Underground Electric Transmission Installations Gaining Traction

By Jeff Griffin, Senior Editor | June 2010 Vol. 65 No. 6
Two jack and bore underground duct installations for Progress Energy in St Petersburg, Fla. Photo: Brierley Associates

Black & Veatch, Overland Park, KS, a global engineering, consulting, construction and construction management company, has played a leading role in constructing power infrastructure containing underground transmission lines.

“The underground cable industry has seen the amount of high-voltage underground transmission lines increase as cable technology has advanced and reliability improved,” says John Rector, Black & Veatch associate vice president and project manager. “In the late 1980s, we were installing 115 kV underground transmission lines. In the early ’90s, Black & Veatch installed the first commercial 230 kV underground transmission project in Orlando, FL. In the years that followed as the number of underground installations grew and the reliability of these systems became evident, more power companies and planners became comfortable with the idea of placing 230 kV transmission lines underground.”

More 230 kV cable was installed, then came a short segment of 345 kV cable.

Additional short 345 kV projects followed and then came the 26-mile Middletown-Norwalk Project in Connecticut, a landmark projects demonstrating the viability of ever advancing high-voltage technology.

“Every time we increase the voltage level of these cable systems, we prove the reliability of this technology,” Rector says. “Europe and Asia for some time have been installing 400 kV and 500 kV systems. The U.S. utilities are a relatively conservative group which, I think, is a good thing. High-voltage cable technology is moving rapidly toward 500 kV in this country. Very soon we will see 500 kV underground transmission lines in the United States, probably in California or on the east coast.”

The need for added capacity in congested areas where overhead lines either are not permitted or are difficult to permit will spur more growth in underground transmission, Rector believes. And a strong indicator that underground transmission will continue to grow, he says, is that a second plant for manufacturing high-voltage dielectric cable opened in the U.S. late last year, making two such facilities to serve North America.

High-voltage underground construction is not for every utility contractor. The skill sets for installing underground transmission is quite specialized and demanding. The higher the voltage, the larger diameter of the cable, complicating logistics of transporting and handling of cable supplies. High voltages are unforgiving and there is little margin for error during installation.