IEC 60826:2017

Design criteria of overhead transmission lines

IEC 60826:2017 specifies the loading and strength requirements of overhead lines derived from reliability-based design principles. These requirements apply to lines 45 kV and above, but can also be applied to lines with a lower nominal voltage.
This document also provides a framework for the preparation of national standards dealing with overhead transmission lines, using reliability concepts and employing probabilistic or semi-probabilistic methods. These national standards will need to establish the local climatic data for the use and application of this standard, in addition to other data that are country- specific.
Although the design criteria in this standard apply to new lines, many concepts can be used to address the design and reliability requirements for refurbishment, upgrading and uprating of existing lines.
This document does not cover the detailed design of line components such as supports, foundations, conductors or insulators strings.
This fourth edition cancels and replaces the third edition published in 2003. It constitutes a technical revision.
The main technical changes with regard to the previous edition are as follows:
This standard has been further simplified by removing many informative annexes and theoretical details that can now be found in CIGRE Technical Brochure 178 and referred to as needed in the text of the standard. Many revisions have also been made that reflect the users experience in the application of this standard, together with information about amplification of wind speed due to escarpments. The annexes dealing with icing data have also been updated using new work by CIGRE.
Key words: Overhead lines, Overhead transmission lines, reliability, energy

General Information

• Status: Published
• Publication Date: 12-Feb-2017
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.240.20 - Power transmission and distribution lines
• Technical Committee: TC 11 - Overhead lines
• Drafting Committee: MT 1 - TC 11/MT 1
• Current Stage: PPUB - Publication issued
• Start Date: 24-Feb-2017
• Completion Date: 13-Feb-2017

Relations

• Revises: IEC 60826:2003 - Design criteria of overhead transmission lines
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60826 ®
Edition 4.0 2017-02
INTERNATIONAL
STANDARD
colour
inside
Overhead transmission lines – Design criteria
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.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland 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.

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IEC 60826 ®
Edition 4.0 2017-02
INTERNATIONAL
STANDARD
colour
inside
Overhead transmission lines – Design criteria

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.20 ISBN 978-2-8322-3884-4

– 2 – IEC 60826:2017 © IEC 2017
CONTENTS
FOREWORD . 7
1 Scope . 9
2 Normative references . 9
3 Terms, definitions, symbols and abbreviations . 9
3.1 Terms and definitions . 9
3.2 Symbols and abbreviations . 12
4 General . 15
4.1 Objective . 15
4.2 System design . 15
4.3 System reliability . 16
5 General design criteria . 16
5.1 Methodology . 16
5.1.1 General . 16
5.1.2 Reliability requirements . 17
5.1.3 Security requirements . 19
5.1.4 Safety requirements. 19
5.2 Load-strength requirements . 19
5.2.1 Climatic loads . 19
5.2.2 Design requirements for the system . 20
5.2.3 Design formula for each component . 21
6 Loadings. 22
6.1 Description . 22
6.2 Climatic loads, wind and associated temperatures . 22
6.2.1 General . 22
6.2.2 Field of application . 22
6.2.3 Terrain roughness . 23
6.2.4 Reference wind speed V . 23
R
6.2.5 Assessment of meteorological measurements. 24
6.2.6 Determination from gradient wind velocities . 25
6.2.7 Combination of wind speed and temperatures . 25
6.2.8 Number of supports subjected in wind action, effect of length of line . 26
6.2.9 Unit action of the wind speed on any line component or element . 26
6.2.10 Evaluation of wind loads on line components and elements . 27
6.3 Climatic loads, ice without wind . 34
6.3.1 Description . 34
6.3.2 Ice data . 34
6.3.3 Evaluation of yearly maximum ice load by means of meteorological data
analysis . 35
6.3.4 Reference limit ice load . 36
6.3.5 Temperature during icing . 37
6.3.6 Loads on support . 37
6.4 Climatic loads, combined wind and ice loadings . 39
6.4.1 General . 39
6.4.2 Combined probabilities – Principle proposed . 39
6.4.3 Determination of ice load . 40
6.4.4 Determination of coincident temperature . 40

6.4.5 Determination of wind speed associated with icing conditions . 40
6.4.6 Drag coefficients of ice-covered conductors . 41
6.4.7 Determination of loads on supports . 42
6.5 Loads for construction and maintenance (safety loads) . 43
6.5.1 General . 43
6.5.2 Erection of supports . 43
6.5.3 Construction stringing and sagging . 44
6.5.4 Maintenance loads . 44
6.6 Loads for failure containment (security requirements) . 45
6.6.1 General . 45
6.6.2 Security requirements . 45
6.6.3 Security related loads – Torsional, longitudinal and additional security
measures. 45
7 Strength of components and limit states . 47
7.1 General . 47
7.2 General formulas for the strength of components . 47
7.2.1 General . 47
7.2.2 Values of strength factor Φ . 48
N
7.2.3 General basis for strength coordination . 49
7.2.4 Strength factor Φ related to the coordination of strength . 50
S
7.2.5 Methods for calculating strength coordination factors Φ . 50
S
7.3 Data related to the calculation of components . 51
7.3.1 Limit states for line components . 51
7.3.2 Strength data of line components . 54
7.3.3 Support design strength . 55
7.3.4 Foundation design strength . 56
7.3.5 Conductor and ground wire design criteria . 56
7.3.6 Insulator string design criteria . 56
Annex A (informative) Technical information – Strength of line components . 58
A.1 Calculation of characteristic strength . 58
Annex B (informative) Formulas of curves and figures . 60
B.1 General . 60
B.2 Formula for G – Figure 4 . 60
c
B.3 Formula for G – Figure 5 . 60
L
B.4 Formula for G – Figure 6 . 60
t
B.5 Formula for C – Figure 8 (flat-sided members) . 60
xt
B.6 Formula for C – Figure 9 (round-sided members) . 61
xt
B.7 Formulas for C – Figure 10 . 61
xtc
Annex C (informative) Atmospheric icing . 62
C.1 General . 62
C.2 Precipitation icing . 62
C.2.1 Freezing rain . 62
C.2.2 Wet snow. 62
C.3 Dry ice . 63
C.4 In-cloud icing . 63
C.5 Physical properties of ice . 64
C.6 Meteorological parameters controlling ice accretion . 64
C.7 Terrain influences . 65

