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Proceedings of the Institution of Electrical Engineers

Volume 117, Issue 10, October 1970

Volumes & issues:

Volume 117, Issue 10

October 1970

Power spectra of digital p.m. signals
  • Author(s): G.J. Marshall
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1909 –1914
  • DOI:  10.1049/piee.1970.0338
  • Type: Article
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  • p. 1909 –1914 (6)
    A formula of Shimbo et al. for the power spectrum of signals pulse-modulated in accordance with random sequences is specialised for Markov chains. In the analysis, z transform techniques are used rather than explicit matrix methods. The resulting expressions may be used to find the spectra of a wide class of digital signals obtained by pulse modulating the amplitude, frequency, phase, or any combination of these, of a radio-frequency carrier. Attention is directed to phase modulation and, in particular, to ideal phase reversal and signals which practical systems might produce as approximations to it. In the first such signal, amplitude modulation is introduced in addition to the phase modulation, while in the other there is a nonzero switching time between the two phase levels. The power spectra of these signals are determined and compared with the phase reversal spectrum.
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Calculating the performance of syllabically companded delta-sigma modulators
Changes in radio field strength at v.h.f. and u.h.f. due to disintegration of reflecting layers in the troposphere
  • Author(s): M.P.M. Hall  and  C.M. Comer
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1925 –1932
  • DOI:  10.1049/piee.1970.0340
  • Type: Article
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  • p. 1925 –1932 (8)
    During prolonged anticyclonic weather conditions, it is well known that abnormally high values of field strength sometimes occur during the night on overland transhorizon radio paths, usually returning to normal values after sunrise. The paper discusses simultaneous recordings of field strength and refractive index, made on two occasions when this occurred. On the first occasion, the return to normal values of field strength occurred within 2h, but, on the second, the change was much slower, taking some 6h. Use of a ray-tracing technique shows that the very high field strength on the first occasion was due to the return of the rays to ground by superrefraction in a thick elevated layer. On the second occasion, the layer was insufficiently thick to support refraction, and a partial reflection occurred. The magnitude of this reflection is computed from linear and cosinusoidal layer models, and the former leads to values of field strength agreeing, to within 5dB, with those measured.
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Electrical conduction in silicon-carbide composites
  • Author(s): J. Shewchun  and  J. Mitchell
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1933 –1940
  • DOI:  10.1049/piee.1970.0341
  • Type: Article
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  • p. 1933 –1940 (8)
    Temperature-and thickness-dependence studies on silicon-carbide composites (fired matrices of silicon-carbide crystallites, clay and graphite) have produced a new insight into the electrical-conduction mechanisms in such devices. Using computer methods, an optimum empirical expression for the current/voltage characteristic has been obtained in the formI = C1 exp (αT)V/L2 + C2 exp (βT)V3/L5 + C3 exp (δT)V6/L7where T is the device temperature and L is the device thickness. The most probable explanation for this equation is that it represents three different electric-field modes of space-charge-limited current flow. The silicon-carbide composite can be thought of as a bulk polycrystalline insulator or semiconductor in which the crystallite-crystallite contact points act as ‘grain boundaries’, the clay holds the crystallites together and the graphite is an impedance moderator; The linear conduction term can be explained by assuming that the carrier drift velocity is independent of electric field at low fields (<1.5 × 103 V/m). The V3/L5 term is due to the field-dominated double-injection process, while the conduction region represented by the V6/L7 term is most probably the diffusion-dominated double-injection process.
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Edge-combination classes of complete graphs
Two-wire multioutput switch with self-synchronising code
Very wideband amplifiers using transistor feedback pairs
Basic nonuniform transmission lines
Modern tungsten-halogen-lamp technology
  • Author(s): J.R. Coaton
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1953 –1959
  • DOI:  10.1049/piee.1970.0346
  • Type: Article
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  • p. 1953 –1959 (7)
    Since the innovation of the practical tungsten-halogen lamp employing iodine as the regenerating agent, there has been continuous research and development in this field of lamp technology. Although there are still gaps in our knowledge, particularly regarding the kinetics of certain reactions, there is now a far better appreciation of the regenerative mechanism and the influence of materials, processing and design on the performance and reliability of lamps. Practical applications are expanding, and one of the most notable is motor-vehicle lamps, where scientific investigation into tungsten transportation using radiochemical tracers has led to the establishment of twin-filament headlamps. The use of bromine, hydrogen and hydrocarbon halides and mixed halogens, including chlorine, in addition to iodine, is quite common practice. The modern tungsten-halogen lamp is now a very reliable light source, in which the halogen additives, dimensions and gasfilling are carefully chosen to give optimum performance. At present, efficacy and life have reached a plateau with existing techniques and materials, but the prospect of alternative materials and techniques indicate that a further major advance could occur within the next few years, and it is not difficult to foresee tungsten-halogen lamps replacing most conventional incandescent lamps.
