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Electrical Engineers, Proceedings of the Institution of

Issue 11 • Date November 1968

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Displaying Results 1 - 25 of 28
  • Shot noise in microwave parametric amplifiers using gallium-arsenide varactors

    Publication Year: 1968 , Page(s): 1587 - 1591
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (533 KB)  

    Measurements of forward-current shot noise in a 4GHz parametric amplifier using a gallium-arsenide varactor are compared with simple theory. Good agreement is obtained for low diode currents (a few microamperes) and low pump levels (or low input/output impedances), but at higher currents or higher pump levels an additional noise source must be included, thought to be due to significant current from stored minority carriers. View full abstract»

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  • Design for a full multiplier

    Publication Year: 1968 , Page(s): 1592 - 1594
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (233 KB)  

    A cellular array is described which has the property of multiplying two binary numbers, and also of adding either one or two other numbers. The array can be extended to any number of bits. It is proposed that this array might be considered as a full multiplier, analogous to a full adder. Some applications of the array are mentioned. These include the synthesis of a quadratic equation, extracting a square root and obtaining a reciprocal of a binary number. View full abstract»

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  • Further evidence of v.h.f. propagation by successive reflections from an elevated layer in the troposphere

    Publication Year: 1968 , Page(s): 1595 - 1596
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (302 KB)  

    The paper gives further experimental evidence to support a recent proposal that propagation by double reflection from an elevated layer may be a significant mechanism in v.h.f. transhorizon propagation. This evidence results from a study of the relationship between field strength over a 320km v.h.f. path and height of tropospheric layers determined from soundings made near the path centre. View full abstract»

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  • Dynamic tracking filter as a low-threshold demodulator in f.m. f.d.m. satellite systems

    Publication Year: 1968 , Page(s): 1597 - 1606
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1138 KB)  

    The paper provides an analysis of the dynamic tracking filter and compares its capability as a low-threshold demodulator with that of the frequency-feedback demodulator. Crossreference is made to the analysis given in a companion paper in order to show the similarities that exist in the equations governing the threshold extension offered by the two forms of low-threshold receiver. Theoretical curves for a 600-channel system are presented which reveal a threshold extension of 4dB. View full abstract»

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  • Frequency-feedback receiver as a low-threshold demodulator in f.m. f.d.m. satellite systems

    Publication Year: 1968 , Page(s): 1607 - 1618
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1810 KB)  

    With application to satellite communication, a concurrent investigation of the threshold extension to be expected in f.m. f.d.m. operation from the frequency feedback demodulator (f.m.f.b.) and the dynamic tracking filter (d.t.f.) has revealed a close similarity, both algebraically in the expressions governing a performance assessment and quantitatively in the predicted threshold extensions. This paper and a companion paper give an analysis of both types of low-threshold demodulator, show comparisons between theory and measurement for a system capacity of 240 channels and present theoretical curves showing the predicted threshold extension for a 600-channel system to be 4dB. The papers provide evidence that the COMSAT formula is unnecessarily pessimistic in its prediction of the threshold extension available for large-capacity f.m. f.d.m. satellite systems. View full abstract»

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  • Unbalanced magnetic pull in a 6-pole induction motor

    Publication Year: 1968 , Page(s): 1619 - 1627
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1090 KB)  

    A 6-pole 10kW induction motor has been specially constructed for a comprehensive series of steady-state and transient measurements of the magnitude of unbalanced magnetic pull resulting from an eccentric air gap. These measurements have shown that unbalanced magnetic pull is critically dependent on Saturation of the magnetic circuit, and that the magnitude in the cage-rotor motor is much less than in the wound-rotor motor. Comparisons between measurements and calculations show that most existing theories inaccurately predict the magnitude of transient unbalanced magnetic pull during starting, the effect of slotting and saturation, the effect of a cage rotor, and the action of load currents. A simple theory is developed which gives reasonable agreement with measurements for the wound-rotor motor over a range of supply voltages about the rated value. View full abstract»

