IEC 61472-2:2021
(Main)Live working - Minimum approach distances - Part 2: Method of determination of the electrical component distance for AC systems from 1,0 kV to 72,5 kV
Live working - Minimum approach distances - Part 2: Method of determination of the electrical component distance for AC systems from 1,0 kV to 72,5 kV
IEC 61472-2:2021 specifies a method for determining the electrical component of the minimum approach distances for live working, for AC systems 1 kV up to and including 72,5 kV. This document addresses system overvoltages and the working air distances between equipment and/or workers at different potentials.
The withstand voltage and minimum approach distances determined by the method described in this document can be used only if the following working conditions prevail:
workers are trained for, and skilled in, working live lines or close to live conductors or equipment;
the operating conditions are adjusted so that the statistical overvoltage does not exceed the value selected for the determination of the required withstand voltage;
transient overvoltages are the determining overvoltages;
tool insulation has no continuous film of moisture present on the surface;
no lightning is observed within 10 km of the work site;
allowance is made for the effect of the conducting components of tools.
Travaux sous tension - Distances minimales d’approche - Partie 2: Méthode de détermination de la distance du composant électrique pour les réseaux en courant alternatif de tension comprise entre 1,0 kV et 72,5 kV
IEC 61472-2:2021 spécifie une méthode pour déterminer la composante électrique des distances minimales d’approche pour le travail en direct, pour les systèmes AC 1 kV jusqu’à 72,5 kV et y compris. Ce document traite des survoltages du système et des distances aériennes de travail entre l’équipement et/ou les travailleurs à différents potentiels.
La tension de résisté et les distances minimales d’approche déterminées par la méthode décrite dans ce document ne peuvent être utilisées que si les conditions de travail suivantes prévalent:
les travailleurs sont formés et qualifiés dans les lignes de travail en direct ou à proximité de conducteurs ou d’équipement vivants;
les conditions d’exploitation sont ajustées de sorte que la surtension statistique ne dépasse pas la valeur sélectionnée pour déterminer la tension de résisté requise;
les survoltages transitoires sont les survoltages déterminants;
l’isolation de l’outil n’a pas de film continu de l’humidité présente à la surface;
aucune foudre n’est observée à moins de 10 km du chantier;
l’effet des composants conducteurs des outils.
General Information
Standards Content (Sample)
IEC 61472-2
®
Edition 1.0 2021-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Live working – Minimum approach distances –
Part 2: Method of determination of the electrical component distance for AC
systems from 1,0 kV to 72,5 kV
Travaux sous tension – Distances minimales d’approche –
Partie 2: Méthode de détermination de la distance du composant électrique pour
les réseaux en courant alternatif de tension comprise entre 1,0 kV et 72,5 kV
IEC 61472-2:2021-03(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61472-2
®
Edition 1.0 2021-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Live working – Minimum approach distances –
Part 2: Method of determination of the electrical component distance for AC
systems from 1,0 kV to 72,5 kV
Travaux sous tension – Distances minimales d’approche –
Partie 2: Méthode de détermination de la distance du composant électrique pour
les réseaux en courant alternatif de tension comprise entre 1,0 kV et 72,5 kV
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.260; 29.240.99; 29.260.99 ISBN 978-2-8322-9220-4
Warning! Make sure that you obtained this publication from an authorized distributor.
Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 61472-2:2021 © IEC 2021
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Minimum approach distance, D . 6
A
5 Factors influencing the minimum approach distance . 7
5.1 Control of system overvoltages . 7
5.2 Statistical overvoltage . 7
5.3 Conductive floating object . 8
5.4 Insulators . 8
5.5 Determination of minimum electrical distance, D . 8
U
6 Example calculation . 8
Annex A (informative) Overvoltages . 11
A.1 General . 11
A.2 Highest voltage of a system . 11
A.3 Temporary overvoltage . 11
A.4 Transient overvoltage . 12
A.4.1 General . 12
A.4.2 Switching overvoltage . 12
A.4.3 Lightning overvoltages . 13
Annex B (informative) Ergonomic considerations . 14
B.1 General . 14
B.2 Training, knowledge and skill . 14
B.3 Protective barriers . 14
B.4 Possibility of error . 14
B.5 Work procedure . 14
B.6 Personal factors . 15
B.7 Monitoring . 15
Bibliography . 16
Table 1 – Distance for rod-to-rod gap from IEEE 516-2009 . 9
Table 2 – Phase-to-earth electrical distance for system voltages from 1,0 kV up to and
including 72,5 kV, u = 3,5. 9
e2
Table 3 – Phase-to-phase electrical distances for system voltages from 1,0 kV up to
and including 72,5 kV, u = 5,2 . 10
p2
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IEC 61472-2:2021 © IEC 2021 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LIVE WORKING –
MINIMUM APPROACH DISTANCES –
Part 2: Method of determination of the electrical component
distance for AC systems from 1,0 kV to 72,5 kV
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
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61472-2 has been prepared by IEC technical committee technical
committee 78: Live working.