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Polyphase windings with multiparallel circuits
  • Author(s): W. Fong
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1960 –1968
  • DOI:  10.1049/piee.1970.0347
  • Type: Article
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  • p. 1960 –1968 (9)
    In conventional polyphase alternating-current machines, the number of parallel circuits per phase is always an integral submultiple of the pole number. This requirement can impose restrictions in relation both to the optimisation of design, and to the practical aspects of the manufacture of medium and large low-voltage machines. A general method is described in this paper, by which several alternative intermediate numbers of parallel circuits per phase and numbers of parallel circuits greater than the pole-number can be derived, for a wide range of combinations of armature slot number and pole number. The design and performance of a 4-pole machine with six parallel circuits per phase, and of a 6-pole machine with four parallel circuits per phase, are considered in detail, by way of example. The new windings are of the double-layer type. It is shown that, on the basis of identical coil pitches, the new type of winding is not inferior in rating or load performance to a standard winding; and that, in addition to the advantage of a free choice of the number of parallel paths, there is the further advantage of improved accelerating characteristics.
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Effect of oscillatory torques on the movement of generator rotors
  • Author(s): G. Shackshaft
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1969 –1974
  • DOI:  10.1049/piee.1970.0348
  • Type: Article
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  • p. 1969 –1974 (6)
    The paper discusses the process whereby some of the kinetic energy stored in a generator rotor is converted to magnetic energy when a generator is short circuited. This gives rise to oscillatory electrical torques at fundamental frequency which, hitherto, have not been recognised as an important factor in the initial angular movement of a generator rotor and have usually been ignored; this is shown to be a serious omission which, when corrected, will influence future studies of generator stability. The effect of these oscillatory torques is to cause a back swing of the rotor when a generator is faulted. This phenomenon has been noticed during several system tests, and the results of such tests are used in the paper to support the theory which is presented. The practical system conditions necessary for the existence of these torques is discussed. Since these torques are of fundamental frequency, the exact calculation of them in digital-computer programs is time consuming, and thus a simple approximate method for simulating their effect on rotor movement is presented.
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Analysis and testing of a direct-voltage induced-e.m.f.-commutated thyristor motor
  • Author(s): C.St.J. Lamb
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1975 –1985
  • DOI:  10.1049/piee.1970.0349
  • Type: Article
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  • p. 1975 –1985 (11)
    A relatively new type of motor which has a stationary armature, wound with a number of independent coils, is the subject of the paper. Its coils are connected in parallel to the supply via thyristors, which are used to control the time intervals during which currents are allowed to flow in the coils. The stator is slotless, and its coils are wound to form a ring-type winding. Alternating- or direct-voltage sources can be applied to the armature of the motor. In the machine being discussed, alternating voltage is applied for starting and low speed, and direct voltage for normal running, which, in this case, is from 600 to 3550rev/min. When a direct voltage is applied, induced-e.m.f. commutation is used to cut off the coil thyristors.
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New approach to distance relays with quadrilateral polar characteristic for e.h.v.-line protection
  • Author(s): N.M. Anil Kumar
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 1986 –1992
  • DOI:  10.1049/piee.1970.0350
  • Type: Article
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  • p. 1986 –1992 (7)
    A new technique is presented using principles of multisignal relaying for the synthesis of a universal-type quadrilateral polar characteristic. The modus operandi consists in the determination of the phase sequence of a set of voltage phasors and the provision of a trip signal for one sequence while blocking for the other. Two versions, one using ferrite-core logic and another using transistor logic, are described in detail. The former version has the merit of simplicity and has the added advantage of not requiring any d.c. supply. The unit is flexible, as it permits independent control of the characteristic along the resistance and reactance axis through suitable adjustments of replica impedance angles. The maximum operating time is about 20ms for all switching angles, and with faults within 95% of the protected section. The maximum transient overreach is about 8%.
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Harmonic-measurement facility for power-supply systems
Discussion on “Overhead-line oscillations and the effect of aerodynamic dampers”
Discussion on “Harmonic reduction in multiplex convertors by triple-frequency current injection”
Discussion on “Fault development control in a.c.-d.c. convertors”
New type of reluctance motor
Effect of m.m.f. and permeance harmonics in electrical machines with special reference to a synchronous machine
Pole-changing motor using π-spread phase windings
Stability of synchronous machine with divided-winding rotor
Short-line fault tests on the cegb 275kV system
Surface-impedance method applied to multilayer cylindrical induction devices with circumferential exciting currents
