Case Study: High-voltage Underground Cable for NY Substation Expansions With Space Constraints

underground cable

by Peter Ebersold, Marmon Utility

Substation expansions can become extremely complicated when space is limited. That’s when high-voltage underground cable becomes a viable option. What makes the option even more favorable is a turnkey approach in which the high-voltage underground cable manufacturer installs the cable and terminations then tests the cable installation and delivers complete project documentation.

During a recent substation expansion near Buffalo, New York, where expansion of a substation yard and extension of an overhead 115-kV bus was impracticable and relocating facilities within the substation was expensive and time-consuming, Seymour, Connecticut,-based Kerite Co. provided turnkey underground cable installation services that allowed new capacitor banks to be installed and energized in a short time with no disruption to other circuits in the substation.

Buffalo-area Project Required Novel Solution

NYSEG, a subsidiary of Iberdrola USA, needed to add capacitor banks to improve the electrical system to handle load growth in the Buffalo area. The utility, which serves 877,000 electricity customers and 261,000 natural gas customers across more than 40 percent of upstate New York, installed two new 115-kV, 25 MVAR switched capacitor banks at Big Tree Substation, an older facility constructed in the 1940s. The substation feeds Ralph Wilson Stadium, home of the Buffalo Bills. New capacitor banks were important for ensuring overall system improvements and supporting system voltage in the area.

Consulting engineers Laramore, Douglass and Popham designed the project. The company provides engineering for investor-owned and cooperative utilities and works on everything from wind farms to industrial clients. Senior substation engineer Stan Bail said that although the Big Tree Substation seems large, it was impossible to add both banks above ground as is common with substation expansions. There was a wide open space on the south side, but the north side was close to a fence, and a house is just outside the fence.

“We came to the conclusion that the banks had to be underground because transmission lines were in the way,” Bail said. “We couldn’t place the capacitor banks off the existing bus because it was 35 feet in the air and there was no room to place the capacitor banks under the existing structure.”

There was room within the substation fence, Bail said, if they could have gotten the overhead wire bus extended to the area where the capacitor banks would fit. But NYSEG needed two capacitor banks and two breakers.

Because the bus was split with one on the north end and one on the south end, the best solution was taking the two locations from overhead to underground. They then ran the underground cable, coming up at one central location, terminating the underground cable and connecting to two circuit breakers and two capacitor banks. The solution is uncommon for a substation; underground cable transmission lines are used more frequently when an airport is nearby and it is important to keep circuits from interfering with airport operations.

After deciding on the engineering approach, Bail began looking for a company that could supply the cable, terminations and testing components.

He consulted with the client about its existing relationships with suppliers of high-voltage underground cable, then began discussions with Kerite, which is known for its high-voltage underground cable and experience in recent installations.

“I explained the substation project and found it was a perfect match,” Bail said. “We needed high-voltage underground cable, and they had services to provide.”

underground cable

Turnkey Approach for Cable Runs

The design included a conduit system to facilitate cable pulling from the bus area to the capacitor bank, including a conduit plan that showed how and where to place the 6-inch PVC conduit, with one conduit per cable per phase.

After the conduit system was installed, Kerite brought the cable to the site for electrical subcontractor Northline Utilities to do the cable pulls. Instead of working with one large 1,300-foot reel, Kerite cut each run individually to length on smaller reels, which are easier to store and make pulling individual runs much faster and simpler.

This allowed the subcontractor the flexibility of pulling one phase and leaving it if necessary, then returning the next morning to pull the next phase.

The northern end connection cable was some 275 feet, and the south bus connection underground cable link was closer to 150 feet.

Each end of the connections requires three terminations (one for each phase), so there were 12 terminations at the substation. The terminations for the end of the cable are 6.5 feet tall, and each termination takes some eight hours to complete.

Because of the project’s complexity, Bail was attracted especially by the turnkey installation services Kerite offered, including supplying the cable, doing the terminations and conducting the testing.

The testing included high-voltage DC high potential testing at the factory to ensure no defects and additional lower-voltage field testing.

Bail said the project went so smoothly that the utility has written into its standard specifications for similar projects that the electrical contractors must hire Kerite for cable and terminations.

“There was a great deal of cooperation between Kerite and Northline Utilities on-site,” Bail said. “When you are terminating cables, it is extremely important to avoid any wet conditions.

Each one of the terminations took hours of sanding and dressing the cable after it was pulled, and Kerite needed a shelter to keep the wind, mist and rain off while doing the terminations.

Northline built a shelter to keep them dry so they could keep working through whatever conditions the weather threw out there.”

He said he plans to use Kerite for another capacitor bank in the Rochester area, where underground cable is needed because there is no space to expand the substation.

“When you are limited by space, underground high-voltage cable is a viable option when compared to other more expensive substation expansion alternatives.”

Peter Ebersold is the director of market and product development for the Kerite and Hendrix brands at Marmon Utility, a Marmon Engineered Wire & Cable/Berkshire Hathaway Company. Prior to Marmon Utility, he was a marketing director at Honeywell and a business unit manager at Perkin-Elmer. He started his career as an electrical design engineer. Ebersold has bachelor’s and master’s degrees in engineering.

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