The increasing demand for renewable power creates subsequent demand for transmission infrastructure to connect clean energy with load centers. While much of this new infrastructure will be overhead lines, portions may be required to go underground as new lines are located near communities and within cities.

In a recent project, Black & Veatch designed the first installation of 500-kV cross-linked polyethylene (XLPE) cable in North America and the first installation of the cable in the world within a duct and manhole system. But what truly made this project unique was the creation of a new engineering record for underground transmission lines traversing steep terrain.

“The terrain for this particular segment of the project included slopes with up to 40 percent grades in some areas,” said John Rector, Associate Vice President and Senior Project Manager for Black & Veatch. “We worked with stakeholders to not only create new cable standards for this type of application, but also the support system and restraints, among other unique construction requirements.”

No cable standards existed that met the needs of this unique project. Black & Veatch worked closely with the client to develop requirements that addressed temperature restriction and circuit ampacity requirements, and allowed for real-time temperature and partial discharge monitoring.

The team also worked closely with the client and vendors to develop a flexible cable racking and support system that allowed for heat expansion and other potential movement with an innovative design approach using finite element analysis.

Other key project elements involved the design and construction of permanent roads to provide crews with access to splice and restraint vaults and temporary roads for construction. Two transition stations, featuring cast-in-place concrete cable trenches, were also constructed along the hilly terrain.

“This project broke new ground and created a frame of reference for users worldwide in the design and construction of high-voltage underground transmission lines.” Rector said. “This is just one example of why Black & Veatch is a global leader in providing critical transmission and distribution infrastructure.”

Full project details are available on T&D World (free registration required).