The text of this International Standard is based on the following documents:
FDIS Report on voting
78/1319/FDIS 78/1326/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 61472 series, published under the general title Live working –
Miminum approach distances, can be found on the IEC website.
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– 4 – IEC 61472-2:2021 © IEC 2021
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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IEC 61472-2:2021 © IEC 2021 – 5 –
LIVE WORKING –
MINIMUM APPROACH DISTANCES –
Part 2: Method of determination of the electrical component
distance for AC systems from 1,0 kV to 72,5 kV
1 Scope
This part of IEC 61472 specifies a method for determining the electrical component of the
minimum approach distances for live working, for AC systems 1 kV up to and including 72,5 kV.
This document addresses system overvoltages and the working air distances between
equipment and/or workers at different potentials.
The withstand voltage and minimum approach distances determined by the method described
in this document can be used only if the following working conditions prevail:
– workers are trained for, and skilled in, working live lines or close to live conductors or
equipment;
– the operating conditions are adjusted so that the statistical overvoltage does not exceed the
value selected for the determination of the required withstand voltage;
– transient overvoltages are the determining overvoltages;
– tool insulation has no continuous film of moisture present on the surface;
– no lightning is observed within 10 km of the work site;
– allowance is made for the effect of the conducting components of tools.
NOTE In some countries, special procedures have been developed to permit live working with surface moisture on
tools at distribution voltages (below 50 kV).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
highest voltage of a system
U
s
highest value of operating voltage (phase-to-phase voltage) which occurs under normal
operating conditions at any time and any point in the system
Note 1 to entry: Transient overvoltages and permanent induction from adjacent lines are not taken into account in
the calculation formula
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– 6 – IEC 61472-2:2021 © IEC 2021
[SOURCE: IEC 60050-601:1985, 601-01-23, modified – the symbol U and the words "(phase-
s
to-phase voltage)" have been added, and Note 1 has been revised.]
3.2
transient overvoltage
short duration overvoltage of a few milliseconds or less, oscillatory or non-oscillatory, usually
highly damped
[SOURCE: IEC 60050-614:2016, 614-03-14]
3.3
nominal system voltage
suitable approximate value of voltage used to designate or identify a system
[SOURCE: IEC 60038:2009, 3.1]
3.4
per unit statistical overvoltage phase-to-earth
u
e2
phase-to-earth per unit overvoltage that has a 2 % probability of being exceeded
3.5
per unit statistical overvoltage phase-to-phase
u
p2
per unit overvoltage that has a 2 % probability of being exceeded
3.6
statistical overvoltage
U
2
overvoltage that has a 2 % probability of being exceeded
3.7
minimum approach distance
D
A
minimum electrical and ergonomic distance in air to be maintained between any part of the body
of a worker, or any conductive tool being directly handled, and any live conductors or equipment
at different potentials
3.8
electrical distance
D
U
electrical component of the minimum air distance between two electrodes which represent live
and/or earthed conductors or equipment, required to prevent sparkover under the most severe
electrical stress that will arise under the chosen conditions
3.9
ergonomic distance
D
E
distance in air added to the electrical distance, to take into account inadvertent movement and
errors in judgement of distances while performing work
[SOURCE: IEC 60050-651:2014, 651-21-13, modified – the symbol D has been added.]
E
4 Minimum approach distance, D
A
The minimum approach distance, D is determined by:
,
A
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IEC 61472-2:2021 © IEC 2021 – 7 –
DD= + D
(1)
AU E
where
D is the required minimum electrical distance, and
U
D is the required ergonomic distance which is dependent on work procedures, level of
E
training, skill of the workers, type of construction, and such contingencies as inadvertent
movement and errors in appraising distances (see Annex B for details).
5 Factors influencing the minimum approach distance
5.1 Control of system overvoltages
The maximum amplitude of overvoltages in the work area can be reduced by the usual practice
of making the circuit-breaker reclosing devices inoperative, or by using protective gaps or surge
arresters.
