BS IEC 60287-2-1-2015 Electric cables Calculation of the current rating Thermal resistance Calculation of thermal resistance《电缆 电流额定值的计算 热阻 热阻的计算》.pdf

1、BSI Standards PublicationElectric cables Calculation of the current ratingPart 2-1: Thermal resistance Calculation of thermal resistanceBS IEC 60287-2-1:2015National forewordThis British Standard is the UK implementation of IEC 60287-2-1:2015. Itsupersedes BS IEC 60287-2-1:1994+A2:2006 which is with

2、drawn.The UK participation in its preparation was entrusted by TechnicalCommittee GEL/20, Electric cables, to Subcommittee GEL/20/16, ElectricCables - Medium/high voltage.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purpor

3、t to include all the necessary provisions ofa contract. Users are responsible for its correct application. The British Standards Institution 2015.Published by BSI Standards Limited 2015ISBN 978 0 580 80953 8ICS 29.060.20Compliance with a British Standard cannot confer immunity fromlegal obligations.

4、This British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 April 2015.Amendments/corrigenda issued since publicationDate Text affectedBRITISH STANDARDBS IEC 60287-2-1:2015IEC 60287-2-1 Edition 2.0 2015-04 INTERNATIONAL STANDARD NORME INTERNATIONALE El

5、ectric cables Calculation of the current rating Part 2-1: Thermal resistance Calculation of thermal resistance Cbles lectriques Calcul du courant admissible Partie 2-1: Rsistance thermique Calcul de la rsistance thermique INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNAT

6、IONALE ICS 29.060.20 ISBN 978-2-8322-2583-7 Registered trademark of the International Electrotechnical Commission Marque dpose de la Commission Electrotechnique Internationale Warning! Make sure that you obtained this publication from an authorized distributor. Attention! Veuillez vous assurer que v

7、ous avez obtenu cette publication via un distributeur agr. 2 IEC 60287-2-1:2015 IEC 2015 CONTENTS FOREWORD. 4 INTRODUCTION . 6 1 Scope 7 2 Normative references 7 3 Symbols 7 4 Calculation of thermal resistances 10 4.1Thermal resistance of the constituent parts of a cable, T1, T2and T310 4.1.1 Genera

8、l . 10 4.1.2 Thermal resistance between one conductor and sheath T1. 10 4.1.3 Thermal resistance between sheath and armour T214 4.1.4 Thermal resistance of outer covering (serving) T3. 14 4.1.5 Pipe-type cables 15 4.2 External thermal resistance T416 4.2.1 Cables laid in free air . 16 4.2.2 Single i

9、solated buried cable 17 4.2.3 Groups of buried cables (not touching) . 18 4.2.4 Groups of buried cables (touching) equally loaded 20 4.2.5 Buried pipes 22 4.2.6 Cables in buried troughs 22 4.2.7 Cables in ducts or pipes . 22 5 Digital calculation of quantities given graphically 24 5.1 General . 24 5

10、.2 Geometric factor G for two-core belted cables with circular conductors . 24 5.3 Geometric factor G for three-core belted cables with circular conductors 25 5.4 Thermal resistance of three-core screened cables with circular conductors compared to that of a corresponding unscreened cable 26 5.5 The

11、rmal resistance of three-core screened cables with sector-shaped conductors compared to that of a corresponding unscreened cable 26 5.6 Curve for Gfor obtaining the thermal resistance of the filling material between the sheaths and armour of SL and SA type cables 27 5.7 Calculation of sby means of a

12、 diagram 27 Bibliography . 42 Figure 1 Diagram showing a group of q cables and their reflection in the ground-air surface . 32 Figure 2 Geometric factor G for two-core belted cables with circular conductors (see 4.1.2.2.2) 33 Figure 3 Geometric factor G for three-core belted cables with circular con

13、ductors (see 4.1.2.2.4) 34 Figure 4 Thermal resistance of three-core screened cables with circular conductors compared to that of a corresponding unscreened cable (see 4.1.2.3.1) 35 Figure 5 Thermal resistance of three-core screened cables with sector-shaped conductors compared with that of a corres

14、ponding unscreened cable (see 4.1.2.3.3) . 36 Figure 6 Geometric factor Gfor obtaining the thermal resistances of the filling material between the sheaths and armour of SL and SA type cables (see 4.1.3.2) 37 Figure 7 Heat dissipation coefficient for black surfaces of cables in free air, laying condi

