By Emily Stifler, Explorebigsky.com Managing Editor

BELGRADE – The transmission line that connects Big Sky to the Gallatin Valley is getting an upgrade, starting this summer.

NorthWestern Energy will start construction on a new 161 kilovolt line in late July or early August and work through the fall, said Claudia Rapkoch, a spokeswoman for the company.

The current 69 kilovolt line between Four Corners and the Meadow Village substation in Big Sky is at capacity or above during some times of the year, Rapkoch said. The other transmission line feeding into Big Sky is a 161kV capacity line that comes into the Lone Mountain substation from Ennis.

NorthWestern is finalizing easements with the majority of private landowners along the new line’s northern segment and will start work there. Traffic delays caused by construction may be possible, Rapkoch said.

The new line will be taller than the current one, and the cross arm will be slightly larger. Most of the supports will again be single pole structures.

The new line will be installed alongside the current one because it cannot be taken down until the new one is operating. Its path will remain mostly the same, differing only in two areas, one near Four Corners and one in Gallatin Gateway. As segments of the new are built and tied into the system, the corresponding segments of the old line will be removed.

“[The upgrade is] important for future growth, and for high demand situations either brought on by extremely cold or hot weather, or during ski season,” Rapkoch said.

As it stands now, if a fallen tree or a wildfire shut down one of the lines during the busy season, the other would be maxed out. In that situation, Rapkoch said, power delivery would be affected.

In addition, because NorthWestern’s grid is interconnected, all parts of the system must perform well for the utility to provide reliable power.

“A problem over here can ultimately create a problem someplace else,” Rapkoch said. “Having [the new line] is important for all for the customers in the area.”

This project is part of NorthWestern Energy’s larger plan to increase capacity and reliability for Big Sky that’s already included the 2010 construction of a new Meadow Village Substation. The Ennis Line will also see an upgrade at some point, Rapkoch said. Because it’s rated at 161kV capacity but energized at only 69kV, the utility will install equipment to increase its capacity instead of having to replace the entire line.

NorthWestern also upgraded the line between Three Rivers and Four Corners seven years ago.

“Because the Gallatin Valley has seen so much growth in the last 10 years, it’s definitely an area we have had to work really hard to keep up with,” Rapkoch said.

NorthWestern Energy’s shareholders will fund the Gallatin Canyon upgrade, which is expected to cost in the range of $35 million over the next few years. The charges will be incorporated into the utility’s rate base, which is regulated by the Montana Public Service Commission and paid by all customers.

The Forest Service is still completing an environmental impact statement for the section of line that runs through public land in Gallatin Canyon. NorthWestern expects to finish that portion over the next two years.