– 4 – IEC 60826:2017 © IEC 2017
C.7.1 In-cloud icing . 65
C.7.2 Precipitation icing . 65
C.8 Guidelines for the implementation of an ice observation program .
...

IEC 60826 ®
Edition 4.0 2017-02
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Design criteria of Overhead transmission lines – Design criteria

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.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland 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.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC 60826 ®
Edition 4.0 2017-02
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Design criteria of Overhead transmission lines – Design criteria

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.20 ISBN 978-2-8322-3960-5

– 2 – IEC 60826:2017 RLV © IEC 2017
CONTENTS
FOREWORD . 7
1 Scope . 9
2 Normative references . 9
3 Terms, definitions, symbols and abbreviations . 9
3.1 Terms and definitions . 9
3.2 Symbols and abbreviations . 12
4 General . 15
4.1 Objective . 15
4.2 System design . 15
4.3 System reliability . 16
5 General design criteria . 16
5.1 Methodology . 16
5.1.1 General . 16
5.1.2 Reliability requirements . 17
5.1.3 Security requirements . 20
5.1.4 Safety requirements. 20
5.2 Climatic Load-strength requirements . 20
5.2.1 Limit Climatic loads . 20
5.2.2 Design requirements for the system . 21
5.2.3 Design equation formula for each component . 21
6 Loadings. 22
6.1 Description . 22
6.2 Climatic loads, wind and associated temperatures . 23
6.2.1 General . 23
6.2.2 Field of application . 23
6.2.3 Terrain roughness . 23
6.2.4 Reference wind speed V . 24
R
6.2.5 Assessment of meteorological measurements. 25
6.2.6 Determination from gradient wind velocities . 26
6.2.7 Combination of wind speed and temperatures . 26
6.2.8 Number of supports subjected in wind action, effect of length of line . 27
6.2.9 Unit action of the wind speed on any line component or element . 27
6.2.10 Evaluation of wind loads on line components and elements . 28
6.3 Climatic loads, ice without wind . 36
6.3.1 Description . 36
6.3.2 Ice data . 36
6.3.3 Evaluation of yearly maximum ice load by means of meteorological data
analysis . 37
6.3.4 Reference limit ice load . 37
6.3.5 Temperature during icing . 39
6.3.6 Loads on support . 39
6.4 Climatic loads, combined wind and ice loadings . 41
6.4.1 General . 41
6.4.2 Combined probabilities – Principle proposed . 41
6.4.3 Determination of ice load . 42
6.4.4 Determination of coincident temperature . 42

6.4.5 Determination of wind speed associated with icing conditions . 42
6.4.6 Drag coefficients of ice-covered conductors . 43
6.4.7 Determination of loads on supports . 44
6.5 Loads for construction and maintenance (safety loads) . 45
6.5.1 General . 45
6.5.2 Erection of supports . 45
6.5.3 Construction stringing and sagging . 46
6.5.4 Maintenance loads . 46
6.6 Loads for failure containment (security requirements) . 47
6.6.1 General . 47
6.6.2 Security requirements . 47
6.6.3 Security related loads – Torsional, longitudinal and additional security
measures. 47
7 Strength of components and limit states . 49
7.1 General . 49
7.2 General equations formulas for the strength of components . 49
7.2.1 General . 49
7.2.2 Values of strength factor Φ . 50
N
7.2.3 General basis for strength coordination . 51
7.2.4 Strength factor Φ related to the coordination of strength . 52
S
7.2.5 Methods for calculating strength coordination factors Φ . 52
S
7.3 Data related to the calculation of components . 53
7.3.1 Limit states for line components . 53
7.3.2 Strength data of line components . 56
7.3.3 Support design strength . 57
7.3.4 Foundation design strength . 58
7.3.5 Conductor and ground wire design criteria . 58
7.3.6 Insulator string design criteria . 58
Annex A (informative) Technical information– Strength of line components . 60
A.1 Calculation of characteristic strength . 78
Annex B (informative) Formulas of curves and figures . 87
B.1 General . 87
B.2 Formula for G – Figure 4 . 87
c
B.3 Formula for G – Figure 5 . 87
L
B.4 Formula for G – Figure 6 . 87
t
B.5 Formula for C – Figure 8 (flat-sided members) . 87
xt
B.6 Formula for C – Figure 9 (round-sided members) . 88
xt
B.7 Formulas for C – Figure 10 . 88
xtc
Annex C (informative) Statistical distribution and their application in probabilistic
design of transmission lines .
Annex C (informative) Atmospheric icing . 89
C.1 General . 89
C.2 Precipitation icing . 89
C.2.1 Freezing rain . 89
C.2.2 Wet snow. 89
C.3 Dry ice . 90
C.4 In-cloud icing . 90
C.5 Physical properties of ice . 91
C.6 Meteorological parameters controlling ice accretion . 91

– 4 – IEC 60826:2017 RLV © IEC 2017
C.7 Terrain influences . 92
C.7.1 In-cloud icing
...