Introduction: PFT in service leak location technique, employing Perfluorocarbon Tracer (PFT) to tag the cable oil. has now been adopted as the main tool in oil leak location which has seen a significant step change in the way in which National Grid responds to oil leaks with improvement to the speed and accuracy of leak location combined with the sensitivity to locate low rate oil leaks, that in the past have been difficult if not impossible to locate with previous techniques, as a result major reduction in outage times to effect repairs (65%) are now being achieved.

Objectives: To provide National Grid with a leak free system oil filled cable system and to inject preventatively all transmission cables with PFT tagged fluid.