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1、BRITISH STANDARD BS 358:1960 Incorporating Amendment No. 1 Method for the Measurement of voltage with sphere-gaps (One sphere earthed) UDC 621.317.32:621.316.933 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 358:1960 This British Standa
2、rd, having been approved by the Electrical Industry Standards Committee and endorsed by the Chairman of the Engineering Divisional Council, was published under the authority of the General Council on 16 November 1960 BSI 08-1999 First published April 1929 First revision December 1939 Second revision
3、 November 1960 The following BSI references relate to the work on this standard: Committee reference ELE/62 Draft for comment CY(ELE) 6400 ISBN 0 580 00614 X Co-operating organizations The Electrical Industry Standards Committee, under whose supervision this British Standard was prepared, consists o
4、f representatives from the following Government departments and scientific and industrial organizations: Admiralty Air Ministry Associated Offices Technical Committee Association of Consulting Engineers (Incorporated) Association of Supervising Electrical Engineers British Electrical and Allied Indu
5、stries Research Association* British Electrical and Allied Manufacturers Association* British Electrical Development Association British Railways, The British Transport Commission Cable Makers Association* Crown Agents for Oversea Governments and Administrations Electric Lamp Industry Council Electr
6、ic Light Fittings Association Electrical Contractors Association (Incorporated) Electrical Contractors Association of Scotland Electricity Council, Generating Board and the Area Boards in England and Wales* Electronic Engineering Association Engineering Equipment Users Association Independent Cable
7、Makers Association Institution of Electrical Engineers Ministry of Aviation Ministry of Labour (Factory Inspectorate) Ministry of Power Ministry of Works National Inspection Council for Electrical Installation Contracting National Physical Laboratory (D.S.I.R.)* Oil Companies Materials Association P
8、ost Office Public Transport Association (Incorporated) South of Scotland Electricity Board War Office The Government departments and scientific and industrial organizations marked with an asterisk in the above list were directly represented on the committee entrusted with the preparation of this sta
9、ndard. Amendments issued since publication Amd. No.Date of issueComments 4586May 1962Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 358:1960 BSI 08-1999i Contents Page Co-operating organizationsInsid
10、e front cover Forewordii 1Scope1 2Standard sphere-gap1 3Requirements for the spheres1 4Construction and mounting of the spheres2 5Height of the spheres above the horizontal earth plane2 6Clearance round the spheres5 7Connection of the sphere-gap5 8Irradiation of the sphere-gap6 9Voltage measurements
11、7 10Sphere-gap flashover values7 11Accuracy of the tables8 12Influence of atmospheric conditions8 Appendix A Range of experimental calibrations10 Appendix B Procedure by which the values in Table 3 and Table 4 have been derived from National Standards and other sources10 Figure 1 Typical vertical sp
12、here-gap3 Figure 2 Typical horizontal sphere-gap4 Table 1 Clearances round the spheres5 Table 2 Air density correction factor9 Table 3 Flashover voltages (50 per cent values in impulse tests) for alternating voltages, for direct voltages of either polarity, and for full negative standard impulses an
13、d impulses with longer tails: one sphere earthed11 Table 4 50 per cent flashover voltages for full positive standard impulses and impulses with longer tails: one sphere earthed14 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 358:1960 ii
14、 BSI 08-1999 Foreword This standard makes reference to the following British Standard: BS 923, Impulse-voltage testing. This British Standard, prepared under the authority of the Electrical Industry Standards Committee, revises and supersedes the 1939 edition. This edition has been drafted concurren
15、tly with the Recommendations for voltage measurement with sphere-gaps prepared by the International Electrotechnical Commission and is in technical agreement with the IEC Recommendations. The revision gives a method of checking the spheres for surface irregularities and also more detailed informatio
16、n regarding the irradiation of the sphere-gaps. Appendix A gives a bibliography of experimental calibrations, and Appendix B indicates the procedure by which the flashover voltage values have been derived. A British Standard does not purport to include all the necessary provisions of a contract. Use
17、rs of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 16 and a back cover. This sta
