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1、BRITISH STANDARD BS IEC 60287-3-3:2007 Electric cables Calculation of the current rating Part 3-3: Sections on operating conditions Cables crossing external heat sources ICS 29.060.20 ? Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Unc
2、ontrolled Copy, (c) BSI BS IEC 60287-3-3:2007 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 29 June 2007 BSI 2007 ISBN 978 0 580 55214 4 National foreword This British Standard was published by BSI. It is the UK implementation of IEC 60287-
3、3-3:2007. The UK participation in its preparation was entrusted by Technical Committee GEL/20, Electric cables, to Subcommittee GEL/20/16, Medium/high voltage cables. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport
4、to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Amendments issued since publication Amd. No. DateComments Licensed Copy: London South Bank University, London So
5、uth Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI INTERNATIONAL STANDARD IEC 60287-3-3 First edition 2007-05 Electric cables Calculation of the current rating Part 3-3: Sections on operating conditions Cables crossing external heat sources Reference number IEC/CEI 6
6、0287-3-3:2007 BS IEC 60287-3-3:2007 Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS IEC 60287-3-3:2007 2 CONTENTS INTRODUCTION.3 1 Scope 4 2 Normative references .4 3 Symbols .4 4 Description of method.5 4.1
7、 General description .5 4.2 Single source crossing.7 4.3 Several crossings 8 4.4 Rating of two crossing cables.9 Annex A (informative) Example calculation.10 Annex B (informative) Temperature rise calculation at any point along the route15 Figure 1 Illustration of a heat source crossing rated cable.
8、6 Figure A.1 Cable configuration .10 Table A.1 Cable and installation data .11 Table A.2 Rating factor for the 300 mm XLPE 10 kV circuit12 Table A.3 Rating factor for the 400 mm 132 kV cable.13 Table A.4 Rating factors.14 Licensed Copy: London South Bank University, London South Bank University, Tue
9、 Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI 3 BS IEC 60287-3-3:2007 INTRODUCTION In the IEC 60287 series, Part 1 provides general formulae for ratings and power losses of electric cables. Part 2 presents formulae for thermal resistance, with Part 2-1 providing general calculation met
10、hods for thermal resistance. Part 2-1 provides calculation methods for dealing with groups of buried cables (see 2.2.3). These methods assume that the cables are laid in parallel and hence every cable acts as a parallel line heat source. This Part 3-3 deals with the crossing of a cable, at right ang
11、les or obliquely with another cable, and, more generally, with any linear heat source, such as steam pipes. When heat sources are installed in the vicinity of a cable, the permissible current-carrying capacity of the cable should be reduced to avoid overheating. But applying formulae that are valid
12、for parallel routes would overestimate the thermal influence of the crossing heat source on the cable. In this standard a general simplified method is provided to estimate the reduction of the permissible current-carrying capacity of a cable crossed by heat sources. Every cable and heat source is as
13、sumed to be laid horizontally. Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS IEC 60287-3-3:2007 4 ELECTRIC CABLES CALCULATION OF THE CURRENT RATING Part 3-3: Sections on operating conditions Cables crossin
14、g external heat sources 1 Scope This part of IEC 60287 describes a method for calculating the continuous current rating factor for cables of all voltages where crossings of external heat sources are involved. The method is applicable to any type of cable. The method assumes that the entire region su
15、rrounding a cable, or cables, has uniform thermal characteristics and that the principle of superposition applies. The principle of superposition does not strictly apply to touching cables and hence the calculation method set out in this standard will produce an optimistic result if applied to touch
16、ing cables. 2 Normative references The following referenced 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 (all
17、 parts), Electric cables Calculation of the current rating 3 Symbols A Conductor cross-sectional area mm DF Ratio of the permissible current when taking into account the presence of crossing heat sources to the permissible current of the isolated cable (derating factor) - I Maximum permissible curre
