IEC 60909-3:2009

Short-circuit currents in three-phase AC systems - Part 3: Currents during two separate simultaneous line-to-earth short circuits and partial short-circuit currents flowing through earth

IEC 60909-3:2009 is also available as IEC Standards+ 60909-3:2009 which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 60909-3:2009 specifies procedures for calculation of the prospective short-circuit currents with an unbalanced short circuit in high-voltage three-phase a.c. systems operating at nominal frequency 50 Hz or 60 Hz, i. e.:
- currents during two separate simultaneous line-to-earth short circuits in isolated neutral or resonant earthed neutral systems;
- partial short-circuit currents flowing through earth in case of single line-to-earth short circuit in solidly earthed or low-impedance earthed neutral systems.
The currents calculated by these procedures are used when determining induced voltages or touch or step voltages and rise of earth potential at a station (power station or substation) and the towers of overhead lines. Procedures are given for the calculation of reduction factors of overhead lines with one or two earth wires. This edition constitutes a technical revision. The main changes with respect to the previous edition are:
- New procedures are introduced for the calculation of reduction factors of the sheaths or shields and in addition the current distribution through earth and the sheaths or shields of three-core cables or of three single-core cables with metallic non-magnetic sheaths or shields earthed at both ends;
- The information for the calculation of the reduction factor of overhead lines with earth wires are corrected and given in the new Clause 7;
- A new Clause 8 is introduced for the calculation of current distribution and reduction factor of three-core cables with metallic sheath or shield earthed at both ends;
- The new Annexes C and D provide examples for the calculation of reduction factors and current distribution in case of cables with metallic sheath and shield earthed at both ends.
This publication is to be read in conjunction with IEC 60909-0:2001.

Courants de court-circuit dans les réseaux triphasés à courant alternatif - Partie 3: Courants durant deux courts-circuits monophasés simultanés séparés à la terre et courants de court-circuit partiels s'écoulant à travers la terre

IEC 60909-3:2009 est disponible sous forme de IEC Standards+ 60909-3:2009 qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
IEC 60909-3:2009 spécifie les procédures applicables au calcul des valeurs présumées des courants de court-circuit lors d'un court-circuit déséquilibré dans les réseaux triphasés à haute tension à courant alternatif fonctionnant à une fréquence nominale de 50 Hz ou 60 Hz, c'est-à-dire:
- les courants durant deux courts-circuits monophasés simultanés séparés à la terre dans les réseaux à neutre isolé ou mis à la terre par une bobine d'extinction;
- les courants de court-circuit partiels s'écoulant à travers la terre, dans le cas d'un seul court-circuit monophasé à la terre dans les réseaux à neutre mis à la terre directement ou par une faible impédance.
Les courants calculés suivant ces procédures sont utilisés pour la détermination des tensions induites ou des tensions de contact ou de pas, et de la montée du potentiel de terre d'un poste (groupe de production, poste), ainsi que les pylônes des lignes aériennes. Des procédures de calcul des facteurs de réduction des lignes aériennes avec un ou deux câbles de garde sont fournies. Cette édition constitue une révision technique. Les modifications principales par rapport à l'édition précédente sont les suivantes:
- De nouvelles procédures sont fournies pour le calcul des facteurs de réduction des gaines ou des écrans, ainsi que pour la répartition du courant par la terre et les gaines ou les écrans des câbles à trois conducteurs ou de trois câbles monoconducteurs avec gaines ou écrans non magnétiques métalliques mis à la terre à chaque extrémité;
- Les informations pour le calcul du facteur de réduction pour lignes aériennes avec câbles de garde sont corrigées et fournies en un nouvel Article 7;
- Un nouvel Article 8 est introduit pour le calcul de la répartition du courant et du facteur de réduction des câbles avec gaine ou écran métallique, mis à la terre à chaque extrémité;
- Les nouvelles Annexes C et D donnent des exemples pour le calcul des facteurs de réduction et de la répartition du courant dans le cas de câbles avec gaine ou écran métallique, mis à la terre à chaque extrémité.
Le contenu du corrigendum de septembre 2013 a été pris en considération dans cet exemplaire.
Cette publication doit être lue conjointement avec la IEC 60909-0:2001.

