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 61472:2013 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.