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  • Self excitation of a variable-speed constant-frequency machine

    Publication Year: 1968 , Page(s): 1628 - 1632
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    Consider a machine having a 3-phase stator and a wound rotor with commutator and brushes; the brushes rotate at a constant speed. The rotor is driven at a variable speed and fed from the stator through a transformer and a rectifier. This machine, thus excited through the rotor by a direct voltage, produces an alternating stator voltage of constant frequency which is independent of the rotor speed. This could be applied to electric-power generation using the wind energy. It is shown here under which conditions this machine charged with an inductive load becomes self-excited. Equations in ¿¿ co-ordinates for the machine and the load are derived. A linear mathematical model for the system is obtained and a known stability criterion is applied. Conclusions are: (a) it is not necessary to use capacitors for self-exciting the machine; (b) it is not necessary, but it is convenient, to work at velocities higher than synchronous; (c) for each relatively high velocity, especially if it is higher than synchronous, there is a range of the feedback gain which makes the system unstable; this range is greater at higher velocities; (d) the self excitation is more easily accomplished if higher frequencies are used. Experimental results, obtained in the laboratory within the limitations of the equipment available, are also presented. They show the same tendencies, thus checking, in general, these conclusions. View full abstract»

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  • Acoustic noise and vibration of rotating electric machines

    Publication Year: 1968 , Page(s): 1633 - 1640
    Cited by:  Papers (18)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1565 KB)  

    In recent years, with the growing public awareness of acoustic noise and current work towards International and British Standards concerned with noise from rotating electric machines, work on rotating-machine noise has progressed, from attempts at a qualitative explanation of the more obvious components of machine noise, towards the prediction of the complete acoustic spectrum from the design data. This paper describes the ways, common to all machines, in which noise is produced by mechanical, magnetic and aerodynamic sources, and reviews methods used to determine the acoustic output and vibration of particular types of machine. The measurement and analysis of machine noise is described, and some general rules for producing quiet machines are given. A bibliography of the main work on machine noise is given. View full abstract»

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  • Close-ratio phase-modulated change-pole machines with improved winding balance

    Publication Year: 1968 , Page(s): 1641 - 1648
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1088 KB)  

    The windings are divided initially into short segments which are balanced by the distribution of the phase-band lengths on a first pole number. Balance for the second pole number is then achieved by interleaving at least two of these segments. The material is supported by some practical tests on both 3- and 2-phase versions of the windings; the 3-phase experimental machine is compared with a single-speed machine in the same frame, while the 2-phase machine is used as a capacitor-run fan drive and is again compared with a single-speed version. View full abstract»

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  • Commutation phenomena in electrical machines. Part 2: Further experiments in flashover

    Publication Year: 1968 , Page(s): 1649 - 1653
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (749 KB)  

    In an earlier paper, it was established that a major mechanism of flashover involved the generation of a series of intersegmental arcs, and further relevant work has been carried out on the properties and characteristics of such arcs and on means by which they may be extinguished. The dependence of the flashover voltage (per gap) on gap width, the velocity of sliding and the brush grade have been investigated. This voltage increases markedly with increasing gap width; but, except at low speeds, it is independent of the velocity for a given gap width. The flashover voltage was found to be only marginally dependent on the brush grade when brushes selected from the main types were tried. Sequences of ciné photographs showed a phenomenon known as `jetting¿, in which molten copper, formed at an upper edge of a segment, is thrown outwards by the pressure of vaporising copper. The method considered whereby short arcs could be extinguished was based on a transverse magnetic field. Under the earlier conditions, the arcs accelerated uniformly; but it was suggested that a terminal velocity should be reached, which has been shown to be correct using additional apparatus. A formula describing the dependence of this terminal velocity on basic parameters has been derived. Further work has been carried out on the practical aspects of extinguishing short arcs by means of an air blast. View full abstract»

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  • Discussion on "Magnetic equivalent circuits for electrical machines"

    Publication Year: 1968 , Page(s): 1653 - 1654
    Save to Project icon | PDF file iconPDF (317 KB)  
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  • Brushless and self-excited 3-phase synchronous machine

