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Physical Science, Measurement and Instrumentation, Management and Education - Reviews, IEE Proceedings A

Issue 8 • Date November 1986

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Displaying Results 1 - 11 of 11
  • Study of airgap breakdown characteristics under ambient conditions of reduced air density

    Page(s): 485 - 492
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (706 KB)  

    The paper summarises data and preliminary observations arising out of engineering and physical studies of airgap breakdown at a moderately high altitude (1425 m), outdoor high-voltage research laboratory in South Africa. It is shown that in the case of positive switching impulses, the application of the present standard IEC atmospheric correction procedures can yield results which lie above the expected `sea level¿¿ trends. The relative influences of humidity (and air density sensitivity) upon airgap breakdown characteristics are also examined, both in engineering breakdown tests, as well as in studies of physical parameters of the discharge. View full abstract»

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  • Electrical test results of UHV airgaps and insulator configurations

    Page(s): 493 - 500
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (835 KB)  

    The paper summarises BPA's (Bonneville Power Administration) 60 Hz and impulse test results on UHV airgaps and insulator configurations performed to evaluate the insulation requirements for 1100 kV transmission lines. Information is presented on the effects of switching impulse waveshape and polarity, the number and type of insulators, grading devices and tower configurations, weather conditions, and the performance of prototype 1100 kV insulator configurations for 60 Hz and switching impulse voltage under artificially contaminated conditions. View full abstract»

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  • Design and operation perspective of a British UHV laboratory

    Page(s): 501 - 522
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4017 KB)  

    The authors have, in the past, been directly involved in the design, planning and supervision of the construction, of a new ultra-high-voltage laboratory. The main purpose of the laboratory was to provide a major facility in the UK for the development of switchgear rated up to 765 kV and in the dielectric research required for such an undertaking. Following the opening of the laboratory in 1970, the author have in recent years been closely connected in the development of new ranges of open terminal and metalclad SF6 switchgear rated up to 525 kV and for fault currents up to 63 kA. These activities have been supported by extensive dielectric research studies, which have enabled the major factors influencing the insulation integrity of practical equipment to be determined. First, this paper outlines the criteria used in designing the laboratory and presents a critical appraisal of the facilities during the first 15 years of operation. Secondly, consideration is given to illustrating some significant laboratory activities. Examples are given of various switchgear and nonswitchgear components for systems ¿765 kV, which have been subjected to rigorous dielectric proving tests in the main test hall. The use of specific high-voltage test procedures (e.g. climatic, artificial rainfall, mixed voltage testing) are described, and important technical factors which have influenced the dielectric design of apparatus are considered. View full abstract»

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  • Measuring properties of IREQ's 5.4 MV voltage divider

    Page(s): 523 - 533
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    The paper presents the results of an investigation into the response characteristics of the Institut de recherche d'Hydro Qu¿¿ebec's 5.4 MV voltage divider, which is suspended from the ceiling of the laboratory. The results obtained differ from those obtained by the Les Renardi¿¿res Group for their floor standing voltage divider. The properties of the divider with three different load geometries were investigated. A computer simulation was compared with experimental results obtained from the divider. The applications of the divider were extended to measuring front chopped impulses with different conductor leads. View full abstract»

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  • Switching-impulse strength of the external insulation of three-phase power transformers

    Page(s): 534 - 542
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (765 KB)  

    The switching-impulse strength phase-to-phase and phase-to-earth has been investigated on a power transformer dummy to provide data for the design of its external clearances. The dummy was equipped with 420 kV bushings, but also simulations were used to obtain smaller or larger distances to earth. The clearances were varied between 2 m and 6 m. The influence of rain is included. The report offers design curves for power transformer clearances covering the range of rated switching-impulse withstand voltages up to 1550 kV, phase-to-earth, and up 2400 kV, phase-to-phase. View full abstract»

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  • Generalised characteristics for the electric strength of phase-to-phase insulation in EHV overhead transmission lines and substations

    Page(s): 543 - 546
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (361 KB)  

