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Electrical Engineers, Proceedings of the Institution of

Issue 2 • Date February 1967

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Displaying Results 1 - 25 of 36
  • Unit-distance cyclic-code synchronous sequential multiphase pulse generation

    Page(s): 181 - 186
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (723 KB)  

    A unit-distance cyclic-code multiphase pulse generator is described. The generator is shown to possess a number of advantages over the better-known techniques using binary counters, ring counters and feedback shift registers. View full abstract»

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  • Statistical probability of worst-case patterns in coincident-current ferrite-core stores

    Page(s): 187 - 194
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1075 KB)  

    In coincident-current ferrite-core stores, there is a particular pattern of stored information associated with any core which gives a large ¿noise signal when that core is read out. Patterns very near to this worst-case pattern also give unwanted ¿noise, and this paper calculates the average frequency with which a particular pattern occurs against its nearness to the complete worst-case pattern. For randomly operated 642planes the complete worst-case pattern occurs very rarely, and hence the large ¿noise associated with it is rarely encountered. However, lower ¿noise voltages from less complete patterns occur significantly often. The mean frequency of occurrence of a particular ¿noise is plotted against its magnitude, expressed as a fraction of full worst-case ¿noise. In 322 and 162planes, complete worst-case patterns occur more frequently. The ¿noise voltages associated with them may be expected to occur significantly often, if the planes are randomly operated. A complete worst pattern may also be disturbed in the worst possible way, creating an `absolute¿ worst-case pattern, which would give the maximum possible ¿noise. This is an extremely rare event, for any of the commonly used plane sizes, and even an incomplete absolute worst-case pattern, with half the cores arranged to give little ¿noise, is still extremely rare for all but 162planes. View full abstract»

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  • Order of complexity of active networks

    Page(s): 195 - 198
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    The topological properties of networks containing resistors, capacitors, self inductors and controlled current generators are considered. A restriction is found on the positioning of such generators so that the network may have a solution. The determinant of the node-admittance matrix of such a network is expanded in terms of some tree-admittance products. The order of complexity is related to a particular tree associated with such an expansion, and a method of calculation is given. It is shown that, for a broad class of networks, the order of complexity can be calculated by considering only the simpler RLC subnetwork. View full abstract»

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  • Correlation effects on direction-finding probability regions

    Page(s): 199 - 200
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (282 KB)  

    For an idealised model of a fix obtained by a network of direction finders on a narrow baseline, it is shown that the major axis of the probability ellipse is decreased, and the minor axis is increased, when positive correlation is present between bearing errors. The area of the ellipse is increased if there are three or more bearings, and the correlation is small. View full abstract»

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  • Attenuation of 8.6 mm-wavelength radiation in rain

    Page(s): 201 - 203
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (398 KB)  

    The difference in the signals returned from two tetrahedral corner reflectors 6.9km apart along the same line of sight has been used as a measure of the attenuation of 8.6mm radiation in rain. Eight recording rain gauges along the line provided an estimate of the rate of rainfall. The relationship between the attenuation and the rate of rainfall was found to be A decibels per kilometre = 0.26(5)R millimetres per hour. Mean values of A over tens of minutes ranged from 0.20R to 0.39R. The relationship A = 0.265R was used to estimate the rainfall from the measured attenuations along the path. Only six of the 23 estimates of the rainfall total fell outside the range 80% < radar rainfall/gauge rainfall < 120%. However, as a practical means of measuring rainfall, the method would be restricted to light and moderate rains, since, in heavy rain, the signal would be attenuated to below the minimum detectable level, except over very short path lengths. View full abstract»

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  • Self bias in filamentary valves

    Page(s): 204 - 205
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    First Page of the Article
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  • Wave propagation in rectangular waveguide containing a semiconducting film

    Page(s): 207 - 210
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    Methods for the calculation of the propagation coefficient of a rectangular waveguide containing a centrally placed semiconducting film are discussed. Numerical solutions for such a system with film resistivities in the range 10¿¿10k¿/square and frequencies in the range 8.4¿12GHz have been made, and confirmed experimentally at 9.25GHz. The theoretical results indicate the possibility of constructing waveguide flap attenuators with high attenuations and very small phase shifts. View full abstract»

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  • Application of transistor techniques to relays and protection for power systems

    Page(s): 213 - 227
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2324 KB)  

    Although there has been active interest in static relays for more than 20 years, it is only with the advent of modern semiconductors that appreciable progress has been made. The increasing performance required of modern protection is reaching the limits of capability of electromechanical relays, and practical development of static protection with higher performance and greater potentiality is becoming increasingly necessary. The paper surveys the broad approach to the development of static protection, the bases of design, the selection of components and the assessment of environmental conditions, all of which are important in producing equipment suitable for manufacture and having the performance and reliability associated with power-system protection. Typical examples of practical equipment are given to illustrate the various approaches and views expressed in the paper. The possible influence of static protection on associated equipment is discussed, and some future trends are predicted. Finally, the present state of development is assessed as being reached mainly by the work of manufacturing organisations, and the view is expressed that further development will require increasing participation by prospective users. View full abstract»

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  • Loading of power transformers

