IEC 60853-2:1989/AMD1:2008

IEC 60853-2
Edition 1.0 2008-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 1
AMENDEMENT 1
Calculation of the cyclic and emergency current rating of cables –
Part 2: Cyclic rating of cables greater than 18/30 (36) kV and emergency ratings
for cables of all voltages
Calcul des capacités de transport des câbles pour les régimes de charge
cycliques et de surcharge de secours –
Partie 2: Régime cyclique pour des câbles de tensions supérieures à 18/30
(36) kV et régimes de secours pour des câbles de toutes tensions

IEC 60853-2:1989/A1:2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: csc@iec.ch
Tél.: +41 22 919 02 11
Fax: +41 22 919 03 00
IEC 60853-2
Edition 1.0 2008-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 1
AMENDEMENT 1
Calculation of the cyclic and emergency current rating of cables –
Part 2: Cyclic rating of câbles greater than 18/30 (36) kV and emergency ratings
for câbles of all voltages
Calcul des capacités de transport des câbles pour les régimes de charge
cycliques et de surcharge de secours –
Partie 2: Régime cyclique pour des câbles de tensions supérieures à 18/30
(36) kV et régimes de secours pour des câbles de toutes tensions

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
K
CODE PRIX
ICS 29.060.20 ISBN 978-2-88910-313-3
– 2 – 60853-2 Amend. 1 © IEC:2008
FOREWORD
This amendment has been prepared by IEC technical committee 20: Electric cables.
The text of this amendment is based on the following documents:
FDIS Report on voting
20/965/FDIS 20/991/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the maintenance result date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
_____________
PREFACE
Replace the quoted IEC publication “287(1982)”, by the following:
IEC 60287-1-1, Electric cables – Calculation of the current rating – Part 1-1: Current rating
equations (100 % load factor) and calculation of losses – General
IEC 60287-2-1, Electric cables – Calculation of the current rating – Part 2-1:Thermal
resistance – Calculation of thermal resistance
IEC 60287-3-1, Electric cables – Calculation of the current rating – Part 3-1:Sections on
operating conditions – Reference operating conditionsand selection of cable type
Throughout the standard, replace all references to “IEC Publication 287” by “the IEC 60287
series”.
Add the following new reference:
IEC 60853-3, 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
1.1 General
Replace the first paragraph by the following:
This standard gives manual methods for calculating cyclic rating factors for cables whose
internal thermal capacitance cannot be neglected; in general this applies to cables for
voltages greater than 18/30 (36) kV. It also gives a method for calculating the emergency
rating for cables of any voltage. IEC 60853-1 deals with cyclic rating factors for cables of
voltages not greater than 18/30 (36) kV where the internal thermal capacitance could be

60853-2 Amend. 1 © IEC:2008 – 3 –
neglected. IEC 60853-3 deals with cyclic rating factors for cables of all voltages when partial
drying of the soil occurs.
Delete the fourth paragraph.
Add the following three new paragraphs at the end of 1.1:
When the load current changes in discrete and multiple steps the method set out in Clause 4
can be used to determine the temperature response of the cable.
This method shall be used carefully where a large number of steps is considered, or long
duration steps are dealt with, or large variations of the load current occur.
As the method involves an iterative process, the convergence criterion shall be adapted to the
different situations.
2 Symbols
Replace the word “sheath” by “metallic sheath or screen” under definitions Q q , q and q
,
s a j s.
Throughout the text, starting with the “Unit” column, replace “J/m.K” with “J/Km” also replace
“K.m/W” with “Km/W”.
Replace the definition for N with “N = number of cables in a group, or, for touching cables, the
number of circuits, see 7.4 b)”
Replace “δ ” by ”σ” in order to align with the French version. Also in the “Unit” column, replace
3 3
“J/K.m “ by “J/Km ”.
Add the following new definition:
Steady-state conductor temperature rise above ambient due to
Δθ Κ
d
dielectric losses
4.2.1.1 Single-core cables
Replace, in the second line, the word “sheath” by “metallic sheath or screen”.
4.2.1.2 Three-core cables
Replace the existing Equation (4-2) by the following new Equation (4-2):
⎛ 2πT ⎞
⎜ ⎟
−
⎜ ⎟
ρ
⎝ i ⎠
d = D e (4-2)
c i
Replace, in the first line after Equation (4-2) and in the first line of 4.2.1.2 b), the word
“sheath” by “metallic sheath or screen”.
4.2.2.1 General
Add, at the end of the subcause, a third paragraph as follows:
For single-core cables in trefoil formation, the values of T and T are adjusted by the
1 3
appropriate factors given in IEC 60287-2-1.

