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Volume 120
Issue 4
Proceedings of the Institution of Electrical Engineers
Volume 120, Issue 4, April 1973
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Volume 120, Issue 4
April 1973
Highresolution microwave holographic technique. Application to the imaging of objects obscured by dielectric media
 Author(s): R.D. Orme and A.P. Anderson
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 401 –406
 DOI: 10.1049/piee.1973.0088
 Type: Article
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A highresolution lowintensity microwave holographicimaging technique is described. It has been successfully applied to the remote imaging of objects obscured by dielectric media. Experimental results show that small objects are clearly imaged through a thick intervening region of dielectric. Basic refraction effects at the dielectric surface enhance the object resolution.
Microwave transmission through a series of inclined gratings
 Author(s): N. Hill and S. Cornbleet
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 407 –412
 DOI: 10.1049/piee.1973.0089
 Type: Article
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p.
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A polarisation cascade matrix is derived which describes the transmission of an arbitrary elliptically polarised wave through an inclined grating of parallel wires. The terms of the matrix are the well established complex reflection and transmission coefficients for a linearly polarised wave incident on a single grating. Hence the matrix can be adapted for gratings with wires or strips of noncircular crosssection. The product of a series of matrices representing a series of gratings whose wires are at different angles to a fixed direction gives the total complex transmission and reflection coefficients. The results are shown to be in agreement with previously published work on a doublegrating system, and are experimentally verified for a series of five gratings. These results confirm that such a series of gratings can be used to design broadband polarisation rotators for linear polarisation. A similar matrix analysis can be applied, for wider wire spacings, to the design of broadband circular or elliptical polarisers or analysers. A sharp resonance reflection condition, which occurs when the gratings are separated by half a wavelength, can have applications as a frequency filter.
Rainfall corosspolarisation at microwave frequencies
 Author(s): P.A. Watson and M. Arbabi
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 413 –418
 DOI: 10.1049/piee.1973.0090
 Type: Article
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An analysis of rainfall crosspolarisation at microwave frequencies is presented, taking into account differential phase shift through rain as well as differential attenuation. Rain models with distorted drops at either constant or distributed canting angles are considered. The implications of an oscillationraindrop model are also discussed. Finally, the theory is compared with measurements of crosspolarisation at 11 GHz, showing good agreement, with the implication that raindrops fall with average canting angles of between 0° and 15°.
Maximum offaxis gain of elliptical beams
 Author(s): J.W. Duncan
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 419 –422
 DOI: 10.1049/piee.1973.0091
 Type: Article
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p.
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Antenna beams of elliptical crosssection are analysed to determine the maximum gain that can be achieved over any particular elliptical crosssection. The analysis is concerned with maximising the gain at specified offaxis angles in the principal planes of the antenna. The maximum achievable gain is completely determined by the specified beam crosssection. Since the analysis applies to a lossless (100%efficient) antenna, it establishes an upper bound to the offaxis gain of ellipticalcrosssection beams. The analysis is based on scalar diffraction theory for a rectangular aperture antenna with a cos^{N} aperturefield distribution. The gain of a 3.5° × 7° beam is derived to show the effect of the aperture distribution on the gain. From a knowledge of practical antenna efficiencies, one can derive realistic values for the gain of elliptical beams produced by array, horn and reflector antennas. The analysis has particular application to communication satellites that radiate beams of elliptical crosssection for regional coverage on the surface of the earth.
Crosspath realtime optical correlator and ambiguityfunction processor
 Author(s): R.A.K. Said and D.C. Cooper
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 423 –428
 DOI: 10.1049/piee.1973.0092
 Type: Article
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p.
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A new type of optical processor is described, and experimental performance data are presented in the form of ambiguity diagrams for various types of signal. The processor uses an ultrasonic light modulator with two electrical inputs and a simple optical arrangement which is relatively easy to align. The ambiguity diagrams are available in real time as light patterns, but the system may be adapted for other modes of operation.
Decoder complexity for BCH codes
 Author(s): B.G. Bajoga and W.J. Walbesser
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 429 –431
 DOI: 10.1049/piee.1973.0093
 Type: Article
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p.