18、ndard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 358:1960 BSI 08-19991 1 Scope T
19、his publication contains rules and recommendations for the construction and use of sphere-gaps for voltage measurement where one sphere is earthed. The rules apply to the measurement of the peak value of: a) alternating voltages, b) full standard impulses (as defined in BS 9231) and impulses with lo
20、nger tails, c) direct voltages. The peak flashover voltages in air for various spacings between the spheres are given in Table 3 and Table 4. Appendix A gives the limits of voltage and frequency over which the tables have been derived from experiment and can be presumed to be accurate within the lim
21、its specified in Clause 11. Appendix B gives the procedure by which the values in the tables have been derived from previous National Standards and other sources. 2 Standard sphere-gap The standard sphere-gap is a peak voltage measuring device constructed and arranged in accordance with the rules in
22、 this document. It consists of two metal spheres of the same nominal diameter (D) and their shanks, operating gear, insulating supports, supporting frame and leads for connection to the points between which the voltage is to be measured. Standard values of D, in centimetres, are 2, 5, 6.25, 10, 12.5
23、, 15, 25, 50, 75, 100, 150 and 200. The spacing between the spheres is designated S. The points on the two spheres which are closest to each other are called the sparking points. Figure 1 and Figure 2 show two arrangements, one of which is typical of sphere-gaps with a vertical axis and the other of
24、 sphere-gaps with a horizontal axis. 3 Requirements for the spheres The spheres shall be carefully made so that their surfaces are smooth and their curvature is as uniform as possible. They shall meet the following requirements: a) General shape. The diameter of each sphere shall nowhere differ from
25、 the nominal value by more than two per cent. b) Freedom from surface irregularities. The spheres shall be reasonably free from surface irregularities in the region of the sparking point. This region is defined by a circle such as would be drawn on the spheres by a pair of dividers set to an opening
26、 of 0.3 D and centred on the sparking point. The freedom from surface irregularities shall be checked by a spherometer of which the feet are between 0.125 D and 0.25 D apart. A spherometer measures the distance h of its central point from the plane passing through the three feet of the instrument, w
27、hich form an equilateral triangle of side a. When the three feet and the central point are in contact with a perfectly spherical surface of radius D/2, a value for h is obtained as follows: 1) BS 923, “Impulse-voltage testing”. Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:0
28、0 2006, Uncontrolled Copy, (c) BSI BS 358:1960 2 BSI 08-1999 When the feet of the spherometer are placed on the spheres in various positions in the region defined above, the difference between the measured values of h and the value given in the formula shall nowhere exceed: 0.1 per cent of the nomin
29、al diameter (D) if this is less than or equal to 100 cm. 0.2 per cent of the nominal diameter (D) if this is greater than 100 cm. If a spherometer is not available, a flat circular gauge may be used for an approximate evaluation of surface irregularities. NOTEThe tolerances on size and shape need us
30、ually only be checked in the manner described above when the spheres are first supplied. It will normally be sufficient to make subsequent examinations by feeling the spheres or inspecting them visually. c) State of the surfaces. In the neighbourhood of the sparking points the spheres shall be free
31、from any trace of varnish, grease or other protective coating. They shall be clean and dry but need not be polished. If the spheres become excessively roughened or pitted in use they shall be reburnished or replaced. NOTEIf the relative humidity of the air exceeds about 90 per cent, moisture may con
32、dense on to the surface and the measurements will then cease to be accurate. 4 Construction and mounting of the spheres a) Vertical gap. When the spheres are mounted vertically, the shank of the high-voltage sphere shall be free from sharp edges or corners and its diameter shall not exceed 0.2 D ove
33、r a length D. This requirement is made in order to reduce the influence of the high-voltage shank on the flashover voltage. If a stress distributor is used at the end of the shank, its greatest dimensions, perpendicular to the axis of the spheres, shall not exceed 0.5 D. Such stress distributors sha
34、ll be at least 2 D from the sparking point of the high-voltage sphere. The earthed shank and the operating gear have a smaller effect and their dimensions are therefore less important. Figure 1 gives the limits of size of the components of a typical vertical sphere-gap. b) Horizontal gap. The limiti
