Helicopters flying rope across the Columbia River provided an unusual sight for those watching the final stages of construction on the Big Eddy-Knight 500-kV transmission line this summer. BPA’s latest high-voltage project, near The Dalles, Oregon, brings innovation to building transmission.
The new line, which spans 28 miles, will provide another path for power to cross between Oregon and Washington. Most importantly, it will bring added capacity to an area that has seen rapid growth in renewable resources and has become a hot spot for energy intensive data centers.
The Big Eddy-Knight project adds 42 circuit miles of high-voltage wires and 128 new towers to the BPA system, with each tower carrying two circuits. The first is the new BE-K line, which connects the existing Big Eddy Substation just east of The Dalles, Ore., with the new Knight Substation in Goldendale, Wash. The second is a rebuilt portion of the Harvalum-Big Eddy 230-kV line. While the second line will operate at 230 kV, the towers, conductor and hardware are being constructed at 500 kV to provide additional capacity if the need arises in the future.
The $200 million project started on the drawing board of Transmission’s Project Engineering back in 2008. What really stands out about the project design is the Columbia River Gorge crossing. The design team had to create towers that could withstand wind and ice storms while supporting nearly 300,000 pounds of bare wires. During extreme weather conditions, the dead-end towers can experience over 1 million pounds of force. The team also had to be conscious to create a tower using the least amount of steel because BPA not only pays for the steel but pays per pound for its installation.
The river crossing consists of three towers — two dead-end towers in either state and one suspension tower on the Oregon side. This is unique because usually there are four to five towers for every mile of line. In the crossing, there are just three towers for 1.2 miles of line with the actual river crossing spanning nine-tenths of a mile.
The Oregon suspension tower stands at an impressive 420 feet tall. To put this in perspective, it is nearly twice as tall as those on either side. However, the tower still weighs less than both of its neighboring towers due to BPA’s custom design.
For observers, the biggest attraction of the river-crossing construction was definitely the stringing. While this may have been the most exciting to watch, it definitely provided the Wilson Construction crew a lot of headaches to complete.
In order to string one conductor across the Gorge, a helicopter first had to fly a light rope through a sheave, a wheel that guides the rope, on the suspension tower and then connect it to the tower on the opposite side of the river. Then came the process of pulling a series of heavier rope and steel cable back and forth across the river until the conductor could finally be pulled through the sheave and into place. For perspective, the river crossing has 18 conductors and two optical ground wires, cables that provide both grounding and communication functions.
If that weren’t challenging enough, the location provided a number of complications. First, the helicopter could only fly when the wind was blowing less than a constant 15 mph. For those of you who have enjoyed outings in the Gorge to watch the wind surfers, you know this is a rare occurrence. Then there was the coordination of traffic underneath the helicopter work. This meant finding a time when there were no barges or trains scheduled to pass below the project as well as coordinating with the Oregon Department of Transportation to temporarily shut down Interstate 84. And yet, against all the odds, the team completed the stringing in under two months and on time. The Wilson crew excels at communication and has been a great team to work with,” says BPA project manager Nathan Mullen, a civil engineer in Project Engineering. “The team worked in all conditions to make sure this project got completed, including stringing in 112° weather. They made sure the river-crossing construction was a success.”
After being approved in 2011, construction will finally be completed in the beginning of September. This is a major milestone for a project that will bring additional transmission capacity to the region. With the lines expected to be in service by the end of the calendar year, BPA and its customers will be benefiting soon.