IEC 61472-2:2021 pdf download

IEC 61472-2:2021 pdf download.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).
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 [SOURCE: IEC 60050-601:1985, 601-01-23, modified – the symbol U s and the words “(phase- 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 E has been added.]
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