35、ng dimensions of a typical sphere-gap for horizontally mounted spheres are given in Figure 2. They are the same for both sides of the gap. NOTEThe sphere shanks shall be reasonably in line, whichever form of gap is used. 5 Height of the spheres above the horizontal earth plane The sphere-gap should
36、be used with the sparking point at a distance A from an earthed plane, such as a conducting network in or on the floor of the laboratory, or some other large conducting surface; the distance A shall be within the limits given in Table 1. This requirement applies whether the axis of the gap is parall
37、el or normal to the earthed plane. Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 358:1960 BSI 08-19993 Figure 1 Typical vertical sphere-gap Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:00 2006, Uncontrolled Cop
38、y, (c) BSI BS 358:1960 4 BSI 08-1999 Figure 2 Typical horizontal sphere-gap Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:39:20 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 358:1960 BSI 08-19995 6 Clearance around the spheres The distance from the sparking point of the high-voltage sphe
39、re to any extraneous objects (such as walls, a ceiling, transformer tanks, bushings, impulse generators, etc.) and also to the supporting framework for the spheres if this is made of conducting material, shall not be less than the value for B given in Table 1. Except as permitted below, B shall not
40、be less than 2 D regardless of the value of S. When made of insulating material, supporting frameworks for the spheres are exempt from this stipulation provided that they are clean and dry and that the spheres are used for the measurement of alternating or impulse voltages only. The distance B betwe
41、en the sparking point of the high voltage sphere and the framework may then be less than is prescribed in Table 1, but it must not be below 1.6 D. Table 1 Clearances round the spheres 7 Connection of the sphere-gap a) Earthing. One sphere shall be connected directly to earth, but, for special purpos
42、es, it may be connected through resisters. In the interests of personal safety, however, such resistors shall be of very low value. b) High-voltage conductor. The high-voltage conductor, including any series resistor not in the shank itself, shall be connected to a point on the shank at least 2 D aw
43、ay from the sparking point of the high-voltage sphere. Within the region where the distance to the sparking point of the high-voltage sphere is less than B, the live conductor, including the series resistor, if any, shall not pass through a plane normal to the axis of the sphere-gap and situated at
44、a distance 2 D from the sparking point of the high-voltage sphere (see Figure 1 and Figure 2 where the plane is shown). c) Protective series resistance in the measurement of alternating and direct voltages. Precautions should be taken to minimize pitting of the spheres and to prevent superimposed os
45、cillations which may cause erratic flashovers. For this purpose a resistance of 100 kilohms to 1 megohm should be inserted in series with the sphere-gap. This range of resistance values applies to measurements of direct voltages and of alternating voltages at power frequencies. For alternating volta
46、ges of higher frequencies, where the effect of the voltage drop in the resistance due to the charging current of the gap may become appreciable, the resistance should be suitably reduced. Sphere diameter, DMinimum value of AMaximum value of AMinimum value of B cm Up to 6.25 10 15 25 7 D 6 D 5 D 9 D
47、8 D 7 D 14 S 12 S 10 S 50 75 100 4 D 4 D 3.5 D 6 D 6 D 5 D 8 S 8 S 7 S 150 200 3 D 3 D 4 D 4 D 6 S 6 S NOTE 1The test conditions may make it impossible for the values of A and B to meet the requirements in the table. In such cases the sphere-gap may nevertheless be regarded as satisfactory if the sp
48、here-gap readings corresponding to some value of a related parameter, e.g. transformer primary voltage with the specified and with the test clearances, do not differ significantly. Small earthed or live objects at less than the distance B from the sparking point of the high-voltage sphere do not aff
49、ect the results appreciably if the sphere-gap spacing is low. When, however, the spacing approaches 0.5 D the presence, even at the distance B, of large conducting surfaces such as walls has an important effect. Table 3 and Table 4 have been derived from experimental calibrations made in open laboratories with not more than one wall at the distance B and the other walls at greater distances. If, therefore, the sphere-gap is placed in an earthed cylindrical container of radius B the calibrations in this document will no longer apply, except at very