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Miles City bridges interconnections for 30 years

Miles City Converter Station
​An aerial view of Miles City Converter Station, which celebrated 30 years of successful operations in July 2015. See more photos at Flickr.


By Lisa Meiman 

Western’s Miles City Converter Station celebrated 30 years of successful operations this past July—an achievement that is a testament to the station’s design and its caretakers.   

Like the Virginia Smith Converter Station, which won an Institute of Electrical and Electronics Engineers Milestone award in May, the Miles City Converter Station is a high-voltage, direct-current, or HVDC, back-to-back tie that provides a connection between the U.S. eastern and western electrical grids. Alternating current from one side is transformed into a universal direct current that is transformed again to match the AC frequency of the other side, allowing two of America’s three electric grids to balance power resources, share energy reserves and provide system operating flexibility.   

“The station also acts as a giant shock absorber so that disturbances in one grid are not reflected into the other,” said Upper Great Plains Electrical Engineer Ben Blaquiere, who is Miles City’s current engineer. As caretaker, Blaquiere is responsible for the operation and maintenance of the Miles City Converter Station and associated equipment, repairs, modifications, additions, testing, long-range planning and budgeting.  

Miles City is different from Virginia Smith as it doesn’t have water-cooled thyristors and instead uses air-cooled ones preferred by General Electric, the station’s design and construction contractor. The thyristors are the semiconductor devices that allow power transfer between the electrical grids. “The cooling system is critical to the life of the thyristors because excess heat kills semiconductors,” said Blaquiere.  

History highlights innovation, dedication 

Miles City was constructed between 1982 and 1985 by G.E. who, at that time, employed a familiar face: Scott Mallard, UGP’s current vice president of transmission system asset management.  

“I was a fresh-out-college field engineer assigned to Miles City in 1983 to oversee and commission major phases of the converter’s construction,” said Mallard. “As part of the contract, G.E. was to provide a warranty engineer that would stay onsite for six months after the station was commissioned. I was selected by G.E. to be that engineer.” Mallard was then picked up by Western in 1986 to serve as the substation engineer in Fort Peck, Montana, beginning his Western career. 

“This station uses technology that was considered old even when it was installed in 1983,” said Mallard. “Its successful operations are a testament to its design and to the Western personnel stationed there taking care of it over the past 30 years.” 

Blaquiere and converter personnel have made a number of improvements to extend the life of Miles City with great success. “Our thyristor failure rate in the past ten years has gone down from an average of ten to only one failure per year,” said Blaquiere. He attributes the significant reduction to replacing system controls for the thyristor cooling system with new custom-tailored hardware and software. 

“We wrote the new control software ourselves,” he said. “This allows us the flexibility to modify the program as we continue to add additional system functionality.” 

Another important upgrade was retrofitting 288 thyristors connected to the Western Interconnection.  

Mallard and Blaquiere agree that Miles City and other converter stations will continue to be necessary well into the future. Right now, the converter stations lining the borders between the Eastern, Western and Electric Reliability Corporation of Texas Interconnections are the best option for bridging America’s power grids. 

“Without ties like Miles City, the electric grid needs more interconnected transmission lines to make a strong, stable and reliable system,” said Blaquiere. “Until then, HVDC systems or possibly newer technology are still necessary for energy exchange and system operating flexibility.”

Page Last Updated: 9/10/2015 9:55 AM