EPRI Discusses Direct Current Design: Report

By Shidan Gouran (ICP) March 08, 2010
Some news relevant to my blog post from a few weeks ago describing Siemens HDC initiatives in China DC: the Future of the Grid, EPRI announced yesterday a report that describes the design of a superconducting direct current cable system capable of moving thousands of megawatts of electricity between regions, and which is practical and ready for commercial development, using today’s technology.
The EPRI analysis points to significant efficiency gains using superconducting DC transmission lines, with the capability to reduce transmission losses at full load by more that 150 percent compared to alternating current or high-voltage DC systems. Assuming the trend continues for cost-performance improvements in superconducting wire, such a line could become an option within a decade along with Extra High Voltage AC lines that are currently used to move large amounts of power over long distances.
The report indicates that the builders of superconducting DC transmission lines could rely on commercially available technology and construction methods similar to those used in natural gas pipeline construction. These include factory manufactured, transportable sections of an outer carbon steel pipe containing inner stainless steel piping for the flowing coolant and superconducting cable, and trucking to the site for assembly, welding and burial.
The lighter, thinner, higher-capacity superconducting cable might be fabricated, shipped and installed with methods and equipment now used for conventional underground transmission cable. Production capacity of superconducting wire today is limited but given substantial demand capacity could possibly be expanded sufficiently for longer lines. Refrigeration and vacuum requirements of the line might be met by equipment and methods utilized in the industrial gas industry.
As designed, the superconducting cable system outlined in the report would provide 10 GW power capacity with a nominal current and voltage of 100 kiloamps and 100 kilovolts. The report also points to the cable system’s potential to enhance the safety, reliability and efficiency of the existing AC power grid.
EPRI also has published two companion reports which can be found here and over here. These highlight the practical issues of integrating a long-distance, high-power superconducting DC link into the existing, lower-power AC transmission and distribution systems, and states that the operation and control of this link will be a key to the viability and acceptance of the concept.
Admittedly, I've only glanced through this report but one thing I didn't find were any price comparisons to high voltage DC. I assume that if the pricing info was reasonable, even if it was a forecast for the next decade, this report would be much more talked about than currently is.
But it is important news; I think this decade will be one where DC transmission initiatives will become common place and we will see some really interesting technologies emerge for directly consuming power from local DC renewable sources that will be the really exciting report to read.

Shidan Gouran is co-founder of Intelligent Communications Partners (ICP), a strategic advisory consultancy focused on the emerging Smart Grid opportunity. To read more of his Smart Grid articles, please visit his columnist page.

Edited by Michael Dinan

Co-founder, Intelligent Communications Partners

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