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1887

Proceedings of the Institution of Electrical Engineers

Volume 117, Issue 6, June 1970

Volumes & issues:

Volume 117, Issue 6

June 1970

Solid-state subnanosecond light switch
  • Author(s): J.M. Ley ; T.M. Christmas ; C.G. Wildey
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1057 –1062
  • DOI:  10.1049/piee.1970.0206
  • Type: Article
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  • p. 1057 –1062 (6)
    The design and realisation of a reliable and simple subnanosecond electro-optic light switch is given. This switch is suitable for controlling a mode-locked laser, or for use as a light shutter where nanosecond or subnanosecond response is necessary. The direct-current and pulse responses of the longitudinal zcut XH2PO4 modulator are considered in detail, and an optimum design established using KD2PO4 with ring electrodes. The pulse-forming network employed incorporates several novel features, to produce an overall jitter time of less than 1 ns for a wavefront of 1–4.3kV and a risetime of 0.65ns.
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New method of synthetising linear digital filters based on convolution integral
  • Author(s): S.S. Haykin  and  R. Carnegie
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1063 –1072
  • DOI:  10.1049/piee.1970.0207
  • Type: Article
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  • p. 1063 –1072 (10)
    A new procedure for realising the cascade and parallel forms of digital filters is presented. The method is based on using a Taylor expansion of the input signal over each sampling interval. The results reported in the paper are largely concerned with the simplest expansion, namely that the input remains constant during the sampling period. The method is shown to be applicable to lowpass and bandpass filters and, with a certain modification (which involves both delay equalisation and frequency doubling), to highpass and bandstop filters too. Another important feature of the method is that the gain at zero frequency is completely independent of the sampling rate. The time-and frequency-domain characteristics of several Butter-worth filters are studied. It is also shown that the so-called impulse-invariant technique of synthetising digital filters can be derived by approximating to the convolution integral in a special manner.
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Autocorrelation threshold-extension f.m. demodulator
  • Author(s): R. Hamer
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1073 –1081
  • DOI:  10.1049/piee.1970.0208
  • Type: Article
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  • p. 1073 –1081 (9)
    A new type of threshold-extension f.m.-signal demodulator containing no feedback loop and no limiters is described. The f.m. signal and a delayed version of it are applied to a homoheterodyne mixer, the difference-frequency output of which is then demodulated by a synchronous-phase detector. The paper describes the basic principle of the demodulator and presents a theoretical analysis of its behaviour. Although the theory has been confirmed in the laboratory, no attempt is made to describe its practical design and measured performance; this will be the subject of a later paper.The new demodulator—termed ‘autocorrelation’ because the signal processing is analogous to deriving the autocorrelation function of the signal—offers some significant advantages in f.m. radio links. It should enable greater threshold extension to be achieved in satellite links, especially when channel signal/noise ratios of 30dB or less are acceptable. Moreover, the fact that no feedback loop is required should prove attractive in applications where baseband frequencies extend to many megahertz.
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Transient response of Legendre filters
  • Author(s): Sheila Prasad ; L.G. Stolarczyk ; J.R. Jackson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1082 –1083
  • DOI:  10.1049/piee.1970.0209
  • Type: Article
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  • p. 1082 –1083 (2)
    The object of the paper is an examination of the lowpass and highpass step and impulse responses of filters using the Legendre polynomial approximation. As in previous papers, the response data are presented in tabular and graphical form for Legendre filters of order n = 1, 2, …, 9, for passband tolerances of 0.5, 1, 2 and 3 dB. The salient features of the transient response of the Legendre filters are discussed and compared, in a general manner, to the corresponding transient response of the Chebyshev filters. Tables and figures not included in the summary are given in the complete paper.
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Simple method of analysing arrays of thin cylindrical dipoles
Theoretical efficiencies of class-D power amplifiers
  • Author(s): J.D. Martin
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1089 –1090
  • DOI:  10.1049/piee.1970.0211
  • Type: Article
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  • p. 1089 –1090 (2)
    The theoretical efficiencies of class-D amplifiers are compared with those of conventional amplifiers by means of a power balance. As a result of certain similarities, it is suggested that class-AD and class-BD modes of operation should be defined. The class-D amplifier converts the collector dissipation of a conventional amplifier into load power components at a large number of modulation frequencies. When these are removed by filtering, a high overall efficiency results. The analysis presented includes an idealised treatment of the class-D amplifier with an inductive load, and enables constructive comparisons to be made.
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Discussion on “Basis for mathematical theory of direction-defining radio beacons”
Computer study of ion-trapping instability in microwave tubes
  • Author(s): H.L. Hartnagel ; V.C.L. Hutson ; P.C. Kendall
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1093 –1097
  • DOI:  10.1049/piee.1970.0213
  • Type: Article
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  • p. 1093 –1097 (5)
