The Prospect of Live-Line Overhead Conductor Replacement

While transmission line conductors are normally replaced with the line de-energized, the have also been replaced with the line operating at full voltage without interruption of load by providing a separate temporary phase position supported by auxiliary structures over the length of the pulling section. This procedure, successfully applied up to 345 kV, requires a major presence on the right-of-way and, since the new conductor is pulled in close proximity to energized conductors carrying full load current, measures to mitigate potential hazards associated with voltages and currents coupled to the conductor being pulled. This paper proposes full voltage, full load, in-situ re-conductoring, thus eliminating the need for a temporary phase position and the need to accommodate currents and voltages coupled to the conductor being pulled. Safety issues, such as step-touch-transfer voltages and coupling to other equipment are no more severe than in more traditional live work. Pulling and tensioning equipment are operated on insulated platforms and the old conductor is used to pull in the new. Right of way access, other than at pulling terminals, is limited to replacement of conductor clamps with pulling sheaves and vice versa when pulling is complete; thus minimizing right of way intrusion. The proposed in situ method is based on current transfer device (CTD) which conveys current from the conductor on the already restrung section onto the conductor being pulled and from the latter to the yet-to-be pulled section. The CTD makes use of a series of contactor wheels pressed against and collecting current from the moving conductor. Current flows from each contactor wheel to a fixed bus through mercury-based rotating contactors widely used in industrial applications. Stringing tension can be controlled within a band much narrower than the range seen by lines in actual service, thus allowing the process to respect minimum line-to-ground clearances. High speed grounding switches and broken conductors sensors assure safe operation. If successfully developed, the method may provide a faster, more cost effective and less intrusive method for live conductor replacement.