Method for location of faults in cables
Tooth-flux distribution in slotted solid iron rotors
Design of optimal systems by a frequency-domain technique
  • Author(s): F. Fallside  and  H. Seraji
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 2017 –2024
  • DOI:  10.1049/piee.1970.0363
  • Type: Article
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  • p. 2017 –2024 (8)
    It is shown, by an extension of the optimality condition in the frequency domain, that certain relationships exist between the response of optimal system, the elements of the weighting matrices of the performance index and the optimal feedback matrix. On the basis of these relationships, and using a root-locus procedure, weighting matrices can be chosen which give a desired optimal response, and the corresponding optimal feedback can be calculated. Though general in its nature, as a computational technique it is at present limited to single-input systems. For single-input systems, a relationship between the performance index and the optimal feedback is also established. For the special case of single-input systems, a direct relationship is obtained between the closed-loop poles and the feedback matrix. Although the resulting system may, or may not, be optimal, this relationship constitutes a useful design procedure. An example is given illustrating the technique.
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Parameter identification for linear time-varying dynamic processes
  • Author(s): F.W. Fairman  and  D.W.C. Shen
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 2025 –2029
  • DOI:  10.1049/piee.1970.0364
  • Type: Article
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  • p. 2025 –2029 (5)
    This paper presents a new method for determining the parameters of a process whose behaviour can be modelled by a linear differential equation with time-varying coefficients in the form of finite-order polynomials. The simplicity of this method lies in the online generation of a set of independent linear time-invariant algebraic equations in the unknown parameters.The development of this method is based on the novel approach of treating the excitation and response signals as distributions, and expanding them in exponentially weighted series of the generalised time derivatives of the impulse distribution. These expansion coefficients are used to form the algebraic equations in the unknown parameters. A practical means of obtaining the expansion coefficients online consists of Poisson filtering the process signals and sampling the filter outputs simultaneously.
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Generalisation of parameter methods and D decomposition
  • Author(s): J.S. Karmarkar  and  G.J. Thaler
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 2030 –2032
  • DOI:  10.1049/piee.1970.0365
  • Type: Article
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  • p. 2030 –2032 (3)
    The parameter methods, namely the parameter-plane and the parameter-matrix formulations, were developed to solve high-order multiloop distributed-parameter problems that were too tedious to be solved using the usual classical techniques. Essentially, the methods give graphical plots relating two design parameters and the zeros of the characteristic equation. The paper summarises the solution for several previously obtained cases relating the parameters and coefficients, and generalises the relationship to a completely unrestricted case, using well known function-minimisation methods, such as the conjugate-gradient technique. Moreover, a useful comparison to the generalised D decomposition method is made.
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Algebraic criterion for absolute stability, optimality and passivity of dynamic systems
  • Author(s): D.D. šiljak
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 2033 –2036
  • DOI:  10.1049/piee.1970.0366
  • Type: Article
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  • p. 2033 –2036 (4)
    The paper presents a solution to the fundamental algebraic problem: find the necessary and sufficient conditions on the coefficients of a real polynomial II(Ω) so that it is nonnegative, i.e.II(Ω)≥0 for all real ω≥0The solution leads to a unique algebraic criterion for absolute stability, optimality and passivity of dynamic systems, which is an alternative to various analytic frequency criteria developed in modern system theory. The algebraic criterion is superior to the analytic criteria since it avoids any graphical construction and is suitable for machine computations.
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Return-difference and return-ratio matrices and their use in analysis and design of multivariable feedback control systems
  • Author(s): A.G.J. MacFarlane
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 117, Issue 10, p. 2037 –2049
  • DOI:  10.1049/piee.1970.0367
  • Type: Article
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  • p. 2037 –2049 (13)
    Bode's concepts of return difference and return ratio are shown to play a fundamental role in the analysis of multivariable feedback control systems. Matrix transfer functions are regarded as operators on linear vector spaces over the field of rational functions in the complex variable s. The eigenvalues of such operators are identified as characteristic transfer functions. The corresponding characteristic frequency responses provide a simple and natural link between classical single-loop design techniques and multivariable-system feedback theory. These concepts then serve as a unifying thread in a coherent and systematic discussion of multivariable-feedback-system design techniques.
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Design of gas-turbine controller using inverse Nyquist method
Analysis and design of 2-variable interacting control systems using inverse polar plots
General 3-dimensional solution of eddy-current and Laplacian fields in cylindrical structures

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