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Electrical Engineers, Proceedings of the Institution of

Issue 4 • Date April 1975

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Displaying Results 1 - 25 of 33
  • `Wild¿ bearings in high-frequency direction finding

    Page(s): 337 - 339
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (583 KB)  

    In high-frequency direction finding there occur, not infrequently, bearing errors which substantially exceed those normally experienced. It is customary to refer to bearings that are found to be very wide of the mark as `wild¿. Since one exceptionally large error in a small group of bearings apparently has a disproportionate effect on the overall result, attempts have been made from time to time to justify the rejection of such `wild¿ bearings on the basis of the size of the error. The justification for such a course is examined in the paper, and an alternative more systematic approach is proposed. Misidentification, i.e. observing the wrong signal, has often been a cause of `wild¿ bearings in the past. Every effort must be made to eliminate this cause. In this connection, it should be noted that propagation conditions rarely produce large errors with signals that are strong, not subject to severe fading and exhibiting sharp steady bearings. A large error associated with such conditions almost certainly points to misidentification. Having excluded misidentification, other cases of wild bearings should be examined against the propagation conditions obtaining. If no true ray path was likely, the signals are probably due to scattering and bearings should be rejected. Light may be shed on the propagation conditions by the signal waveform and the nature of the fading. The rejection of bearings solely on the basis of magnitude of the error is deprecated. View full abstract»

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  • Use of the numerical phase-difference filter for the digital channel bank

    Page(s): 340 - 344
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    The use of the numerical phase-difference filter in the single-sideband modulation scheme for frequency-division multiplexing is investigated and compared with the Weaver-modulator scheme proposed by Freeny et al. A simple algebraic solution to the approximation problem for arbitrary specifications in the stopband is given. The sensitivity of the stopband attenuation is the main problem that precludes the use of RC active structures; it is shown that the digital version can be implemented with a reasonable coefficients wordlength. The structure of the filter is optimised for round-off noise performance. Finally, the two modulation schemes are compared. View full abstract»

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  • Inductive detection of underground metallic pipes

    Page(s): 345 - 348
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (494 KB)  

    A widely used instrument for locating underground metallic pipes consists of two coils: one of which (the transmitting coil) excites eddy currents in the pipe, and the other (the receiving coil) detects the magnetic field of. these eddy currents. Irregularities in the response of this type of instrument appear during certain search operations. These irregularities cause uncertainty about the position of the line of the pipe. They are explained quantitatively in this paper. The analysis shows how the reaction field of the pipe varies with the depth and diameter of the pipe, and with its electrical and magnetic properties. A theoretical estimate of the diameter of the smallest pipe that can be detected is given. View full abstract»

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  • Synthesis of a single null response in an otherwise omnidirectional pattern using a circular array

    Page(s): 349 - 352
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (523 KB)  

    The paper discusses a method for designing an antenna array having an omnidirectional pattern in the horizontal plane plus a single steerable null. Such a system has applications in communications when it is required to reject interfering signals from an unwanted source, while maintaining communication coverage in other directions. Parameters such as null width, null depth and the gain ripple in the directions of coverage are defined in order to make sensible comparisons between performance of various null patterns. An efficient and simple method for the synthesis of such a pattern, using a circular array, is presented. It involves the appropriate combination of a beamcophasal pattern with that of an omnidirectional pattern, and it is shown that by choosing a phase-sequence omnidirectional pattern for this purpose, a narrower `single-zero¿ null may be obtained. The calculated results show that attractive pattern characteristics can be achieved through this method of synthesis. View full abstract»

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  • Method of tuning dipoles using capacitors and variable-capacitance diodes

    Page(s): 353 - 357
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    A method of tuning dipoles using discrete capacitors is presented with a theoretical model and experimental verification. Two or more capacitors are placed at various points across the two wires of a folded dipole to cancel the reactive part of the driving-point impedance for single-frequency tuning. Variable-capacitance diodes can be used in place of the capacitors to tune a dipole over a very wide band of frequencies. These tuning techniques are demonstrated for a 7.5 cm monopole at frequencies from 500 to 1270 MHz. Methods are described and demonstrated for suppressing the harmonics which are intrinsically generated by the diodes. View full abstract»

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  • Gain degradation of a 25 m paraboloidal aerial on 2 GHz transhorizon radio paths