    Publication Year: 1968 , Page(s): 1655 - 1660
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (809 KB)  

    The paper describes a brushless and self-excited synchronous machine, which uses current compounding in auxiliary stator and rotor windings to produce an excitation current which increases as the load current is increased. With the machine used as an isolated alternator, the effect is sensitive to the power factor of the load, and the increase in excitation current is greater as the load becomes more inductive. The constancy with which the terminal voltage of an experimental machine is controlled as the load varies is comparable with that obtained with typical static current-compounded excitation schemes, and a feature of the new scheme is the very rapid recovery of the terminal voltage following a sudden increase in load. As with static schemes, the new system is readily adapted to control either the power factor or the reactive power of the input to the machine, operated as a synchronous motor on an infinite busbar. Results obtained from the experimental machine again indicate an accurate control, from no load to well beyond full load. View full abstract»

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  • Consideration of the effect of pollution on the potential distribution of insulator systems

    Publication Year: 1968 , Page(s): 1661 - 1666
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (657 KB)  

    Two methods are outlined for the determination of the effects of a surface pollution film on the potential distribution of insulator systems. One method involves a suitably modified electrolytic tank, and the other is by numerical methods using a digital computer. Examples of both methods are given. View full abstract»

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  • Switching-impulse flashover of air gaps and insulators in an artificially polluted atmosphere

    Publication Year: 1968 , Page(s): 1667 - 1671
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    Rod-rod and rod-plane gaps and a selection of insulators, mostly of dimensions relevant to 110¿132kV systems, have been subjected to switching impulses in artificial pollution. It has been shown that the flashover voltages of the gaps were little affected by the presence of fogs, either of water or of 120g/l salt solution. Substantial reductions, increasing with fog salinity, were found in the flashover voltages of the insulator surfaces. In highly saline fog, the flashover voltages were well under half the values for dry insulators. The preapplication of alternating service voltage to the polluted insulators always led to further reductions in flashover voltage. View full abstract»

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  • Discussion on "Land and sea transportation of very heavy power-station equipment"

    Publication Year: 1968 , Page(s): 1671 - 1676
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  • New 3-phase invertor circuit

    Publication Year: 1968 , Page(s): 1677 - 1683
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (920 KB)  

    A 3-phase variable-frequency invertor is described. It is capable of controlling the output voltages by an on-off method. The commutation circuit is simple, and is so arranged that the invertor output voltages are independent of the load conditions. The triggering circuit and a protection scheme are also described. The overall efficiency of the invertor is of the order of 90% View full abstract»

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  • Discussion on "Logic behaviour of h.v. d.c. convertors during normal and abnormal conditions" and "Direct digital protection of h.v. d.c. convertors"

    Publication Year: 1968 , Page(s): 1683 - 1684
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  • Behaviour of multiterminal a.c.-d.c. interconnections with series-connected stations

    Publication Year: 1968 , Page(s): 1685 - 1692
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    All the existing h.v. d.c. schemes are varieties of point-to-point interconnection between two a.c. systems. However, multiterminal interconnections are being proposed and considered, together with general problems of a.c.¿d.c. multiterminal schemes. In this paper, the behaviour of series d.c. links is investigated as regards various types of convertor control and these are discussed and analysed. A mathematical model is developed for the solution of steady-state problems of the overall system under balanced conditions and with normal convertor operation. Results are obtained for a sample case of a 3-terminal single-source system both with and without compounding. View full abstract»

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  • D.C. power control for aluminium and electrolytic loads

    Publication Year: 1968 , Page(s): 1693 - 1704
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1144 KB)  

