50 ELECTRICALCONTRACTOR | JUN. 16 | WWW.ECMAG.COM
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“You see the same general developments you see in all
power electronics,” Rosenqvist said. “That drives down the cost
because you drive down the footprint and the power losses.”
“Historically, any kind of substation has had a lot of cable
coming in from the yard,” Rosenqvist said.
Today, however, the communications infrastructure is based
on fiber optic busses.
“The new station is just a small part of the footprint the
original equipment had,” he said.
Solid-state control devices called thyristors have been the
technology standard for converter station controls since the
late 1970s and form the basis of systems both ABB and Siemens, the world’s two leading HVDC technology suppliers,
brand as “HVDC Classic.” In the last 15 years or so, new systems based on voltage source converters (VSCs) have come
to market, enabling the capacities and distances now being
considered at the cutting edge of HVDC technology, according to Wayne Galli, executive vice president for transmission
and technical services at Clean Line Energy Partners. The
Houston company is behind the most ambitious U.S. projects
now in planning stages. ABB calls its version of VSC-based
systems “HVDC Light,” while Siemens dubs it “HVDC Plus.”
While technologists may have addressed many of the operational
challenges of bringing DC back into the transmission business,
they have not been quite as successful at meeting the political
roadblocks raised by the kind of long-distance, interstate projects
for which HVDC is well-suited, as Galli’s company knows only
too well. Recently, though, interest in boosting the presence of
renewable energy in the U.S. generation mix has prompted federal intervention in a fight over one Clean Line effort in a manner
that could set a new precedent favoring long-haul HVDC transmission development as a matter of national interest.
The Plains & Eastern Line is proposed to run approximately 700 miles, from the wind-rich Texas and Oklahoma
panhandle region, through Arkansas, to Memphis, Tenn., carrying 3,500 MW of wind-generated electricity to the mid-South
and Southeast. A mid-Arkansas converter station could supply
an additional 500 MW to the state’s customers. The project
is estimated to cost $2.5 billion and could mean $140 million
in voluntary payments to Arkansas coffers over the course of
40 years. However, a strong opposition movement has threatened to derail development—that is, until the U.S. Department
of Energy (DOE) stepped in this spring.
For the first time, the DOE exercised authority granted
under Section 1222 of the Energy Policy Act of 2005 to recognize the transmission line as a necessary means for reducing
congestion and meeting electricity demand. In essence, this
could allow Clean Line to acquire property for its required
rights of way through eminent domain, though it would be
required to compensate property owners at a fair market value.
“That is a very groundbreaking decision, because it’s the
first time the federal government has been involved in a
transmission project,” said Peter Kohnstam, HVDC business
development manager for Siemens.
He also noted exceptions for federally owned grids, such as
the BPA and the Tennessee Valley Authority.
“It’s quite a contentious decision as well,” he said. “It’s a
Favorable economics for the future
Clean Line still has plenty of work to do signing up cus-
tomers at the line’s receiving end, and the actual right-of-way
acquisition process hasn’t yet begun. As this is the first use of
a provision passed by Congress 11 years ago, legal battles are
almost certain to ensue. However, the move could strengthen
the company’s position in regard to two other HVDC projects
also aimed at bringing wind power from west to east.
While Clean Line Energy Partners is focused on HVDC over
long distances, others say the technology is becoming more
affordable for shorter runs, especially in challenging settings. It
performs well in underground applications, for example, where
AC transmission can be limited to 30–50 miles. It’s often the
only feasible option for underwater cables of any significant distance because AC cables have extremely high line losses in such
installations. Additionally, the falling cost of HVDC’s required
power electronics along means the added expense of control stations is becoming less of a concern in larger financial decisions.
HVDC systems offer advantages that run beyond more efficient transmission over long distances. For example, HVDC
offers the opportunity to isolate connected grids from each
other, in the case of a failure on either end, which could prevent a regional outage from cascading into multistate event. In
dense urban environments, HVDC’s added carrying capacity
could allow for distribution upgrades requiring significantly
less room than equivalent AC designs would demand.
“It allows us to cross thresholds,” Kohnstam said of the
intangible benefits HVDC technology can offer to system plan-ners looking beyond first-cost calculations and toward a more
efficient and resilient grid. “When that changes the economics,
that’s when it will change the break-even point.”
RO SS is a freelance writer located in Brewster, Mass. He can be
reached at email@example.com. I S T
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