    Microwave tubes are known to exhibit low-frequency instabilities due to ion bunching. These instabilities are treated theoretically for an idealised model in two dimensions. The problem is rendered soluble by using supersized charge carriers whose equations of motion are formulated exactly by using complex variable techniques. These equations of motion are integrated numerically to obtain a complete solution of the idealised problem. The results agree with earlier experimental work and support strongly the qualitative theory of the instability. The computations enable one to predict ways of preventing its occurrence.
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Small-hole coupling of resonant cavities and waveguides
Rack-and-pinion motors: hybrid of linear and rotary machines
  • Author(s): E.R. Laithwaite  and  M.T. Hardy
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1105 –1112
  • DOI:  10.1049/piee.1970.0215
  • Type: Article
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  • p. 1105 –1112 (8)
    The field over an open-sided linear motor contains a rotating component which can be used to spin rotors of a variety of types. If the field of the linear motor is visualised as a magnetic ‘river’, the motion is analogous to a mechanical rack and pinion. The paper concentrates on reluctance- and hysteresis-type rotors which can develop substantial torque in small sizes. It is shown that the possible acceleration of steel rotors increases with decrease in size. The effect of linear-motor fields on iron and steel filings is investigated and a demonstration of rack-and-pinion action using a permanent magnet is described.
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Low-speed brushless alternating-current motor
  • Author(s): E.R. Laithwaite  and  D.R. Turner
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1113 –1117
  • DOI:  10.1049/piee.1970.0216
  • Type: Article
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  • p. 1113 –1117 (5)
    Following the discovery that a steel rod can be made to roll along the surface of a linear induction motor in the same direction as that of the travelling magnetic field, the phenomenon was investigated with a view to the development of a low-speed high-torque brushless a.c. motor. It was found that the torque was increased when the rod rolled at an angle to the direction of the field. The paper describes the development of a rotor motor using these principles in which the stator winding is conventional, except that the slots are very heavily skewed to make use of the angled-field effect. Some initial theoretical calculations are included.
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Developments in amplitude-comparator techniques for distance relays
  • Author(s): H.P. Khincha ; K. Parthasarathy ; B.S. Ashok Kumar
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1118 –1124
  • DOI:  10.1049/piee.1970.0217
  • Type: Article
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  • p. 1118 –1124 (7)
    The paper reports the development of new amplitude-comparator techniques which allow the instantaneous comparison of the amplitude of the signals derived from primary line quantities. These techniques are used to derive a variety of impedance characteristics. The merits of the new relaying system are: the simple mode of the relay circuitry, the derivation of closed polar characteristics (i.e. quadrilateral) by a single measuring gate and sharp discontinuities in the polar characteristics. Design principles and circuit models in their schematic form are described and, in addition, a comprehensive theoretical basis for comparison is also presented. Dynamic test results are presented for a quadrilateral characteristic of potentially general application.
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Discussion on “Surge-transference characteristics of generator-transformer installations” and “Surge transfer through transformer-generator units”
Calculation of machine end-winding inductances with special reference to turbogenerators
  • Author(s): P.J. Lawrenson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1129 –1134
  • DOI:  10.1049/piee.1970.0219
  • Type: Article
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  • p. 1129 –1134 (6)
    A simple numerical procedure for the determination of the self and mutual inductances of coils of arbitrary shape is presented. The basic method involves the use of a digital computer and is capable of yielding results of very high accuracy. For application to machine end windings, the influences of the various permeable and/or eddy-current-carrying boundaries near the end coils (i.e. core end, coil-retaining ring, casing) are treated approximately (although it is believed entirely adequately) by employing the method of images. For the particular example of turbogenerator involute coils, the numerical procedure for the determination of self inductance is used to establish a simple equation which reduces routine design calculations to trivial manual ones. The equation allows for the true shape and the cross-section of the coils. The evaluation of mutual inductance between stator coils is reduced to the use of a single curve. The mutual inductance with the rotor is estimated. The numerical results presented permit good estimates, for general use, of the magnitudes of the various boundary influences on the inductances and of the variation in inductance between steady-state and transient conditions. Large differences between inductances under steady-state and transient conditions are found to occur, and the small value of the latter is emphasised.
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Discussion on “Thyristor control of a multiload system with d.c. supply”
Asynchronous tests for D and Qaxis subtransient time constants
  • Author(s): V.J. Gosbell  and  F.J. Evans
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1137 –1142
  • DOI:  10.1049/piee.1970.0221
  • Type: Article
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  • p. 1137 –1142 (6)