5.2 Statistical overvoltage
The electrical stress at the work area shall be known. The electrical stress is described as the
statistical overvoltage that can be present at the work area. In a three-phase AC power system
the statistical overvoltage U between phase and earth is:
e2
U = 2/ 3 Uu
( )
e2 s e2
(2)
where
U is the highest voltage of the system, and
s
u is the statistical overvoltage phase-to-earth expressed in per unit.
e2
Similarly:
U = 2/ 3 Uu
( )
p2 s p2
(3)
where
u is the statistical overvoltage phase-to-phase expressed in per unit.
p2
If the per unit phase-to-phase data are not available, an approximate value can be derived from
u by the following formula:
e2
uu1,35+ 0,45 (4)
p2 e2
The transient overvoltages to be considered are those caused by system faults and switching
operations, whether they occur on the lines being worked, or on adjacent lines or associated
equipment.
The values of statistical overvoltages shall be those measured or determined by a transient
network analyzer (TNA) or by digital computer studies. If such studies do not provide the
statistical overvoltages (2 % values) but only the "truncated values", without the statistical
distribution, the transformation of the truncated values into 2 % values can be made.
=
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– 8 – IEC 61472-2:2021 © IEC 2021
Application and typical values of statistical overvoltages are shown in Annex A, for use when
no other values are available.
5.3 Conductive floating object
The conductive floating object(s) is(are) accounted for by the distance F which is the sum of all
dimensions, in the direction of the gap axis of the conductive floating object(s) in the air gap.
This distance is considered in the determination of the minimum approach distance, D :
A
D= DD++ F
A U E
(5)
5.4 Insulators
The influence of metallic caps and pins of suspension insulators is negligible and shall be
ignored.
5.5 Determination of minimum electrical distance, D
U
The minimum electrical distance is determined from the impulse rod-to-rod withstand voltage of
IEEE 516-2009, Table 1, and presented in Table 2 and Table 3. For systems using other per
unit overvoltage factors the minimum electrical distance may be derived from Table 1 using
linear interpolation.
6 Example calculation
Determine the minimum phase-to-earth electrical distance, D , for a 20 kV system. The highest
U
system voltage for this example is chosen to be 1,05 times the nominal system voltage (see
Clause A.3):
U = 21 kV
s
Applying the per unit statistical overvoltage factor, u = 3,5 to the highest system peak phase-
e2
to-earth voltage using Formula (2), the statistical overvoltage becomes
U = 60 kV
e2
Interpolating from the data of Table 1:
66,3 kV − 58,6 kV = 7,7 kV
and correspondingly
6 cm − 5 cm = 1 cm or 10 mm.
Therefore the distance for 60 kV is found by:
10 mm / 7,7 kV = 1,3 mm/kV
66,3 kV – 60 kV = 6,3 kV
6,3 kV × 1,3 mm/kV = 8 mm
60 mm – 8 mm = 52 mm or 5,2 cm.
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IEC 61472-2:2021 © IEC 2021 – 9 –
Table 1 – Distance for rod-to-rod gap from IEEE 516-2009
Impulse (TOV) 60 Hz rod-to-rod Gap spacing from
rod-to-rod withstand sparkover IEEE Std 4:1995
(kV peak) (kV peak) (cm)
27,6 25 2
39,8 36 3
50,8 46 4
58,6 53 5
66,3 60 6
77,4 70 8
87,3 79 10
95 86 12
105 95 14
115 104 16
123,8 112 18
132,6 120 20
158 143 25
184,5 167 30
212,2 192 35
240,9 218 40
268,5 243 45
298,4 270 50
355,8 322 60
Table 2 – Phase-to-earth electrical distance for system voltages
a)
from 1,0 kV up to and including 72,5 kV, u = 3,5
e2
b)
Highest system voltage Statistical overvoltage
Electrical distance
U U D
s e2 U
kV (RMS) kV (peak) mm
c)
> 1,0 2,9
20
12,5 36 27
17,5 50 40
24,0 69 64
26,4 75 76
36,0 103 136
40,5 116 162
52,0 149 232
72,5 207 341
a)
Refer to A.4.2.
b)
IEEE 516-2009, Table 2, impulse (TOV) rod-rod withstand (kV peak).
c)
This distance is beyond the range of data from IEEE 516-2009, Table 2, and is
considered acceptable for application.
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– 10 – IEC 61472-2:2021 © IEC 2021
Table 3 – Phase-to-phase electrical distances for system voltages
a)
from 1,0 kV up to and including 72,5 kV, u = 5,2
p2
b)
Highest system voltage Statistical overvoltage
Electrical distance
U U D
s p2 U
kV (RMS) kV (peak) mm
c)
> 1,0 4,2
20
12,5 53 43
17,5 74 74
24,0 101 133
26,4 112 153
36,0 152 238
40,5 171 275
52,0 220 363
72,5 306 514
a)
u = 1,35 u + 0,45. Refer to A.4.2.
p2 e2
b)
IEEE 516-2009, Table 2, impulse (TOV) rod-rod withstand (kV peak).
c)
This distance is beyond the range of data from IEEE 516-2009, Table 2, and is
considered acceptable for application.