– 4 – 60853-2 Amend. 1 © IEC:2008
4.2.2.2 Representation of common types of cable
Replace, after Equation (4-6), in the definition for Q and twice in the definition for q , the word
s s
“sheath” by “metallic sheath or screen”.
4.2.4.1 Buried cables (directly or in ducts)
Replace the existing Equation (4-36) by the following new Equation (4-36):
⎧ 2 2 ⎫
⎡ ⎤
2 ⎡ ⎤
⎡ ⎤ k=N −1 ⎛ ⎞ ⎛ ⎞
⎛ ⎞ ′
2 − (d ) - (d )
⎡ ⎤
ρ W − D ⎛ ⎞
⎪ ⎜ pk ⎟ ⎜ pk ⎟ ⎪
− L ⎢ ⎥
T I ⎜ e ⎟ ⎢ ⎥
⎢ ⎥
⎜ ⎟
θ (t ) = − Ei −⎢− Ei ⎥ + − Ei − − Ei (4-36)
⎨ ⎜ ⎟ ⎜ ⎟ ⎬
⎜ ⎟ ∑ ⎢ ⎢ ⎥⎥
e
⎢ ⎜ ⎟ ⎥
4π 16tδ tδ 4tδ 4tδ
⎜ ⎟ ⎢ ⎥
⎪ ⎜ ⎟ ⎜ ⎟ ⎪
⎝ ⎠
⎣ ⎦ ⎢ ⎥
k=1 ⎢ ⎥
⎢ ⎝ ⎠ ⎥
⎣ ⎦
⎝ ⎠ ⎝ ⎠
⎣ ⎦
⎣ ⎦
⎩ ⎭
Replace the final sentence of 4.2.4.1 beginning “This formula has been simplified … “ by the
following new paragraph:
Equation (4-36) is the general equation for the transient response of buried cables and its
application for cyclic rating purposes is given in Clause 7. It is noted that this equation cannot
be used directly for cables in unfilled troughs.
4.3.2.1 General
Add, at the end of this subclause, a new paragraph as follows:
For single-core cables in trefoil formation the values of T and T are adjusted by the
1 3
appropriate factors given in IEC 60287-2-1.
4.3.2.2 Representation of common types of cable
Replace the existing Equation (4-47) by the following new equation:
T = T + q T + q T + q T (4-47)
B 1 s f a 2 j 3
4.4.1 Transient temperature response
Add the following new text after item b).
When the temperature response to a current that changes in discrete and multiple steps is
calculated, the calculations described in this clause should be repeated for every partial step
of the current. In the calculation of these partial transients, the correct heat source (the heat
gained or lost in the partial current step) and the correct temperatures (for the calculation of
electrical resistances) shall be used in the formulas above. One way of accomplishing this is
to perform iterative calculations for each load step as follows:
1) Start with the temperature achieved at the end of the previous load step.
2) Calculate the electrical resistances corresponding to this temperature and obtain power
losses.
3) With these losses calculate the temperature at the end of the time step.
4) Use this temperature to recalculate the electrical resistances and power losses and go to
step 3.
5) Repeat steps 3 and 4 until convergence is achieved and go to the next load step.
The total temperature response per partial step will be found by using the appropriate
formulae in this clause. The complete total temperature response of the cable circuit will be

