SIST EN 60909-3:2004

SLOVENSKI SIST EN 60909-3:2004

STANDARD
junij 2004
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
ICS 17.220.01 Referenčna številka
SIST EN 60909-3:2004(en)
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

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EUROPEAN STANDARD EN 60909-3
NORME EUROPÉENNE
EUROPÄISCHE NORM November 2003

ICS 17.220.01; 29.240.20


English version


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
(IEC 60909-3:2003)


Courants de court-circuit dans les réseaux Kurzschlussströme in Drehstromnetzen
triphasés à courant alternatif Teil 3: Ströme bei Doppelerdkurzschluss
Partie 3: Courants durant deux court-circuits und Teilkurzschlussströme über Erde
monophasés simultanés séparés à la terre (IEC 60909-3:2003)
et courants de court-circuit partiels
s'écoulant à travers la terre
(CEI 60909-3:2003)






This European Standard was approved by CENELEC on 2003-11-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60909-3:2003 E

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EN 60909-3:2003 - 2 -
Foreword

The text of document 73/127/FDIS, future edition 2 of IEC 60909-3, prepared by IEC TC 73, Short-circuit
currents, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 60909-3 on 2003-11-01.

The following dates were fixed:

– latest date by which the EN has to be implemented
 at national level by publication of an identical
 national standard or by endorsement (dop) 2004-08-01

– latest date by which the national standards conflicting
 with the EN have to be withdrawn (dow) 2006-11-01

Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annex ZA is normative annexes A and B are informative.
Annex ZA has been added by CENELEC.
__________

Endorsement notice

The text of the International Standard IEC 60909-3:2003 was approved by CENELEC as a European
Standard without any modification.
__________

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- 3 - EN 60909-3:2003
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 60909-0 2001 Short-circuit currents in three-phase a.c. EN 60909-0 2001
systems
Part 0: Calculation of currents

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NORME CEI
INTERNATIONALE
IEC
60909-3
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2003-09
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
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
© IEC 2003 Droits de reproduction réservés ⎯ Copyright - all rights reserved
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utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch  Web: www.iec.ch
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Pour prix, voir catalogue en vigueur
For price, see current catalogue

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60909-3 © IEC:2003 – 3 –
CONTENTS
FOREWORD . 7
1 Scope .11
2 Normative reference .13
3 Terms and definitions .13
4 Symbols.17
5 Currents during two separate simultaneous line-to-earth short circuits.19
5.1 Calculation method .19
5.1.1 Initial symmetrical short-circuit current.19
5.1.2 Peak short-circuit current, symmetrical short-circuit breaking current
and steady-state short-circuit current .23
5.1.3 Distribution of line-to-earth short-circuit currents during two separate
simultaneous line-to-earth short circuits.23
6 Partial short-circuit currents flowing through earth in the case of an unbalanced
short circuit.25
6.1 Calculation method .25
6.1.1 General.25
6.1.2 Line-to-earth short circuit in a station.25
6.1.3 Line-to-earth short circuit far outside a station .29
6.1.4 Line-to-earth short circuit in the vicinity of a station .33
6.1.5 Reduction factor for overhead lines and cables.35
Annex A (informative) Example for the calculation of two separate simultaneous line-
to-earth short-circuit currents .41
Annex B (informative) Examples for the calculation of partial short-circuit currents
through earth .45
Figure 1 – Driving point impedance Z of an infinite chain, composed of the earth-wire
P
impedance Z = Z´ ·d and the footing resistance R of the towers, with equal
W W T T
distances d between towers.15
T
Figure 2 – Driving point impedance Z of a finite chain with n towers, composed of
Pn
the earth-wire impedance Z = Z´ ·d , the footing resistance R of the towers with
W W T T
equal distances d between towers and the earthing impedance Z (Equation (28)) of
T EB
a station B.17
Figure 3 – Characterization of two separate simultaneous line-to-earth short circuits
"
and the current I .19
kEE
Figure 4 – Partial short-circuit currents in the case of a line-to-earth short circuit inside
the station B.27
Figure 5 – Partial short-circuit currents in the case of a line-to-earth short circuit at
tower T of an overhead line.29
Figure 6 – Distribution of the total earth current I .31
Etot
Figure 7 – Partial short-circuit currents in the case of a line-to-earth short circuit
at tower n of an overhead line in the vicinity of station B .33
Figure 8 – The magnitude r of the reduction factor for non-magnetic earth wires
in relation to soil resistivity ρ .39
Figure A.1 – Two separate simultaneous line-to-earth short circuits on a single fed
radial line, see Table 1.41

