1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationElectric cables Calculation of the current ratingPart 3-2: Sections on operating conditions Economic optimization of power cable sizeBS IEC 60287-3-2:2012BS 7769-3-2:2012National
2、 forewordThis British Standard is the UK implementation of IEC 60287-3-2:2012.The UK participation in its preparation was entrusted by Technical CommitteeGEL/20, Electric cables, to Subcommittee GEL/20/16, Electric Cables Medium/high voltage.A list of organizations represented on this committee can
3、be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisions of acontract. Users are responsible for its correct application. The British Standards Institution 2012Published by BSI Standards Limited 2012ISBN 978 0 580 81133 3ICS 29.060.20Compliance
4、 with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of the StandardsPolicy and Strategy Committee on 30 November 2012.Amendments issued since publicationAmd. No. Date Text affectedBRITISH STANDARDBS IEC 60287-3-2:2012IEC 60287
5、-3-2 Edition 2.0 2012-07 INTERNATIONAL STANDARD NORME INTERNATIONALE Electric cables Calculation of the current rating Part 3-2: Sections on operating conditions Economic optimization of power cable size Cbles lectriques Calcul du courant admissible Partie 3-2: Sections concernant les conditions de
6、fonctionnement Optimisation conomique des sections dme de cbles lectriques de puissance INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE W ICS 29.060.20 PRICE CODE CODE PRIX ISBN 978-2-83220-151-0 Registered trademark of the International Electrotechnical Commissi
7、on Marque dpose de la Commission Electrotechnique Internationale Warning! Make sure that you obtained this publication from an authorized distributor. Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agr. BS IEC 60287-3-2:2012 2 60287-3-2 IEC:2012 CONTENTS
8、FOREWORD . 3 INTRODUCTION . 5 1 Scope . 8 2 Normative references . 8 3 Symbols . 8 4 Calculation of total costs 10 5 Determination of economic conductor sizes 13 5.1 First approach: economic current range for each conductor in a series of sizes . 13 5.2 Second approach: economic conductor size for a
9、 given load . 13 5.2.1 General equation . 13 5.2.2 Linear cost function for cable costs 14 5.2.3 Effect of charging current and dielectric losses 15 Annex A (informative) Examples of calculation of economic conductor sizes 17 Annex B (informative) Mean conductor temperature and resistance . 33 Bibli
10、ography 38 Figure A.1 System layout . 26 Figure A.2 Economic current ranges 27 Figure A.3 Variation of cost with conductor size . 28 Table A.1 Economic current ranges for cable sizes 25 mm2to 400 mm2. 19 Table A.2 Summary of costs 23 Table A.3 Cable details 23 Table A.4 Economic loading . 24 Table A
11、.5 Current-carrying capacity criterion . 24 Table A.6 Economic loading, standard conductor size for all sections Standard size: 150 mm2 25 Table A.7 Economic loading, standard conductor size for all sections Standard size: 185 mm225 Table A.8 Economic loading, standard conductor size for all section
12、s Standard size: 240 mm226 Table A.9 Cable details 29 Table A.10 Steady state current ratings . 30 Table A.11 Total costs . 31 Table A.12 Total cost versus anticipated operational life 31 Table A.13 Losses versus anticipated operational life 32 Table B.1 Required data for conductor sizes for the abo
13、ve example 34 BS IEC 60287-3-2:201260287-3-2 IEC:2012 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ ELECTRIC CABLES CALCULATION OF THE CURRENT RATING Part 3-2: Sections on operating conditions Economic optimization of power cable size FOREWORD 1) The International Electrotechnical Commission (IEC) i
14、s 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 to
15、 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 in
16、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 condit
17、ions 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 Natio
18、nal 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 way
19、 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 IEC
20、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. IE
21、C 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 its
22、 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 othe
23、r 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 the
24、subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 60287-3-2 has been prepared by IEC technical committee 20: Electric cables. This second edition cancels and replaces the first edition, published in 1995 and its Amen
25、dment 1:1996. This edition consitutes a technical revision. This edition incorporates Amendment 2 which was not published separately due to the number of changes and pages. The main changes with respect to the previous edition are as follows: update of the normative references; clarification of some
26、 symbols; correction of some formulae; introduction of a second example in Annex A for the calculation of the economic conductor size. BS IEC 60287-3-2:2012 4 60287-3-2 IEC:2012 The text of this standard is based on the first edition, its amendment 1 and the following documents: FDIS Report on votin
27、g 20/1367/FDIS 20/1373/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 parts in the IEC 60287 series can be found
28、 on the IEC website under the general title: Calculation of the current rating. The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the IEC web site under “http:/webstore.iec.ch“ in the data related to the specific publication.