General Information

• Status: Published
• Publication Date: 08-Mar-2009
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 17.220.01 - Electricity. Magnetism. General aspects
• ICS: 29.240.20 - Power transmission and distribution lines
• Technical Committee: TC 73 - Short-circuit currents
• Current Stage: PPUB - Publication issued
• Start Date: 28-Feb-2009
• Completion Date: 09-Mar-2009

Relations

• Corrected By: IEC 60909-3:2009/COR1:2013 - Corrigendum 1 - Short-circuit currents in three-phase AC systems - Part 3: Currents during two separate simultaneous line-to-earth short circuits and partial short-circuit currents flowing through earth
• Effective Date: 05-Sep-2023
• Revises: IEC 60909-3:2003 - Short-circuit currents in three-phase a.c. systems - Part 3: Currents during two separate simultaneous line-to-earth short circuits and partial short-circuit currents flowing through earth
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60909-3 ®
Edition 3.0 2009-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Short-circuit currents in three-phase AC systems –
Part 3: Currents during two separate simultaneous line-to-earth short circuits
and partial short-circuit currents flowing through earth

Courants de court-circuit dans les réseaux triphasés à courant alternatif –
Partie 3: Courants durant deux courts-circuits monophasés simultanés séparés
à la terre et courants de court-circuit partiels s'écoulant à travers la terre

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.

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et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
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publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

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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.

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IEC 60909-3 ®
Edition 3.0 2009-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Short-circuit currents in three-phase AC systems –
Part 3: Currents during two separate simultaneous line-to-earth short circuits
and partial short-circuit currents flowing through earth

Courants de court-circuit dans les réseaux triphasés à courant alternatif –
Partie 3: Courants durant deux courts-circuits monophasés simultanés séparés
à la terre et courants de court-circuit partiels s'écoulant à travers la terre

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XA
CODE PRIX
ICS 17.220.01; 29.240.20 ISBN 978-2-88910-328-7
– 2 – 60909-3 © IEC:2009
CONTENTS
FOREWORD.5
1 Scope and object.7
2 Normative references .8
3 Terms and definitions .8
4 Symbols .10
5 Calculation of currents during two separate simultaneous line-to-earth short
circuits .12
5.1 Initial symmetrical short-circuit current .12
5.1.1 Determination of M and M .12
(1) (2)
5.1.2 Simple cases of two separate simultaneous line-to-earth short
circuits.13
5.2 Peak short-circuit current, symmetrical short circuit breaking current and
steady-state short-circuit current .13
5.3 Distribution of the currents during two separate simultaneous line-to-earth
short circuits.14
6 Calculation of partial short-circuit currents flowing through earth in case of an
unbalanced short circuit.14
6.1 General .14
6.2 Line-to-earth short circuit inside a station .15
6.3 Line-to-earth short circuit outside a station.16
6.4 Line-to-earth short circuit in the vicinity of a station.18
6.4.1 Earth potential U at the tower n outside station B .19
ETn
6.4.2 Earth potential of station B during a line-to earth short circuit at the
tower n .19
7 Reduction factor for overhead lines with earth wires .20
8 Calculation of current distribution and reduction factor in case of cables with
metallic sheath or shield earthed at both ends.21
8.1 Overview .21
8.2 Three-core cable .22
8.2.1 Line-to-earth short circuit in station B .22
8.2.2 Line-to-earth short circuit on the cable between station A and
station B .23
8.3 Three single-core cables .26
8.3.1 Line-to-earth short circuit in station B .26
8.3.2 Line-to-earth short circuit on the cable between station A and
station B .26
Annex A (informative) Example for the calculation of two separate simultaneous line-
to-earth short-circuit currents.30
Annex B (informative) Examples for the calculation of partial short-circuit currents
through earth .33
Annex C (informative) Example for the calculation of the reduction factor r and the
current distribution through earth in case of a three-core cable .43
Annex D (informative) Example for the calculation of the reduction factor r and the
current distribution through earth in case of three single-core cables .48

