Substation expansions can become extremely complicated when space is limited. That’s when use of high voltage underground cable comes into its own as a viable option. What makes the option even more favorable is a turnkey approach, in which the high voltage underground cable provider provides the cable, terminations, and testing and documentation.
At a recent substation expansion project located near Buffalo, NY, where expansion of a substation yard and extension of an overhead 115 kV bus was impracticable and relocating facilities within the substation was not an option, Seymour, CT-based Kerite Company provided turnkey underground cable installation services that allowed new capacitor banks to be installed and energized in a reasonable amount of time and for reasonable cost.
Buffalo area project required novel solution
New York State Electric and Gas (NYSEG), a subsidiary of Iberdrola USA, needed to add capacitor banks to improve the electrical system to handle load growth in the Buffalo NY area. The utility, which serves 877,000 electricity customers and 261,000 natural gas customers across more than 40 percent of upstate New York, chose to install two new 115 kV, 25 MVAR switched capacitor banks at Big Tree Substation, an older facility constructed in the 1940s. The substation feeds the Ralph Wilson Stadium, home of the Buffalo Bills, and new capacitor banks were important for ensuring overall system improvements and supporting system voltage in the area.
Consulting engineers were brought in to design 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 explains that, while the Big Tree Substation seemed large, it was actually impossible to add both banks above ground as is commonly done with substation expansions. There was a wide open space on the south side, but the north side was very close to a fence, with a house just outside the fence.
“We came to the conclusion that the banks had to be underground because transmission lines were in the way,” said Bail. “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.”
According to Bail, they had room within the substation fence if the overhead wire bus extended to the area where the capacitor banks would fit. The issue was that NYSEG needed two capacitor banks and two breakers. Since the bus was split, with one on the north end and one on the south end, the best solution would be 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 different circuit breakers and two different capacitor banks. The solution was an uncommon one for a substation; underground cable transmission lines are more frequently used 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 their existing relationships with suppliers of high voltage underground cable, and then began discussions with the turnkey firm as it that had a reputation for high quality high voltage underground cable and a great deal of recent installation experience. He decided that Kerite was a good fit. “I explained the substation project and found it was a perfect match – we needed high voltage underground cable and they had services to provide.”
Turnkey approach selected 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 showing 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 an electrical subcontractor to do the cable pulls. Instead of working with one large 1300 foot reel, it cut each run individually to length on smaller reels, which are easier to store and make pulling the 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 north end connection cable was about 275 feet, while the south bus connection underground cable link was approximately 150 feet. Each end of the connections requires three terminations (one for each phase), so there were a total of 12 terminations at the substation, each one being 6.5 feet tall.
Because of the complexity of the project, Bail was especially attracted by the turnkey installation services that were offered, including supplying the cable, doing the terminations, and conducting the testing. The testing included both high voltage DC high potential testing at the factory to ensure that there were no defects, and additional lower voltage field testing.
According to Bail, the project went so smoothly that they have now written into their standard specifications for similar projects that the electrical contractors are required to hire Kerite for cable and terminations.
“There was a great deal of cooperation between Kerite and Northline Utilities onsite,” said Bail. “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 adds that he plans to use the companye for another capacitor bank in the Rochester, NY 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.”
About the author
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. Peter has Bachelor’s and Master’s degrees in Engineering.