60853-2 Amend. 1 © IEC:2008 – 5 –
found by adding all the partial transients, thereby taking the time differences between the
partial steps into account.
4.4.1.2 Cables in air
Replace the last paragraph by the following:
T is the external thermal resistance due to air in the steady-state, calculated according to
IEC 60287-2-1, and shall be expressed as a quantity per conductor or equivalent conductor.
4.4.2 Correction to transient temperature response for variation in conductor losses
with temperature (emergency ratings only)
Replace the heading of this subclause with the words “Not used”.
Delete the text of this subclause, including Equation (4-73).
4.4.3.2 Cables at voltages higher than 275 kV
Replace, in the third line, and in the penultimate paragraph, the word “sheath” by “metallic
sheath or screen”.
Add, at the end of the subclause, the following new text:
Information on the voltages above which dielectric losses should be considered is given in
IEC 60287-1-1.
5.1 General
Replacethe existing Equation (5-1) by the following new Equation (5-1):
θ = Y θ (1) + Y [θ (2) − θ ()1 ]+ Y [θ (3) − θ (2)]
max 0 R 1 R R 2 R R
(5-1)
+Y[]θ (6) − θ (5) + μ[θ (∞) − θ (6)]
5 R R R R
5.2.1 Any load cycle of known shape
Replace the existing Equation (5-3) by the following new Equation (5-3):
M =
(5-3)
1/ 2
⎛ ⎞
⎡ θ()i + 1 θ ()i ⎤ ⎡ θ ()6 ⎤
⎜ R R R ⎟
Y − + μ 1 −
⎢ ⎥ ⎢ ⎥
∑
i
⎜ ⎟
θ ()∞ θ ()∞ θ ()∞
⎢ ⎥ ⎢ ⎥
⎣ R R ⎦ ⎣ R ⎦
i=0
⎝ ⎠
5.2.2 Flat top load cycle
Replace the existing Equation (5-5) by the following new Equation (5-5):
1/ 2
⎡ 1 ⎤
M = (5-5)
⎢ ⎥
()1−()1 − μ[]1 − α(6) + kα(6){1− β(6)}
⎣ ⎦
7.2 Single isolated circuit
Under item a) 1), replace ” … for cables in ducts, in trefoil or flat touching formation….” by
”….for cables in trefoil or flat touching formation or in ducts… “

