Most of the power lines that we build are 69- kilovolt (kV) or 115-kV lines, and are much smaller than landowners expect. The large lattice towers that often come to mind are rarely used any longer.
The type of transmission structures used for any project is determined by the characteristics of the transmission line’s route, including terrain and existing infrastructure. The illustrations below show typical transmission poles and structures, starting with the smaller structures Great River Energy typically uses and ending with very large towers.
A transmission line is a set of wires, called conductors, that carries electricity from power plants to substations. When you think of the power line system that delivers electricity to you, think of the large transmission lines as interstate freeways with the distribution lines that carry electricity to homes, farms and businesses being the smaller state or county highways.
The 69-kV through 23-kV systems transmit power to the distribution substations throughout the Great River Energy system. These lines also provide connection to some of the more remote and sparsely populated areas in our service territory. Many of the smaller rural industrial and larger commercial customers of our member-owner cooperatives receive their power directly from these systems. We operate more than 3,000 miles of transmission line that operate at 69 kV line or less.
The 161-kV and 115-kV system is the workhorse of the transmission system. It is responsible for transmitting power from the larger transmission system and generation facility throughout the entire service area. 161-kV and 115-kV transmission lines are the main arteries for electricity, carrying it to and from every geographical area we serve. Some large industrial customers are served directly from the 115-kV transmission system. We currently operate approximately 45 miles of 161-kV transmission lines and 560 miles of 115-kV transmission lines, connecting more than 105 substations.
The 345-kV and 230-kV systems provide the backbone of a transmission system. These transmission lines are the main connection for reliability purposes between Great River Energy’s service area and the region’s bulk power systems. They also provide connections from our HVDC line and other large generating facilities. By operating transmission lines at such a high voltage, line losses and voltage drops can be minimized while the lines deliver large amounts of energy to customers throughout the system.
The ±400 kV and 500 kV transmission lines are the super highways in the Great River Energy system, although large lattice towers such as these are rarely used any longer. Some 1,000 megawatts of electricity can flow across Great River Energy’s ±400 kV transmission line that runs 436 miles from Coal Creek Station, in central North Dakota, to Minnesota. Only electricity generated at Coal Creek Station and then converted into DC at the plant’s converter station can flow across the HVDC, or high-voltage direct current, line. More than 1,600 lattice steel towers carry the HVDC transmission line across both states. Once in Minnesota, the DC power is converted back to alternating current (AC) power and sent along the local transmission systems for use in Minnesota homes and businesses. Great River Energy also operates 70 miles of 500 kV transmission lines.