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Proceedings of the IEE - Part C: Monographs

Volume 107, Issue 11, March 1960

Volumes & issues:

Volume 107, Issue 11

March 1960

Discussion on “Eddy-current losses in thin ferromagnetic sheets”
A frequency-response method for the predetermination of synchronous-machine stability
  • Author(s): A.S. Aldred  and  G. Shackshaft
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 2 –10
  • DOI:  10.1049/pi-c.1960.0002
  • Type: Article
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  • p. 2 –10 (9)
    The paper presents a new concept for the predetermination of synchronous-machine stability. The concept is based on the realization of a basic closed-loop pattern for a synchronous generator, which, when established, can be subjected to the frequency-response procedure of the Nyquist stability criterion. The basic closed-loop pattern emerges from the application of small-displacement theory to Park's equations for a synchronous generator. The method is applicable to a machine with or without a voltage regulator, but is more useful in the latter case, and this forms the majority of the applications presented in the paper.It is shown that, as a by-product of the analysis, expressions for the damping in a synchronous machine may be derived. Since this is considered to be of some interest, the influence of some of the more important parameters of the machine and regulator on the damping coefficient is demonstrated.
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Analogue treatment of eddy-current problems involving two-dimensional fields
  • Author(s): J. Roberts
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 11 –18
  • DOI:  10.1049/pi-c.1960.0003
  • Type: Article
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  • p. 11 –18 (8)
    The paper deals with the RC-analogue representation of electromagnetic fields involving unidirectional current flow, such as those associated with current-carrying conductors lying in armature slots. The resulting magnetic field is in general 2-dimensional and is fully represented in the analogue. Capacitor current in the latter is directly equivalent to current flow in the corresponding section of the conductor, and the eddy-current loss in a conductor may be calculated from the distribution of current between the several capacitors. Some simple examples illustrate the translation of field boundary conditions into analogue terms.
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Discussion on “Analogue treatment of eddy-current problems involving two-dimensional fields”
Surface-integral methods of calculating forces on magnetized iron parts
  • Author(s): C.J. Carpenter
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 19 –28
  • DOI:  10.1049/pi-c.1960.0005
  • Type: Article
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  • p. 19 –28 (10)
    The force exerted on an iron part in a magnetic field may be calculated by a number of different methods, all of which give equivalent force distributions confined principally to a surface. Seven different methods, giving rise to five different surface force intensities, are shown to result in the same total force. Additional volume force components are obtained and a new expression for the actual distribution of force, consistent with all of the methods of calculation, is derived. A common interpretation of the well-known Maxwell field stresses in iron is shown to be incorrect. When the field is specified numerically the calculation of force in terms of surface integrals has certain advantages over the virtual-work method, and it is shown that simple analytic expressions for force which are usually obtained in this way may be easily derived as surface integrals. Practical applications are considered.
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Discussion on “Surface-integral methods of calculating forces on magnetized iron parts”
Microwave tubes—an introductory review with bibliography
  • Author(s): A.F. Harvey
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 29 –59
  • DOI:  10.1049/pi-c.1960.0007
  • Type: Article
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  • p. 29 –59 (31)
    The paper reviews the various types of electron vacuum tubes employed for amplification and generation at microwave frequencies. Emphasis is placed on principles of operation and on tubes recently developed to give high power output, oscillations at the highest frequencies and low noise factors. The treatment is restricted to conventional tubes in which the output energy is derived from the d.c. input. The subject is interpreted in terms of published work, the text being closely associated with a bibliography which is complete up to the Microwave Valve Convention of May, 1958.After a general introduction, the first part discusses grid-controlled tubes. It is then shown how the interaction of space-charge waves with resonant cavities and slow-wave circuits results in the various forms of drift-space and growing-wave tubes. The second part deals with crossed-field interaction in planar and circular geometry and includes an examination of the magnetron. An account is given of novel methods of generation of submillimetre waves and the usual sources of electrons are described. The third part analyses noise phenomena in oscillators and amplifiers.
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Discussion on “Microwave tubes—an introductory review with bibliography”
The optimization of a class of non-linear filters
  • Author(s): J.K. Lubbock
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 60 –74
  • DOI:  10.1049/pi-c.1960.0009
  • Type: Article
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  • p. 60 –74 (15)
