CU is the designation of a line for high voltage direct current (HVDC) transmission between the Coal Creek Station

Coal Creek Station

Coal Creek Station is the largest power plant in the U.S. state of North Dakota. Located at near the Missouri River between Underwood, North Dakota and Washburn, North Dakota, it is the largest lignite-fired electricity plant in North Dakota...

 power plant south of Underwood, North Dakota

Underwood, North Dakota

As of the census of 2000, there were 812 people, 323 households, and 229 families residing in the city. The population density was 910.8 people per square mile . There were 381 housing units at an average density of 427.3 per square mile . The racial makeup of the city was 96.80% White, 1.11%...

 at 47°22′24"N 101°9′23"W and the Dickinson converter station near Rockford, Minnesota

Rockford, Minnesota

As of the census of 2000, there were 3,484 people, 1,296 households, and 929 families residing in the city. The population density was 2,021.2 people per square mile . There were 1,333 housing units at an average density of 773.3 per square mile...

 at 45°06′40"N 93°48′36"W.

The designation most likely refers to two Minnesota-based power generation/transmission cooperatives that originally partnered to build the Coal Creek plant and associated line - Cooperative Power Association and United Power Association, which later merged to become Great River Energy

Great River Energy

Great River Energy is an electric transmission and generation cooperative in the U.S. state of Minnesota; it is the state's second largest electric utility, based on generating capacity, and the fifth largest generation and transmission cooperative in the U.S. in terms of assets...

.

The CU project controversy

CU project controversy

The CU Project Controversy involved years of protest against a proposed high-voltage direct current powerline that was erected on the property of hundreds of farmers in west central Minnesota in the late 1970s...

 in 1978 and 1979 was a result of protests by farm landowners in the path of the CU line right of way.

The CU line, which went in service in 1979, can transfer an electrical power of 1,000 megawatts at a symmetrical transmission voltage of 400 kV. An overhead line connection 426 miles (710 kilometers) long is used, with two conductors per pole. As is the case in all modern HVDC systems, thyristor

Thyristor

A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...

 static inverters are used.

Crossing of HVDC powerlines

Southwest of Wing, North Dakota

Wing, North Dakota

As of the census of 2000, there were 124 people, 68 households, and 32 families residing in the city. The population density was 210.3 people per square mile . There were 89 housing units at an average density of 150.9 per square mile . The racial makeup of the city was 99.19% White, and 0.81% from...

, at 47°02′48"N 100°05′49"W CU crosses Square Butte

Square Butte

Square Butte is the designation of a high voltage direct current transmission line in the USA between the Milton R. Young Power Plant near Center, North Dakota at and the Arrowhead converter station near Adolph, MN at . It was built by Minnkota Power Cooperative and Minnesota Power and went in...

, another HVDC powerline. This is the only crossing point of two HVDC overhead powerlines in the Western hemisphere.