    The paper discusses critically the control of large d.c. power blocks, often exceeding 100 MW in one unit. Only power supply from silicon rectifiers is considered, since all other power supplies are now obsolete and many existing installations using mercury arc, mechanical rectifiers or machines are likely to change to silicon in the future. The large aluminium line is taken as an example of a difficult control problem, and the choice of control range, stability of current and method of initiating tap changes are considered in turn. A new master-local control scheme is described which brings all the rectifiers of one installation under a single master control, keeps total load current/power or voltage (as desired) constant, maintains maximum possible efficiency with minimum harmonic current in the supply, minimises tap changes and widens effective control range. The scheme permits any desired combination of rectifiers to operate under local or master control within chosen power-factor limits and is applicable to transductor-controlled installations or thyristor installations. The three possible control aims of constant current, unregulated voltage and constant power are discussed and their consequences are examined. View full abstract»

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  • Slip-energy-recovery schemes and the use of pole-change windings

    Publication Year: 1968
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  • Slot-shape considerations in electrical machinery

    Publication Year: 1968 , Page(s): 1705 - 1706
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  • Initiation of dry bands on polluted insulation

    Publication Year: 1968 , Page(s): 1707 - 1712
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    The loss of moisture and the initiation of dry-band formation on wet contaminated insulation has been studied by measuring the insulation resistance of the contaminated specimen as a function of the degree of contamination, relative humidity, applied voltage and time. Drying of the wet contamination consistently occurred when the power dissipated by the surface leakage currents became sufficient to raise the surface temperature by rather less than 1 deg C. The loss of moisture caused by a subsequent increase in the power dissipation is inevitably nonuniform and leads to the formation of a dry band. View full abstract»

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  • Stress control for sphere-sphere and sphere-plane electrode configurations

    Publication Year: 1968 , Page(s): 1713 - 1716
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (518 KB)  

    The highest potential gradient between a sphere and plane has been calculated by the method of images for various gap-length/sphere-diameter ratios. It is shown that, if the distance between the plane and the most distant point on the sphere is fixed at S, while the sphere diameter is allowed to vary, the highest stress on the sphere surface has the minimum attainable value of 5 16/S times the voltage, and the gap length is then 1 4 times the sphere radius. Measurements made at voltages up to 200kV for a fixed value of S confirm that, to an accuracy of within 1 or 2%, the minimum breakdown voltage occurs for the sphere diameter that makes the stress a minimum. The relevance of this result to the design of a stress shield surmounting a high-voltage terminal is discussed. The potential gradient has also been calculated between three spheres of variable diameter having their centres in line at a fixed distance d apart. It has been deduced that the highest gradient on the spheres is a minimum when the diameters are 2d/3, d/3 and d/3, corresponding to imposed voltages of V, 0, 0, or about 5d/9, 4d/9 and 4d/9 when the voltages are V, ¿ V/2 and ¿ V/2. This applies when the two lower-voltage electrodes are of equal diameter, but results are also given for various combinations of electrode diameter. The values quoted are discussed in terms of choosing suitable diameters of spherical stress shield for use on the terminals of 3-phase transformers during induced overpotential tests. View full abstract»

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  • Constriction resistance of a circular cylinder

    Publication Year: 1968 , Page(s): 1717 - 1720
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    An approximate method is used to calculate the resistance of a circular cylinder with current entering by a concentric circular electrode in one plane face and leaving by the other. Evidence is given suggesting that the values found are highly accurate. The resistance of any cylinder with a step in the radius can be deduced. The results are important in electric-contact theory; the method may be generally useful for resistance problems with mixed boundary conditions. View full abstract»

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  • Use of induction mechanism of kilowatt-hour meters for torque measurements

    Publication Year: 1968 , Page(s): 1721 - 1725
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    The paper analyses the properties of the induction mechanism of a kilowatt-hour meter as a source of the standard torque compared with the tested torque in a state of stable equilibrium. Theoretical considerations are used to define the limits of applicability of the torque-comparing method and the conditions required for the minimisation of error. The ambient temperature and the nominal frequency of the meter supply voltage are assumed to be maintained. The results of the considerations might be used when investigating the braking torques in the meters themselves; e.g. when measuring friction torque in bearings or in the register mechanism, or when designing special measuring equipment to be used when investigating torques in high-precision mechanisms. 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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