    An optimum linear filter, in the mean-square-error sense, is no better than the optimum attenuator if there is no dissimilarity between the spectral densities of the signal and the noise. However, non-linear filters can use more statistical information about the signal and noise, so that, although they both possess the same spectral densities, a non-linear filter may be able to introduce a significant improvement in the mean-square error (i.e. it can do better than the optimum attenuator). For this reason the use of a non-linear filter in certain circumstances may well justify the greater difficulties encountered in its optimization and physical realization.The class of filters considered in the paper may be defined by a general expression relating output to input:y(t) =∑r=tR∫0∞ωr(τ)θr[x(t−τ)]dτAn almost routine procedure is proposed whereby the optimum set of weighting functions, ωr(τ), can be determined given either long enough samples of the combined input and the signal or sufficient statistical information about their characteristics. Some worked examples demonstrate that:(a) A significant improvement in mean-square error is possible even under the condition when the signal and noise possess the same spectral densities.(b) The class of non-linear filters under consideration can be optimized unhindered by the need to evaluate difficult integrals.(c) Although the physical complexity of the filter increases rapidly with the value of R, the mean-square error may converge rapidly to an asymptotic value as R is increased; in one example the performance was found to be within about 5% of the asymptotic value with R = 2.
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Discrimination between h.r.c. fuses and miniature circuit-breakers
  • Author(s): H.D. Einhorn
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 75 –81
  • DOI:  10.1049/pi-c.1960.0010
  • Type: Article
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  • p. 75 –81 (7)
    After a review of the aims and merits of protective devices for low-voltage installations, the joint use of h.r.c. fuses and miniature circuit-breakers is shown to be functional in many installations. The hypothesis that the 0.01 sec fusing current forms a criterion for discrimination is subjected to experimental tests and the statistical nature of discrimination is analysed. Practical conclusions for installation design are drawn, and a new fuse series and various other methods for backing-up miniature circuit-breakers are suggested.
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The use of silicon diodes in d.c. modulators and their applications to drift correctors for computing amplifiers
  • Author(s): T. Glucharoff  and  C.P. Gilbert
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 82 –90
  • DOI:  10.1049/pi-c.1960.0011
  • Type: Article
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  • p. 82 –90 (9)
    The basic computing element of an electronic analogue computer is the high-gain d.c. amplifier, but in order to overcome its inherent drift some form of auxiliary drift-correcting amplifier is frequently used.The paper describes a silicon diode modulator for use in such drift correctors, and shows that the zero stability which can be achieved is comparable with that given by the conventional relay modulator. It is also shown that the use of the diode circuit results in a number of improvements in the overall drift-corrector performance, such as a higher frequency response and practically unlimited life; the design of such a drift corrector for use with a given d.c. amplifier is described in detail and the resulting performance is assessed.
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The conductivity of oxide cathodes. Part 7: Solid semiconduction
  • Author(s): G.H. Metson  and  E. MacArtney
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 91 –97
  • DOI:  10.1049/pi-c.1960.0012
  • Type: Article
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  • p. 91 –97 (7)
    The properties of the solid conductivity state below 600° K are considered in the present Part. For comparative purposes the conductivity at 420° K is given the title of ‘low-temperature reference conductivity σ420’, and this function is studied in relation to its environment. It is found that σ420 increases in almost linear fashion with increase of conditioning temperature and that it also increases with increase of chemical activity of the core metal. At constant temperature σ420 is invariant over a wide range of applied voltage and current, and shows a high order of stability with time. Perhaps the most surprising result to emerge is the observed vulnerability of the solid conductivity to low-pressure oxygen attack, even at a temperature as low as 300° K.
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An optimum ratio of copper losses and iron losses for a transformer with variable load
  • Author(s): G.S. Brosan  and  D.O. Bishop
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 98 –99
  • DOI:  10.1049/pi-c.1960.0013
  • Type: Article
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  • p. 98 –99 (2)
    When a power transformer is loaded so that it is operating at maximum efficiency the copper losses are equal to the iron losses The ‘efficiency’ is, of course, the ‘power efficiency’, i.e. the ratio of output power to input power. The same condition applies for maximum ‘energy efficiency’ only if the load is constant for the period being considered.With most transformers the load varies considerably over a load cycle and the optimum ratio of copper losses to iron losses calculated on the assumption of constant load for a given period can only be, at least, a rough approximation.The paper suggests a method of obtaining a more accurate optimum ratio in cases where the load variation of the transformer can be estimated in advance. The assumption is made that the copper resistance is constant.
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A note on the optimum design of non-uniform transmission lines
  • Author(s): L. Solymar
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 100 –104
  • DOI:  10.1049/pi-c.1960.0014
  • Type: Article
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  • p. 100 –104 (5)
    The optimum design of non-uniform transmission-lines for a given bandwidth is discussed, and it is stated that the shorter the non-uniform transmission line the more violently its characteristic impedance varies. The concept of complexity of this characteristic impedance function is introduced and a design method is suggested for minimizing the complexity.Numerical examples are given to illustrate the method, and it is shown that it is possible to design tapers even shorter than the Chebyshev type.The method is capable of further extension.
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Some tests for the number of positive zeros and for the numbers of real and complex zeros of a real polynomial
  • Author(s): O.P.D. Cutteridge
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 105 –110
  • DOI:  10.1049/pi-c.1960.0015
  • Type: Article
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  • p. 105 –110 (6)