60909-3 © IEC:2009 – 3 –
Figure 1 – Driving point impedance Z of an infinite chain, composed of the earth wire
P
'
impedance Z =Zd and the footing resistance R of the towers, with equal
T
QQ T
distances d between the towers.9
T
Figure 2 – Driving point impedance Z of a finite chain with n towers, composed of the
Pn
'
earth wire impedance Z =Z d , the footing resistance R of the towers, with equal
T
Q Q T
distances d between the towers and the earthing impedance Z of station B from
T EB
Equation (29) .10
Figure 3 – Characterisation of two separate simultaneous line-to earth short circuits
"
and the currents I .12
kEE
Figure 4 – Partial short-circuit currents in case of a line-to-earth short circuit inside

station B .15
Figure 5 – Partial short-circuit currents in case of a line-to-earth short circuit at a
tower T of an overhead line .16
Figure 6 – Distribution of the total current to earth I .17
ETtot
Figure 7 – Partial short–circuit currents in the case of a line-to-earth short circuit at a
tower n of an overhead line in the vicinity of station B .18
Figure 8 – Reduction factor r for overhead lines with non-magnetic earth wires
depending on soil resistivity ρ .21
Figure 9 – Reduction factor of three-core power cables .23
Figure 10 – Reduction factors for three single-core power cables .27
Figure A.1 – Two separate simultaneous line-to-earth short circuits on a single fed
overhead line (see Table 1) .30
Figure B.1 – Line-to-earth short circuit inside station B – System diagram for stations
A, B and C .34
Figure B.2 – Line-to-earth short circuit inside station B – Positive-, negative- and zero-
sequence systems with connections at the short-circuit location F within station B.34
Figure B.3 – Line-to-earth short circuit outside stations B and C at the tower T of an
overhead line – System diagram for stations A, B and C .36
Figure B.4 – Line-to-earth short circuit outside stations B and C at the tower T of an
overhead line – Positive-, negative- and zero-sequence systems with connections at
the short-circuit location F.37
Figure B.5 – Earth potentials u = U /U with U = 1,912 kV and u = U /U
ETn Etn ET ET EBn Ebn EB
with U = 0,972 kV, if the line-to-earth short circuit occurs at the towers n = 1, 2, 3, .
EB
in the vicinity of station B .42
Figure C.1 – Example for the calculation of the cable reduction factor and the current
distribution through earth in a 10-kV-network, U = 10 kV; c = 1,1; f = 50 Hz .44
n
Figure C.2 – Short-circuit currents and partial short-circuit currents through earth for
the example in Figure C.1.45
Figure C.3 – Example for the calculation of current distribution in a 10-kV-network with
...

IEC 60909-3
Edition 3.0 2009-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Short-circuit currents in three-phase AC systems –
Part 3: Currents during two separate simultaneous line-to-earth short circuits
and partial short-circuit currents flowing through earth

Courants de court-circuit dans les réseaux triphasés à courant alternatif –
Partie 3: Courants durant deux courts-circuits monophasés simultanés séparés
à la terre et courants de court-circuit partiels s'écoulant à travers la terre

S+ IEC 60909-3:2009
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: [e-mail]
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.
 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.
 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.
 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.
 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: [e-mail]
Tel.: [phone]
Fax: [phone]
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.
 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.
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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.
 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.
 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: [e-mail]
Tél.: [phone]
Fax: [phone]
IEC 60909-3
Edition 3.0 2009-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Short-circuit currents in three-phase AC systems –
Part 3: Currents during two separate simultaneous line-to-earth short circuits
and partial short-circuit currents flowing through earth

Courants de court-circuit dans les réseaux triphasés à courant alternatif –
Partie 3: Courants durant deux courts-circuits monophasés simultanés séparés
à la terre et courants de court-circuit partiels s'écoulant à travers la terre

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.01; 29.240.20 ISBN 978-2-8891-0328-7
IEC 60909-3 ®
Edition 3.0 2009-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Short-circuit currents in three-phase AC systems –
Part 3: Currents during two separate simultaneous line-to-earth short circuits
and partial short-circuit currents flowing through earth

Courants de court-circuit dans les réseaux triphasés à courant alternatif –
Partie 3: Courants durant deux courts-circuits monophasés simultanés séparés
à la terre et courants de court-circuit partiels s'écoulant à travers la terre

