6.4.5.2 High-voltage-resistant insulated down conductors (HVI Conductors)

The basic concept of the high-voltage-resistant insulated down conductor is to completely sheath the lightning current-carrying conductor in an electrically high-strength insulating material so that the required separation distance s to other conductive parts of the building structure, electrical cables and pipes is maintained without the need for spatial separation. The insulating capacity of a high-voltage-resistant insulated down conductor (HVI Conductor) is characterised by the equivalent separation distance s effective in air, which corresponds to the minimum distance at which there is no unacceptable risk of flashover in air under atmospheric conditions.

Requirements for high-voltage-resistant insulated down conductors

• Dielectric strength: Dielectric strength (also known as dielectric breakdown strength or breakdown voltage) is the maximum electric field strength that an insulating material can withstand without electrical breakdown – i.e. the formation of a conductive path through the material as a result of ionisation or material failure. The insulation must be adequately dimensioned against lightning voltage impulses along the entire length of the conductor.
• Prevention of creeping discharges: Creeping discharge is a form of electrical discharge that occurs on the surface of insulating materials (dielectrics) along the interface between a gas space (e.g. air) and a solid insulator (e.g. cable insulation). The design of the conductor (geometry and material selection) and the proper processing of the high-voltage-resistant insulated down conductor prevent the formation and propagation of creeping discharges.