IEC method of calculation minimum approach distances for liveworking

摘要

After 10 years and as many drafts, the proposed IEC standard 61472nis now in the final voting stage. The standard, when published, willndefine the IEC method of calculating minimum approach distances (MAD)nfor live working for use worldwide. The standard 61472 provides a methodnof calculating MAD for voltages between 1 kV and 800 kV AC. In commonnwith other standards, the MAD is taken to consist of two components: annelectrical component, DU, and an ergonomic component, DE. The componentnDU is calculated to minimize the risk of breakdown for all voltagesnexpected at the worksite. The rationale for calculating DU is based onnIEC Publications 71-1 and 71-2. The component DE depends on worknprocedures, training, workers' skill, type of construction,ncontingencies such as inadvertent movement and errors in judgingndistances. Guidelines for selection of DE are included in IEC 61472, butnwithout giving specific values. Atmospheric conditions and specificndetails of the worksite (such as the effects of broken insulators andnelectrically floating conductive objects) are counted for through thenapplication of correction factors. Guidelines for selecting the valuesnfor these factors are included. This paper provides an overview of thenIEC method of calculating MAD, its background and theoreticalnfoundations, and gives comparisons with the IEEE/ESMOL method, which isndefined in IEEE Std 516-1995. The paper concentrates on systems voltagenlevels above 72.5 kV, and on phase-to-ground distances