OH Transmission Line Without Arching Horn

It depends primarily on the transmission line BIL (basic impulse insulation level which defines the maximum impulse the insulation can withstand without flashover), insulation coordination, and the quality and type of insulation.

Arcing horns provide a protective air gap in parallel with the insulator string. Their flashover characteristics are generally the same as a rod gap of the same spacing. They are normally set to a spacing that will guarantee flashover at a lower voltage than the insulators the gap is protecting. Overvoltages will flash over the arcing horn thereby protecting the insulators by keeping the flashover arc away from the insulators.

They were commonly used in the early years because of the rather poor quality of some insulators that simply could not withstand flashover arcs along the insulator surfaces. Normally unnecessary with modern insulators or other self-restoring insulation. May be used with non self-restoring insulation for overvoltage protection although there are more appropriate and more consistent devices available for that purpose (such as metal oxide gapless surge arresters installed in parallel with the line insulation). See Protecta*Lite at www.hubbellpowersystems.com for additional information about one such device.