    Page(s): 228 - 232
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    For many years, the maximum temperature power-transformer insulation would withstand was regarded as fixed, and was used as the basis of standard kVA ratings and of overload calculations. Later, the life of the insulation was found to be a thermal-aging process; so the maximum permissible temperature now became a variable with time. The derived aging formulas and the parameters in present use, together with the resulting standard overload values, are reviewed. Practical life studies to set bounds to the permissible temperatures have not been successful; so only relative conclusions can be drawn, and the absolute limit is still unknown. It is, however, clear that quite large margins are available over present-day practice, and some part of these have been incorporated in the more recent loading guides. The desirability of increasing present ratings to utilise these margins is considered. Analysis suggests that any extra rating thus derived cannot be economically realised and is better reserved for emergencies. It is concluded that loading capacity is not the only, or even the major, factor in determining the expectation of life of a transformer. There are other, more exigent, limits. Nevertheless, for practical-operation purposes and to permit systematic planning, a standard loading practice, however arbitrary, must be established. The national loading guides fulfil this function in a relatively simple and practical manner. In particular operating conditions where the loading requirements can be more closely prescribed, it is possible to work directly on the hottest-spot temperature and dispense with some of the orthodox restrictions. The `integrated system transformer¿, to which brief reference is made, is the first practical application of this principle. View full abstract»

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  • Power electrics at Trawsfynydd power station

    Page(s): 239 - 251
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1623 KB)  

    The paper deals with the power aspect of the electrical design of Trawsfynydd nuclear power-station. It gives the reasons for the unusual system design, describes the problems encountered in choice of gas-circulator drive, and explains the reasoning behind the choice of the essential-supplies system. Cable design in nuclear-power stations presents problems to the designer, and a description is given of some of its facets. Some details of the novel low-frequency control-rod system are given. View full abstract»

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  • Mutual impedance of crossing earth-return circuits

    Page(s): 253 - 257
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (470 KB)  

    The mutual impedance between two straight-line earth-return circuits, making an angle different from zero with each other, is considered in the paper. Furthermore, it is shown that, when the angle between the lines is small, the mutual impedance may he determined from the expression concerning parallel wires. Tables are given for the functions P(r, ¿) and Q(r, ¿), which appear in equations for mutual impedances. View full abstract»

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  • Performance of some magnetic slot wedges in an open-slot induction motor

    Page(s): 258 - 260
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (389 KB)  

    The paper presents an experimental assessment of magnetic slot wedges for use in induction motors with open stator slots. Four sets of magnetic wedges were investigated, and the results show that a good wedge design can so improve the electrical performance of an open-slot machine that it approaches the performance of the equivalent machine with semiclosed stator slots. The main advantages gained are reductions in magnetising current and in high-frequency pulsation losses on no load, with consequent improvements in efficiency and power factor. Leakage reactances are increased slightly by the use of magnetic wedges. In this respect, the performance of a machine with magnetic slot wedges lies between the performance of the equivalent machines with open and semiclosed slots, respectively. The requirements for an ideal magnetic-slot-wedge design are indicated. View full abstract»

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  • Digital-computer program for design synthesis of large squirrel-cage induction motors

    Page(s): 261 - 268
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1047 KB)  

    An appraisal is made of the general problem of system-design synthesis by digital computers. Published literature on the design of electrical machines by computer is surveyed, and it is concluded that the majority of this work may be categorised as design analysis and partial design synthesis. The development of a pilot program for the design synthesis of large squirrel-cage induction motors is described, with emphasis on the methods adopted in the search for solutions. Particular attention is given to the development of special techniques dealing with the major discrete parameters, e.g. frame size and numbers of slots and conductors per slot. The final program comprises a marriage of methods of solution, including iterative techniques and preknowledge of the system functions, which was considered essential to achieve an economical convergence scheme. Results are presented, illustrating that the program produced satisfactory convergence to meet required performance specifications. A number of alternative solutions are obtained for each case of input data. There is considerable scope for the improvement and refinement of the program. View full abstract»

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  • Current-compounded self excitation of synchronous motors

    Page(s): 269 - 275
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (939 KB)  

    When the load on a synchronous motor is liable to substantial variation, there is much to commend the use of some form of excitation control to provide either constant power factor or constant reactive power for all normal motor loading. The basic principles of control by static current-compounded self excitation are discussed in the paper, and ways in which the controlled quantity may be adjusted by voltage, current, or control-impedance shift are explained. An alternative method of adjustment over a given range simply by means of a variable resistor is also outlined. The use of a capacitor and nonlinear control reactor to compensate for errors due to changes in supply voltage or motor temperature is explained. Experimental results are given showing a motor power factor very accurately controlled over a wide range of loading and operating conditions, together with a pullout torque much greater than is obtained with reasonable values of constant excitation. View full abstract»

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  • Temporal development of spark breakdown in nitrogen and air

    Page(s): 277 - 283
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1063 KB)  

    Measurements have been made of the formative time lag of spark breakdown in nitrogen, dry air and humid air, for overvoltages of 0.05¿5%. The effects of variation of gap length and pressure have been investigated for gap lengths of 1¿3cm and pressures in the range 200¿750mm Hg, and the influence of humidity on the formative time in air has been studied for water-vapour partial pressures up to 10mm Hg. A comparison of results obtained using ultraviolet irradiation with those obtained using cobalt 60 irradiation has shown that the former is to be preferred for accurate formative-time-lag measurements. The influence of pressure, overvoltage and electrode conditioning on the shape of the breakdown oscillogram has been studied, and the significance of the form of the voltage collapse is discussed. The measured time lags in nitrogen are in good agreement with those calculated on the basis of Davidson's theory with 100% photoelectric secondary process, and the correlation is supported by comparison of calculated values of current-growth constant with those measured from oscillographic observations using a photomultiplier technique. The results for dry air are discussed using a simplified theory, and are found to be consistent with a Townsend process having a photoelectric secondary mechanism. It is suggested that the statistical fluctuations in the formative time, observed in humid air, are due principally to the effects of nonuniformity of the cathode surface. View full abstract»

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Aims & Scope

The Proceedings of the Institution of Electrical Engineers was published by the IET between 1963 and 1979.

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