By Nick Fitzmaurice and Anne Hedges
A large proposed transmission line from Colstrip to North Dakota would create innumerable benefits to Montana and states across the West, helping accelerate decarbonization, clean energy development, and reliability. Montana’s transmission system is old and complicated. Upgrades are long overdue. That is why a new proposal to build a large connector line across eastern Montana is an important step in the right direction. But first, what makes Montana’s system so complicated?
Montana’s electric grid is split into two parts: The electric transmission system in the western two-thirds of the state is connected to the western grid of the United States, and the transmission system in eastern Montana is connected to the eastern grid of the U.S. (see map in top right). These two transmission systems divide the country from Canada to Texas because their frequencies are not synchronized. Straddling these separate systems and with limited connectivity across state borders, Montana is severely limited in its ability to move large amounts of power across the state and to trade power with utilities in other states. In essence, Montana is a cul-de-sac for electricity.
This issue has created an obstacle to an affordable and efficient electricity system in the West. Fortunately, one developer has stepped up to try and solve the problem. Grid United plans to develop a large power line between the western and eastern grids from Colstrip, Montana, to two locations in North Dakota. The U.S. western and eastern electric grids run on alternating current (AC), but the two systems aren’t synchronized and therefore power cannot move directly between them. Instead, the east and west grids share limited amounts of power through a complex system using smaller direct current (DC) lines, where electricity is converted from AC, transported as DC, then converted back to AC and fed onto the neighboring grid. These connections are limited, but Grid United’s North Plains Connector seeks to create an additional 525-kilovolt high voltage DC connection between the grids. This line would carry a whopping 3,000 megawatts of power. The project is currently seeking permitting and regulatory approval from the Montana Department of Environmental Quality and the U.S. Department of Energy. Construction is projected to span from 2028 to 2032.
The proposed line would be approximately 415 miles long and connect substations in Colstrip, Montana; St. Anthony,
North Dakota; and Center, North Dakota.
In an effort to assist communities along the proposed path, deal with the construction impacts, and upgrade the downstream transmission system in Montana to handle the increased power from this new line, the federal government issued the State of Montana two grants this summer. The first grant of $47.5 million will help offset community impacts to the Northern Cheyenne Tribe, and Rosebud, Custer, and Fallon Counties. The second grant worth $700 million will help address infrastructure needs for the grid system, including $70 million to help upgrade the existing transmission line from eastern Montana to NorthWestern’s service territory and west coast utilities.
The importance of this project cannot be overstated. Two Colstrip power plant owners that plan on exiting the plant in coming years have signed agreements indicating they intend to own a share of the new transmission line. Avista Energy, who is giving its share of the Colstrip plant to NorthWestern Energy, is keeping its ownership of the Colstrip transmission system. Avista just announced it intends to own 10% of the new transmission line. Portland General Electric, another plant owner, must exit the Colstrip plant by 2030. It signed an agreement in May 2024 to eventually own 10% of the new power line. It also maintains its ownership share of the Colstrip transmission system. Both utilities clearly intend to use the new line and their existing share of the Colstrip line to move wind power from North Dakota to Idaho, Washington, and Oregon. While Montana has an excellent wind resource, North Dakota does as well and the two wind profiles are different enough to complement each other and boost reliability for west coast utilities.
To date, Grid United has proactively engaged with communities along the planned transmission corridor to gain community support for the project. It has avoided public lands and has worked with willing landowners. So far, the project is gaining support from across the political spectrum. Scoping meetings for the environmental impact statements in November and December will help indicate what issues the state and federal governments need to address to minimize impacts. For now, this long-overdue project seems to be moving in the right direction.
