KEARNEY – Tons of concrete and rebar, miles of roads and electrical cables, and some mighty big cranes are the materials and tools required to build the Broken Bow Wind farm.
The general contractor, Wanzek Construction, has constructed more than 60 wind farms of 20 turbines or more. That includes six projects for Edison Mission Group, owner of the project now under construction in the hills of southern Custer County.
Jake Nikle of Wanzek’s Fargo, N.D., office provided the Hub with some details about the materials, machines and manpower involved in the project.
Wanzek and its subcontractors, including several area businesses, are preparing sites for 50 wind turbines that will have a combined generating capacity of 80 megawatts. The structures will be erected as the towers, blades and nacelles are delivered over the next several weeks.
There probably are 85 people on site now and that could increase to 100 or more during peak construction time from May to August.
The initial work includes building roads through pastures to the hills where foundations and electrical cables are installed. The concrete foundations now hidden underground are octagon shaped, but high in the middle and sloping to the sides.
Each foundation is about 8 feet below ground and is 56 feet across at its base.
The “pedestal” on top of the ground goes down three feet. Each of the 14-foot concrete circles has 128 bolts in two circular rows. The 8-foot-long bolts are anchored through a ring in the concrete foundation that also has 23 tons of rebar.
Holes in the bottom of a turbine tower flange fit over the bolts.
One by one, the hydraulic head on each bolt will be stretched to an engineered tension and released. Then, all 128 bolts will be rechecked to ensure they meet the specifications. The process ensures that the nuts not only are tight, but the tightness is consistent around the circle.
About 250 yards of concrete were required for each foundation. To support the weight of a turbine, 750,000 pounds of concrete and 46,000 pounds of steel are used.
More than 45 miles of underground cable will be buried to link the turbines to a substation.
Nebraska Public Power District, which has a power purchase agreement with Edison Mission Group, is building a nine-mile transmission line between the wind farm substation and an existing NPPD substation south of Highway 2 near Broken Bow.
Getting equipment to the turbine sites isn’t easy. About 24 miles of roads have been built, including some that included filling in parts of pasture canyons that must be crossed.
Turbine construction will be done in two phases, with cranes putting a section of each tower put onto the pedestals.
Then a larger, 550-ton-capacity crane will lift the top section – nacelle, rotors and blades – into place. It will require about 30 semitrailer trucks to haul that crane’s components.
Depending on the configuration of the load, it will take eight or nine trucks to haul each turbine.
At times when one of the three 42-meter (about 140 feet) blades extends straight up from the tower, the turbine will rise about 400 feet from the ground.
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