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Electrical Engineers, Proceedings of the Institution of

Issue 3 • Date March 1968

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Displaying Results 1 - 18 of 18
  • Subjective quality of television pictures impaired by sinewave noise and low-frequency random noise

    Publication Year: 1968 , Page(s): 371 - 375
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    Transistorised amplifiers for video transmission over coaxial cables incorporate power units with d.c.-d.c. convertors that produce an aggregate effect similar to that of band-limited random noise at low frequency. The subjective effect of such noise, centred at 3.2 and at 7.5kHz, has been investigated. Tests were also made with sinewave noise at the frequencies giving the worst effect in the regions of 1 and 3.2kHz and 1 and 3.2MHz. Results are summarised in the form of signal/noise ratios for a series of `imp¿ mark points that has recently been introduced. View full abstract»

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  • Proper flow paths in vertex-weighted communication nets

    Publication Year: 1968 , Page(s): 376 - 380
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (765 KB)  

    In a communication net in which the maximum attainable flows are determined by the vertex capacities, there is, in general, a high degree of redundancy among the paths available for flow assignments in the net. A technique is given by which the set of all nonredundant paths, called proper flow paths, is uniquely determined. The method employs a direct and simple means of eliminating the redundancies in a pathfinding routine proposed previously by Paz, involving symbolic noncommutative multiplications among the entries of a modified vertex-adjacency matrix. A useful byproduct ensues with the immediate identification of vertexes which are not in any vertex cut set. This simplifies the problem of identifying all vertex cut sets in the net. A presentation of proper-flow-path theory in communication nets is included in the paper. View full abstract»

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  • Electromagnetic waves in media with finite discontinuities

    Publication Year: 1968 , Page(s): 381 - 386
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (621 KB)  

    The approach adopted is to write down a wave equation which applies to the medium as a whole. The physical parameters of the medium appear in the coefficients in this equation. It is shown that meaningful solutions can be obtained when the physical parameters possess finite discontinuities. A similar approach was suggested by Brillouin, but was not successfully completed. Some examples are given in which solutions may be obtained by other methods; e.g. using boundary conditions at surfaces of discontinuity. View full abstract»

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  • Statistical methods applied to the control of loadings of h.v./m.v. transformers on a distribution network

    Publication Year: 1968 , Page(s): 387 - 396
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1165 KB)  

    At the present time the Area Boards are spending between £8 million and £20 million on capital work, mainly connected with the expansion of the supply network. The cost of equipment to transform from high to medium voltage, together with associated substation equipment and the connections to the high- and medium-voltage networks, represents in the Merseyside and North Wales Electricity Board (Manweb) area somewhere of the order of 30% of the total capital costs. Consequently, a small percentage saving in the number of substations required for the network can represent a considerable sum of money. This saving could result from a decrease in the number of transformers installed if an increase in the mean loading of the existing and future transformers could be considered acceptable. As this mean or average loading is increased, so also is the load on the most heavily loaded transformers, and this has to be limited, owing to the possibility of a certain number of these transformers exceeding the loading at which deterioration is excessive. The load on these transformers has to be considered under conditions of inclement weather and/or outage conditions, which could occur at any time. From a statistical survey of the network conditions in the Merseyside and North Wales Electricity Board area, it can be shown that, within a given probability, a higher mean loading can be considered acceptable, provided that the variation from this mean, i.e. the standard deviation of the individual loadings to the mean, is controlled. The form of this control is considered. View full abstract»

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  • Digital simulation program for multiterminal h.v. d.c. systems

    Publication Year: 1968 , Page(s): 397 - 406
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1242 KB)  

    The interaction between the controllers of h.v. d.c. convertors connected to the same d.c. system raises problems in the design and analysis of the dynamic behaviour of the convertors under transient conditions. Studies of controller behaviour can be made on d.c.-system models, but the modelling procedure is usually costly and time-consuming. For the initial investigation of suitable controller parameters for a multiterminal d.c. system, a simplified method is proposed in the paper for which a digital program has been written. The program enables the d.c.-system response to a step change of a.c. or d.c. conditions to be studied for about 200ms after the disturbance, a time period comparable with the response of most d.c.-system controllers. The a.c. system is not represented in any detail, but the d.c. system is simulated by a distributed-constant line to enable the effect of surges to be taken into account. Examples are given of the behaviour of h.v. d.c.-convertor controllers incorporating gain linearisation, staleness factors and control changeover after a voltage disturbance on the a.c. side. The paper concludes with an estimation of the accuracy of the method for initial-design purposes and the computer-storage and time requirements. View full abstract»

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  • Discussion on ¿An integrated system of metropolitan electricity supply: experiences in design¿

    Publication Year: 1968
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  • Computer solution of e.h.v. underground-cable cooling problems

    Publication Year: 1968 , Page(s): 407 - 417
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1171 KB)  

    Resistance-network analogues have been used experimentally for longitudinal step-by-step solution of the thermal problem in separate-water-pipe cooling of underground e.h.v. cables. In parallel with this technique, mathematical models have been programmed for digital and analogue computers. The feature of the digital solution is the use of two programs; the first need only be run once, giving results which are applicable as boundary conditions to various cable and pipe geometries in the second program, in which both radial and square meshes are used. The analogue program in which the digital results are used is simple, versatile and suitable for general application to most cable geometries. The derivations of the thermal equations and the development of the computer programs are given in detail, and results for typical cable systems are presented. View full abstract»

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  • Static sampling distance relays

    Publication Year: 1968 , Page(s): 418 - 424
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (822 KB)  

    A sampling technique has been developed which allows a comparison of instantaneous values derived at different instants of time, thereby dispensing with the need to phase-shift or mix signals derived from the primary line quantities. Both amplitude and phase comparisons are used to derive a variety of impedance characteristics. The relays combine high sensitivity with a high resistance to interference. Detailed results are presented for a current-polarised relay with a characteristic surrounding the probable fault area. View full abstract»

