BS IEC 60287-1-3-2003 Electric cables - Calculation of the current rating - Current rating equations (100 % load factor) and calculation of losses - Current sharing between parallei.pdf

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1、BRITISH STANDARD BS IEC 60287-1-3:2002 Electric cables Calculation of the current rating Part 1-3: Current rating equations (100 % load factor) and calculation of losses Current sharing between parallel single-core cables and calculation of circulating current losses ICS 29.060.20 BS IEC 60287-1-3:2

2、002 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 15 October 2003 BSI 15 October 2003 ISBN 0 580 42727 7 National foreword This British Standard reproduces verbatim IEC 60287-1-3:2002 and implements it as the UK national standard. The UK pa

3、rticipation in its preparation was entrusted by Technical Committee GEL/20, Electric cables, to Subcommittee GEL/20/16, MV/HV cables, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British St

4、andards which implement international publications 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 publicat

5、ion does not purport to include all the necessary 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. aid enquirers to understand the text; present to the responsible international/

6、European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the IEC title pag

7、e, pages 2 to 20, an inside back cover and a back cover The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsNORME INTERNATIONALE CEI IEC INTERNATIONAL STANDARD 60287-1-3 Premire dition First editio

8、n 2002-05 Cbles lectriques Calcul du courant admissible Partie 1-3: Equations de lintensit du courant admissible (facteur de charge 100 %) et calcul des pertes Rpartition du courant entre des c bles unipolaires disposs en parallle et calcul des pertes par courant de circulation Electric cables Calcu

9、lation of the current rating Part 1-3: Current rating equations (100 % load factor) and calculation of losses Current sharing between parallel single-core cables and calculation of circulating current losses Numro de rfrence Reference number CEI/IEC 60287-1-3:2002 BSIEC6028713:2002 CONTENTS FOREWORD

10、.3 INTRODUCTION. .4 1 Scope.5 2 Normative references .5 3 Symbols. .5 4 Description of method .6 4.1 General .6 4.2 Outline of method .7 4.3 Matrix solution . .10 Annex A (informative) Example calculations .11 Annex B (informative) Example of the computation of the coefficient for hollow core conduc

11、tors. 19 Bibliography 20 Figure B.1 . Representation of a hollow core conductor 19 Table 1 . Values of for conductors 9 Table A.1 . Calculated values of d j,k 15 Table A.2 . Calculated values of zz 15 Table A.3 . Array Z including coefficients for currents. .16 2 BSIEC6028713:2002INTERNATIONAL ELECT

12、ROTECHNICAL COMMISSION _ ELECTRIC CABLES CALCULATION OF THE CURRENT RATING Part 1-3: Current rating equations (100 % load factor)and calculation of losses Current sharing between parallel single-core cables and calculation of circulating current losses FOREWORD 1) The IEC (International Electrotechn

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

14、end and in addition to other activities, the IEC publishes International Standards. Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organ

15、izations liaising with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of the IEC on tec

16、hnical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested National Committees. 3) The documents produced have the form of recommendations for international use and are published

17、in the form of standards, technical specifications, technical reports or guides and they are accepted by the National Committees in that sense. 4) In order to promote international unification, IEC National Committees undertake to apply IEC International Standards transparently to the maximum extent

18、 possible in their national and regional standards. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter. 5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equip

19、ment declared to be in conformity with one of its standards. 6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights. International Stand

20、ard IEC 60287-1-3 has been prepared by IEC technical committee 20: Electric cables. The text of this standard is based on the following documents: FDIS Report on voting 20/522/FDIS 20/535/RVD Full information on the voting for the approval of this standard can be found in the report on voting indica

21、ted in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 3. Annexes A and B are for information only. The committee has decided that this publication remains valid until 2008. At this date, in accordance with the committees decision, the publication w

22、ill be reconfirmed; withdrawn; replaced by a revised edition, or amended. 3 BSIEC6028713:2002INTRODUCTION When single-core cables are installed in parallel the load current may not share equally between the parallel cables. The circulating currents in the sheaths of the parallel cables will also dif

23、fer. This is because a significant proportion of the impedance of large conductors is due to self reactance and mutual reactance. Hence the spacing and relative location of each cable will have an effect on the current sharing and the circulating currents. The currents are also affected by phase rot

24、ation. The method described in this standard can be used to calculate the current sharing between conductors as well as the circulating current losses. There is no simple rule by which the circulating current losses of parallel cables can be estimated. Calculation for each cable configuration is nec

25、essary. The principles and impedance formulae involved are straightforward but the difficulty arises in solving the large number of simultaneous equations generated. The number of equations to be solved generally precludes the use of manual calculations and solution by computer is recommended. For n

26、 cables per phase having metallic sheaths in a three-phase system there are six n equations containing the same number of complex variables. For simplicity the equations set out in this standard assume that the parallel conductors all have the same cross-sectional area. If this is not the case, the

27、equations may be adapted to allow for different resistances for each conductor. The effect of neutral and earth conductors can also be calculated by including these conductors in the appropriate loops. The method set out in this standard does not take account of any portion of the sheath circulating

28、 currents that may flow through the earth or other extraneous paths. The conductor currents and sheath circulating currents in parallel single-core cables are unlikely to be equal. Because of this, the external thermal resistance for buried parallel cables should be calculated using the method set o

