1、BRITISH STANDARD BS IEC 60853-3:2002 Calculation of the cyclic and emergency current rating of cables Part 3: Cyclic rating factor for cables of all voltages, with partial drying of the soil ICS 29.060.20 BS IEC 60853-3:2002 This British Standard, having been prepared under the direction of the Elec
2、trotechnical Sector Policy and Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on 23 September 2002 BSI 23 September 2002 ISBN 0 580 40398 X National foreword This British Standard reproduces verbatim IEC 60853-3:2002 and implements it as the UK n
3、ational standard. The UK participation in its preparation was entrusted by Technical Committee GEL/20, Electric cables, to Subcommittee GEL/20/16, Medium/high voltage cables, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its s
4、ecretary. Cross-references The British Standards 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 o
5、f British Standards Online. This publication 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;
6、present to the responsible international/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,
7、 an inside front cover, the IEC title page, pages 2 to 15 and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsNORME INTERNATIONALE CEI IEC INTERNATIONAL STANDARD 60853-3 Premire dit
8、ion First edition 2002-02 Calcul des capacits de transport des cbles pour les rgimes de charge cycliques et de surcharge de secours Partie 3: Facteur de capacit de transport cyclique pour des cbles de toute tension, avec asschement partiel du sol Calculation of the cyclic and emergency current ratin
9、g of cables Part 3: Cyclic rating factor for cables of all voltages, with partial drying of the soil Numro de rfrence Reference number CEI/IEC 60853-3:2002 BSIEC608533:2002CONTENTS FOREWORD.3 INTRODUCTION.4 1 Scope.5 2 Normative references .5 3 Symbols .6 4 Description of method.7 4.1 General descri
10、ption .7 4.2 Principles 7 4.3 Formulae.8 Annex A (informative) Example calculation 11 Annex B (informative) Details of cables and load used for example14 BSIEC608533:20022INTERNATIONAL ELECTROTECHNICAL COMMISSION _ CALCULATION OF THE CYCLIC AND EMERGENCY CURRENT RATING OF CABLES Part 3: Cyclic ratin
11、g factor for cables of all voltages, with partial drying of the soil FOREWORD 1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote inte
12、rnational co-operation on all questions concerning standardization in the electrical and electronic fields. To this 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
13、 subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with condi
14、tions determined by agreement between the two organizations. 2) The formal decisions or agreements of the 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 Nati
15、onal Committees. 3) The documents produced have the form of recommendations for international use and are published 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 uni
16、fication, IEC National Committees undertake to apply IEC International Standards transparently to the maximum extent 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
17、. 5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment 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 pat
18、ent rights. The IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 60853-3 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 20/493/FDIS 20/51
19、2/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 3. Annexes A and B are for information only. The committee has decided that the
20、contents of this publication will remain unchanged until 2007. At this date, the publication will be reconfirmed; withdrawn; replaced by a revised edition, or amended. BSIEC608533:20023INTRODUCTION Methods for calculating cyclic ratings for cables installed in the ground are given in IEC 60853-1 and
21、 IEC 60853-2. Part 1 is applicable to cables having negligible thermal capacitance; Part 2 is applicable to cables where their thermal capacitance cannot be neglected. A fundamental assumption in Part 1 and Part 2 is that the thermal properties of the soil are uniform throughout the thermal field of
22、 the cable. For many installations, such an assumption is acceptable and further refinement is unnecessary. However, higher working temperatures increase the probability that the soil immediately around a cable may lose so much of its moisture that it dries out to a significantly higher value of the
23、rmal resistivity than that corresponding to its normal site condition. The reduction in permissible current-carrying capacity of a cable, necessary to avoid overheating, can be significant. BSIEC608533:20024CALCULATION OF THE CYCLIC AND EMERGENCY CURRENT RATING OF CABLES Part 3: Cyclic rating factor
24、 for cables of all voltages,with partial drying of the soil 1 Scope This part of IEC 60853 gives a method for calculating the cyclic rating factor, for cables of all voltages, where partial drying out of the surrounding soil is anticipated. The method is based on one of the three methods published i
25、n a CIGRE 1document. The method is applicable to any type of cable, but it is recommended that it should be applied only to installations of one multi-core cable or to three single-core cables or to groups of circuits where the intercircuit spacing is sufficient to permit free vertical movement of s
26、oil moisture between the zones of dry soil associated with each circuit. This standard does not preclude the use of other methods of calculation where full details of the load cycle are not known. The method assumes that the entire region surrounding a cable or cables has uniform thermal characteris
27、tics prior to drying out; the only non-uniformity being that caused by drying. As a consequence the method should not be applied, without further consideration, to installations where special backfills, having properties different from the site soil, are used. 2 Normative references The following re
28、ferenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60287-2-1, Electric cables Calculation of the current rating
29、Part 2-1: Thermal resistance Calculation of thermal resistance IEC 60853-1, Calculation of the cyclic and emergency current rating of cables Part 1: Cyclic rating factor for cables up to and including 18/30 (36) kV IEC 60853-2:1989, Calculation of the cyclic and emergency current rating of cables Pa
