IEC 61472:2013
(Main)Live working - Minimum approach distances for a.c. systems in the voltage range 72,5 kV to 800 kV - A method of calculation
Live working - Minimum approach distances for a.c. systems in the voltage range 72,5 kV to 800 kV - A method of calculation
IEC 61472:2013 describes a method for calculating the minimum approach distances for live working, at maximum voltages between 72,5 kV and 800 kV. This standard addresses system overvoltages and the working air distances or tool insulation between parts and/or workers at different electric potentials. The required withstand voltage and minimum approach distances calculated by the method described in this standard are evaluated taking into consideration
- if the workers are trained for, and skilled in, working in the live working zone;
- if the anticipated overvoltages do not exceed the value selected for the determination of the required minimum approach distance;
- if transient overvoltages are the determining overvoltages;
- if tool insulation has no continuous film of moisture or measurable contamination present on the surface;
- if no lightning is seen or heard within 10 km of the work site;
- if allowance is made for the effect of conducting components of tools; and
- if the effect of altitude, insulators in the gap, etc, on the electric strength is taken into consideration. For conditions other than the above, the evaluation of the minimum approach distances may require specific data, derived by other calculation or obtained from additional laboratory investigations on the actual situation. This third edition cancels and replaces the second edition of IEC 61472 published in 2004. It constitutes a technical revision. Significant changes with regard to the second edition are:
- the clarification of the scope;
- the review of the definitions;
- the clarification of the methodology of determining whether live working is permissible and the calculation of the minimum approach distances;
- the modification of the basic equation for calculation of the minimum approach distance; and
- the introduction of Table 1 for altitude correction factor simplification ka. The contents of the corrigendum of October 2015 have been included in this copy.
Travaux sous tension - Distances minimales d'approche pour des réseaux à courant alternatif de tension comprise entre 72,5 kV et 800 kV - Une méthode de calcul
La CEI 61472:2013 décrit une méthode de calcul des distances minimales d'approche pour des travaux sous tension réalisés à des tensions maximales comprises entre 72,5 kV et 800 kV. La présente norme traite des surtensions de réseau et des distances de travail dans l'air ou de l'isolation des outils entre des pièces et/ou des travailleurs à des potentiels électriques différents. La tension de tenue requise et les distances minimales d'approche calculées suivant la méthode décrite dans la présente norme sont évaluées en prenant en compte
- si les travailleurs sont formés et qualifiés pour travailler dans la zone de travail sous tension;
- si les surtensions attendues ne dépassent pas la valeur choisie pour la détermination de la distance minimale d'approche requise;
- si les surtensions transitoires sont les surtensions déterminantes;
- si l'isolation des outils ne présente pas sur la surface un film continu d'humidité ou un niveau de pollution mesurable;
- si aucun éclair n'est vu ni entendu à moins de 10 km du lieu de travail;
- si l'influence des parties conductrices des outils est prise en compte;
- et si l'effet de l'altitude, de la présence d'isolateurs dans l'intervalle, etc. sur la tenue électrique est pris en compte. Pour des conditions autres que celles ci-dessus, l'évaluation des distances minimales d'approche peut exiger des données spécifiques, provenant d'autres calculs ou obtenues à partir d'études additionnelles en laboratoire sur la situation concrète. Cette troisième édition annule et remplace la deuxième édition de la CEI 61472, publiée en 2004. Elle constitue une révision technique. Les modifications techniques majeures par rapport à la deuxième édition sont:
- la clarification du domaine d'application;
- la revue des définitions;
- la clarification de la méthodologie pour déterminer si le travail sous tension est acceptable et pour calculer les distances minimales d'approche;
- la modification de l'équation de base pour calculer la distance minimale d'approche;
- et l'introduction du Tableau 1 pour une simplification du facteur de correction en fonction de l'altitude ka. Le contenu du corrigendum d'octobre 2015 a été pris en considération dans cet exemplaire.
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IEC 61472 ®
Edition 3.0 2013-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Live working – Minimum approach distances for a.c. systems in the voltage
range 72,5 kV to 800 kV – A method of calculation
Travaux sous tension – Distances minimales d'approche pour des réseaux à
courant alternatif de tension comprise entre 72,5 kV et 800 kV – Une méthode de
calcul
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IEC 61472 ®
Edition 3.0 2013-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Live working – Minimum approach distances for a.c. systems in the voltage
range 72,5 kV to 800 kV – A method of calculation
Travaux sous tension – Distances minimales d'approche pour des réseaux à
courant alternatif de tension comprise entre 72,5 kV et 800 kV – Une méthode de
calcul
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 13.260; 29.240.20; 29.260.99 ISBN 978-2-83220-717-8
– 2 – 61472 © IEC:2013
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Terms, definitions and symbols . 6
2.1 Terms and definitions . 6
2.2 Symbols used in the normative part of the document . 8
3 Methodology . 9
4 Factors influencing calculations . 10
4.1 Statistical overvoltage . 10
4.2 Gap strength . 10
4.3 Calculation of electrical distance D . 11
U
4.3.1 General equation . 11
4.3.2 Factors affecting gap strength . 11
5 Evaluation of risks . 16
6 Calculation of minimum approach distance D . 17
A
Annex A (informative) Ergonomic distance . 18
Annex B (informative) Overvoltages . 20
Annex C (informative) Dielectric strength of air . 24
Annex D (informative) Gap factor k . 26
g
Annex E (informative) Allowing for atmospheric conditions . 28
Annex F (informative) Influence of floating conductive objects on the dielectric
strength . 32
Annex G (informative) Live working near contaminated, damaged or moist insulation . 40
Bibliography . 45
Figure 1 – Illustration of two floating conductive objects of different dimensions and at
different distances from the axis of the gap . 13
Figure 2 – Typical live working tasks . 15
Figure B.1 – Ranges of u at the open ended line due to closing and reclosing
e2
according to the type of network (meshed or antenna) with and without closing
resistors and shunt reactors . 22
Figure F.1 – Influence of the length of the floating conductive objects – phase to earth
rod-rod configuration – 250 µs /2 500 µs impulse . 35
Figure F.2 – Influence of the length of the floating conductive objects – phase to phase
conductor-conductor configuration – 250 µs /2 500 µs impulse . 36
Figure F.3 – Reduction of the dielectric strength as a function of the length D for
constant values of β – Phase to earth rod-rod configuration . 37
Figure F.4 – Reduction of the dielectric strength as a function of the length P for
constant values of β – Phase to phase conductor-conductor configuration . 37
Figure G.1 – Strength of composite insulators affected by simulated conductive and
semi-conductive defects . 43
Table 1 – Average k values . 12
a
Table 2 – Floating conductive object factor k . 14
f
Table B.1 – Classification of overvoltages according to IEC 60071-1 . 20
61472 © IEC:2013 – 3 –
Table D.1 – Gap factors for some actual phase to earth configurations . 27
Table E.1 – Atmospheric factor k for different reference altitudes and values of U . 30
a 90
Table G.1 – Example of maximum number of damaged insulators calculation (gap
factor 1,4) . 41
Table G.2 – Example of maximum number of damaged insulators calculation (gap
factor 1,2) . 42
– 4 – 61472 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LIVE WORKING –
MINIMUM APPROACH DISTANCES FOR A.C. SYSTEMS
IN THE VOLTAGE RANGE 72,5 kV TO 800 kV –
A METHOD OF CALCULATION
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