Unlike with AC transmission, there is no distance limitation when using HVDC cables for underground or submarine transmission. HVDC transmission is directly controllable firming up capacity by mitigating congestion on parallel paths.

HVDC (high voltage, direct current) and Grid Modernization

Mike Bahrman | ABB Inc.

Can you fill us in on the technical aspects of HVDC --- what is it, what does it do and why is it important?

HVDC transmission has a number of important applications which complement traditional AC transmission.  These include bulk power transmission, asynchronous interconnections, and long underground or submarine cable connections.  More power can be transmitted more efficiently over longer distance using fewer, less expensive transmission lines with HVDC transmission, making it more economic for bulk power transmission.  Different grids can be interconnected asynchronously in a controlled manner via HVDC links while serving to isolate disturbances in one grid from impacting the other grid.

Unlike with AC transmission, there is no distance limitation when using HVDC cables for underground or submarine transmission.  HVDC transmission is directly controllable firming up capacity by mitigating congestion on parallel paths.

What is the significance of this new HVDC Converter Station upgrade project with Bonneville Power for the western power grid and for west coast residents when it's completed?

The bipolar capacity of the Pacific DC Intertie will be increased from 3100 MW to 3800 MW as a result of the upgrade.  This will allow customers in Southern California to access additional renewable energy resources from the Pacific Northwest such as hydro and wind when available such as during the spring runoff.  Similarly, if there is a shortage of hydro capacity during peak load in the NW power flow on the Intertie can reverse.  The DC Intertie facilitates a reduction in the average cost of energy for the western power grid.

What features will be included in this HVDC upgrade that did not exist previously? 

The power capacity of the Pacific DC Intertie capacity has been increased over the years in stages by addition of series-connected and parallel-connected converters to respectively increase the DC voltage and DC current. The upgrade will replace multiple converters of different vintage at BPA's Celilo Converter Station with a single bipolar set of higher capacity converters housed under 'one roof' with a common redundant control and protection system.

How does this benefit BPA's efforts to improve reliability for its customers? 

Consolidation of the station's capacity into a single modern bipolar system will simplify the station configuration, reduce the amount of equipment and subsystems thereby reducing the operation and maintenance requirements and improving system reliability and availability.  

I see ABB has won the 4 most recent major HVDC bids in the US since last year (in Michigan, Texas and the Sharyland power-sharing intertie between Texas and Mexico), worth around half a billion dollars combined. What is ABB's HVDC vision in a nutshell? 

Advancements in HVDC transmission technology has expanded the range of HVDC transmission applications.  The expanded role of HVDC transmission includes access to remote non-traditional renewable generation resources including offshore wind, extended use of underground transmission along shared rights of way, and higher capacity overhead transmission. There is also a trend to install HVDC for flow control, asynchronous grid interconnections and short circuit current limitation.

What is typically involved in one of these HVDC projects?

An HVDC project is usually executed on a turn-key basis including project management, engineering, manufacturing and procurement, transport, civil works, installation and commissioning along with equipment and performance warranties.

How does HVDC benefit the increasing Renewable Energy initiatives in America? How does HVDC help interconnect wind and solar power to the grid efficiently and reliably?

HVDC transmission enables access to large scale, remote renewable resources at a lower delivery cost.  This is primarily due to use of fewer, less expensive transmission lines with lower losses.  A bipolar transmission line uses only two sets of insulated conductors compared to a double circuit AC line which uses 6 sets of insulated conductors.  The best developable renewable resources in America are mostly located remote from major load centers.  The controllable attributes of HVDC transmission makes congestion on parallel transmission paths less likely to curtail transmission thereby firming transmission capacity over a broad range of system conditions.

What is the future of HVDC in the United States (inc. HVDC for offshore wind farms), short term and long term?

The future of HVDC transmission looks strong in the US and globally.  There are a number of high capacity, long distance HVDC transmission links under development in the United States many of which are for accessing large scale wind generation across the Great Plains.  Rated capacity of some of these proposed transmission links are in the same range as the Pacific DC Intertie.  Additional interconnections are planned between asynchronous grids some of which cross international borders.  Several proposed projects use cable transmission.  The State of Hawaii is working to increase its use of renewable energy including that delivered from other islands via HVDC submarine cables.  Offshore wind has been proposed for the mid-Atlantic region.

How extensive in terms of dollars and number of potential projects is the opportunity for HVDC upgrades in the US?

Many of the existing vintage systems in the US have already been upgraded in one form or another.  Some involve control replacements.  Others have also included replacement of the power electronics and cooling system.  In some cases the entire station has been replaced to avoid downtime of the existing system during implementation.  There are a still about a half dozen projects in the US which could be upgraded in the future.  Occasionally, as in the case of the BPA upgrade, capacity can be increased as part of the upgrade.

Is HVDC technology used internationally?

Very much so.  HVDC is undergoing increased use in not only in North America but also in Europe, Asia, Africa and South America.  HVDC is also used in Australia, New Zealand and the Philippines.  There is extensive use of submarine cable interconnections including those for offshore applications in Europe.  HVDC is used extensively in China and India to deliver remote resources especially hydro to distant load centers.  A similar situation exists in Brazil. In the long term there are plans to tap large scale solar power in North Africa to help serve load in Europe.


Michael Bahrman, HVDC Business Development Manager, ABB Grid Systems, North America

Michael Bahrman has been responsible for system analysis, system design, project engineering and project management for various ABB HVDC and FACTS projects in North America.  He is currently responsible for business development of HVDC systems in North America. He has been active in assessing transmission alternatives for large scale renewable energy projects. Prior to joining ABB, Mr. Bahrman was with Minnesota Power where he held positions as Transmission Planning Engineer, HVDC Control Engineer and Manager of System Operations. Mr. Bahrman holds a degree in Electrical Engineering from Michigan Tech and is a registered professional engineer in the state of Minnesota.

The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag

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