CU is the designation of a line for high-voltage direct current transmission between the Coal Creek Station power plant south of Underwood, North Dakota at 47°22′24″N 101°9′23″W and the Dickinson converter station near Buffalo, Minnesota 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. Wikipedia