Consumers want electrical power where they want it and when they want it, but often they do not realize the challenges of getting it to them. The Bonneville Power Administration’s (BPA’s) Big Eddy-Knight Transmission Project is designed to get more power to them by adding a 500 kilovolt (kV) line to the existing right-of-way of a 230 kV line for half of the project’s 28-mile length and then installing new towers for the final 14 miles.
The estimated $180 million project – construction of which began in September 2011 and is scheduled for completion in December 2014 – extends from the Big Eddy substation in the Dalles, Ore., to a proposed new Knight substation approximately four miles northwest of Goldendale, Wash. Challenges of the project include crossing the Columbia River without damaging a cave with historic pictographs inside or the archaeological site of a Native American village.
Easements for the transmission line had to be obtained from a multitude of agencies and private landowners. The project crosses U.S. Forest Service land to the Columbia River scenic gorge, which is maintained under the jurisdiction of the U.S. Army Corps of Engineers. It also crosses land in Klickitat County and state land overseen by the Department of Natural Resources (DNR).
“There’s also a privately owned wind farm we’re snaking through, and we had to get an easement through there,” recounts Emmanuel Jaramillo, project manager for the Bonneville Power Administration. “They are a lessee of the DNR.”
BPA’s contractor HDR sited and designed the transmission line and the new substation. PAR Electrical Contractors Inc. has built the new substation, and Wilson Construction Co is building access roads and stringing the electrical line on towers they erected. Jaramillo estimated PAR used three subcontractors and Wilson at least two subcontractors.
One of the challenges has been siting the towers at the river crossing. “There is a lot of cultural and archaeological significance in this area,” Jaramillo points out. “One of the tools we are utilizing is LiDAR (light detection and ranging) to evaluate tower location alternatives. We decided to locate the new towers in the same location as the old to try and minimize disturbance. Prior to any construction at the river crossing, we are doing excavation to see if there are potential artifacts on the footprints where we’re going to be placing the new towers.”
LiDAR is a remote sensing technology that measures distance with a laser and analyzes the reflected light. This resource is being used to provide a highly accurate 3-D topographical map of the transmission line’s route by flying the LiDAR equipment over the entire line route. Ground-based LiDAR is also being used to provide a vertical cut of the cave. “We are going to look at the LiDAR information to document the conditions of the cave and its integrity,” Jaramillo says.
At the bottom of the bluff on top of which the transmission line towers are to be built is a cave with ancient pictographs in it from early residents of the area. Since construction of the towers requires controlled blasting to install foundations for them, “One of the concerns of state agencies, landowners and tribes was how were we going to protect the cave?” Jaramillo asks. “We performed a third-party vibratory analysis report on the cave to see if there was going to be any type of vibratory impacts on the cave during our controlled blasting, which we determined there won’t be. We’ll have tribal cultural monitors onsite during the work to monitor our activity as we start construction at the river crossing.”
To speed the project, BPA ordered the steel for the towers approximately 13 months before construction began. “We are using multiple series of the towers for this voltage level,” Jaramillo notes. “They include single-circuit, double-circuit and special river crossing tower series, all with different heights, weights and tower configurations.”
New double-circuit towers were erected for the existing section of the line to hold an additional line. “The existing lattice tower structures are for a single circuit line, so they don’t have the configuration or structural integrity to be able to hold that load,” Jaramillo points out. “We also designed a new river crossing tower series that is taller and beefier than the existing single-circuit tower. It will be able to sustain the load for a double-circuit, 500kV-line river-crossing span – meaning we can put one circuit on one side of the tower and another circuit run on the other side.”
One of the more exciting tower installation methods is done using a helicopter. “Once they’re done with the foundations, their assembly crew comes in and builds the bottom half of the tower,” Jaramillo explains. “If the helicopter can sustain the weight, it will set the top half, and the assembly crew will bolt it and assemble the bottom and top half together.”
Jaramillo estimates 70 percent of the project is completed. “Currently, the substations are complete,” he says. “They’re just waiting to be energized or placed into service. On the Oregon side, the only thing that is left to do is the river crossing to the Washington side and the transmission line miles eight through 10 and miles 14 to 28.”