29、At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition, or amended. BS IEC 60287-3-2:201260287-3-2 IEC:2012 5 INTRODUCTION 0.1 General part The procedure generally used for the selection of a cable size leads to the minimum admissible cross-sectional area, which
30、also minimizes the initial investment cost of the cable. It does not take into account the cost of the losses that will occur during the life of the cable. The increasing financial and environmental cost of energy, together with the energy losses which follow from conductors operating at high temper
31、atures, requires that cable size selection be considered on wider grounds. Rather than minimizing the initial cost only, the sum of the initial cost and the cost of the losses over the anticipated operational life of the system should be minimized. For this latter condition, a larger size of conduct
32、or than would be chosen based on minimum initial cost will lead to a lower power loss for the same current. This, when considered over its anticipated operational life, will reduce the energy losses and the total cost of the system. Where thermal consideration dictates the use of the largest practic
33、al conductor size, the installation of a second parallel cable circuit can result in a reduction in the total cost over the life of the installation. The formulae and examples given in this standard are arranged to facilitate the calculation of the economic conductor size after factors such as syste
34、m voltage, cable route, cable configuration and sheath bonding arrangements have been decided. Although these factors are not considered in detail, they have an impact on both the installation and operating costs of a cable system. The effect of changing any of the above factors on the total cost ov
35、er the anticipated operational life of the system can be determined using the principles set out in this standard. Future costs of energy losses during the anticipated operational life of the cable can be calculated by making suitable estimates of load growth and cost of energy. The most economical
36、size of conductor is achieved when the sum of the future costs of energy losses and the initial cost of purchase and installation are minimized. The saving in overall cost, when a conductor size larger than that determined by thermal constraints is chosen, is due to the considerable reduction in the
37、 cost of the joule losses compared with the increase in cost of purchase. For the values of the financial and electrical parameters used in this standard, which are not exceptional, the saving in the combined cost of purchase and operation is of the order of 50 % (see A.2.5). Calculations for much s
38、horter financial periods can show a similar pattern. A further important feature, which is demonstrated by examples, is that the savings possible are not critically dependent on the conductor size when it is in the region of the economic value, see Figure A.3. This has two implications: a) the impac
39、t of errors on financial data, particularly those which determine future costs, is small. While it is advantageous to seek data having the best practicable accuracy, considerable savings can be achieved using data based on reasonable estimates; b) other considerations with regard to the choice of co
40、nductor size which feature in the overall economics of an installation, such as fault currents, voltage drop and size rationalization, can all be given appropriate emphasis, without losing too many of the benefits arising from the choice of an economic size. The formulae given in this standard are w
41、ritten for a.c. systems but they are equally applicable to d.c. systems. Clearly, for d.c. systems, the d.c. resistance is used in place of the a.c. resistance and the sheath and armour loss factors are set to zero. BS IEC 60287-3-2:2012 6 60287-3-2 IEC:2012 0.2 Economic aspects In order to combine
42、the purchase and installation costs with costs of energy losses arising during the anticipated operational life of a cable, it is necessary to express them in comparable economic values, that is values which relate to the same point in time. It is convenient to use the date of purchase of the instal
43、lation as this point and to refer to it as the “present“. The “future“ costs of the energy losses are then converted to their equivalent “present values“. This is done by the process of discounting, the discounting rate being linked to the cost of borrowing money. In the procedure given here, inflat
44、ion has been omitted on the grounds that it will affect both the cost of borrowing money and the cost of energy. If these items are considered over the same period of time and the effect of inflation is approximately the same for both, the choice of an economic conductor size can be made satisfactor
45、ily without introducing the added complication of inflation. To calculate the present value of the costs of the losses it is necessary to choose appropriate values for the future development of the load, annual increases in kWh price and annual discounting rates over the anticipated operational life
46、 of the cable, which could be 25 years or more. It is not possible to give guidance on these aspects in this standard because they are dependent on the conditions and financial constraints of individual installations. Only the appropriate formulae are given: it is the responsibility of the designer
47、and the user to agree on the economic factors to be used. The formulae proposed in this standard are straightforward, but in their application due regard should be taken of the assumption that the financial parameters are assumed to remain unchanged during the anticipated operational life of the cab
48、le. Nevertheless, the above comments on the effect of the accuracy of these parameters is also relevant here. There are two approaches to the calculation of the economic size, based on the same financial concepts. The first, where a series of conductor sizes is being considered, is to calculate a ra
49、nge of economic currents for each of the conductor sizes envisaged for particular installation conditions and then to select that size whose economic range contains the required value of the load. This approach is appropriate where several similar installations are under consideration. The second method, which may be more suitable where only one installation is involved, is to calculate the optimum cross-sectional area for the required load an