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The logic complexity and computational complexity of decoders for BCH codes are investigated, and bounds on complexity are obtained. These are compared with earlier. results of Savage for arbitrary block codes and for some special decoding rules. It is found that decoders for the class of BCH codes are of much lower complexity.
Review of methods for numerical solution of the hollowwaveguide problem
 Author(s): P.A. Laura and J.B. Davies
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 431 –432
 DOI: 10.1049/piee.1973.0094
 Type: Article
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Present state of development of a gaspressurised lappedpolythene cable for E.H.V. transmission
 Author(s): J.A.M. Gibbons and A.W. Stannett
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 433 –439
 DOI: 10.1049/piee.1973.0095
 Type: Article
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Polythene tape in association with sulphur hexafluoride under pressure is an attractive dielectric for underground transmission cables because it has low dielectric loss, low relative permittivity and high thermal conductivity. Unfortunately, polythene tape has a high coefficient of thermal expansion, and care is consequently needed in the design of the conductor electrostatic screen to achieve adequate electric strength. Because of the low thermal conductivity of sulphur hexafluoride between layers of tape, good contact needs to be obtained by controlling the interfacial pressure in the dielectric wall to achieve good heat transfer. It has been demonstrated by work on models and 650 mm^{2} 275 kV cable that this type of cable is technically feasible
Lowercost urban electricitydistribution systems by automatic control. Application to 11 kV and 33 kV systems
 Author(s): W.A. McNab and A.J. Bode
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 440 –446
 DOI: 10.1049/piee.1973.0096
 Type: Article
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The paper outlines a philosophy for applying automatic control to 11 kV and 33 kV distribution systems in urban areas to effect an improvement in transformerutilisation factor of primary substations from a maximum of 50% to 75% and Grid substations from a maximum of 50% to 69%. A comparison of costs derived by the use of hypothetical network patterns and an assumed load density of 30 MW/km^{2} indicates possible cost reductions of 15% by the application of automatic control to the 11 kV system, and 20–23% by the application of automatic control to the 33 kV system.
Computation of eddycurrent losses in cable sheaths and busbar enclosures
 Author(s): P.G. Heyda ; G.E. Kitchie ; J.E. Taylor
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 447 –452
 DOI: 10.1049/piee.1973.0097
 Type: Article
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p.
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The usual method of calculating cablesheath eddycurrent losses gives satisfactory results for highresistance sheaths but not for lowresistance sheaths. A method developed by Dwight for calculating this type of loss in unbonded busbar enclosures is applicable for lowresistance cable sheaths, but is not presented in a generalised form. A general method is given for the calculation of eddycurrent losses in parallel and arbitrarily spaced thin tubes, some or all of which may contain other tubes. Two special cases are derived: one for three tubes equally spaced in triangular formation and the other for three tubes equally spaced lying in a plane. A table of loss factors has been prepared and deposited in the IEE Library. It covers wide ranges of two basic parameters, which enables it to be applied both to cable sheaths and busbar enclosures. Extracts from the table are given in the paper. It is shown that the finite wall thickness of the tubes can introduce appreciable additional losses, and an approximate formula for these is given.
Armatureconductor impedances and commutation in d.c. machines
 Author(s): M. Hancock
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 453 –460
 DOI: 10.1049/piee.1973.0098
 Type: Article
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Subject to certain approximations about the configuration of the flux associated with armature conductors in slots, the currentdensity distribution in the conductors is determined by a 1dimensional diffusion equation, and solutions of this equation when the total current in the conductor may have any prescribed form of variation are obtained. The associated voltages for typical idealised reversal waveforms of armature current are then derived, and it is shown that the eddycurrent effects in deep unlaminated conductors may have a significant influence on these voltages. Failure to take sufficient account of these effects may be a major cause of certain discrepancies in the results of some elaborate analyses of commutation in large d.c. machines that have been published, although further work would be necessary for definite confirmation of this.
Synchronousmachine model including eddy currents
 Author(s): G.J. Rogers and J.R. Smith
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 461 –468
 DOI: 10.1049/piee.1973.0099
 Type: Article
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p.