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60909-3 © IEC:2003 – 5 –
Figure B.1 – Line-to-earth short circuit inside station B – System diagram for stations
A, B and C .47
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.47
Figure B.3 – Line-to-earth short circuit outside stations A, B and C at tower T of an
overhead line – System diagram for stations A, B and C. .51
Figure B.4 – Line-to-earth short circuit outside the stations A, B and C at tower T of an
overhead line – Positive- negative- and zero-sequence systems with connections
at the short-circuit location F .53
Figure B.5 – Earth potentials u = U /U with U = 1,912 kV and u =
ETn ETn ET ET EBn
U /U with U = 0,972 kV, if the line-to-earth short circuit occurs at the towers n
EBn EB EB
= 0, 1, 2, 3, in the vicinity of station B according to 6.1.4 (see the example for n = 10 in
Clause B.4). .63
Table 1 – Calculation of initial line-to-earth short-circuit currents in simple cases.23
Table 2 – Resistivity ρ and equivalent earth penetration depth δ for different soil types.35

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60909-3 © IEC:2003 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
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
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60909-3 has been prepared by IEC technical committee 73: Short-
circuit currents.
This second edition cancels and replaces the first edition published in 1995. This edition
constitutes a technical revision.

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60909-3 © IEC:2003 – 9 –
The text of this standard is based on the following documents:
FDIS Voting report
73/127/FDIS 73/128/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until 2008.
At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.

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60909-3 © IEC:2003 – 11 –
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
1 Scope
This part of IEC 60909 specifies procedures for calculation of the prospective short-circuit
currents with an unbalanced short circuit in high-voltage three-phase AC systems operating at
nominal frequency 50 Hz or 60 Hz, i.e.
a) currents during two separate simultaneous line-to-earth short circuits in isolated neutral or
resonant earthed neutral systems;
b) 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).
This standard does not cover:
a) short-circuit currents deliberately created under controlled conditions as in short-circuit
testing stations, or
b) short-circuit currents in the electrical installations on board ships or aeroplanes, or
c) single line-to-earth faults in isolated or resonant earthed systems.
The object of this standard is to establish practical and concise procedures for the calculation
of line-to-earth short-circuit currents during two separate simultaneous line-to-earth short
circuits and partial short-circuit currents through earth from electrical installations, leading to
conservative results with sufficient accuracy. For this purpose, the current is determined
by considering an equivalent voltage source applied at the short-circuit location with all
other sources set to zero. The procedure is suitable for determination by manual methods
or digital computation.
This standard is an addition to IEC 60909-0. General definitions, symbols and calculation
assumptions refer to that publication. Special items only are defined or specified in this
document. This does not exclude the use of special methods, for example the superposition
method, adjusted to particular circumstances, if they give at least the same precision.
As stated in IEC 60909-0, short-circuit currents and their parameters may also be determined
by system tests.
The calculation of the short-circuit parameters based on the rated data of the electrical
equipment and the topological arrangement of the system has the advantage of being
possible both for existing systems and for systems at the planning stage.

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60909-3 © IEC:2003 – 13 –
2 Normative reference
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60909-0:2001, Short-circuit currents in three-phase a.c. systems – Part 0: Calculation
of currents
3 Terms and definitions
For the purposes of this standard, the following definitions apply.
3.1
two separate simultaneous line-to-earth short circuits
line-to-earth short circuits at different locations at the same time on different conductors of
a three-phase AC system having a resonant earthed or an isolated neutral.
3.2
initial short-circuit currents during two separate simultaneous
"
line-to-earth short circuits I
kEE
r.m.s. value of the initial short-circuit currents flowing with the same magnitude at both
locations at the instant of the two separate simultaneous line-to-earth short circuits.
3.3
total earth current I at the short-circuit location
Etot
r.m.s. value of the earth current at the short-circuit location flowing through the earthing
system of a station (power station or substation) or the footing resistance of an overhead line
tower far away from a station and through earthed conductors to earth (Figures 4 and 5).
Such conductors may be earth wires of over-head lines or sheaths, shielding or armouring of
cables.
3.4
earth current I
ETn
r.m.s. value of the earth current causing the potential to rise above earth at an overhead line
tower n in the vicinity of a station
3.5
earth current I
EBn
r.m.s. value of the earth current causing the potential to rise above earth U of station B, in
EBn
case of a line-to-earth short circuit at an overhead line tower n in the vicinity of the station B
3.6
partial short-circuit current through earth r·3I
(0)
part of the total current flowing through earth remote from the short-circuit location and
the earthing system of a station, where the distribution of the total current between earthed
conductors and earth is nearly constant. Its magnitude depends on the reduction factor r.

