IEC 60909-3:2009

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: 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.
 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It also gives information on projects, withdrawn and replaced publications.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: 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.
 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.
 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.
 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: csc@iec.ch
Tél.: +41 22 919 02 11
Fax: +41 22 919 03 00
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 .
...