1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58Part 3-3: Sections on operating conditions Cables crossing external heat sourcesICS 29.060.20Electr
2、ic cables Calculation of the current rating BRITISH STANDARDBS IEC 60287-3-3:2007BS IEC 60287-3-3:2007This British Standard was published under the authority of the Standards Policy and Strategy Committee on 29 June 2007 BSI 2007ISBN 978 0 580 55214 4Amendments issued since publicationAmd. No. Date
3、CommentsThis 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 cannot confer immunity from legal obligations.National forewordThis British Standard was published by BSI. It is the U
4、K implementation of IEC 60287-3-3:2007.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.INTERNA
5、TIONAL STANDARD IEC60287-3-3First edition2007-05Electric cables Calculation of the current rating Part 3-3: Sections on operating conditions Cables crossing external heat sources Reference number IEC/CEI 60287-3-3:2007 BS IEC 60287-3-3:2007 BS IEC 60287-3-3:2007 2 CONTENTS INTRODUCTION.3 1 Scope 4 2
6、 Normative references .4 3 Symbols .4 4 Description of method.5 4.1 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
7、route15 Figure 1 Illustration of a heat source crossing rated cable.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 3 BS IEC 6
8、0287-3-3:2007 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 methods for thermal resistance. Part 2-1 provides calculation methods for
9、 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 angles or obliquely with another cable, and, more generally, with any lin
10、ear 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 for parallel routes would overestimate the thermal influence of the cr
11、ossing 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 assumed to be laid horizontally. BS IEC 60287-3-3:2007 4 ELECTRIC CABLES
12、 CALCULATION OF THE CURRENT RATING Part 3-3: Sections on operating conditions Cables crossing 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.
13、 The method is applicable to any type of cable. The method assumes that the entire region surrounding 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 calcu
14、lation method set out in this standard will produce an optimistic result if applied to touching 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
15、latest edition of the referenced document (including any amendments) applies. IEC 60287 (all 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 t
16、he permissible current of the isolated cable (derating factor) - I Maximum permissible current 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 h m N Number of intervals in the spatial discretization for the calculations 1T T
17、hermal resistance per core between conductor and sheath Km/W2T Thermal resistance between sheath and armour Km/W3T Thermal resistance of external serving Km/W4T Thermal resistance of surrounding medium (ratio of cable surface temperature rise above ambient to the losses per unit length) Km/WmhT Mutu
18、al thermal resistance between cable and heat source Km/WT Equivalent thermal resistance of cable per conductor Km/WrT Total thermal resistance of cable per conductor Km/WLT Thermal longitudinal resistance of a conductor K/m/W dW Dielectric losses per unit length per phase W/m 5 BS IEC 60287-3-3:2007
19、 gW Heat generated in the rated cable, due to losses in a conductor, assuming a conductor temperature of 20 C W/m hW Heat generated by external heat source h W/m k Number of heat sources, crossing the rated cable - rz Location of the hottest point on the route of the rated cable(z co-ordinate) when
20、several crossings are considered m zmaxDistance 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 Kelvin K-1 Crossing angle Radian Attenuation factor m-1 1 Ratio
21、 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/Wcr Conductor thermal resistivity Km/Wmax Maximum permissible conductor temperatu
22、re 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 z in the cable route K (0) Temperature rise of the conductor(s) of t
23、he rated cable, due to crossing heat sources, at the hottest point in the cable route K ()uhzTemperature rise of the conductor(s) of the rated cable, due to the heat source, h, without taking into account longitudinal heat flux K W Incremental heat generated due to change of conductor resistance W/K
24、mz 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 heat source can be located either above or below the rated cable(s) with
25、 the crossing angle ranging from parallel to perpendicular. An example of such situation is shown in Figure 1. BS IEC 60287-3-3:2007 6 z y Heat source Ground surface Cable Crossing angle x z Plan view Sectional view x LhL IEC 742/07 Figure 1 Illustration of a heat source crossing rated cable The con
26、ductor temperature rise along the route of the rated cable, caused by the heat generated 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 a
27、long the cable route, where the longitudinal heat flux is negligible, is denoted by zmax. 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, com
28、pared to the case when this longitudinal flux is ignored. The maximum permissible current 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,
29、 related to the heating due to the heat source: ()dmaxDF=01 (1) where is the temperature rise of the conductor due to the crossing heat source, at the crossing point. ()0 7 BS IEC 60287-3-3:2007 4.2 Single source crossing The value of is obtained from the following formula by dividing the distance z
30、()0maxinto N intervals, each of length z: ()( ) ()( )()( )=+=NhhzzhzLLzLLeeW12222sinsinln410 (2) where is the soil thermal resistivity; hW is the heat generated by external heat source; is the crossing angle; L is the laying depth of the rated cable; Lh is the laying depth of the heat source. The at
31、tenuation factor is expressed as ()rLTTTW = 1 (3) with 610=ATcrL(4) ( )4321TTTnTTr+= (5) () ( )(432121111 TTTnTT += ) (6) (+=43212TTTnTWdd ) (7) ()=dWWmax001 (8) ()201max202200+= IRW (9) where cr is the conductor thermal resistivity; For copper Kxm/W; for aluminium Kxm/W. 6002,0=cr 9004,0=crA is the
32、 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 when isolated. The remaining variables are defined in other parts of the IEC 60287 series. BS IEC 60287-3-3:2007 8 Typicall
33、y a value of m may be used. It has to be verified that: 01,0=z 500First estimate of C()()2,199,020,19,020,1ln4390,258,022=+13 First estimate of W W/K m 075,0652,1911064,102=8 First estimate of m1()07,2745,167,888,1075,01=3 Final estimate of (second iteration) C14,1 2 Derating factor DF 89,0651,141 =
34、 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 (see 4.4
35、). 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 resistance of the conductors LT K/mW 5,610400/6002,06=4 rT Km/W ()44,2445,009,03835,0 =+ 5 T Km/W ()66,2445,009,0135,13835,0 =+ 6 maxC 602585 = dC ()1
36、,4445,009,032835,001,2 =+ 7 0W W/m ()2231059,6208593003,0158593003,0105061,0=+9 Computing derating factor With: z = 0,01 m N 500 First estimate of C()()()()7,27072,09,02,1072,09,02,1ln2 9,02,19,02,1ln461,378,0222222=+17 First estimate of W W/Km 033,02,5607,2711059,62=8 First estimate of m1()558,144,
37、25,666,2033,01=3 First estimate of mutual thermal resistance: 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 82,0605,181 = 1 The derating factor calculated
38、above is that which is applied to the current rating 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). BS IEC 60287-3-3:2007 14 Simult
39、aneous 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 as follows: Table A.4 Rating factors Rating of the two links Cable type Rating factor 300 m
40、m XLPE 10 kV 0,92 400 mm 132 kV 0,85 15 BS IEC 60287-3-3:2007 Annex B (informative) Temperature rise calculation at any point along the route The temperature rise at every point, z, can be derived from: () ( )zmzmuheBeAzmz+= for (1)mzz m z +the constants Amand Bmbeing derived from the following recu
41、rsive relationships: () ()() ()0011(0) (0)21(1)21(1)2uhuh uhmmuh uhmmABmz m zmzAA emz m zmzBB e= = = _ BS IEC BSI389 Chiswick High RoadLondonW4 4AL60287-3-3:2007BSI British Standards InstitutionBSI is the independent national body responsible for preparing British Standards. It presents the UK view
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