Calculation of field factor for a vertical sphere gap, taking account of surrounding earthed surfaces

摘要: Using a digital computer, field factor has been calculated for spherical electrodes by the image-charge method, taking account of adjacent plane or boundary surfaces. The method applied to vertical asymmetric sphere gap represented pair spheres above an infinite earth within enclosing earthed sphere. Graphs are presented showing percentage increase in value applicable isolated spheres, different positions surface; these graphs enable values be deduced, geometries represented, with accuracy better than 0.1%.For standard BS3581 and IEC52,2 varying position over full permitted range leads changes up 0.4% (±0.2%) factor, spacing one radius. When clearance from additional surfaces, representing walls ceilings laboratory, is varied minimum about five times this value, as close allowed, falls 0.5%.