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A simple dynamic model is developed for smoothrotor solidpole synchronous machines which takes account of rotor eddy currents. The model (in the same form as that of Park, but with an increased number of damper windings) is developed from the field solution for a machine of simplified geometry, by using Green's functions. The final field is expressed in terms of a series of modal eddy currents; by truncating the series, only the dominant eddycurrent modes are retained; each retained mode is represented in the model by a damper winding. The method is applied to the Goldington generator, and the results computed from eddycurrent models are compared with those computed from Shackshaft's model and with the test result.
Fieldtheory approach to inductionmotor analysis
 Author(s): C.E. Tindall and M.J. Lees
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 469 –476
 DOI: 10.1049/piee.1973.0100
 Type: Article
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p.
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The parameters of a complete inductionmotor equivalent circuit are calculated following a direct solution of Poisson's equation over a radial crosssection of the machine with current in but a single coil side. This device leads to certain advantages over conventional methods with regard to cohesion, convenience and versatility, and facilitates the estimation of secondary effects due to factors such as slot openings and skew.
Certain approaches to the analysis of singlesided linear induction motors
 Author(s): S.A. Nasar and L. del Cid
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 477 –483
 DOI: 10.1049/piee.1973.0101
 Type: Article
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p.
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The performance characteristics of singlesided linear induction motors (s.l.i.m.s) are obtained from quasirealistic and realistic models using Fourier transforms and numerical methods, respectively. The results thus obtained are compared with those given by analytical solutions for idealised models. The discrepancy in results is pointed out and a justification of the models presented in the paper is thus made. The problems related to computational aspects for the numerical solutions are discussed, and it is shown how to combine the Fouriertransform method with some numerical technique to yield the desired results. Interesting characteristics of s.l.i.m. emerging from the two approaches are mentioned.
Diakoptics and system operations: automatic generation control in multiareas
 Author(s): H.H. Happ
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 484 –490
 DOI: 10.1049/piee.1973.0102
 Type: Article
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p.
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A procedure for the instantbyinstant control of all the generation, or the socalled automatic generation control, of power pools is described. The multicomputer configuration formed by the multiplicity of individual company computers present is utilised in the procedure. The method is an extension of the present basepointandparticipationfactor approach used in the USA for the control of the generation in a single area. The paper first summarises the singlearea method, and then presents the necessary multiarea theory; this is followed by the multiareadispatch algorithm and the procedure for the automatic generation control of power pools. It is shown that the hierarchy of multilevel control can be readily extended to a multiplicity of power pools or socalled ‘superpools’.
Saturistor control of induction motor
 Author(s): G.K. Dubey and G.C. De
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 491 –496
 DOI: 10.1049/piee.1973.0103
 Type: Article
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p.
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A simple analytical method is given for calculating inductionmotor performance with a saturistor, alone or in series with a resistor, in its woundrotor circuit. A digitalcomputer program, with fast convergence for iterative calculations, is developed for considering the resistor and saturistor in parallel. Despite the nonlinearity of the saturistor reactance and resistance, as well as motor saturation, the d.c. dynamicbraking stopping time is computed analytically with reasonable accuracy. A wide range of speed/torque characteristics, appropriate for special applications, are shown to be available by varying the saturistor turns with suitable parallel resistors.
Modified travellingwave techniques to solve electrical transients on lumped and distributed constant circuits. Refractioncoefficient method
 Author(s): A. Ametani
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 497 –504
 DOI: 10.1049/piee.1973.0104
 Type: Article
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p.
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The paper describes a newly developed travellingwave technique, the ‘refractioncoefficient method’, to solve electrical transients on complicated lumped constant circuits connected to distributed lines. Travelling waves on distributed constants are calculated with the ordinary refraction coefficients, and travelling waves on lumped constants are dealt with by the modified refraction coefficients of the new method. The new method makes it possible to solve complicated lumped constant circuits, which have been regarded as almost impossible to handle by the travellingwave technique. Typical applications are shown for overvoltages due to a lightning stroke on a line connected to a complicated lumped constant circuit, and for switching surges due to energisation of a line, followed by a line fault and deenergisation. As is illustrated by the applications, the computation time needed by the new technique is considerably less than that required by the existing methods, and the accuracy is also very high.