18、nt of the rated cable when isolated A L Depth of laying, to cable axis, of the rated cable m Lh Depth of laying of heat source hm N Number of intervals in the spatial discretization for the calculations 1 T Thermal resistance per core between conductor and sheath Km/W 2 T Thermal resistance between
19、sheath and armour Km/W 3 T Thermal resistance of external serving Km/W 4 T Thermal resistance of surrounding medium (ratio of cable surface temperature rise above ambient to the losses per unit length) Km/W mh T Mutual thermal resistance between cable and heat source Km/W T Equivalent thermal resist
20、ance of cable per conductor Km/W r T Total thermal resistance of cable per conductor Km/W L T Thermal longitudinal resistance of a conductor K/m/W d W Dielectric losses per unit length per phase W/m Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00
21、:00 2007, Uncontrolled Copy, (c) BSI 5 BS IEC 60287-3-3:2007 g W Heat generated in the rated cable, due to losses in a conductor, assuming a conductor temperature of 20 C W/m h W Heat generated by external heat source h W/m k Number of heat sources, crossing the rated cable - r z Location of the hot
22、test point on the route of the rated cable(z co-ordinate) when several crossings are considered m zmax Distance along the cable route from the hottest point to the point where longitudinal heat flux is negligible m n Number of cores - 20 Temperature coefficient of electrical resistivity at 20 C, per
23、 Kelvin K-1 Crossing angle Radian Attenuation factor m-1 1 Ratio of the total losses in metallic sheaths to the total conductor losses(sheath/screen loss factor) - 2 Ratio of the total losses in armour to the total conductor losses (armour loss factor) - Soil thermal resistivity Km/W cr Conductor th
24、ermal resistivity Km/W max Maximum permissible conductor temperature C d Conductor temperature rise due to dielectric losses K max Maximum permissible conductor temperature rise above ambient K ( ) z Temperature rise of the conductor(s) of the rated cable, due to crossing heat sources, at the point
25、z in the cable route K (0) Temperature rise of the conductor(s) of the rated cable, due to crossing heat sources, at the hottest point in the cable route K ( ) uh z Temperature rise of the conductor(s) of the rated cable, due to the heat source, h, without taking into account longitudinal heat flux
26、K W Incremental heat generated due to change of conductor resistance W/Km z Length of an interval used in the calculations m 4 Description of method 4.1 General description The conditions examined in this standard involve an external heat source crossing the route of the rated cable(s). The crossing
27、 heat source can be located either above or below the rated cable(s) with the crossing angle ranging from parallel to perpendicular. An example of such situation is shown in Figure 1. Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncon
28、trolled Copy, (c) BSI BS IEC 60287-3-3:2007 6 z y Heat source Ground surface Cable Crossing angle x z Plan view Sectional view x Lh L IEC 742/07 Figure 1 Illustration of a heat source crossing rated cable The conductor temperature rise along the route of the rated cable, caused by the heat generated
29、 by the crossing heat source, may be calculated using Kennellys principle. The temperature rise is maximum at the crossing point and decreases with the distance from the crossing. The distance from the crossing along the cable route, where the longitudinal heat flux is negligible, is denoted by zmax
30、. As a consequence of the varying temperature rise along the cable length, a longitudinal heat flux is generated in the conductor, which leads to a reduction in the conductor temperature rise at the crossing, compared to the case when this longitudinal flux is ignored. The maximum permissible curren
31、t in the cable to be rated, taking into account the presence of a crossing heat source, is obtained by multiplying the steady-state rating of the cable, without the crossing heat source, by a derating factor, DF, related to the heating due to the heat source: ( ) dmax DF = 0 1 (1) where is the tempe
32、rature rise of the conductor due to the crossing heat source, at the crossing point. ( )0 Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI 7 BS IEC 60287-3-3:2007 4.2 Single source crossing The value of is obtai