15、tion #1 to #4 . 38 BS IEC 60287-2-1:2015IEC 60287-2-1:2015 IEC 2015 3 Figure 8 Heat dissipation coefficient for black surfaces of cables in free air, laying condition #5 to #8 . 39 Figure 9 Heat dissipation coefficient for black surfaces of cables in free air, laying condition #9 to #10 . 40 Figure

16、10 Graph for the calculation of external thermal resistance of cables in air . 41 Table 1 Thermal resistivities of materials 29 Table 2 Values for constants Z, E and g for black surfaces of cables in free air . 30 Table 3 Absorption coefficient of solar radiation for cable surfaces 31 Table 4 Values

17、 of constants U, V and Y 31 BS IEC 60287-2-1:2015 4 IEC 60287-2-1:2015 IEC 2015 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ ELECTRIC CABLES CALCULATION OF THE CURRENT RATING Part 2-1: Thermal resistance Calculation of thermal resistance FOREWORD 1) The International Electrotechnical Commission (IEC)

18、 is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition

19、to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested i

20、n the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with cond

21、itions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC Nat

22、ional Committees. 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the w

23、ay in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IE

24、C Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity.

25、IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of i

26、ts technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any ot

27、her IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be th

28、e subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 60287-2-1 has been prepared by IEC technical committee 20: Electric cables. This second edition of IEC 60287-2-1 cancels and replaces the first edition, published i

29、n 1994, Amendment 1:2001, Amendment 2:2006 and Corrigendum 1:2008. The document 20/1448/CDV, circulated to the National Committees as Amendment 3, led to the publication of this new edition. This edition constitutes a technical revision. This edition includes the following significant technical chan

30、ges with respect to the previous edition: a) inclusion of a reference to the use of finite element methods where analytical methods are not available for the calculation of external thermal resistance; b) explanation about SL and SA type cables; BS IEC 60287-2-1:2015IEC 60287-2-1:2015 IEC 2015 5 c)

31、calculation method for T3 for unarmoured three-core cables with extruded insulation and individual copper tape screens on each core; d) change of condition for X in 5.4; e) inclusion of constants or installation conditions for water filled ducts in Table 4. The text of this standard is based on the

32、following documents: FDIS Report on voting 20/1561/FDIS 20/1588/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. A list of all p

33、arts in the IEC 60287 series, published under the general title Electric cables Calculation of the current rating, can be found on the IEC website. The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the IEC website under “http:

34、/webstore.iec.ch“ in the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition, or amended. BS IEC 60287-2-1:2015 6 IEC 60287-2-1:2015 IEC 2015 INTRODUCTION IEC 60287 has been divided into three parts so that revisions o

35、f, and additions to the document can be carried out more conveniently. Each part is subdivided into subparts which are published as separate standards. Part 1: Formulae of ratings and power losses Part 2: Formulae for thermal resistance Part 3: Operating conditions This part of IEC 60287-2 contains

36、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 design and materials used. The values given in the tables are either internation

37、ally 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 this latter category, some of the values given are not characteristic of the quali

38、ty 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 standard. However, where it is known with certainty that other values are more appro

39、priate 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 cables are liable to vary considerably from one country to another. For instance, wi

40、th 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 lead to erroneous conclusions if they are not based on common criteria: for examp

41、le, 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 of soil thermal resistivity, it is well known that this quantity is very sensi

42、tive 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 the various parameters should, therefore, be adopted: Numerical values should pr

43、eferably 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 country in question; a survey of such values is given in IEC 60287-3-1. A sugges

44、ted list of the information required to select the appropriate type of cable is given in IEC 60287-3-1. BS IEC 60287-2-1:2015IEC 60287-2-1:2015 IEC 2015 7 ELECTRIC CABLES CALCULATION OF THE CURRENT RATING Part 2-1: Thermal resistance Calculation of thermal resistance 1 Scope This part of IEC 60287 i

45、s solely applicable to the conditions of steady-state operation 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 “stea

46、dy state“ is intended to mean a continuous constant current (100 % load factor) just sufficient to produce asymptotically the maximum conductor temperature, the surrounding ambient conditions being assumed constant. This part of IEC 60287 provides formulae for thermal resistance. The formulae given

47、are essentially literal and designedly leave open the selection of certain 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

48、 published work; parameters related to the surrounding conditions which 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 se

49、rvice (for example, maximum conductor temperature). Equations given in this part of IEC 60287 for calculating the external thermal resistance of a cable buried directly in the ground or in a buried duct are for a limited number of installation conditions. Where analytical methods are not available for calculation of external thermal resistance finite element methods may be used. Guidance on the use of finite element methods for calculating cable curre