Other distances may be used according to particular system requirements.
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IEC 61472-2:2021 © IEC 2021 – 11 –
Annex A
(informative)
Overvoltages
A.1 General
In establishing the minimum approach distance five distinct types of electrical stresses are
considered. Each type of stress has its own influence; all may not be present at any one time.
They are as follows:
1) nominal system voltage (see 3.3);
2) highest voltage of a system U (see 3.1);
s
3) temporary overvoltage (IEC 60050-614:2016, 614-03-13);
4) transient overvoltage (see 3.2):
• switching;
• lightning;
5) induced voltage:
• power frequency electrical (capacitive);
• power frequency magnetic (inductive);
• transient.
A discussion follows of the essential points associated with each electrical stress as related to
the minimum approach distance.
Nominal system voltages are presented in IEC 60038. These voltages are associated with
standard ranges. Actual system voltages may not follow these guidelines.
A.2 Highest voltage of a system
In reality, the calculation of the overvoltage is based on the highest voltage of a system, U
s,
which is specific to the operating system and may or may not be known. Unless its actual value
is known, U may be derived from the nominal voltage of the system by using the corresponding
s
value of the highest voltage for equipment, U , given in IEC 60038, i.e. the highest RMS value
m
of the phase-to-phase voltage for which the equipment is designed.
A.3 Temporary overvoltage
A temporary overvoltage can be generated by system faults, resonance, sudden load rejection
and some other operating conditions. Its most common and significant use in establishing the
minimum approach distance is for earth fault-generated overvoltage, which arises on the
unfaulted phases and can reach 1,7 per unit at the fault point on some systems.
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– 12 – IEC 61472-2:2021 © IEC 2021
A.4 Transient overvoltage
A.4.1 General
A transient overvoltage has a shape which can be regarded for the minimum approach distance
as that associated with a number of factors, including:
– energization;
– fault initiation;
– fault clearing;
– de-energizing and reclosing of a portion of the transmission system or its equipment
(e.g. transformers or capacitor banks).
In systems with high earth fault factors (e.g. in resonant earthed or unearthed neutral systems),
transient overvoltages due to earth faults are considered.
Transient overvoltages that can appear at the work site vary considerably in shape and
magnitude, but they are generally highly damped and of short duration.
A.4.2 Switching overvoltage
The maximum switching overvoltages that can reach the work site are usually due to switching
of the line or equipment on which work is being performed. When feasible, the reclosing devices
are made inoperative during live working, so that the line is not re-energized should it trip while
work is in progress. This serves two purposes. Firstly, should there be an accidental flashover
in the work area, it allows time for workers to safeguard the work area before re-energization
of the installation. Secondly, it limits the source of maximum overvoltages to de-energizing
transients, except in the exceptionally rare instance of a circuit-breaker restriking.
The magnitude of the switching overvoltage depends on the performance of the circuit-breaker
and the electrical characteristics of the line. Therefore, it varies from one system to another.
With circuit-breakers using closing, reclosing and opening resistors, or when metal oxide surge
arresters are installed and operating properly, the magnitude is highly reduced.
The value of switching overvoltages for each voltage level of a power system can be determined
by a transient network analyzer (TNA) or a digital computer study. Such a study should provide
a value for the 2 % statistical overvoltage U from which the minimum approach distance can
2
then be determined. Where statistical overvoltage for the system is unknown, a value of 3,5 per
unit is suggested. If the overall maximum per unit overvoltage is known, this value is taken to
be the truncated value, that is, the value beyond which no overvoltages occur and which is
taken (IEC 60071-2) to be three deviations above the mean.
The following empirical relationships given in IEC 60071-2 can then be used to estimate the
2 % statistical overvoltage U from the truncated values (using the "phase-peak" method in
2
each case).
For phase-to-earth overvoltages:
For the 2 % statistical overvoltage u in per unit:
e2
standard deviation σ = 0,25 (u − 1)
e e2
truncated value u = 1,25 u − 0,25
et e2
hence:
u = (u + 0,25) / 1,25
e2 et
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IEC 61472-2:2021 © IEC 2021 – 13 –
For phase-to-phase overvoltages:
For the 2 % statistical overvoltage phase-to-phase u :
p2
standard deviation σ = 0,25 (u − 1,73)
p p2
truncated value u = 1,25 u − 0,43
pt p2
hence:
u = (u + 0,43) / 1,25
p2 pt
If the per unit phase-to-phase d
...
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