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1887

Proceedings of the Institution of Electrical Engineers

Volume 124, Issue 9, September 1977

Volumes & issues:

Volume 124, Issue 9

September 1977

Subjective effects of d.p.c.m. errors and predictor leak on visual telephone pictures
  • Author(s): J.A. Kitchen ; R.C. Nicol ; J.M. Corbett
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 737 –742
  • DOI:  10.1049/piee.1977.0161
  • Type: Article
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  • p. 737 –742 (6)
    A technique for reducing the visibility of transmission errors in television signals which have been digitally encoded using differential pulse-code modulation(d.p.c.m.) is to weight the predicted value of the signal by a factor less than unity. This prediction ‘leak’ has the effect of reducing the extent of the propagation, and hence the visibility, of transmission errors, but it may also increase the quantising distortion. A closely controlled subjective investigation of this error visibility against quantising distortion trade-off is described. Details of both the equipment and procedure followed are given and a mathematical model is derived to allow the plotting of curves of constant impairment for varying leak factor and error rate. The investigation indicated that for moderate channel error rates, a leak factor of 15/16 is a good compromise between error visibility and quantisation distoration.
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State-space thyristor computer model
  • Author(s): B.W. Williams
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 743 –746
  • DOI:  10.1049/piee.1977.0162
  • Type: Article
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  • p. 743 –746 (4)
    The paper describes a general computer model for a power thyristor that will accurately simulate thyristorstatic and -dynamic characteristics. The state-space equations of the nonlinear model facilitate programmable and controllable gate characteristics, turn on and off time, reverse recovery characteristics, holding and latching current and dv/dt triggering effects. These properties, along with the model derivation, are presented and discussed in relation to a computer simulated impulsed-commutated d.c. chopper; the results of which are in excellent agreement with experimental results.
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IEE North Midland Centre: Chairman's address. Little is beautiful—domestic applications of integrated circuits
Multiport network analysis by matrix renormalisation: extension to four ports
  • Author(s): D. Woods
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 749 –753
  • DOI:  10.1049/piee.1977.0164
  • Type: Article
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  • p. 749 –753 (5)
    Two- and three-port network analysis by scattering renormalisation, the principle of which was described in earlier papers, is extended to the 4-port case by derivation of the 4-port renormalisation transforms. The transforms are completely general and take into account complex normalising impedances that are different for all ports as well as passive and active nonreciprocal networks. As in previous associated papers, scattering parameter definitions are based on the voltage-wave concept with complex normalisation derived directly from classical transmission line theory in which the characteristic impedance and propagation constant are both complex. A few examples of 4-port circuit analysis are given including a rigorous solution of the 4-port directional coupler. The method employed in deriving the transforms is briefly described.
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Active RC filters with zero Q-sensitivity
Near-Field measurements over experimental modified goubau line
Interactive design of electricity networks using spare-capacity reinforcement algorithms
Future of incandescent and tungsten-halogen lamps
  • Author(s): J.R. Coaton  and  J.M. Rees
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 763 –767
  • DOI:  10.1049/piee.1977.0168
  • Type: Article
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  • p. 763 –767 (5)
    Development of the tungsten-halogen lamp has produced a wide range of light sources with a higher luminous efficacy and longer life than conventional incandescent lamps, but ultimate failure is still filament burnout caused by the formation of hot spots. Recent research has been directed towards reviewing other means of securing further improvements and has included alternative materials infrared reflecting coatings and the application of double quantum phosphors. However, the major area of progress has been in the development of tungsten-halogen lamps with a selfhealing regenerative cycle to delay the formation of hot spots. Experimental lamps have already been made that have double the life of established tungsten-halogen counterparts.
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Discussion on “On-site investigation of electrohydraulic governors for water turbines”
Some characteristics of the single-phase travelling-wave machine
  • Author(s): D.B. Watson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 771 –774
  • DOI:  10.1049/piee.1977.0170
  • Type: Article
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  • p. 771 –774 (4)
    A single-phase axial-flux travelling-wave machine is described, which has series connected windings on a doublesided linear stator block, and shunt connected capacitors. When driving an aluminium disc, the force/speed curve is similar to that of a conventional 3-phase linear induction motor. The maximum speed, however, can be changed by changing the shunt capacitance. With a fixed value of shunt capacitance, and when the machine is loaded, there is a contraction in wavelength, i.e. the travelling-wave machine is found to have no fixed synchronous speed. There is also attenuation that increases as the rotor speed falls. The paper includes an analysis based on a simplified model using the current-sheet method.
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Design criteria for pole-changing windings
  • Author(s): K.C. Rajaraman
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 775 –783
  • DOI:  10.1049/piee.1977.0171
  • Type: Article
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  • p. 775 –783 (9)
    A set of rational criteria are identified for assessing the merits of pole-changing windings for cage induction motors, in terms of capacity and performance of the two speed settings. It is shown that a change-pole setting is simply a nonstandard design that differs from the standard design essentially in respect of flux density and winding factor. In terms of these two quantities, relative performance indexes are derived that are pure numerics, with unity for the standard machine. Optimum coil spans are obtained for the familiar 1:2 pole, changing winding. Other criteria are the quality of the winding in terms of balance and m.m.f.harmonics, and the size of the controller. The uses of the main criteria are illustrated by application to some existing designs. Earlier criteria are surveyed and shown to be either incomplete or incorrect. The new criteria form a logical basis on which meaningful comparison can be made, not only between pole. changing machines and standard machines, but also between different designs of two-speed machine for a given pole combination.
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Thyristor and diode controlled variable voltage drives for 3-phase induction motors
  • Author(s): S. Rahman  and  W. Shepherd
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 784 –790
  • DOI:  10.1049/piee.1977.0172