    The electric strength characteristics of a multi-electrode insulation system can be defined by considering those of a grounded neighbouring electrode (or grounded neighbouring electrodes in a three-phase system). A form for generalising the characteristics is given, and it is hoped that this will simplify both the execution of experimental investigations and the selection of necessary dimensions for insulation systems. View full abstract»

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  • Statistical design of large UHV electrodes in air

    Page(s): 547 - 551
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (690 KB)  

    The large electrodes of UHV testing equipment are usually designed on the basis of the optimisation of their electric fields. But it is necessary to consider the inception of the streamer and leader discharges. The paper deals with basic models of the statistics of the streamer and leader inception. Examples for the design of UHV electrodes are given. View full abstract»

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  • Breakdown characteristics of insulator strings stressed by short tail waves

    Page(s): 552 - 561
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (799 KB)  

    Traditionally, the withstand voltage of an insulator string to lightning impacts is checked using the standard impulse 1.2/50 ¿¿s. First, the authors show that when a lightning stroke hits the tower or a ground wire, the resulting overvoltages are characterised by much shorter tail durations than the tail of incident lightning currents. The analysis of wave shapes, in particular tail durations of the overvoltages affecting the insulator strings, is carried out in the form of a detailed parametric study. Secondly, the authors describe the routine tests carried out in a HV laboratory to evaluate the withstand voltage of various insulator strings as a function of tail duration of the applied impulses. Five strings of different lengths were tested, with impulse tail durations between 50 ¿¿s and 4 ¿¿s. In conclusion, it clearly appears, when considering the mechanisms resulting in back flashover, that the withstand voltage of insulator strings is much higher than their conventional value for the 1.2/50 ¿¿s impulse. View full abstract»

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  • Corona, breakdown and humidity in the rod-plane gap

    Page(s): 562 - 568
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    A survey is given of our knowledge of the effects of humidity on corona and breakdown when a positive impulse is applied to a rod-plane gap. It is shown that the minimum in the humidity correction factor Kh which exists, when the impulse wavefront is increased in the range 1 < Tcr < 1000 ¿s, is now substantiated by a number of experimental observations. The potential gradient for streamer propagation is discussed; its variation with humidity is similar to that of the breakdown condition with the lightning impulse (Tcr ~ 1 ¿S). The changes that occur for longer wavefronts are discussed in terms of the known facts relating to the increased probability of leader formation and propagation, as humidity increases. View full abstract»

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  • Observation of corona phenomena at very high direct voltages

    Page(s): 569 - 572
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Corona currents of negative polarity flowing from a variety of earthed electrodes of small radii of curvature have been measured up to direct voltages of 1000 kV. The upper, high-voltage electrode has been either a sphere of 2 m diameter or a plane of 130 cm diameter (with curved edges). Over a current range extending from 0.5 ¿¿A to 2500 ¿¿A the current rises very nearly according to the fairly well established equation i = A(V¿¿V0)V where V0 is the threshold voltage for corona development, an equation applicable to corona in small gaps. Gaps of 25 cm up to 4 m have been studied. The corona is emitted in a series of pulses, generally known as Trichel pulses (1938), each probably lasting less than 1 ¿¿sec; the number rises almost linearly with current at least up to a rate of 1 pulse per ¿¿s, the maximum rate recorded at 600 kV across a 2.5 m gap. Their amplitude diminishes slightly with increasing voltage, falling from 600 kV to about half their value at 60 kV. Corona currents from earthed points 4 m below a 500 kV DC transmission line can amount to several microamperes. View full abstract»

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  • Evaluation of space-charge behaviour in long airgap using Pockels' cells

    Page(s): 573 - 576
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The behaviour of space charge produced by the first corona in a long rod-plane gap under a negative switching impulse voltage was analysed based on the measurements of electric field using Pockels' effect. After examining the reproducibility of the discharge phenomena, the radial and axial electric-field intensities in the gap were measured. The electric-field distribution was obtained based on the measurement at 39 positions in the gap during a series of voltage applications. The space-charge field was analysed assuming an axial symmetry of the phenomena, and the spatial expansion of the charge was discussed. View full abstract»

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