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60909-3 © IEC:2003 – 15 –
3.7
reduction factor r
factor which determines the part of the zero-sequence current flowing through earth remote
from the short-circuit location and the earthing system of a station.
3.8
driving point impedance Z of an infinite chain
P
in the case of an overhead line, the driving point impedance, according to Figure 1, is
composed of the earth-wire impedance Z = Z' ·d between two towers with earth return and
W W T
the footing resistance R of the overhead line towers:
T
2
Z = 0,5 ⋅ Z +()0,5 ⋅ Z + Z R (1)
T
P W W W
dT dT dT
ZW ZW ZW
Earth wire
~ ~ ~
Z
P
R R R
T T T
Reference earth
IEC  2230/03
Figure 1 – Driving point impedance Z of an infinite chain, composed of the earth-wire
P
impedance Z = Z´ ·d and the footing resistance R of the towers, with equal
W W T T
distances d between towers
T
The driving point impedance Z can be assumed constant at a distance from the short-circuit
P
location F longer than the far-from-station distance D defined by Equation (18).
F
In the case of power cables, a similar approach may be used, but special considerations are
necessary.
3.9
driving point impedance Z of a finite chain
Pn
driving point impedance Z of an overhead line, with n towers as given in Figure 2 and
Pn
with the earth impedance Z of a station B at the end, can be calculated according to
EB
Equation (2):
n − n
ª º
§ · § · § ·
Z Z + Z ⋅ k + Z Z − Z + 2 ⋅ Z − Z Z + Z ⋅ k
¨ ¸ ¨ ¸ ¨ ¸
P P « P P W W W »
© EB ¹ © EB ¹ © EB ¹
¬ ¼
Z = (2)
Pn
n − n
§ ·
()Z + Z ⋅ k − Z − Z + Z ⋅ k
¨ ¸
EB P P W
© EB ¹
§ ·
1 1
¨ ¸
with k = 1+ Z + (3)
W
¨ ¸
R Z
T
P
© ¹
NOTE For n → ∞ , Equation (2) is leading to Equation (1). In practical cases, this is already true for
n ≈ 10.15 .

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60909-3 © IEC:2003 – 17 –
d d d d d
T T T T T
Z Z Z Earth wire
W n 3 W 2 Z 1 W 0 Z
n -1 W W
~ ~ ~ ~ ~
B
Z
Pn
R R R R R
T T T T T
~
Z
EB
Reference earth
IEC  2231/03
Figure 2 – Driving point impedance Z of a finite chain with n towers,
Pn
composed of the earth-wire impedance Z = Z´ ·d , the footing resistance R
W W T T
of the towers with equal distances d between towers and
T
the earthing impedance Z (Equation (28)) of a station B
EB
4 Symbols
All equations are written as quantity equations, in which the symbols represent physical
quantities possessing both numerical values and dimensions. Symbols of complex quantities
are underlined, e.g. Z = R + jX.
c Voltage factor according to Table 1 of IEC 60909-0
cU /¥3 Equivalent voltage source, see IEC 60909-0
n
D Far-from-station distance
F
d Distance between towers
T
I Short-circuit breaking current in the case of two separate simultanious line-to-
bEE
earth short circuits
I Total earth current at the short-circuit location
Etot
I
ETn Earth current at the short-circuited tower in the vicinity of a station
"
I Initial line-to-earth short-circuit current
k1
"
I Initial short-circuit current in the case of two separate simultaneous line-to-
kEE
earth short circuits
"
I Initial short-circuit current flowing to earth in the case of a line-to-line short
kE2E
circuit with earth connection, see IEC 60909-0
I Earth wire current
W
i Peak short-circuit current in the case of two separate simultanious line-to-earth
pEE
short circuits
I Short-circuit current through the tower
T
M , M Coupling impedance, in the positive- and negative-sequence system
(1) (2)
R Resistance of earth grid
E
R Footing resistance of an overhead line tower
T
r Reduction factor
rҏ3I Partial short-circuit current through earth at a distance longer than D
(0)җF
Z , Z Positive-sequence short-circuit impedance of the three-phase AC system at the
(1)A (1)B
short-circuit locations A and B

