The power behind your electric cooperative Great River Energy is a not-for-profit wholesale electric power cooperative that provides electricity to HVDC transmission system ® 28 member-owner distribution cooperatives. Together, our systems provide power to approximately two-thirds of Minnesota geographically and parts of Wisconsin, serving 700,000 families, farms and businesses. With $3.9 billion in assets, Great River Energy is the second largest electric power supplier in Minnesota and one of the largest generation and transmission cooperatives in the nation. Great River Energy’s unique high-voltage direct- When Great River Energy’s predecessor Learn more at greatriverenergy.com. current (HVDC) transmission system is one of companies, Cooperative Power and United the best-performing HVDC systems in the world, Power Association, were planning to build Coal and it has maintained an outstanding record for Creek Station, they determined it would be less reliability since it was energized in 1978. expensive to transmit electricity over a long distance than to haul coal over a long distance. In basic terms, the system acts as an extension That’s why the plant was built near the Falkirk cord between Great River Energy’s Coal Creek coal mine near Underwood. Station power plant in North Dakota and the Arrowhead Minnesota transmission system. The transmission This vision included an innovative transmission North Itasca line begins at a “converter station” at Coal system to deliver the electricity from the plant to Co-op Lake Country Light & Creek Station and ends at another converter Minnesota. The end result was the unique 436- Power Power station, the Dickinson Converter Station, near mile HVDC transmission line that Great River Itasca-Mantrap Buffalo, Minnesota. Energy still has today.

Crow Wing A unique, long-distance way How unique is it? Todd- Mille Lacs Lake Region Wadena to save money There are two kinds of electric current: alternating

East Central There is a reason that Coal Creek Station is current (AC) and direct current (DC). Almost all Runestone Energy located in central North Dakota even though it electric systems use AC current. In fact, there are Stearns provides electricity for homes and businesses in only five HVDC systems in the United States, and Agralite Connexus Minnesota and Wisconsin. Great River Energy has one of them. Kandiyohi Wright- Meeker Hennepin

McLeod Minnesota Dakota Valley Redwood Goodhue Brown County County Steele- Coal Creek Station Waseca South Central BENCO Nobles CMYK

Federated Great River Energy service area

The HVDC transmission line delivers electricity from Coal Creek Station to Minnesota. greatriverenergy.com

10/27/2020 Power is generated in a conventional AC generator at Coal Creek Station. A converter Quick facts station located next to the power plant converts Direct current the AC electricity produced by the plant into The HVDC transmission line: DC power. A special device called a thyristor  Is 436 miles long converts the electricity by allowing the current  Contains more than to pass through in only one direction, much 1,600 lattice steel like a check valve on a water system. Thyristors towers also control the amount of current flow by firing, Alternating current  Operates at ±400 or turning on, when ordered by the control kilovolts system.  Transmits nearly 70% Many thyristors are connected together to In direct current (DC), electrons travel continuously in one direction. In alternating of Great River Energy’s construct a “valve”, which has the high power current (AC), electrons alternate directions. power capability needed for the conversion process. Both are used in electric transmission, but There are 4,320 thyristors in each converter AC is much more common. station.

Why DC power was better Second, the DC system offers added reliability. Incoming AC power is three-phase, which than AC power For example, the system includes two independent means it has three conductors with individual sets of equipment, called poles. If one pole is out waveforms. Each phase is connected to two Project designers chose to design the system of service, the second pole can still continue to separate valves that are fired in a sequence so using DC power over the traditional AC power transmit 50% of the power the plant can generate. that the currents on the three AC phases can for a number of reasons. The DC system also allows for better control of be added or subtracted to form the DC output First, when electricity is transmitted, some of power exchange and the ability to operate at a of the converter. The result is a six-pulse system the power is lost in the process and using a DC reduced voltage if necessary. that produces a DC current; however, at this point, there are unacceptable levels of voltage system over this long distance minimizes losses. Finally, choosing a DC system over an AC distortion, or harmonics, which can cause system helped reduce impact to property owners operational problems on the AC system. Two when the line was built. The transmission line six-pulse converters are then placed in a series corridor was narrower and fewer towers were to reduce harmonics and produce “cleaner” needed. DC power. The power is then transmitted down How it works, technically the line to Minnesota. It arrives at the Dickinson speaking Converter Station where the process works in reverse – the electricity is converted back to Nearly all homes and businesses in the U.S. use AC so it can be used by customers. 60-cycle AC power. That means the electrons Also, since both converter stations contain in the conductors (the transmission line wires) identical equipment, if required, electricity alternate the direction of their flow 60 times a could be converted and sent the other direction, A look inside the valve hall at the Dickinson second. With DC power, the electrons travel enhancing the reliability of this unique system. Converter Station at the Minnesota end of through the conductors in a constant, or direct line. the HVDC line. The converter stations’ valve Regular maintenance helps keep the system halls were upgraded in 2019. reliable.