《BS-7769-2-2.1-1997 IEC-60287-2-1-1994.pdf》由会员分享，可在线阅读，更多相关《BS-7769-2-2.1-1997 IEC-60287-2-1-1994.pdf（36页珍藏版）》请在三一文库上搜索。
1、BRITISH STANDARD BS 7769-2-2.1: 1997 IEC 60287-2-1: 1994 Incorporating Amendment No. 1 Electric cables Calculation of the current rating Part 2: Thermal resistance Section 2.1 Calculation of thermal resistance ICS 29.060.20 ? Licensed Copy: London South Bank University, London South Bank University,
2、 Fri Dec 08 12:10:35 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7769-2-2.1:1997 This British Standard, having been prepared under the direction of the Electrotechnical Sector Board, was published under the authority of the Standards Board and comes into effect on 15 February 1997 BSI 24 July 2002
3、 The following BSI references relate to the work on this standard: Committee reference GEL/20 Draft announced in BSI Update May 1995 ISBN 0 580 26922 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee GEL/20, Electric cabl
4、es, upon which the following bodies were represented: Association of Consulting Engineers Association of Manufacturers of Domestic Electrical Appliances BEAMA (Electrical Cable and Conductor Accessory Manufacturers Association) British Approvals Service for Cables British Cable Makers Confederation
5、British Iron and Steel Producers Association British Plastics Federation Department of Trade and Industry (Consumer Safety Unit, CA division) Electricity Association London Regional Transport The following bodies were also represented in the drafting of the standard, through subcommittees and panels
6、: ERA Technology Ltd. Institution of Incorporated Executive Engineers London Underground Ltd. Amendments issued since publication Amd. No.DateComments 1366524 July 2002See national foreword Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:10:35 GMT+00:00 2006,
7、 Uncontrolled Copy, (c) BSI BS 7769-2-2.1:1997 BSI 24 July 2002 i Contents Page Committees responsibleInside front cover National forewordii Introduction1 1General1 1.1Scope1 1.2Symbols2 2Calculation of thermal resistances3 2.1Thermal resistance of the constituent parts of a cable, T1, T2 and T34 2.
8、2External thermal resistance T49 3Digital calculation of quantities given graphically14 3.1General16 3.2Calculation of ?s by means of a diagram (Figure 8)19 Figure 1 Diagram showing a group of q cables and their reflection in the ground-air surface22 Figure 2 Geometric factor G for two-core belted c
9、ables with circular conductors23 Figure 3 Geometric factor G for three-core belted cables with circular conductors24 Figure 4 Thermal resistance of three-core screened cables with circular conductors compared to that of a corresponding unscreened cable25 Figure 5 Thermal resistance of three-core scr
10、eened cables with sector-shaped conductors compared with that of a corresponding unscreened cable26 Figure 6 Geometric factor for obtaining the thermal resistances of the filling material between the sheaths and armour of SL and SA type cables27 Figure 7 Heat dissipation coefficient for black surfac
11、es of cables in free air28 Figure 8 Graph for the calculation of external thermal resistance of cables in air31 Table 1 Thermal resistivities of materials20 Table 2 Values for constants Z, E and g for black surfaces of cables in free air 21 Table 3 Absorption coefficient of solar radiation for cable
12、 surfaces 22 Table 4 Values of constants U, V and Y 22 G Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:10:35 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7769-2-2.1:1997 ii BSI 24 July 2002 National foreword This Section of BS 7769 has been prepared by Tec
13、hnical Committee GEL/20. It is identical with IEC 60287-2-1:1994, Electric cables Calculation of the current rating Part 2: Thermal resistance Section 1: Calculation of thermal resistance, including amendment 1:2001, published by the International Electrotechnical Commission (IEC). The start and fin
14、ish of text introduced or altered by amendment is indicated in the text by tags ?. Tags indicating changes to IEC text carry the number of the IEC amendment. For example, text altered by IEC amendment 1 is indicated by ?. From 1 January 1997, all IEC publications have the number 60000 added to the o
15、ld number. For instance, IEC 27-1 has been renumbered as IEC 60027-1. For a period of time during the change over from one numbering system to the other, publications may contain identifiers from both systems. Cross-references The British Standards which implement international or European publicati
16、ons referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessa
17、ry provisions of a contract. Users are responsible for its 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 31 and a back cover.