    Page(s): 358 - 360
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    The apparent loss of gain referred to as `gain degradation¿, or `aperture-medium coupling loss¿, is normally severe on high-gain aerials when used on tropospheric scatter (beyond line-of-sight) radio paths. The paper reports measurements made using a 25 m-diameter paraboloidal aerial on two 300 km troposcatter radio paths at 2 GHz, compares these with data previously published, and emphasises that this gain degradation may increase significantly for small time percentages. View full abstract»

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  • Intermodulation products from nonlinearities in transmission lines and connectors at microwave frequencies

    Page(s): 361 - 367
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (773 KB)  

    An experimental investigation of intermodulation products generated by nonlinear effects at contacts between similar and dissimilar metals has been carried out, and the results are reported and discussed here. Seven contact materials were used, and the effects of oxidation and electroplating of contacts were observed. Measurements of 3rd-order (2fA-fB) and 5th-order (3fA-2fB) intermodulation products were made using two S-band signal sources, of frequencies fA and fB, respectively, with a centre frequency of 3 GHz. View full abstract»

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  • Large transient neutral currents during energisation of 3-phase transformers

    Page(s): 369 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (471 KB)  

    A magnetising inrush phenomenon characterised by a large exponentially decaying direct component of current in the neutral has been recorded in a number of 275 kV transformers. Laboratory investigations have shown that the effect can be produced in 3-limb transformers with certain combinations of nonsimultaneous energisation of the three phases. In particular, for the first two limbs to have their windings energised the sum of the fluxes in those limbs must be greater than the flux in the third limb when the third winding is energised. The initial magnitude of the d.c. component is proportional to the difference between these fluxes. View full abstract»

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  • Determination of surge-diverter voltage/current characteristic

    Page(s): 373 - 376
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    A mathematical model has been proposed to determine the voltage/current characteristic of the surge diverter for a wide range of currents of short duration of 8/20 and 4/10¿s waveshapes. Experimental data agree well with the proposed model. View full abstract»

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  • Airgap and stator flux distribution in Guy-type medium-frequency inductor generators

    Page(s): 377 - 386
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1197 KB)  

    The first part of this paper is concerned with no-load permeance variations and overall flux distribution in the airgap of Guy-type inductor alternators. Teledeltos models were used to predict the permeance variation over a rotor pitch and over a whole stator main tooth for a complete cycle. The flux utilisation coefficient calculated from the permeance variation across a whole main tooth gave a better prediction of the open-circuit curve than when a rotor slot pitch was considered. Teledeltos models were also constructed to investigate how the depth of slot and the slope of side of the slots affects the flux utilisation coefficient. A simple approximation to the airgap permeance allows the airgap-permeance variation and the flux utilisation coefficient to be calculated for any tooth-slot geometry for 3 kHz machines. Detailed flux distribution in the airgap region was also predicted from Teledeltos plots. The asymmetry that exists between the two main teeth over a d.c. pole pitch causes flux variations to link the field winding, resulting in high voltages across individual field coils unless suitable damping windings are used. The second part considers in detail the open-circuit and load flux distribution in the siriall stator teeth of Guy-type inductor alternators. Although the flux variation across the total tooth surface is approximately sinusoidal, a considerable amount of harmonic flux is present in small sections of the surface. Under load conditions, an additional m.m.f. due to armature reaction acts on the airgap permeance, resulting in a nonuniform distribution of flux across the tooth surface; from these flux waveforms, it is possible to calculate the losses in the stator teeth with a greater degree of accuracy than was previously achieved. A companion paper (see p. 387) discusses rotor flux distribution in Guy-type medium-frequency inductor alternators. View full abstract»

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  • Rotor flux distribution in Guy-type medium-frequency inductor alternators

    Page(s): 387 - 391
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (526 KB)  

    The paper discusses flux distribution in the rotor teeth and core of a 44.4 kVA Guy-type inductor alternator. Flux measurements, made under open-circuit and load conditions, showed the similarity between stator and rotor flux waveforms over a rotor pitch, modified by the heteropolar flux which links the rotor teeth and core. For any given load condition, the flux waveforms on the rotor can easily be determined by relating the output of a search coil on the rotor to a given reference on the stator surface. From an understanding of the flux distribution at the tooth surface and at the tooth root, it was possible to estimate the losses in the rotor teeth and in the core. Airgap and stator flux distribution are discussed in a companion paper (see p. 377). View full abstract»

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  • Demagnetisation phenomena in high-performance d.c. servomotors

    Page(s): 392 - 394
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (378 KB)  