    The numbers of positive, real and complex zeros of a polynomial with real coefficients are shown to be related to the number of changes in sign along one or two sequences of determinants whose elements consist of the coefficients of the given polynomial and of its derivative. This in turn is related to the number of negative signs occurring in a certain continued fraction. Some numerical examples illustrate the application of both methods, and the simplification of and the relationship between the two sequences of determinants is also discussed.
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Discussion on “The stability criteria for linear systems”
Some results on the cross-capacitances per unit length of cylindrical three-terminal capacitors with thin dielectric films on their electrodes
  • Author(s): D.G. Lampard  and  R.D. Cutkosky
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 112 –119
  • DOI:  10.1049/pi-c.1960.0017
  • Type: Article
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  • p. 112 –119 (8)
    The effect on the cross-capacitances per unit length of cylindrical 3-terminal capacitors of thin dielectric films on the capacitor electrodes is discussed.It is assumed that the cross-section of such dielectric films remains constant throughout the length of the capacitor. Some conformal transformations of basic cylindrical capacitor cross-sections are given. When these are applied to a symmetric cylindrical capacitor with a thin dielectric film on its electrodes, the results suggest that the mean capacitance per unit length may remain constant to the first order despite the presence of the dielectric film. The same methods also suggest that the individual cross-capacitances per unit length may remain constant to the first order provided that the dielectric film is disposed symmetrically with respect to the capacitor symmetry plane.Further support for these conjectures is given by the results of a detailed calculation of the cross-capacitances per unit length of a parallel-plate cylindrical capacitor with a thin uniform dielectric film on one electrode. In the last Section, a lemma concerning the existence of an equivalent dielectricless capacitor is given and this is followed by the proof of general results of the type suggested by the previous working.
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Explicit form of f.m. distortion products with white-noise modulation
  • Author(s): R.G. Medhurst
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 120 –126
  • DOI:  10.1049/pi-c.1960.0018
  • Type: Article
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  • p. 120 –126 (7)
    When a frequency-modulated wave passes through a network whose phase or amplitude characteristics vary non-linearly with frequency, distortion terms appear as both frequency and amplitude modulation of the output wave. If the characteristics are expressed as power series, these distortion terms appear, to first order, as products of powers of time derivatives of the unwanted frequency modulation. When the frequency modulation may be simulated by a band of random noise (as in multiplex telephony carrying large numbers of channels), the spectra of the distortion products can, in principle, be described by simple algebraic functions of the characteristics (i.e. the minimum and maximum frequencies and the r.m.s. frequency deviation) of the modulating noise band.Except in certain special cases, the derivation of these algebraic formulae by straightforward analytical methods becomes prohibitively tedious for distortions of order much above the second. However, once the formulae are found, the insertion of numerical values for particular cases is straightforward. In the present paper it is shown how the problem can be reduced to the repetition of a number of standard operations which can be carried out using a digital computer. The technique is illustrated by application to fourth-order distortion appearing in the amplitude modulation, generated by terms in the amplitude characteristic up to sixth degree. Even in such an apparently simple case as this it appears from the literature that the closed form of the distortion formula has not hitherto been obtained. This example is of direct practical interest since, for example, the amplitude characteristic of a maximally-flat-amplitude triple-tuned circuit is of sixth degree in the region around the midband frequency. With a minor modification, the resulting formula also applies to fourth-order distortion appearing in the frequency modulation, owing to terms in the phase characteristic up to sixth degree.Use is made of a discontinuous contour integral applied to a similar, but somewhat simpler, case by Bennett;1 a closely analogous course can be followed using the more recently developed theory of generalized functions,2 but in this particular problem the contourintegral method is more economical.Formulae for the various orders of distortion in the top channel due to amplifier and discriminator characteristics are given in tabular form.
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An approximation to the harmonic response of saturating devices
  • Author(s): R.J. Kavanagh
  • Source: Proceedings of the IEE - Part C: Monographs, Volume 107, Issue 11, p. 127 –133
  • DOI:  10.1049/pi-c.1960.0019
  • Type: Article
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  • p. 127 –133 (7)
    The paper derives an analytical expression for the describing function and for the Fourier coefficients corresponding to saturating systems which are excited by sinusoidal signals. The saturation characteristics are assumed to be symmetrical and single valued. The method involves an approximation of the actual system characteristic by means of an exponential curve.The results are given in the form of graphs of the fundamental and third-harmonic components of the system output and a graph of the system describing function. The latter will be of use in the analysis of non-linear feedback systems. A comparison is shown between the present method and the technique of approximating saturation characteristics by means of straight lines. Formulae are given by means of which the higher-order harmonic components of the system output may be computed.Secondary results of this paper are Tables of the modified Struve functions L1(z) and L2(z) which are not available elsewhere in the literature.
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Discussion on “Effects of argon content on the characteristics of neon-argon glow-discharge reference tubes”
Discussion on “The square-loop ferrite core as a circuit-element”

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