18、 The BSI copyright notice displayed in this document indicates when the document was last issued. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:10:35 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7769-2-2.1:1997 BSI 24 July 2002 1 Introduction IEC 60287 has
19、 been divided into three parts and sections so that revisions of, and additions to, the document can be carried out more conveniently. Each part is divided into sections which are published as separate standards. Part 1: Formulae of ratings and power losses; Part 2: Formulae for thermal resistance;
20、Part 3: Sections on operating conditions. This section of IEC 60287-2 contains methods for calculating the internal thermal resistance of cables and the external thermal resistance for cables laid in free air, ducts and buried. The formulae in this standard contain quantities which vary with cable d
21、esign and materials used. The values given in the tables are either internationally agreed, for example, electrical resistivities and resistance temperature coefficients, or are those which are generally accepted in practice, for example, thermal resistivities and permittivities of materials. In thi
22、s latter category, some of the values given are not characteristic of the quality of new cables but are considered to apply to cables after a long period of use. In order that uniform and comparable results may be obtained, the current ratings should be calculated with the values given in this stand
23、ard. However, where it is known with certainty that other values are more appropriate to the materials and design, then these may be used, and the corresponding current rating declared in addition, provided that the different values are quoted. Quantities related to the operating conditions of cable
24、s are liable to vary considerably from one country to another. For instance, with respect to the ambient temperature and soil thermal resistivity, the values are governed in various countries by different considerations. Superficial comparisons between the values used in the various countries may le
25、ad to erroneous conclusions if they are not based on common criteria: for example, there may be different expectations for the life of the cables, and in some countries design is based on maximum values of soil thermal resistivity, whereas in others average values are used. Particularly, in the case
26、 of soil thermal resistivity, it is well known that this quantity is very sensitive to soil moisture content and may vary significantly with time, depending on the soil type, the topographical and meteorological conditions, and the cable loading. The following procedure for choosing the values for t
27、he various parameters should, therefore, be adopted: Numerical values should preferably be based on results of suitable measurements. Often such results are already included in national specifications as recommended values, so that the calculation may be based on these values generally used in the c
28、ountry in question; a survey of such values is given in Part 3, Section 1. A suggested list of the information required to select the appropriate type of cable is given in Part 3, Section 1. 1 General 1.1 Scope This section of IEC 60287 is solely applicable to the conditions of steady-state operatio
29、n of cables at all alternating voltages, and direct voltages up to 5 kV, buried directly in the ground, in ducts, in troughs or in steel pipes, both with and without partial drying-out of the soil, as well as cables in air. The term “steady state” is intended to mean a continuous constant current (1
30、00 % load factor) just sufficient to produce asymptotically the maximum conductor temperature, the surrounding ambient conditions being assumed constant. This section provides formulae for thermal resistance. The formulae given are essentially literal and designedly leave open the selection of certa
31、in important parameters. These may be divided into three groups: parameters related to construction of a cable (for example, thermal resistivity of insulating material) for which representative values have been selected based on published work; parameters related to the surrounding conditions which
32、may vary widely, the selection of which depends on the country in which the cables are used or are to be used; parameters which result from an agreement between manufacturer and user and which involve a margin for security of service (for example, maximum conductor temperature). Licensed Copy: Londo
33、n South Bank University, London South Bank University, Fri Dec 08 12:10:35 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7769-2-2.1:1997 2 BSI 24 July 2002 1.2 Symbols The symbols used in this standard and the quantities which they represent are given in the following list: D?aexternal diameter of a