29、ut in 3.1 of IEC 60287-2-1. Because the external thermal resistance and sheath temperatures are functions of the power dissipation from each cable in the group it is necessary to adopt an iterative procedure to determine the circulating current losses and the external thermal resistance. 4 BSIEC6028

30、713:2002ELECTRIC CABLES CALCULATION OF THE CURRENT RATING Part 1-3: Current rating equations (100 % load factor) and calculation of losses Current sharing between parallel single-core cables and calculation of circulating current losses 1 Scope This part of IEC 60287 provides a method for calculatin

31、g the phase currents and circulating current losses in single-core cables arranged in parallel. The method described in this standard can be used for any number of cables per phase in parallel in any physical layout. The phase currents can be calculated for any arrangement of sheath bonding. For the

32、 calculation of sheath losses, it is assumed that the sheaths are bonded at both ends. A method for calculating sheath eddy current losses in two circuits in flat formation is given in IEC 60287-1-2. 2 Normative references The following referenced documents are indispensable for the application of t

33、his document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60287-1-2:1993, Electric cables Calculation of the current rating Part 1: Current rating equations (100 % load factor) and

34、 calculation of losses Section 2: Sheath eddy current loss factors for two circuits in flat formation IEC 60287-2-1:1994, Electric cables Calculation of the current rating Part 2: Thermal resistance Section 1: Calculation of thermal resistance 3 Symbols d c diameter of the conductor, mm d s mean dia

35、meter of the sheath, mm f frequency, Hz i, k elements in the series of conductors m, n elements in the series of cables p number of cables per phase D mn axial spacing between conductors, mm I p current in the conductor of cable p, A I sp circulating current in the sheath of cable p, A R resistance

36、of a conducting element, /m 5 BSIEC6028713:2002R c a.c. resistance of conductor at maximum operating temperature, /m R s resistance of sheath at operating temperature, /m X i,k apparent mutual reactance of a pair of conductors V conductor voltage drop coefficient depending on the construction of the

37、 conductor p sheath loss factor of cable p due to circulating currents angular frequency of system (2f), s 1 4 Description of method 4.1 General The method calculates the proportion of the phase current carried by each parallel conductor and the circulating current in the sheath of each cable. The l

38、oss factor () for each case is then calculated as the ratio of the losses in a sheath caused by circulating currents to the losses in the conductor of that cable. The method of calculation set out below only considers voltage drop along the conductors. Any unbalance in the load which would lead to u

39、nbalanced phase currents is ignored. The equations to be solved for the unknown currents in the parallel conductors and their sheaths are built up from a consideration of the basic formulae for the impedance associated with a loop consisting of two long conductors lying parallel to each other and th

40、e formulae for the mutual impedance between a loop and an adjacent conductor. Consideration of these equations leads to a system of simultaneous equations for the impedance voltage for all the conductors and sheaths in a three-phase parallel cable system. The impedance voltages for all conductors in

41、 parallel in the same phase are equal. Also for the conductors representing the bonded sheaths the voltages are equal. Hence the impedance voltages can be eliminated from the equations. The sum of the currents in the parallel conductors is equal to either the known phase current or zero for the shea

42、ths. This provides the additional information needed for solution of the simultaneous equations. It should be noted that all the currents are complex quantities containing both real and imaginary parts. The mutual impedance between conductors is a function of their relative positions. Hence, if the

43、relative positions of the cables vary along the route, or the sheaths are cross-bonded, then the impedance for each section shall be calculated individually and the vector results summed in order to obtain the total impedance of each loop. If the route length is very short, then significant errors m

44、ay occur in the calculated result due to the change in the relative positions of the cables as they approach the terminations. The equations set out in this standard can also be used to calculate the current sharing between cables without a metallic sheath or armour and between cables with the sheat

45、hs connected together at one end only, single-point bonded. For such calculations, the circulating current in each sheath is zero. Where cable sheaths are bonded at one end only, the standing voltage at the open circuit end of the sheath can also be determined using this method of calculation. For t

46、he method set out in this standard, it is recommended that the solution of the equations is achieved by a process of matrix algebra. This has the advantage that the solution achieved is unique and not a function of an iterative process. 6 BSIEC6028713:20024.2 Outline of method The loss factor for th

47、e sheath in a given cable in a parallel circuit is given by: c s 2 p sp p R R I I = (1) where p is the sheath loss factor of cable p due to circulating currents; I sp is the circulating current in the sheath of cable p, in A; I p is the current in the conductor of cable p, in A; R s is the resistanc

48、e of sheath at operating temperature, in /m; R c is the a.c. resistance of conductor at operating temperature, in /m. The currents I spand I pare obtained by solution of equations of the following form where there are p conductors in parallel and a total of n conductors. To simplify matters, both th

49、e phase conductors and the sheaths are referred to as conductors. The phase conductor currents are I 1 , I 2etc. The sheath currents are I 3p+1 , I 3p+2 , I 3p+3 , etc. For convenience in the calculations, the following notation is used: Cable references C i r c u i t 1 i p Phase R 1 i p Phase S p + 1 p + i 2p Phase T 2p + 1 2p + i 3p The conductors can th