Switchyard nearly complete at Garrison Dam power plant

PICK CITY A new electrical switchyard at the Garrison Dam power plant has been long overdue. That’ll change this year as contractors bring a major project to a close.

The switchyard currently in use was constructed in the mid-1950s and has exceeded its life expectancy. A new and larger switchyard is nearing completion.

“The old yard was original equipment, for the most part. The new yard will be new technology,” said Dale Evenson, power plant supervisor. “A lot of the coal plants in the area changed their breakers out two or three times compared to our one. We had a lot of maintenance issues with the old equipment.”

According to Evenson, one big change with the new switchyard is an upgrading of circuit breakers. Existing breakers use insulating oil to suppress electrical arcs when opening them. The new breakers will utilize sulfur hexaflouride gas to suppress the arc. The change is significant.

“They won’t have any environmental issues (as) with oil,” explained Evenson. “The new breakers will not have any oil in them.”

The new switchyard, located immediately southeast of the existing yard, is the last major project in an on-going rehabilitation program at the Garrison Dam power plant. Turbines and generators were upgraded several years ago.

“We moved out from there,” explained John Palenski, U.S. Army Corps of Engineers, Omaha, Neb. “This is really the biggest project since the turbines 10 years ago. The whole key is an upgraded power house allows the plant to create more power, but we are limited by the existing system. A new switchyard can generate additional power that is available, more power with the same amount of water that runs through it.”

The new switchyard will replace an aging one that was in need of more and more maintenance each year while its reliability was diminishing. The switchyard is where hyrdo-power generated by the Garrison Dam power plant is collected and sent through transmission lines that carry electricity to homes and businesses.

“The power to be delivered to our customers will be more reliable,” said Evenson. “Our equipment had aged.”

The new switchyard will be divided into two sections, one that distributes 230,000 volts and another that handles 115,000 volts.

“Three transmission lines are tied to the 230 KV yard. Four lines transfer power on the 115 KV line,” said Evenson. “They give us different voltages and options, step downs to different voltage. Eventually it gets to the end user at 110 volts inside the house.”

The first phase of completion of the new switchyard is expected sometime this spring, said Palenski. The first portion of the switchyard to come on-line will be the 230,000 volt yard.

“Both yards are within the same footprint. Considerable progress has been made. They started last year. A control house is currently being constructed,” said Palenski. “The 115 KV switchover will occur sometime this fall.”

The current Garrison Dam power plant has a maximum production capacity of 490 megawatts of electricity.

“With these upgrades, theoretically, we can generate an additional 72 megawatts of power,” said Palenski, “The potential is there to generate more power at optimum water levels.”

In conjunction with the construction of the new switchyard, Western Area Power Association is erecting new power poles adjacent to the site. The towering poles will allow new lines to come off and connect to the transmission system at the switchyard and then distribute electricity to customers.