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60909-3 © IEC:2003 – 19 –
Z , Z Negative-sequence short-circuit impedance of the three-phase AC system at
(2)A (2)B
the short-circuit locations A and B
Z Zero-sequence short-circuit impedance of the entire network between the
(0)
short-circuit locations A and B (admittances between line conductors and earth
are disregarded)
Z Earthing impedance of a station according to Equation (28)
E
Z Earthing impedance of the short circuited tower according to Equation (27)
ET
Z Total earthing impedance of a station according to Equation (16)
Etot
Z Total earthing impedance of the short circuited tower according to
ETtot
Equation (21)
Z Driving point impedance of an infinite chain (Equation (1) and Figure 1)
P
Z Driving point impedance of a finite chain (Equation (2) and Figure 2)
Pn
Z Input impedance of sheaths, shielding or armouring of cables
U
'
Z = Z ·d Earth-wire impedance between two towers
W T
W
'
Z Per unit length earth-wire impedance with earth return
W
'
Z Per unit length mutual impedance between earth wires and the line conductors
WL
with common earth return
δ Equivalent earth penetration depth
ρ Soil resistivity
5 Currents during two separate simultaneous line-to-earth short circuits
5.1 Calculation method
5.1.1 Initial symmetrical short-circuit current
"
Figure 3 shows the short-circuit current I during two separate simultaneous line-to-earth
kEE
short circuits on different line conductors at the locations A and B with finite distance between
them, i.e. distance ≠ 0. It is assumed that the locations A and B are far from stations.
Distance ≠
0
A B
L1
L2
L3
'' ''
I I
kEE kEE
IEC  2232/03
NOTE The direction of current is chosen arbitrarily.
Figure 3 – Characterization of two separate simultaneous
"
line-to-earth short circuits and the current I
kEE

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60909-3 © IEC:2003 – 21 –
In systems with isolated neutral or with resonant earthed neutral the initial symmetrical short-
"
circuit current I is calculated using
kEE
3cU
"
n
I = (4)
kEE
Z + Z + Z + Z + M + M + Z
(1)A (2)A (1)B (2)B (1) (2) (0)
NOTE For derivation of Equation (4) see CCITT – Directives concerning protection of telecommunication lines
against harmful effects from electric power and electrified railway lines, Volume V: Inducing currents and voltages
in power transmission and distribution systems. Geneva 1999.
In the case of a far-from-generator short circuit, where Z = Z and M = M , the initial
(1) (2) (1) (2)
short-circuit current becomes
3cU
" n
I = (5)
kEE
2Z + 2Z + 2M + Z
(1)A (1)B (1) (0)
5.1.1.1 Determination of M and M
(1) (2)
The positive- and negative-sequence coupling impedances M and M are determined as
(1) (2)
follows:
A voltage source U is introduced at the short-circuit location A as the only active voltage of
A
the system. If I and I are the currents due to this voltage source in the positive- and
(1)A (2)A
negative- sequence systems at the short-circuit location A and if U and U are the
(1)B (2)B
resulting voltages in the positive- and negative-sequence systems at the location B, then
U U
(1)B (2)B
M = M = (6)
(1) (2)
I I
(1)A (2)A
The coupling impedances M and M may also be determined at the short-circuit location B
(1) (2)
instead of the location A by using
U U
(1)A (2)A
M = M = (7)
(1) (2)
I I
(1)B (2)B
5.1.1.2 Simple cases of two separate simultaneous line-to-earth short circuits
In simple cases, the two separate simultaneous line-to-earth short-circuit currents can be
calculated as shown in Table 1 provided it is presumed that Z = Z and M = M . With
(1) (2) (1) (2)
this presumption Equations (8) to (10), shown in Table 1, are derived from Equation (5). The
indices in Equations (8) to (10) refer to the relevant impedances in the respective circuits.

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60909-3 © IEC:2003 – 23 –
Table 1 – Calculation of initial line-to-earth
short-circuit currents in simple cases
d f
a) Single-fed radial line
L1
L2
L3
3cU
" n
A B
I =              (8)
kEE
6Z + 2Z + Z
(1)d (1)f (0)f
d g
b) Two single-fed radial lines
L1
L2
L3 3cU
" n
A
I =  (9)
kEE
6Z + 2(Z + Z ) + Z + Z
(1)d (1)g (1)h (0)g (0)h
L1
L2
L3
B
h
c) Double-fed single line
d f e
L1
L2
L3 3cU
" n
I = (10)
kEE
A B
6Z Z + 2 Z (Z + Z )
(1)d (1)e (1)f (1)d (1)e
+ Z
(0)f
Z + Z + Z
(1)d (1)f (1)e
The voltage factor c shall be taken from Table 1 of IEC 60909-0
5.1.2 Peak
...