By Lisa Meiman
Desert Southwest electricians and linemen were afforded the rare opportunity to view Hoover Dam from a unique angle while performing critical maintenance on the roof of a Hoover powerhouse, 643 feet below the dam’s crest.
From November 2013 to March 2015, a joint electrician and lineman crew replaced four sets of 50- and 60-year-old potential transformers with current-coupling voltage transformers on the Nevada side of the Colorado River.
“They were old; some were leaking,” said DSW Foreman I Electrician Bob Conklin. “We started changing out the transformers in 2013, doing one set at a time.” Each set included three transformers—one for each phase of a transmission line.
The Bureau of Reclamation owned the transformers until about five years ago when Western took over their care. These transformers do double duty on the powerhouse roofs. In addition to stepping down the voltage outside Hoover Dam, the transformers monitor the status of the line and feed power into relays that help keep the connecting transmission lines functioning properly.
The crew completed each replacement in a little more than a week: two days of travel, one day to haul the equipment to the river, one day of set up and four days of work.
“The job went great. I was really impressed with how Bob Conklin lined everything out,” said DSW Foreman II Lineman Bo Mortensen. “We were done ahead of schedule, and the safety and preparation of the crews was top notch. In this job, we mixed up the craft—electricians and linemen—which we don’t do very often. We had great rapport with the electricians. It’s enjoyable to work around people who want to work and enjoy their work.”
Several electrician apprentices also joined different parts of the job. “It allowed them exposure to the unique work environment and coordination efforts required with interagency jobs,” said Conklin.
DSW also took advantage of the special access to conduct other maintenance on the roof. “We repaired or replaced jumpers, aircraft warning lights and broken insulators,” said Mortensen. “It was nice to maximize our time and the opportunity.”
817 feet to go
The location of the project, at one of the most accessible dams in the world, was the job’s biggest challenge. Hoover’s powerhouses are located on each side of the dam at the river’s edge and 730 feet below the dam’s crest.
There is only one narrow tunnel road to the base of the dam on each side of the river, capable of admitting only pickup trucks, so Western turned to old-school technology to get the rest of the equipment to the base of the dam.
A 1,256-foot-long crane system, used for Hoover’s construction in the 1930s, lowered a 90-ton crane, aerial lifts, replacement transformers and other equipment one at a time in a cradle to the base of the dam.
“It’s amazing it all still works,” said Mortensen. “The Bureau of Reclamation crane operator can’t see where he’s lowering the equipment, so he and Reclamation employees go back and forth on the radio to make sure the equipment was lowered safely and in the right spot.”
The 90-ton crane, operated by a contractor, then lifted the replacement transformers, vehicles and other equipment 87 feet to the roof of the powerhouse, which had been overlaid with plywood to distribute the weight of all the equipment as much as possible. The powerhouse roofs are fragile to continuous pressure even though it was reinforced with three feet of concrete and three feet of dirt to withstand a bomb blast.
Each of the four replacements went better than the one before it, but still required considerable coordination and planning between Western, the Bureau of Reclamation and the smaller crane operator. “We started coordinating in September 2013 for the first set of replacements in December 2013,” said Conklin. “After the first set, it was easier to plan because we knew all the little traps and tasks that needed to get done.”
According to Mortensen, Conklin had everything prepared in baskets and laid out in order at the top and base of the dam, speeding up the work considerably.
The remaining potential transformers on the Arizona side, which are in better condition, are expected to be replaced in the next few years.
Check out more photos at Western's Flickr collection.