30、rt 2: Cyclic rating of cables greater than 18/30 (36) kV and emergency ratings for cables of all voltages _ 1Methods for calculating cyclic ratings for buried cables with partial drying out of the surrounding soil: Electra No 145, December 1992, page 32. BSIEC608533:200253 Symbols a, b coefficients
31、used for calculating cable partial temperature rise, s 1 e 2,7183 i time, in hours (h) k steady-state ratio of cable surface temperature rise to conductor temperature rise, above ambient n number of cores t time, in seconds (s) v ratio of dry to wet soil thermal resistivities (v = d/ w ) A, A , B in
32、termediate variables, used in 4.3.1 and 4.3.2 D e cable external diameter, in meters (m) Ei exponential integral function L depth a cable is laid below ground surface, in meters (m) M cyclic rating factor M 1 cyclic rating factor corrected for moisture migration Q A , Q B elements of two part therma
33、l circuit of cable, J/m K T a, T b apparent thermal resistances used to calculate cable partial transient, K m/W T A , T B elements of equivalent thermal circuit of cable, K m/W T 1 thermal resistance of cable insulation per conductor, K m/W T 3 thermal resistance of cable covering, K m/W T 4 extern
34、al thermal resistance of cable, K m/W W d dielectric losses per cable, W/m Y i cable losses, expressed as a fraction of their maximum value, at a time i (h) prior to the time of maximum conductor temperature, W/m (t) attainment factor of temperature difference between cable surface and conductor (t)
35、 attainment factor of temperature difference between ambient and the cable surface soil thermal diffusivity, m 2 /s armour/sheath loss factor loss load factor w soil thermal resistivity for moist soil, K m/W d soil thermal resistivity for dry soil, K m/W c conductor temperature rise due to total cab
36、le losses, in kelvins (K) c conductor temperature rise due to joule losses only, in kelvins (K) c (i) conductor temperature rise at time i (h), in kelvins (K) x critical value of soil temperature rise above ambient, in kelvins (K) NOTE All temperature symbols refer to rises above ambient. BSIEC60853
37、3:200264 Description of method 4.1 General description This method is an extension of the techniques used in IEC 60853-1 and IEC 60853-2 for calculating cyclic rating factors for a cable in uniform soil. The method relies on a knowledge of the soil critical temperature; this is the temperature at wh
38、ich drying out of the soil takes place rapidly. NOTE In the absence of more precise information, this temperature may be taken as 50 C. The size of the dry zone changes substantially with critical temperature. For a given conductor temperature the size of the dry zone will have a significant effect
39、on the steady- state rating but the cyclic factor multiplying that steady-state rating is largely unaffected. It is assumed initially that the soil critical temperature is equal to the peak cyclic value of the cable surface temperature, i.e. a dry zone is on the point of occurring, so that the soil
40、surrounding the cable has uniform properties appropriate to its wet, on-site, state. The cyclic rating factor for these conditions is derived by the methods already given in IEC 60853-1 or IEC 60853-2. This factor is then adjusted so that it applies to the steady-state rating for the same assumed va
41、lue of critical temperature, when there will be a dried-out zone. This adjustment is effected using formulae for the cable external thermal resistance appropriate to the steady-state procedure. Such a factor can then be used to multiply the steady-state rating for any other soil critical temperature
42、 in order to obtain the appropriate permissible peak current. 4.2 Principles In general, the size of a dry zone where the boundary just achieves a certain critical temperature rise with cyclic loading is smaller than the zone which will form for the same critical temperature rise with steady-state l
43、oading. The situation where the cable surface temperature rise is just equal to the soil critical temperature, and a dry zone forms only with steady-state loading, is a particular case. However, a rating factor determined for this latter case is applicable to the steady-state rating with any other c
44、ritical temperature rise and size of dry zone. One further step is necessary in order to use a cyclic factor based on a critical temperature equal to the cable surface temperature. Because of the nature of the computation used in IEC 60853-1 and IEC 60853-2 to derive cyclic rating factors, the value
45、 of the factor obtained assumes that the cable external thermal resistance is the same for both cyclic and steady- state loading. The correct value of peak current for the load cycle is obtained when the cyclic factor multiplies the steady-state rating for this value of resistance. While this equali
46、ty of external thermal resistance applies for the uniform non-migration conditions assumed in IEC 60287-2-1, IEC 60853-1 and IEC 60853-2, it is not so when drying can take place. The size of the dry zone, and hence the cable external thermal resistance, changes with the type of loading. In the latte
47、r case the rating factor has to be adjusted so that it can be used to multiply the rating for the higher external thermal resistance occurring with the steady-state. Such an adjustment can be made by using the ratio of the appropriate external thermal resistances. BSIEC608533:20027The computation of
48、 a cyclic rating factor, for any critical temperature, is effected as follows: the thermal response of the cable, including the effect of its internal thermal capacitance, is obtained by the use of appropriate formulae from 4.2.1, 4.2.2 and 4.2.3 of IEC 60853-2; the thermal response of the soil, and
49、 the effect of adjacent cables in a group (if any), are obtained by the use of formulae from clauses 5 to 7 of IEC 60853-2; the effect of drying out is obtained by the use of 4.3.2. 4.3 Formulae 4.3.1 Without drying out There are optional formulae for a cyclic rating factor in clause 5 of IEC 60853-2 but the general one is as follows: 5 , 0 1 B A M (1) where
