General

Massive new transmission towers near Louisville will help OPPD harden grid

OPPD is one step closer to installing the most significant transmission structures in the utility’s history to support reliable power throughout eastern Nebraska. 

Contractors recently installed eight tube-shaped rebar cages into foundation holes near the Platte River in Louisville. 

The tall, sturdy cages will provide a strong foundation for the 347-foot PyraMax transmission towers. They will be by far the largest towers in OPPD’s service area. Once installed, the structures will carry three different voltage types and stand taller than the Union Pacific Center in downtown Omaha and almost as tall as the Nebraska Capitol in Lincoln. 

“These structures are engineered and tested to harden the grid by withstanding wind speeds up to 150-175 mph. That’s  increasingly important because of potential weather conditions, said Mohammad Amrollahi, OPPD’s Transmission Engineering lead. “They’re ideal for tough terrains, like river crossings. As with any other structure, foundations play a major role in stability. They help absorb the stresses imposed by weather and other forces.” 

Each new tower will support two high-voltage transmission lines and one distribution line across a half-mile span of the Platte River, between Louisville and Springfield. The towers are part of the Cass to Sarpy Transmission Line project, which runs between OPPD’s Cass County Station and Turtle Creek Station. 

Preparation and precision

Made from galvanized steel that can withstand extreme weather, the towers will replace existing structures. Crews drilled four foundation holes on each side of the river to hold the towers. The towers must be tall enough to account for wire sagging at the stretch over the river. 

The new foundations are 6.5 feet wide and about 100 feet deep, with depths varying slightly by location due to different soil profiles. In November and December, crews used special drilling equipment to tunnel into the ground at about two feet per hour. 

They struck bedrock exactly where engineers predicted, a testament to the preparation, precision and teamwork of numerous groups. Within OPPD, the project has required coordination across engineering, transmission, distribution and construction teams. 

A major effort

OPPD contractors laid the rebar tubes horizontally on the ground before installation. They placed special rollers on the cages to help them slide easily into the ground and keep some space between the rebar and the ground. After a thorough final inspection, they lifted each cage into a vertical position using cranes. Then they aligned the cages with the foundation hole and slowly lowered them into position. 

From there, multiple concrete trucks filled each foundation and let them cure to ensure a sturdy base for each structure. 

Crews are scheduled to install the two structures later this month, one on each side of the river. They’re slated to string wires across the river in April, barring any unforeseen developments. 

Crews dismantled and removed the original structures in February, cutting them into manageable pieces for shipping to a recycling facility. 

The Cass to Sarpy project is part of a multiyear, billion-dollar-plus infrastructure build-out to accommodate tremendous load growth and meet customer needs within OPPD’s service district.