IEC TR 61597:2021

IEC TR 61597 ®
Edition 2.0 2021-06
TECHNICAL
REPORT
Overhead electrical conductors – Calculation methods for stranded bare
conductors
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IEC TR 61597 ®
Edition 2.0 2021-06
TECHNICAL
REPORT
Overhead electrical conductors – Calculation methods for stranded bare

conductors
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.20 ISBN 978-2-8322-9938-8

– 2 – IEC TR 61597:2021 © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Symbols, units and abbreviated terms . 7
4.1 Symbols and units. 7
4.2 Abbreviated terms . 8
5 Current carrying capacity . 8
5.1 General . 8
5.2 Heat balance equation . 8
5.3 Calculation method . 9
5.4 Joule effect . 9
5.5 Solar heat gain . 9
5.6 Radiated heat loss . 9
5.7 Convection heat loss . 10
5.8 Method to calculate current carrying capacity (CCC) . 10
5.9 Determination of the maximum permissible aluminium temperature . 10
5.10 Calculated values of current carrying capacity . 11
6 Alternating current resistance, Inductive and capacitive reactances . 11
6.1 General . 11
6.2 Alternating current (AC) resistance . 11
6.3 Inductive reactance . 12
6.4 Capacitive reactance . 14
7 Elongation of stranded conductors . 14
7.1 General . 14
7.2 Thermal elongation . 15
7.3 Stress-strain properties . 18
7.4 Assessment of final elastic modulus . 20
8 Conductor creep . 22
8.1 General . 22
8.2 Creep of single wires . 23
8.3 Total conductor creep . 24
8.4 Prediction of conductor creep . 24
8.5 Creep values . 24
9 Loss of strength . 25
Annex A (informative) A practical example of CCC calculation . 27
A.1 Basic Assumptions . 27
A.2 CCC calculation . 27
Annex B (informative) Indicative conditions for CCC calculation . 29
Bibliography . 30

Figure 1 – Typical creep curve . 23
Figure 2 – Loss of strength of aluminium A1 as a function of temperature . 26
Figure 3 – Loss of strength of aluminium A2 . 26

Table 1 – Values of K for inductive reactance calculations . 13
g
Table 2 – Coefficient of linear expansion β of inhomogeneous conductors designated
Ax/Sxy . 17
Table 3 – Coefficient of linear expansion β of inhomogeneous conductors designated
Ax/20SA . 18
Table 4 – Typical stress-strain data of stranded conductors based on published test
results . 21
Table 5 – Final modulus of elasticity calculated with E = 55000 MPa and
a
E = 190000 MPa . 22
s
Table 6 – Final modulus of elasticity calculated with E = 55000 MPa and
a
E = 159000 MPa (20SA) . 22
s
Table 7 – Indicative creep values of stranded conductors(25 %RTS, 20 ℃) . 25
Table B.1 – Indicative conditions for CCC calculation . 29

– 4 – IEC TR 61597:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OVERHEAD ELECTRICAL CONDUCTORS – CALCULATION
METHODS FOR STRANDED BARE CONDUCTORS

FOREWORD
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IEC TR 61597 has been prepared by IEC technical committee 7: Overhead electrical
conductors. It is a Technical Report.
This second edition cancels and replaces the first edition published in 1995. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Addition of Clause 2 and Clause 3 since the “Normative references” and “Terms and
definitions” clauses are mandatory elements of the text according to the new IEC
template.
b) In Clause 6, addition of new kinds of aluminium alloy and aluminium clad steel and their
values of temperature coefficients of resistance.
c) In Clause 6, addition of guidelines for the calculation of AC resistance taken into account
hysteresis and eddy current losses.

d) In Clause 7, addition of the values of coefficient of linear expansion of aluminium alloy
conductor aluminium-clad steel reinforced series.
e) Deletion of Clause 8 “Calculation of maximum conductor length on drums” in the last
version.
f) Annex A, replaced by “A practical example of CCC calculation”.
g) Annex B, replaced by “Indicative conditions for CCC calculation”.
The text of this Technical Report is based on the following documents:
Draft Report on voting
7/704/DTR 7/707/RVDTR
Full information on the
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