Effects of dry-band arc current on ageing of self-supporting dielectric cables in high fields

All-dielectric self-supporting fibre optic cables which are hung on long-span, high voltage, overhead power lines are subjected to longitudinal electric fields. When the cable is polluted and wet, these fields can lead to dry-band arc activity and, ultimately, damage to the cable. The properties of the arcs are reviewed to explain why currents of a few milliamps are more damaging than either higher or lower currents. New measurements which investigate the importance of arc stability and arc compression to ageing processes are presented and discussed. It is suggested that a limit to the current of 1 mA should be set. If currents greater than this are present it is argued that a danger of catastrophic product failure exists. Such a current limit will be more restrictive in coastal conditions and areas of high pollution, where the resistance per unit length of the cable can fall significantly below typical values