    The paper draws attention to difficulties in measuring the subtransient time constants, which are relatively fast in machines with rated outputs of the order of tens to hundreds of kilowatts. The frequency-response approaches, consisting of asynchronous tests with field open- and also short-circuited, are proposed as the most suitable test methods, and corrections for resistance effects are developed. A new experimental technique is used to separate the D and Q axis quantities in these asynchronous tests. The Park transformation is performed by physical means, using two 3-phase shaft-driven tachometers and Hall-effect (or quarter-square) multipliers. This results in generated voltages proportional to the hypothetical D and Q axis voltages and currents in the machine. From an ultraviolet-recorder output, one can then obtain the D and Q axis operational admittances or impedances. A curious anomaly in the measured operational impedances in the vicinity of 50% slip is explored, and is shown to be due to crosscoupling between the D and Qaxes through the stator resistance. In small machines, this effect is experimentally evident over a much wider range of slips than might be expected. It is inferred that this effect should also be present in even the largest machines provided that the stator resistance is not identically zero, although it would be evident over a much smaller range of slip. The effect depends on rotor asymmetry, either electric or magnetic, and is related to the Görges phenomenon.
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Effect of harmonics on hunting of synchronous machines
  • Author(s): K.C. Rajaraman  and  G.W. Carter
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1143 –1150
  • DOI:  10.1049/piee.1970.0222
  • Type: Article
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  • p. 1143 –1150 (8)
    Existing analyses of small oscillations in synchronous machines are based on the 2-axis theory, which assumes an ‘ideal’ machine defined by Park and Kron. Real machines, however, have been shown to depart considerably from the Park-Kron definition in that windings produce m.m.f. harmonics in addition to the fundamental, and air-gap permeance harmonics higher than the second are significant. The effects of such a departure on the hunting behaviour of a synchronous machine are studied in the paper. The electromechanical performance equations of free hunting are derived in the holonomic frame, with the significant harmonics taken into account. The frequency of oscillation, and hence the decrement, are obtained by solving the equations numerically on a digital computer. They are also calculated by the 2-axis theory, and the two sets of results are compared with experimental observations on a small synchronous motor. It is found that, for 3-wire star connection of the armature, the 2-axis theory gives correct results; but, in 4-wire star and delta connections, it can lead to appreciable error if the harmonic effects are pronounced. In the latter cases, the analysis presented can be used to predict the hunting behaviour more accurately.
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Economic comparisons in planning for electricity supply
Losses in roebel bars: reactance of slot portion to circulating currents between the conductor stacks
Transfer-function matrix approach to observer design
Transient response of Euler-Cauchy-type time-varying nonlinear systems using multidimensional Mellin transforms
Optimum solution of model-reduction problem
Numerical solution of 2nd-order hyperbolic partial differential equations by the method of continuous characteristics
  • Author(s): R.J.A. Paul  and  A.I.S. Ahmad
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1166 –1174
  • DOI:  10.1049/piee.1970.0228
  • Type: Article
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  • p. 1166 –1174 (9)
    The paper is concerned with two possible numerical variations based on the use of characteristics, and the results obtained provide a basis for comparison with an analogue method described in another paper. The more common approach of differencing along both sets of characteristics and solving at the characteristic-grid points is compared with the alternative approach of numerically solving the ordinary differential equations arising from the analogue approach. Digital-computer solutions, based on these two alternative methods, are obtained for three typical hyperbolic equations. The results give some indication of the significant advantage to be gained by the latter method over the characteristic-grid method, while retaining the advantage of convergence of the grid method. These advantages are of special interest in approximate modelling of distributed-parameter systems involved in the application of control methods.
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Analogue solution of 2nd-order hyperbolic partial differential equations by method of continuous characteristics
  • Author(s): R.J.A. Paul  and  A.I.S. Ahmad
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1175 –1184
  • DOI:  10.1049/piee.1970.0229
  • Type: Article
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  • p. 1175 –1184 (10)
    Hybrid methods based on the method of characteristics are developed for the solution of three different forms of hyperbolic differential equations. The techniques developed extend the early work of Hartree. It is shown that linear equations may be solved by a conventional analogue machine with iterative logic. Nonlinear problems require, in addition, the use of generalised integrators. Solutions obtained are compared with digital-computer solutions, and indicate thesignificant advantage of the hybrid machine in respect of computing time. The technique described provides a rapid method for modelling distributed-parameter systems which is of particular relevance to online-control applications.
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The sixtieth Kelvin Lecture. The pursuit of measurement
Engineering and the UK Science Research Council
Fringing field of finite parallel-plate capacitors
  • Author(s): K.P.P. Pillai
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 6, p. 1201 –1204
  • DOI:  10.1049/piee.1970.0232
  • Type: Article
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  • p. 1201 –1204 (4)
    The effect of finite plate width on the fringing field of a parallel-plate capacitor is determined, and an exact expression is derived for the total capacitance by applying conformal transformation to a finite parallel-plate configuration. With small values of the plate-width/plate-separation ratio, finiteness of plate width is shown to have a predominant effect on the correction factor for capacitance as well as on the fringing field. The analysis is extended to shielded parallel plates and expressions are derived for capacitance and field distribution as functions of shield separation, plate width and plate separation. The effect of shielding on capacitance and fringing field is determined.
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