– 6 – 60853-2 Amend. 1 © IEC:2008
7.4 Group of “N”circuits, each of three single-core identical touching cables or ducts,
all cables having equal losses
Replace the existing title and text of this subclause by the following:
7.4 Group of circuits, each of three single-core identical touching cables or ducts, all
cables having equal losses
The methods are the same as those given in 7.3 above, except that:
a) The external thermal resistance T , on which the value of k is dependent, relates to
4 1
⎡ ⎤
⎛ ⎞
1,5 4L
ρ In⎜ ⎟ − 0,630 (7-13)
T =
⎢ ⎥
4 T
⎜ ⎟
π D
⎢ ⎥
⎝ e⎠
⎣ ⎦
for metallic sheathed and part-metallic covered cables (where helically laid armour or
screen wires cover from 20 % to 50 % of the cable circumference),
or
⎡ ⎤
⎛ ⎞ ⎛ 2 ⎞
1 4L
L
⎜ ⎟ ⎜ ⎟
T = P In + 2 In (7-14)
⎢ ⎥
4 T
⎜ ⎟ ⎜ ⎟
2π D D
⎢ e e ⎥
⎝ ⎠ ⎝ ⎠
⎣ ⎦
for non-metallic sheathed cables
where
ρ is the soil thermal resistivity, in Km/W;
T
L is the depth of laying, in metres (m);
D is the external diameter of cable or duct, in metres (m).
e
b) The symbols N, d' and d used for the calculation of γ (i), F and d in equations (7-7),
pk pk
f
(7-8) and (7-9) are defined as:
– N is the number of circuits (of three single-core cables per circuit)
– d is the distance from the centre of circuit k to the centre of the circuit containing
pk
the hottest cable;
– d' is the distance of the image of the centre of circuit k to the centre of the circuit
pk
containing the hottest cable.
c) Additional external thermal resistance caused by heating from other cables in a group is
expressed by:
3ρ ln F
T
Δ = (7-15)
T
2π
where F is given by item b) above.
d) W is the total loss per unit length per single cable or duct.
e) The value of the cable or duct diameter to be assumed for the calculation of γ (i) is that of
an isolated cable or duct.
8.1 Thermally isolated circuits
Replace, against definition θ ()t “ θ ()t is calculated in Sub-clause 4.4” by ”see the
R R
calculation for θ()t in 4.4”
60853-2 Amend. 1 © IEC:2008 – 7 –
Insert, immediately after Equation (8-1), the following new paragraph:
This equation takes account of the variation of conductor resistance with temperature. Thus
Equation (8-3) should not be applied when Equation (8.1) is used. Where armour, screen or
metallic sheath losses are high, it is recommended that the losses at the final armour, screen
or metallic sheath temperature are used in determination of the transient temperature
response.
After Equation (8-2), replace “(See IEC Publication 287, Clause 3)” by ”(See IEC 60287-1-1.)”
8.2 Groups of circuits
Add, after 8.2, a new subclause 8.3 as follows:
8.3 Correction to transient temperature response to take account of variation in conductor
losses with temperature
The change in conductor resistance with temperature during the transient period results in
conductor losses being variable with time. Allowance for the variation of conductor loss with
temperature gives the corrected temperature rise:
θ(t )
θ (t ) = (8-3)
α
1 + α()θ(∞) − θ(t )
where
θ(t) is the conductor transient temperature rise above ambient without correction for
variation in conductor loss, and is based on the conductor resistance at the end of the
transient period;
θ(∞) is the conductor steady-state temperature rise above ambient;
α is the temperature coefficient of electrical resistivity of the conductor material at the
start of the transient.
NOTE α =
β + θ
i
where
β is the reciprocal of temperature coefficient at 0 °C (see Table E.2);
θ is the conductor temperature at the start of the transient period.
i
Appendix E – Physical constants of materials
In the second footnote beneath Table E.1, replace “in Sub-clause 9.7.1 of IEC Publication
287” by “in IEC 60287-2-1”.
F.2 Cable and installation details
Replace, in the third line of the first paragraph, “1 580 A” by “1 550 A”.
Table F.1 – Cable details
Replace, in the fifth column, “13,35” by “14,75” against the item “Dielectric”.

– 8 – 60853-2 Amend. 1 © IEC:2008
Replace, in the summation row, “45,75” by “47,15”.
F.3 Derivation of thermal circuit of the cable
Replace, in the fifth line “T ” by “T ”.
i 1
Replace, In the equations labelled “(from equation (4-1))” and “(from equation (4-6))”, the
symbol “ρ” by “p”.
Replace “(from equation 4-6))” by “(from equation 4-7))”.
Replace “(from equation 4-7))” by “from equation 4-6))”.
F.4 Example of the calculation of the transient response
Add, at the end of the first paragraph, the following new paragraph:
In the following example, the transient response is based on the formulae in 4.2 for a
transient of long duration. As the first time step chosen is less than one-third of the time
constant of the cable, the use of the formulae in 4.3 could be justified for the first time step.
However, this would lead to a discontinuity in the temperature rise curve that cannot be
justified.
F.4.1 Calculation of the response of the cable circuit
Replace the equation for T by the following:
a
1 ⎡ 1 ⎤
−4 −4
T = − 1,45 ×10()0,488 + 0,04 = 2,42 ×10 Km/W
a ⎢ ⎥
−3 −4
12 966
()
2,48 ×10 − 1,45 ×10 ⎣ ⎦
F.4.3 Calculation of the complete temperature transient
Replace the line that starts “Correcting for variation … “ as follows:
Correcting for variation of conductor losses using equation (8-3):
Replace the equation as follows: :
7,1
θ (1) = = 6K (8-3)
a
1+ (85 − 31,3 − 7,1)
234,5 + 31,3
Replace the existing note by the following new note:
NOTE Initial temperature = 31,3 °C due to 21,3 K dielectric loss contribution. Act
...