33、ned from the following formula by dividing the distance z( )0 max into N intervals, each of length z: ( ) ()()() ()() = + + = N h hz z h zLL zLL e eW 1 22 22 sin sin ln 4 1 0 (2) where is the soil thermal resistivity; h W is the heat generated by external heat source; is the crossing angle; L is the
34、 laying depth of the rated cable; Lh is the laying depth of the heat source. The attenuation factor is expressed as () r L T T TW=1 (3) with 6 10 = A T cr L (4) () 4321 TTTnTTr+= (5) ()() ( 4321211 11TTTnTT+=) (6) ( += 432 1 2 TTTn T Wd d ) (7) ( ) = d WW max 0 0 1 (8) ()201 max20 2 20 0 + = IR W (9
35、) where cr is the conductor thermal resistivity; For copper Kxm/W; for aluminium Kxm/W. 6002, 0= cr 9004, 0= cr A is the conductor cross-sectional area; 20 is the temperature coefficient of electrical resistivity for the conductor material; I is the maximum permissible current of the rated cable whe
36、n isolated. The remaining variables are defined in other parts of the IEC 60287 series. Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS IEC 60287-3-3:2007 8 Typically a value of m may be used. It has to be v
37、erified that: 01, 0=z 500 First estimate of C () () 2 ,19 9 , 020, 1 9 , 020, 1 ln 4 390,258 , 0 2 2 = + 13 First estimate of W W/K m 075, 0 65 2 ,19 11064,10 2 = 8 First estimate of m1 () 07, 2 745, 1 67, 888, 1075, 01 = 3 Final estimate of (second iteration) C 14,1 2 Derating factor DF 89, 0 65 1
38、,14 1= 1 The derating factor calculated above is that which is applied to the current rating of the 10 kV cables to take account of the temperature rise due to the crossing 132 kV cable. This factor does not take account of the temperature rise in the 132 kV cable due to the crossing 10 kV cables (s
39、ee 4.4). Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI 13 BS IEC 60287-3-3:2007 Table A.3 Derating factor for 400 mm 132 kV cable Cable type: 400 mm 132 kV Characteristics Equation longitudinal thermal resist
40、ance of the conductors L T K/mW 5 , 610400/6002, 0 6 = 4 r T Km/W ()44, 2445, 009, 03835, 0=+ 5 T Km/W ()66, 2445, 009, 0135, 13835, 0=+ 6 maxC 602585= dC ()1 , 4445, 009, 03 2 835, 0 01, 2= + 7 0 W W/m () 2 23 1059, 6 208593003, 01 58593003, 0105061, 0 = + 9 Computing derating factor With: z = 0,01
41、 m N 500 First estimate of C () () () () 7 ,27 072, 09 , 02 , 1 072, 09 , 02 , 1 ln2 9 , 02 , 1 9 , 02 , 1 ln 4 61,378 , 0 22 22 2 2 = + + + + 17 First estimate of W W/Km 033, 0 2 , 560 7 ,27 11059, 6 2 = 8 First estimate of m1 () 558, 1 44, 2 5 , 666, 2033, 01 = 3 First estimate of mutual thermal r
42、esistance: Left cable Middle cable Right cable Km/W Km/W Km/W 0,156 0,165 0,174 16 16 16 Second estimate of (1st iteration) C 18,6 15 Final estimate of (2nd iteration) C 18,5 15 + 16 Derating factor DF 82, 0 60 5 ,18 1= 1 The derating factor calculated above is that which is applied to the current r
43、ating of the 132 kV cable to take account of the temperature rise due to the crossing 10 kV cables. This factor does not take account of the temperature rise in the 10 kV cable due to the crossing 132 kV cables (see 4.4). Licensed Copy: London South Bank University, London South Bank University, Tue
44、 Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS IEC 60287-3-3:2007 14 Simultaneous rating of the two links Using the method set out in 4.4, four iterations were necessary to get the derating factors of the two links when taking into account mutual thermal effects. The final result is
45、as follows: Table A.4 Rating factors Rating of the two links Cable type Rating factor 300 mm XLPE 10 kV 0,92 400 mm 132 kV 0,85 Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI 15 BS IEC 60287-3-3:2007 Annex B (
46、informative) Temperature rise calculation at any point along the route The temperature rise at every point, z, can be derived from: ( )() z m z muh eBeAzmz += for (1)mzzmz + the constants Am and Bm being derived from the following recursive relationships: ()() ()() 00 1 1 (0)(0) 2 1 (1) 2 1 (1) 2 uh
47、 uhuh mm uhuh mm AB mzmz mz AAe mzmz mz BBe = = = _ Licensed Copy: London South Bank University, London South Bank University, Tue Jul 03 01:02:59 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS IEC 60287-3-3:2007 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British Standards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter