IEEE Power & Energy Magazine - May/June 2019 - 118

the United States, and the first to use modular multilevel converters,
is the Trans Bay link, a 53-mi (85 km) underwater cable system that
has been operational since 2010. Running from Pittsburg, California,
to San Francisco, it has ratings of ±200 kV dc, 400 MW. It is said to
provide 40% of the power demand of urban San Francisco. The small
footprint (minimal switchyard) of this Siemens project enables an
effective urban application.
Applications in the range of 500 kV have been reported in the
literature, well beyond the 125-kV introductory levels of just a few
years ago. Germany is considering north-south HVdc VSC cable
links to replace nuclear plants that are expected to be decommissioned. The objective is to bring off-shore wind power from the
North Sea to Bavaria. In the United States, this technology may have
applications for off-shore wind farms along the Atlantic coast (north
of Boston or along the New Jersey coast). The Soo Green Renewable
Rail project in the U.S. Midwest is getting serious attention. This is
a 500-kV VSC cable system buried along a railroad track. It would
deliver energy from wind generation in Iowa to suburban Chicago.

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In the United States, will we see large HVdc projects of the scale of
those in China or India? In my view, probably not. New hydro power
is certainly not available, and remote large wind-driven power systems are not attracting sufficient interest in the continental United
States. The economics appear to be unfavorable, and there is the perennial political issue of not crossing a state without dropping some
portion of the power there. (VSC is more feasible than current-source
converters for this application.)
Will we see special applications using the more compact VSC
technology? Yes. Space-constrained applications like the Trans Bay
link will likely be developed. Will new circuit configurations emerge
with high-speed switching and low losses? Yes. Will advances appear to make currently impractical urban applications possible (i.e.,
VSC plus buried cross-linked polyethylene cable)? Certainly. Will
there be more improvements in reliability? Of course. What about
technology breakthroughs? Look for higher-temperature semiconductors resulting in lower losses.
It would be easier to consider these expectations if more research
dollars were made available-especially if some bright young researcher had a breakthrough in mind. Or if a forward-looking utility
or energy laboratory could see an objective through the fog. Meanwhile, we wait.

For Further Reading
C. Adamson and N. G. Hingorani, High Voltage Direct Current Power Transmission. London: Garaway Limited, 1960.
E. W. Kimbark, Direct Current Transmission Volume 1. New
York: Wiley, 1971.
E. Uhlmann, Power Transmission by Direct Current. Berlin:
Springer-Verlag, 1975.
M Korytowski, "Uno Lamm: The father of HVdc transmission,"
IEEE Power Energy Mag., vol. 15, no. 5, pp. 92-102, Sept.-Oct., 2017.
D. Jovcic and K. Ahmed, High Voltage Direct Current Transmission:
Converters, Systems, and DC Grids. Hoboken, NJ: Wiley, 2015.
p&e

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IEEE Power & Energy Magazine - May/June 2019

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