Transmission 101: the basics of how the system works

Transmission lines are sets of wires, called conductors, that carry electric power from generating plants to the substations that deliver power to customers. At a generating plant, electric power is “stepped up” to several thousand volts by a transformer and delivered to the transmission line. At numerous substations on the transmission system, transformers step down the power to a lower voltage and deliver it to distribution lines. Distribution lines carry power to farms, homes and businesses. 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.      

Typical transmission line structures

•  High-voltage (230-kV, 345-kV, 400-kV (DC), 500-kV (DC):

Currently in Minnesota, the high-voltage system is generally comprised of 230-kiloVolt and 345-kV systems. There are also two direct current (DC) lines, one of 400-kV and one at 500-kV.

Structures are generally steel lattice towers, wooden H-Frames or single-pole steel. (photos below of each).

•  Lower voltage transmission systems:

161-kV and 115-kV systems are responsible for transmitting power from the larger transmission system and generation facility throughout the entire state. Some large industrial customers may be served directly from 161-kV and 115-kV systems.

161-kV and 115-kV structures are generally single pole structures between 70 and 95 feet tall.

69-kV through 23-kV systems transmit power to distribution substations. These also provide connection to some of the more remote and sparsely populated areas in greater Minnesota. Many smaller and rural industrial customers receive power directly from these systems.

Structures are generally single pole towers, constructed of either wood or steel and range from 50-70 feet tall.

Transmission Nominal Voltage: +/- 400 kV HVDC
Type: Tower
Typical Tower Height:
145-180 feet

Typical Right-of-Way Width:
160-180 feet

Transmission Nominal Voltage: 500 kV
Type: Tower
Typical Tower Height:
90-150 feet
Typical Right-of-Way Width:
160-200 feet

Transmission Nominal Voltage: 345 kV
Type: Double Ckt Pole
Typical Tower Height:
115-150 feet

Typical Right-of-Way Width:
140-160 feet

Transmission Nominal Voltage: 230 kV
Type: H-Frame
Typical Tower Height:
60-90 feet

Typical Right-of-Way Width:
100-160 feet

Transmission Nominal Voltage: 161 kV
Type: Single Pole
Typical Tower Height:
70-95 feet
Typical Right-of-Way Width:
100-150 feet

Transmission Nominal Voltage: 115 kV
Type: Single Pole
Typical Tower Height:
55-80 feet

Typical Right-of-Way Width:
90-130 feet


Transmission Nominal Voltage: 69 kV
Type: Single Pole
Typical Tower Height:
50-70 feet
Typical Right-of-Way Width:
70-100 feet



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How dependable electricity reaches you


Generation and transmission cooperatives (G&Ts), like Great River Energy, operate power generating facilities. At a steam generating plant, the fuel (coal, nuclear or biomass) heats water to make steam and drive a turbine. In a combustion turbine, the fuel (gas or oil) is burned and the hot gas drives a turbine. Wind hydro and solar are other forms of energy producers.


transmission lines

Transformers at the generating plant increase the voltage up to a transmission voltage (69 kV, 115 kV, 230 kV, 500 kV, 765 kV), so it can travel long distances over high-voltage transmission lines. G&Ts operate these lines, which carry the electric energy from the generating stations to the places where electricity is used.


Transformers reduce the electric energy down to
a lower voltage (69 kV, 34 kV) making it suitable for high-volume delivery over short distances.

Transformers reduce the electric energy down to a lower
voltage (69 kV, 34 kV) making it suitable for high-volume delivery over short distances.

Large industrial user
Most industries need 2,400 to 4,160 volts to run heavy machinery. They usually have their own substation at the facility.

Distribution lines
Lines belonging to local electric co-ops carry electricity to transformers that reduce power levels to 120/240 or 120/208 volts for use in schools, farms, small businesses and homes.


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SOURCE: Minnesotta Electric Transmission Planning