34、rmourmm Ddinternal diameter of ducmm Deexternal diameter of cable, or equivalent diameter of a group of cores in pipe-type cable mm D*eexternal diameter of cable (used in 2.2.1)m Doexternal diameter of ductmm Dsexternal diameter of metal sheathmm Docthe diameter of the imaginary coaxial cylinder whi
35、ch just touches the crests of a corrugated sheath mm Dotthe diameter of the imaginary coaxial cylinder which would just touch the outside surface of the troughs of a corrugated sheath = Dit + 2ts mm Dicthe diameter of the imaginary cylinder which would just touch the inside surface of the crests of
36、a corrugated sheath = Doc 2ts mm Ditthe diameter of the imaginary cylinder which just touches the inside surface of the troughs of a corrugated sheath mm Econstant used in 2.2.1.1 F1coefficient for belted cables defined in 2.1.1.2.2 F2coefficient for belted cables defined in 2.1.1.2.5 Ggeometric fac
37、tor for belted cables geometric factor for SL and SA type cables Hintensity of solar radiation (see 2.2.1.2)W/m2 Kscreening factor for the thermal resistance of screened cables KAcoefficient used in 2.2.1 Ldepth of laying, to cable axis or centre of trefoilmm LGdistance from the soil surface to the
38、centre of a duct bankmm Nnumber of loaded cables in a duct bank (see 2.2.7.3) T1thermal resistance per core between conductor and sheathK?m/W T2thermal resistance between sheath and armourK?m/W T3thermal resistance of external servingK?m/W T4thermal resistance of surrounding medium (ratio of cable s
39、urface temperature rise above ambient to the losses per unit length) K?m/W T*4external thermal resistance in free air, adjusted for solar radiationK?m/W T?4thermal resistance between cable and duct (or pipe)K?m/W T?4thermal resistance of the duct (or pipe)K?m/W T?4thermal resistance of the medium su
40、rrounding the duct (or pipe)K?m/W U V constants used in 2.2.7.1 Wddielectric losses per unit length per phaseW/m Wklosses dissipated by cable kW/m WTOTtotal power dissipated in the trough per unit lengthW/m Ycoefficient used in 2.2.7.1 Zcoefficient used in 2.2.1.1 G ? ? ? Licensed Copy: London South
41、 Bank University, London South Bank University, Fri Dec 08 12:10:35 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7769-2-2.1:1997 BSI 24 July 2002 3 daexternal diameter of belt insulationmm dcexternal diameter of conductormm dcmminor diameter of an oval conductormm dcMmajor diameter of an oval condu
42、ctormm dMmajor diameter of screen or sheath of an oval conductormm dmminor diameter of screen or sheath of an oval conductormm dxdiameter of an equivalent circular conductor having the same cross-sectional area and degree of compactness as the shaped one mm gcoefficient used in 2.2.1.1 hheat dissipa
43、tion coefficientW/m2K5/4 lnnatural logarithm (logarithm to base e) nnumber of conductors in a cable pthe part of the perimeter of the cable trough which is effective for heat dissipation (see 2.2.6.2) m r1circumscribing radius of two or three-sector shaped conductorsmm s1axial separation of two adja
44、cent cables in a horizontal group of three, not touchingmm tinsulation thickness between conductorsmm t1insulation thickness between conductors and sheathmm t2thickness of the beddingmm t3thickness of the servingmm tithickness of core insulation, including screening tapes plus half the thickness of
45、any non-metallic tapes over the laid up cores mm tsthickness of the sheathmm u in 2.2.2 uin 2.2.7.3 x, ysides of duct bank (y x) (see 2.2.7.3)mm ?mean temperature of medium between a cable and duct or pipe?C ?permissible temperature rise of conductor above ambient temperatureK ?factor to account for
46、 dielectric loss for calculating T4 for cables in free airK ?factor to account for both dielectric loss and direct solar radiation for calculatingfor cables in free air using Figure 8 K ?difference between the mean temperature of air in a duct and ambient temperatureK ?difference between the surface
47、 temperature of a cable in air and ambient temperature K ?temperature rise of the air in a cable troughK ?ratio of the total losses in metallic sheaths and armour respectively to the total conductor losses (or losses in one sheath or armour to the losses in one conductor) ?1mloss factor for the midd
48、le cable Three cables in flat formation without transposition, with sheaths bonded at both ends ?11loss factor for the outer cable with the greater losses ?12loss factor for the outer cable with the least losses ?thermal resistivity of earth surrounding a duct bankK?m/W ?thermal resistivity of concr
49、ete used for a duct bankK?m/W 2L De - - L G r b - - T4 * ? ? ? ? ? Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:10:35 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7769-2-2.1:1997 4 BSI 24 July 2002 2 Calculation of thermal resistances 2.1 Thermal resistance of the constituent parts of a cable, T1, T2 and T3 This clause gives the formulae for calculating the th