Helicopter lineman's ladder and method for energized powerline repair

#High voltage powerlines carrying voltages in the hundreds of kilowatt range have been constructed to extend from spaced towers high above terrain which is often practically inaccessible to land vehicles. In recent years, a number of methods and devices have been developed to facilitate the repair of remote high voltage powerlines which are accessed by helicopter.

#Helicopter transported landing platforms and work scaffolds which can be attached to the cross arm of a utility pole have been developed to permit a lineman to disembark from a helicopter and descend vertically along the utility pole to the powerlines supported thereby. Such devices are heavy and bulky, and are often difficult to maneuver. More importantly, however, is the fact that these devices position a lineman in close proximity to a grounded utility pole, so that the powerlines must be deenergized before repair can occur. Otherwise it is dangerous for a lineman to remain in the electrically charged space between energized high voltage conductors and a grounded tower or utility pole. A helicopter-mountable landing platform and work scaffold adapted to be mounted by a utility pole is illustrated in U.S. Pat. No. 3,863,736 to McWilliams.

#In order to avoid an extensive power outage which might occur when a high voltage powerline is deenergized for repair, it is desirable to provide live maintenance on energized high voltage conductors. To accomplish this, linemen first bond to the energized transmission line to become energized to the same potential as that of the line. This permits the lineman to work safely on the energized line so long as he maintains sufficient spacing from grounded structures, such as support towers, to prevent the risk of flashover. To facilitate live maintenance on energized high voltage powerlines, various lineman support structures have been developed which are suspended from a helicopter over a powerline pair remote from the support towers. These support structures are formed either partially or totally from electrically conductive material and include skids or rollers which engage a pair of parallel lines. Such lineman support structures are shown by U.S. Pat. Nos. 4,478,312 to Kurtgis and 5,494,132 to Hansen. Not only are these structures bulky and somewhat cumbersome, but it is difficult to position the conductive skids or rollers on the energized powerline pair from a helicopter. Also, these support structures may inadvertently move into dangerous proximity with a grounded tower structure.

#FIG. 1 is a perspective view of high voltage tower supported powerlines;

#FIG. 2 is a perspective view of the helicopter lineman's ladder of the present invention;

#FIG. 3 is a view in side elevation of the helicopter lineman's ladder of FIG. 2; and

#With reference to FIG. 1, high voltage AC transmission lines normally include at least three powerline conductors 2, 4 and 6, with each powerline conductor carrying a voltage which is 120° out of phase with the voltages carried by the remaining conductors. These powerline conductors extend over substantial distances and are supported to extend between spaced towers 8 and 10. Each powerline conductor is suspended beneath a tower cross arm 12 by elongate insulators 14.

#In accordance with the method of the present invention, a helicopter 16 offloads one or more linemen 18 directly onto a tower 8. This can be accomplished by having linemen sit on a helicopter skid 20 or upon a platform placed across the helicopter skids which extends laterally of the helicopter. By having the helicopter directly deposit linemen onto a stable tower structure which is insulated from the powerline conductors, unstable tethers which can swing a lineman into an energized powerline are eliminated.

#Once the lineman is on the tower, the problem to be solved is how the lineman can safely descend to the energized powerline conductors 2, 4 and 6 and bond onto a conductor to raise his body voltage to the powerline conductor voltage. This cannot be done from the grounded tower structure or even from within an area close to the tower structure where flashover can occur. A flashover area, indicated at 22, must be avoided if live maintenance on energized powerline conductors is to be safely accomplished. OSHA safety regulations require that a flashover area of at least eleven feet from the tower be maintained for energized high voltage transmission line repair and that this area must be avoided by linemen bonded to a powerline conductor.