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  • Hydraulic-turbine transfer function for use in governing studies

    Publication Year: 1968 , Page(s): 424 - 426
    Cited by:  Papers (7)
    Save to Project icon | PDF file iconPDF (314 KB)  
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  • Optimisation of alternator voltage regulators for steady-state stability using the Mitrovic method

    Publication Year: 1968
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  • Conformal transformation employing direct-search techniques of minimisation

    Publication Year: 1968 , Page(s): 427 - 431
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (657 KB)  

    The paper deals with the transformation by numerical techniques of fields having polygonal boundaries. Modern direct-search techniques for the minimisation of multivariable functions are employed, together with a method of integration in which the step length is continuously and automatically varied. The complete solution procedure is highly efficient; it converges smoothly for all boundary shapes studied and has the important feature for general application that it is virtually independent of experience on the part of the analyst. A discussion of typical functional variations and a transformation simplifying the integration of functions with complex limits are included. An example is considered to show the application of the method, and guidance is given on the performance to be expected in the general application of the method. View full abstract»

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  • Dielectric losses in solids at cryogenic temperatures

    Publication Year: 1968 , Page(s): 432 - 440
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1130 KB)  

    Measurements were made of the permittivity and loss tangent of polyethylene, poly(4-methyl pentene-1), polyethylene terephthalate, polyvinyl chloride (containing 33% tritolyl phosphate), poly-¿-undecanolactum, cellulose triacetate and insulating paper for temperatures between 4.2 and 295°K over a frequency range from 47Hz to 89.5kHz. In polyethylene and poly(4-methyl pentene-1), a single small absorption region (maximum value, 1¿2×10¿4 was observed in the temperature range 150¿200°K. The loss tangent of polyethylene decreased to a constant value (~2×10¿5) near absolute-zero temperature, whereas, in the case of poly(4-methyl pentene-1), below 70°K it increased with increasing frequency and decreasing temperature. With the exception of polyvinyl chloride, which did not exhibit any distinct absorption regions, the remaining materials investigated possessed one or more loss regions with a maximum loss tangent between 4×10¿3 and 3×10¿4. The peaks occurred in the temperature range 150¿300°K. The loss tangent of these materials decreased to 1¿3×10¿4 as the temperature was reduced to 4.2°K, with the exception of poly-¿-undecanolactum, for which it was 3×10¿5 View full abstract»

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  • Scottish Centre: Chairman's address. Engineering science or scientific engineering

    Publication Year: 1968 , Page(s): 441 - 442
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (353 KB)  

    First Page of the Article
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  • Flashover of polluted h.v. insulators under switching surges

    Publication Year: 1968
    Cited by:  Papers (1)
    Save to Project icon | PDF file iconPDF (172 KB)  
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  • Electronic rotational-speed/time recorder incorporating stroboscopic speed-interval detection

    Publication Year: 1968 , Page(s): 443 - 444
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    First Page of the Article
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  • Stability of nonlinear oscillations predicted by harmonic-linearisation technique

    Publication Year: 1968 , Page(s): 445 - 452
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (913 KB)  

    An analytic method of establishing the stability of oscillations which occur under both forced and limit-cycle conditions in nonlinear systems of any order is presented. The method allows the rate at which oscillations diverge or converge to be calculated. it is shown that the normally used graphical argument for assessing the stability of limit cycles is an approximate solution of the theory, obtained by neglecting the frequency and damping dependence of the nonlinearity. The theory is also used to derive a general stability bound on forced oscillations occurring in nonlinear systems. Application of the theory to a relay system stabilised by integral control indicates that stability is always predicted correctly and that divergence of stable oscillations is calculated with sensible accuracy. The jump phenomenon in a ferroresonant circuit is also examined, and a formula is derived for the stability boundaries. Digital-computer modelling is used to verify the predicted exponential change in sinusoidal output for step changes in input amplitude and frequency. View full abstract»

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  • Stability and noise sensitivity of a digital-analogue control system for the automatic loading of a power system

    Publication Year: 1968 , Page(s): 453 - 459
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (739 KB)  

    The performance of an automatic control system for load dispatching is examined. The control system comprises a digital computer and analogue-control equipment for regulating the power outputs of the generating units via the turbine throttle valve. The behaviour of the control system is determined in terms of the interaction which takes place between the local analogue loops and the digital load-scheduling system. The dynamic equations of the overall control scheme are established, and the stability boundaries are derived for the case when the digital controller is slow acting compared with the analogue control loops. The sensitivity of the control scheme to metering and telecommunication noise entering the digital system, as well as the significance of the digital sampling rate, is determined. View full abstract»

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  • Design analysis of model reference adaptive control systems applied to a gas-turbine aircraft engine

    Publication Year: 1968 , Page(s): 460 - 466
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (654 KB)  

    A gas-turbine aero-engine speed-control system has been investigated on an analogue computer to determine the possibility of using a model reference adaptive control device to maintain constant dynamic behaviour of engine speed irrespective of altitude and aircraft forward speed. A conventional type of speed-control arrangement has been used in the main loop, and an auxiliary feedback loop has been introduced which biases the flow-control unit by an amount which is proportional to the derivative of engine speed. The constant of proportionality is the parameter which is being changed by the adaptive loop. The adjustment is such that a minimum in the value of integral of error squared is sought, where the error signal used is the instantaneous difference between engine and model speed outputs. The results suggest that it would be physically reasonable to produce such a controller, and that substantially similar dynamic behaviour is obtainable under changing environmental conditions. Such a loop could be added to existing speed-control systems without major modifications in design. 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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