The Turlock Irrigation District made a series of high-flying repairs to damaged high voltage transmission lines last month, with linemen dangling from a helicopter to repair the broken conductors.
The work came after damage was discovered on two TID high-voltage transmission lines, the Westley to Walnut and Westley to Parker 230-kilovolt lines. The lines are located west of the San Joaquin River, and east of the California Aqueduct.
Due to wind and other vibration the “hairpin”-style spacers that were used to separate conductor lines caused damage, cutting nearly halfway through the lines in places. In some instances, 12 strands were broken of a 31-strand conductor line.
The damage was first noticed from the ground by regular patrols. Then specialized helicopter pilots were called in to hover close to the lines, so TID staff could get a better look at the damage.
Due to the damage, the lines were derated on April 30; where they can normally carry 1,600 amperes of current, the lines were only allowed to carry 1,276 amperes.
The derating led to emergency repairs to the line, and work to add more spacers, dampers, and change to a different style of spacer – known as a “dogbone” – which uses urethane bushings to cushion the conductor cable.
The traditional approach would have seen the lines repaired from the ground, using basket trucks. The arduous work would have taken three crews, pulling the lines from service for a week. Though replacing the spacers is quick work, the truck would have had to carefully reposition for each spacer in a time-consuming process.
But instead, TID opted to use a new approach – a helicopter-based repair team.
The work saw two linemen suspended from a basket 60 feet below a hovering helicopter. As the linemen were not grounded, they were able to quickly move from spacer to spacer like a bird, changing out parts in a matter of minutes while an expert pilot hovered at a dead stop.
The speedy helicopter was able to complete all repairs in one day. A ground crew followed up and repaired a further small stretch of conductor.
The work was done by a contractor, American Site Builders of Amarillo, Tex., at a cost of $34,000. The traditional approach would have cost $45,000, plus a further $50,000 loss each day the transmission line was down.