The transmission capacity of existing overhead lines can be increased by using different cabling (replacement), allowing the weather to determine the use of overhead lines (operational management), or converting the circuits from AC to DC. While the first two options have already been described in standards or VDE application guides, there is need for standardization for the third option; this is to be met in the form of a VDE application guide. It could involve e.g. converting an existing circuit from AC to DC transmission on an existing pylon (AC/DC overhead line) or constructing a parallel DC overhead line in close proximity to an AC power line.
Both require additions to, or the modification of, the existing design criteria of the AC overhead power line standard. Work is therefore currently being carried out on a VDE application guide to specify the electrical requirements (insulation coordination, distances, earthing, etc.) for overhead line insulators and fittings for AC/DC or DC power lines. These will apply to the planning and construction of high-voltage overhead power lines with AC/DC systems as well as with DC systems with a rated voltage of over 45 kV. They will, however, be independent of the converter technology.