  • Type: Article
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  • p. 784 –790 (7)
    The steady state and transient operation of thyristor and diode controllers for variable voltage control of three-wire 3-phase induction motors is considered. Throughout the analysis the state-space form of system representation is used, which facilitates the application of switching constraints at the stator (primary) terminals. The steady state solution for constant speed was obtained in a closed form in terms of state transition matrices with the motor represented in stationary d-q-axes. The results of experimental studies on a motor show good correlation with theoretical results. It was found that the losses in thyristor and diode controlled motors are mostly due to operation at high slips, and that time harmonic currents produce very little additional losses, especially at high speed. Compared with an inverse-parallel thyristor pair in each supply line the thyristor-diode or thyrode connection has an economic advantage but results in rather worse copper losses, mainly due to a predominant second harmonic component of current. The start-up transient currents, torques and speed of a 3-phase induction motor were obtained for sinusoidal, thyristor and thyrode control. A comprehensive computer-aided analysis gave good agreement between measured and calculated current transients. The thyrode controller resulted in larger peak currents and larger negative shaft torques than the corresponding thyristor controller.
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Theory and performance of solid-rotor induction and hysteresis machines
Optimal and suboptimal control of dual-excited synchronous generators
Impulse-commutated thyristor chopper
Mutual impedance simulation network
Identification of periodic nonstationary antenna stabilisation control systems by crosscorrelation techniques
  • Author(s): P.J. Lawrence  and  R.D. Dawson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 797 –801
  • DOI:  10.1049/piee.1977.0177
  • Type: Article
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  • p. 797 –801 (5)
    A novel crosscorrelation technique of obtaining dynamic measurements on the systems controlling a 2-axis stable platform carrying a large antenna is reported. Rotation of the antenna causes platform control parameters to be periodically time varying, the periodicity being comparable with control-system time constants. A theoretical analysis of the technique is reported that shows that measurements are realistic, uncorrupted and suitable for determining the nature of compensating device such as a digital filter. Results from measurements on the system, together with results from offline and online simulations, are presented.
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S-domain solution for the fixed end-point optimal-control problem
Frequency-domain dual-locus method for design of multivariable control systems
  • Author(s): G.K. Steel  and  P.F. Lister
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 809 –813
  • DOI:  10.1049/piee.1977.0179
  • Type: Article
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  • p. 809 –813 (5)
    A design method is presented for linear multivariable systems with cascade controllers. The method is restricted to general systems with two input and two output variables and is applied in the frequency domain using dual-locus plots. Loci are formed that relate directly to the closed loop characteristic polynomial of the system and conditions are derived from an unambiguous indication of stability. The loci are chosen so that the effects of controller elements can be readily assessed, and this leads to an iterative procedure for controller design. The method has been applied to a position control system for a 2-axis gyroscope and is shown to yield high performance although retaining simplicity in the controller functions.
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Suboptimal regulator-design method for improved system stability
  • Author(s): J.R. Smith ; D.C. Stringfellow ; G.J. Rogers
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 814 –816
  • DOI:  10.1049/piee.1977.0180
  • Type: Article
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  • p. 814 –816 (3)
    A regulator-design algorithm is described in which a systematic numerical technique is used to predetermine the performance criterion J = ∫0∞ (xtQx+u2)dt. The constraints imposed on the system response by the design specification are associated with the movement of the eigenvalue locations to give actual values for the elements of Q. The algorithm described here, for the linear single-input system, is based on the sensitivity of the elements of Q to shifts in the eigenvalue locations to produce a performance criterion for improved system stability. A practical example of the method, applied to the voltage control of a synchronous machine, is included.
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Design of decentralised load-frequency regulators
Design of optimal machine-control systems
  • Author(s): M.J. Grimble
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 821 –827
  • DOI:  10.1049/piee.1977.0182
  • Type: Article
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  • p. 821 –827 (7)
    A method is described for the design of optimal linear servomechanisms. The system to be controlled is assumed to be linear, time invariant and multivariable. The cost function to be minimised is quadratic and is measured over an infinite time interval. Expressions are given to enable the optimal controllers for both open-loop and closed-loop systems to be calculated. A result is obtained that allows the cost function weighting terms to be related to the optimal-compensated system pole positions, and hence to the system transient response. The relationship can be used when choosing the weighting constants. The design procedure is illustrated in the design of a controller for a strip processing line for which the tension in the strip and the speed of the drives is to be controlled. A new method of spectral factorisation is also introduced. This can only be used on a restricted-class matrices having a degree of symmetry; however, it is much easier to use than previous methods.
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Time delay to firing of a triggered vacuum gap with barium titanate in trigger gap
  • Author(s): G.R. Govinda Raju ; R. Hackam ; F.A. Benson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 124, Issue 9, p. 828 –832
  • DOI:  10.1049/piee.1977.0183
  • Type: Article
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  • p. 828 –832 (5)
    The time delay to the firing of a triggered vacuum gap (t.v.g.) containing barium titanate in the trigger gap is investigated as a function of the main gap voltage, main gap length, trigger pulse duration, trigger current and trigger voltage. The time delay decreases steadily with increasing trigger current and trigger voltage until it reaches saturation. The effect of varying the main gap length and voltage on the time delay is not strong. Before ‘conditioning’ the t.v.g. two groups of time delays, long (>100μs) and short (<10μs), are simultaneously observed when a large number of trials are conducted. After conditioning, only the group of short time delays are present. This is attributed to the marked reduction of the resistance of the trigger gap across the surface of the solid dielectric resulting directly from the conditioning effect.
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Calibration of a reference capacitor using general-purpose precision instruments

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