Discussion on “Design features of auxiliary electrical machines for rolling stock”
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 505 –507
 DOI: 10.1049/piee.1973.0105
 Type: Article
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p.
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Optimal stationary feedback control with specified relative stability
 Author(s): J.K. Pal and A.K. Mahalanabis
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 509 –513
 DOI: 10.1049/piee.1973.0106
 Type: Article
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p.
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The paper presents a systematic procedure for designing optimal feedback control systems with the poles restricted either to the left of the line Re(s) =−α or in a cone tan^{−1}{I_{m}(s)/Re(s)} =±θ. Simple transformations of the complex variable s are utilised to find a characteristic polynomial for the desired closedloop system. It is then shown that this polynomial can be used with the frequencydomain optimality condition and the observability condition to find a proper quadratic index. It is also shown that it may be necessary to include a product of the control variable and the state variable in the quadratic index so that arbitrary pole placement may be possible.
Impulse flashover of particlecontaminated spacers in compressed sulphur hexafluoride
 Author(s): B.F. Hampton and S.P. Fleming
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 514 –518
 DOI: 10.1049/piee.1973.0107
 Type: Article
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p.
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The impulse flashover stresses of coaxialdisc spacers, both clean and when contaminated with conducting particles, have been measured for pressures of the ambient SF_{6} gas between 0.47 and 1.5 MN/m^{2}. Clean spacers had a higher flashover stress on positive than on negative polarity, but, for contaminated spacers, the positive stress was reduced much more than the negative stress. The effect of particles increased with their size over the 35–210 μm range used in these experiments, and was greater at the higher gas pressures. Insulating particles of similar sizes had little effect. Experimental results followed a Gaussian distribution, and could be extrapolated to give stresses at which the flashover probability was very low.
Control of corona and sparkover of coaxial systems by irradiation
 Author(s): R.T. Waters and W.B. Stark
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 519 –522
 DOI: 10.1049/piee.1973.0108
 Type: Article
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p.
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The glow and streamercorona discharge forms occurring in air at the positive central conductor of a coaxialcylinder system are examined. It is found that, for conductor diameters up to 1.2 cm, a glow discharge can be established, whereas for larger conductors streamer channels are always formed. For gaps preionised by irradiation from a ^{90}Sr source of strength 0.4 mCi, the glow discharge is sustained for all conductor diameters. This produces a reduction in corona current of up to threefold and a decrease in acoustic noise. The critical diameter of the central conductor which gives a minimum sparkover voltage for the system is found to be dependent on whether alternating voltage or direct voltage is applied. This difference is interpreted in terms of the different corona development in the two cases, since the glow discharge suppresses streamer development and inhibits spark breakdown. Irradiation of the directvoltage system thus increases the sparkover voltage for a positive central conductor; for a 1.27 cm conductor diameter the average field strength across the gap at sparkover is increased from 0.47 MV/m to 0.74 MV/m. No increase in sparkover voltage is found for alternatingvoltage systems.
Role of gas breakdown in the charging and discharging of macron clouds
 Author(s): P.R. Smy
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 523 –526
 DOI: 10.1049/piee.1973.0109
 Type: Article
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p.
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When a pile of dust is dispersed by a blast of air, a charged cloud is formed. The action of gas breakdown due to intense spacecharge fields generated on dispersal is shown to explain a surprising invariance in the net charge of the cloud with flow velocity, particle size and material. When the cloud subsequently discharges to a small earthed electrode, the associated energy is of the order of that required to initiate a chemical explosion (this may be of significance in supertankers, where discharges from a charged mist are suspected to be a possible cause of explosions). The collision of particles in an electric field is shown to be an effective charging mechanism during dispersal, and later in the creation of a dust 'plasma'. Electrical oscillations of approximately the calculated ‘plasma’ frequency (10^{3}−10^{4} Hz) are observed.
On the special theory of relativity
 Author(s): J.A. Clark ; D.A. Bell ; T.B. Tang ; Ian McCausland
 Source: Proceedings of the Institution of Electrical Engineers, Volume 120, Issue 4, p. 527 –528
 DOI: 10.1049/piee.1973.0110
 Type: Article
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p.
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