysis by F.W. Carter
Erratum: Comparison of alternative skew-effect parameters of cage induction motors
Erratum: Economic comparisons in planning for electricity supply
Crosscorrelation identification of linear time-varying processes using pseudorando sequences
  • Author(s): R. Hoffman ; M.M. Gupta ; P.N. Nikiforuk
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 237 –242
  • DOI:  10.1049/piee.1972.0053
  • Type: Article
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  • p. 237 –242 (6)
    The extension of the crosscorrelation technique, using pseudorandom sequences, to the identification of time-varying processes is considered. Two equivalent techniques are proposed which can track the weighting sequence of a time-varying process, provided that the rate of variation is sufficiently smooth. The methods are based on the assumption that the time variation of each term of the weighting sequence can be described over a period of at least im + 1 times the process settling time by the im terms of a Taylor-series expansion. The periodicity of the input is essential to the methods proposed. Digital-computer results are presented to show the effectiveness of the proposed methods.
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Computer-program description. Root-locus plotting by digital computer using operational-array technique
  • Author(s): F.L. N-Nagy  and  M.N. Al-Tikriti
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 243 –246
  • DOI:  10.1049/piee.1972.0054
  • Type: Article
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  • p. 243 –246 (4)
    The objective of the paper is to present a general program for computation of the root locus of time-invariant systems. The method adopted for root-locus location is to express the characteristic equation in polynomial form for every chosen value of the static-loop sensitivity; the factorisation then gives the location of the poles. In addition, the breakaway points are also individually computed and graphically superimposed on the already computed and plotted root-locus diagrams. The break points are where the locus departs from the real axis or returns to it; hence the terms breakaway and break-in points, respectively. In more general interpretation, the breakpoints are where two or more root-locus branches come into contact anywhere in the complex plane. The interpretation above is wholly implemented in the program.
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Interactive graphics technique for the design of single-input feedback systems
  • Author(s): F. Fallside ; R.V. Patel ; H. Seraji
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 247 –254
  • DOI:  10.1049/piee.1972.0055
  • Type: Article
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  • p. 247 –254 (8)
    The design technique is applicable to a large class of linear systems described by state equations or cascaded transfer functions. It is based on closed-loop pole assignment which the designer performs by moving the system poles by means of the light pen. The program (SISD) calculates and displays the required feedback coefficients and then a variety of responses, transient and frequency, and further options can be displayed to allow the system performance to be assessed and modified if required. Computation times are very short, of the order of a few seconds, allowing truly interactive design. The technique is fairly general, allowing the use of complete or incomplete state or output feedback. Two illustrative examples are given.
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Condition for structural monotonic instability of interacting linear multivariable control systems with integrating controllers
Design of optimal constant-output feedback controllers for asynchronous machine
Near-optimal control of discrete-time nonlinear stochastic systems
Application of 3-port coaxial junction to r.f.-immittance standardisation and measurements
  • Author(s): D. Woods
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 261 –268
  • DOI:  10.1049/piee.1972.0059
  • Type: Article
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  • p. 261 –268 (8)
    The calibration of immittance bridges and reflection-coefficient meters over the complete radio-frequency spectrum requires a wide range of fixed standards of complex immittances or reflection coefficients. This can be accomplished with a relatively small number of fixed standards by connecting them in series or parallel and computing the value of the composite standard. The series connection is readily achieved by using precision coaxial connectors which form an integral part of the standards, and has already been described in a previous paper. Parallel connection, however, requires a multiport coaxial junction, the parameters of which enter into the immittance characteristic of the composite standard. The symmetrical 3-port coaxial junction is analysed, and it is found that the most convenient method of characterising it at the highest level of standardisation is in terms of scattering parameters normalised to its complex characteristic impedance. The low-frequency scattering matrix, comprising real numbers only, is evaluated in terms of d.c. concepts. It is then shown that the general matrix applicable at all frequencies is given by multiplying the d.c. matrix by e−2(α+jβ)1, where 1 is the length of each arm. Formulas are given for the input reflection coefficient of one arm of the junction in terms of the reflection coefficients of the fixed standards connected to the remaining two ports. Various techniques are discussed for evaluating the scattering parameters of the junction to an accuracy that would not significantly degrade the accuracy of the fixed standards, assumed to be in the order of 0.1%. The technique is considered to be equally as applicable to low frequencies as to microwave frequencies, thus enabling a unified computing program to be employed. Extension of the technique to cascaded 3-port junctions is also considered, whereby more than two fixed standards can be connected in parallel. For less-accurate standardising work, as performed by certain calibration laboratories, it is shown that adequate accuracy can be achieved by adopting a simpler procedure, whereby the scattering parameters of the junction and the reflection coefficients of the standards are all normalised to an ideal real characteristic resistance Rn.
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Erratum: Coaxial 2-port resistor and its application to r.f. measurements and standards
Resistance of large earth-electrode systems
  • Author(s): G.F. Tagg
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 119, Issue 2, p. 269 –272
  • DOI:  10.1049/piee.1972.0061
  • Type: Article
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  • p. 269 –272 (4)
    In three earlier papers by the same author, methods have been suggested for the measurement of the resistance of large earth-electrode systems, which presents certain difficult problems. These methods are all based on certain assumptions, and it may be that, in practice, these assumptions are not fully justified, and so errors may occur. Again, each of these methods has its own advantages and disadvantages, and it is the purpose of this paper to summarise and compare the three methods and to determine the errors which may arise in certain cases where the basic assumptions are not fully justified. It is shown that the three methods can give equally accurate results, but that two of them are more reliable than the third. Also, that some departure from the basic assumptions does not cause serious error.
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IEE East Anglian Centre: Chairman's address. Kilovolts, microamperes and ångstroms
Uniform-field breakdown-voltage measurements in sulphur hexafluoride
Partial-discharge detection between parallel-plate gaps

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