– 2 – 60909-3 © IEC:2009
CONTENTS
FOREWORD.5
1 Scope and object.7
2 Normative references .8
3 Terms and definitions .8
4 Symbols .10
5 Calculation of currents during two separate simultaneous line-to-earth short
circuits .12
5.1 Initial symmetrical short-circuit current .12
5.1.1 Determination of M and M .12
(1) (2)
5.1.2 Simple cases of two separate simultaneous line-to-earth short
circuits.13
5.2 Peak short-circuit current, symmetrical short circuit breaking current and
steady-state short-circuit current .13
5.3 Distribution of the currents during two separate simultaneous line-to-earth
short circuits.14
6 Calculation of partial short-circuit currents flowing through earth in case of an
unbalanced short circuit.14
6.1 General .14
6.2 Line-to-earth short circuit inside a station .15
6.3 Line-to-earth short circuit outside a station.16
6.4 Line-to-earth short circuit in the vicinity of a station.18
6.4.1 Earth potential U at the tower n outside station B .19
ETn
6.4.2 Earth potential of station B during a line-to earth short circuit at the
tower n .19
7 Reduction factor for overhead lines with earth wires .20
8 Calculation of current distribution and reduction factor in case of cables with
metallic sheath or shield earthed at both ends.21
8.1 Overview .21
8.2 Three-core cable .22
8.2.1 Line-to-earth short circuit in station B .22
8.2.2 Line-to-earth short circuit on the cable between station A and
station B .23
8.3 Three single-core cables .26
8.3.1 Line-to-earth short circuit in station B .26
8.3.2 Line-to-earth short circuit on the cable between station A and
station B .26
Annex A (informative) Example for the calculation of two separate simultaneous line-
to-earth short-circuit currents.30
Annex B (informative) Examples for the calculation of partial short-circuit currents
through earth .33
Annex C (informative) Example for the calculation of the reduction factor r and the
current distribution through earth in case of a three-core cable .43
Annex D (informative) Example for the calculation of the reduction factor r and the
current distribution through earth in case of three single-core cables .48

60909-3 © IEC:2009 – 3 –
Figure 1 – Driving point impedance Z of an infinite chain, composed of the earth wire
P
'
impedance Z =Zd and the footing resistance R of the towers, with equal
T
QQ T
distances d between the towers.9
T
Figure 2 – Driving point impedance Z of a finite chain with n towers, composed of the
Pn
'
earth wire impedance Z =Z d , the footing resistance R of the towers, with equal
T
Q Q T
distances d between the towers and the earthing impedance Z of station B from
T EB
Equation (29) .10
Figure 3 – Characterisation of two separate simultaneous line-to earth short circuits
"
and the currents I .12
kEE
Figure 4 – Partial short-circuit currents in case of a line-to-earth short circuit inside

station B .15
Figure 5 – Partial short-circuit currents in case of a line-to-earth short circuit at a
tower T of an overhead line .16
Figure 6 – Distribution of the total current to earth I .17
ETtot
Figure 7 – Partial short–circuit currents in the case of a line-to-earth short circuit at a
tower n of an overhead line in the vicinity of station B .18
Figure 8 – Reduction factor r for overhead lines with non-magnetic earth wires
depending on soil resistivity ρ .21
Figure 9 – Reduction factor of three-core power cables .23
Figure 10 – Reduction factors for three single-core power cables .27
Figure A.1 – Two separate simultaneous line-to-earth short circuits on a single fed
overhead line (see Table 1) .30
Figure B.1 – Line-to-earth short circuit inside station B – System diagram for stations
A, B and C .34
Figure B.2 – Line-to-earth short circuit inside station B – Positive-, negative- and zero-
sequence systems with connections at the short-circuit location F within station B.34
Figure B.3 – Line-to-earth short circuit outside stations B and C at the tower T of an
overhead line – System diagram for stations A, B and C .36
Figure B.4 – Line-to-earth short circuit outside stations B and C at the tower T of an
overhead line – Positive-, negative- and zero-sequence systems with connections at
the short-circuit location F.37
Figure B.5 – Earth potentials u = U /U with U = 1,912 kV and u = U /U
ETn Etn ET ET EBn Ebn EB
with U = 0,972 kV, if the line-to-earth short circuit occurs at the towers n = 1, 2, 3, .
EB
in the vicinity of station B .
...