    The paper describes the experimental results obtained from mounting Hall plates in the airgap of a high-performance permanent-magnet d.c. machine. It is found that the flux-density distribution over the pole face during transient operating conditions is nonuniform. These results suggest that the conventional single-recoil-line theory is deficient, and that each point on the surface of the permanent-magnet material operates along a separate recoil line. The spread of these recoil lines in the second quadrant is particularly significant if the armature of the machine is subjected to reversals, and the permanent-magnet poles are only short-circuit stabilised. View full abstract»

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  • Modern cable-fault-location methods

    Page(s): 395 - 402
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1063 KB)  

    The modern method of effective cable-fault location is to establish an approximate fault locality and then to accurately confirm the fault position. The paper reviews fault-location methods developed over the past few years, these have proved to be very accurate and generally quicker than classical methods. The main causes of failure are analysed and, since the majority of cable faults occur on the electricity-supply distribution systems, the scope is limited to the location of faults on h.v. and m.v. cables and associated pilot cables. Present equipment limitations mean that a complete fault-location system is achieved only by combining different equipment and different methods. However, until a reliable universal fault locator has been developed, cable-fault location will remain an art rather than a science, particularly in the field of m.v./l.v. cable faults. Future developments are suggested for locating faults on m.v. networks which generally present a special problem. View full abstract»

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  • Cable-fault location by impulse-current method

    Page(s): 403 - 408
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (766 KB)  

    The paper presents a new approach to cable-fault location based on the use of high-voltage impulse generators. It is shown that, when an impulse generator is connected onto a faulty cable, the waveform of the generator output current can be used to determine the position of a fault. Several advantages are gained by the use of a linear coupler to provide the signal to the instrumentation, and it is shown that the signal also indicates whether or not an acoustic signal is being produced at the fault. The nonlinear characteristics of faults, which introduce errors and complications into most existing methods of fault location, are fully exploited with the new technique. Digital transient recorders are shown to have many advantages over the currently used methods of recording impulse waveforms. The information stored in the memory of a transient recorder can be easily transmitted to another location for interpretation by an experienced engineer. The more complex waveforms obtained on multibranched networks would be interpreted with the aid of a computer. It is suggested, that both the hardware and software being developed for cable-fault location purposes will also find application in the growing field of diagnostic testing. View full abstract»

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  • Control of power on a large diesel-electric locomotive of new design

    Page(s): 409 - 413
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    To control the power of a large locomotive effectively the driver must be provided with some form of automatic control of tractive effort and engine power. This must ensure that the engine is never overloaded, and that the most efficient use is made of the available adhesion. Some details of load control are discussed from a stability point of view, and ways and means of using the available power are discussed. An ideal characteristic is proposed and the limitations of existing machine systems are described. A description of a locomotive, in which the principles described were used, is given with a block diagram of the control system. A simplified schematic diagram of the control system used is given, and the function of the principal elements in it is explained. Finally, the paper draws some broad conclusions from the experience gained during operation of the system in service. View full abstract»

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  • Optimisation of static-capacitor installations and switching schedules in distribution systems

    Page(s): 415 - 420
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    In distribution systems, static-capacitor banks are installed to reduce energy losses and to achieve voltage correction. The determination of the sizes and locations of the capacitor installations is formulated as an optimisation problem in the paper. The objective function is taken to be the sum of the annual cost of energy loss and the annual cost of additional capacitor installations. To schedule switching operations, the year is divided into a number of periods based on seasonal variations in the cost of energy and in the load requirements during the year, and the day is divided into a number of intervals based on the hour-to-hour variations in the cost of energy. The load currents are assumed to remain constant within each interval. The method of solution consists of first minimising the annual cost of energy loss alone, by quadratic programming, and then minimising the total annual cost by a step-by-step iterative procedure. The method takes account of the discrete nature of the capacitor installations and supplytransformer tap settings. The solution yields the optimum capacitor installations together with the optimum capacitor switching and transformer tap-changing schedules. View full abstract»

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  • Simplified stability analysis of a distribution system in a chemical plant with induction motors

    Page(s): 421 - 429
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (887 KB)  

    The need for a simple method of stability analysis has become apparent now that the problem of voltage-dip protection is often encountered. Simplifying assumptions such as approximate vector addition, neglecting motorfault contributions and transients, are explained. The stability of a typical plant after a voltage dip is then calculated by slide rule using only motor torque/slip and current/slip curves. The results agree well with those obtained by a rigourous computer study. Methods of improving plant stability and points to be noted in the design of ancillary equipment are briefly noted. View full abstract»

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  • New combination: motor-levitator

    Page(s): 430 - 431
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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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