Flexible Power Transmission

By Martin Gross, Global Head of Grid Systems Business, ABB


Transmission solutions for fast-track, integrated renewable power

Advances in global long-haul, high-powered transmission technologies and capacity create an imperative for renewable generation in the U.S. and beyond.

It certainly is an interesting time in history to be involved with electricity.  The power industry is on the verge of the biggest breakthroughs in generation and grid transformation since the days of Thomas Edison and George Westinghouse. As we all know, George got it right and AC transmission has been dominating the power infrastructure until lately. However, during the last decade, DC transmission technology has made great strides and has become a vital part of modern, intelligent and flexible transmission systems. The name of the game is no longer AC against DC – it’s the intelligent combination of both.

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ABB's new 800 kV UHVDC (Ultra High Voltage DC) transformer can deliver vast amounts of electricity over very long distances. This transformer is being used on the world's longest power transmission link across more than 2,000 kilometers in China.

Today, three major issues are on the minds of citizens, government officials and policy makers in many nations around the globe:

  • the status of the global economy
  • energy reliability and independence
  • environmental sustainability

Electricity providers are directly impacted by these issues as they seek to responsibly apply alternative generation sources, energy efficiency technology and engineering solutions that will not only deal with these issues, but help them move forward into a new decade fueled by an ever-growing portfolio of renewable generation.

This article will briefly explore how recent breakthroughs around the world in power transmission systems have led to an imperative in the United States to develop a more intelligent, flexible, long-haul transmission network that has the ability to carry renewable energy from remote locations to major population centers.

Renewable Portfolio Standards are driving the build out of renewable generation

Today in the United States, 33 out of 50 states have some kind of renewable standard.  These Renewable Portfolio Standards (RPS), and their corresponding deadlines for compliance, have had significant impact on recent generation spending.

Proposed goals for a national renewable portfolio standard vary from 12 to 25 percent, and should such a national standard be released by the government, it is estimated that incremental capacity additions of over 300 GW will need to occur.  However, transmission capacity for this new and mostly remote generation currently does not exist.

And with an average construction schedule of 60-72 months for a 500MW at 345kV transmission line, it could take well beyond 2025 until it would be in place.

Among other things, NERC’s October 2009 publication, “2009 Long Term Reliability Assessment 2009 – 2018,” notes that although existing reserve margins are adequate across the U.S. for the next few years, the first priority must be to expand the grid and increase the capacity of transmission to handle the expected growth of renewable generation.

The report concludes by saying: “More than 11,000 miles (or 35 percent) of transmission above 200kV proposed and projected in this report must be developed on time to ensure reliability over the next five years.”  NERC strongly believes that construction siting is the most urgent issue for the electric power industry, now and well into the future. 

Bulk transmission capacity: Prerequisite for large-scale renewable generation

If utilities are to harvest the vast renewable power potential in remote locations of America, or anywhere in the world, they need to be able to move it in a highly efficient manner from its production point to cities and load centers where people live and work.

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Renewable resources and transmission in the western United States. Western USA holds vast wind and solar resources, but many are not served by existing HV* transmission lines.

* Shown: 500kV and above

Bulk transmission capacity is a pre-requisite for large scale renewable generation. While the intermittent nature of many renewable power sources creates new challenges for grid reliability, there are indeed proven, readily-available and cost-effective transmission technologies to mitigate their impact. Reliable, cost-effective transmission technology exists to support massive amounts of new renewable generation, and they are available right now.  These technologies include:

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High-voltage direct current (HVDC) systems, like this Sharyland HVDC station connecting power grids between Texas and Mexico, enable bulk transmission across long distances.

High Voltage Direct Current (HVDC) and HVDC Light

High voltage direct current (HVDC) transmission moves bulk power from remote generation areas to load centers, by using DC rather than AC transmission. Though this technology was pioneered more than 50 years ago, it is enjoying increasing popularity now.

Similarly, ABB introduced “HVDC Light” just over 10 years ago.  HVDC Light is a landmark HVDC technology that enables a host of new applications such as wind parks far out at sea and underground power transmission over long distances. This technology is now running on four continents, and is ideal for transporting renewable energy without many of the common siting and overhead line political and regulatory issues of recent years. For remote offshore power it is the key enabler as the usage of AC cable technology becomes unfeasible beyond a certain distance.

Direct current transmission technology has lower losses and a smaller footprint than alternating current systems (AC). HVDC Light is based on voltage-source converters (VSC’s) and uses IGBT’s (Insulated Gate Bipolar Transistors) to convert electrical current from AC to DC. HVDC Light is now available at a power level of 1,200 megawatts (MW).

Flexible AC Transmission Systems (FACTS)

Intelligent transmission systems like Flexible AC Transmission Systems (FACTS) increase the capacity of existing transmission networks, improve reliability and enable effective integration of renewable generation.  The replacement of local generation with remote generation requires additional reactive power support.  The intermittent nature of wind and solar may require dynamic VAR support for system stability.

One FACTS power system growing in popularity is known as a Static Var Compensator (SVC). SVC systems provide fast-acting reactive power compensation in high-voltage electricity networks, which enhances stability by countering fluctuations in the voltage and current of an electric grid, and by allowing more power to flow through the network. SVC’s also improve the local environment, since much less local generation is required due to the increased capacity on existing networks.

In the last three years, ABB has built the world’s largest cluster of SVC’s for a major utility in Texas and the largest single SVC power solution in western Maryland. These FACTS devices will facilitate and enable future integration of wind and solar power as more and more renewable energy sources go online in the near future.

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Flexible AC transmission systems (FACTS) enable and support remote variable generation with great reliability.

There are several key transmission projects in the U.S. today that are focused on transmitting renewable generation. For example:

·       FPL’s NextEra Energy has completed much of its merchant transmission associated with its Horse Hollow Wind Energy Center project in Texas.

·       Southern California Edison continues to add transmission to support wind generation in the Tehachapi region. 

·       San Diego Gas & Electric – SDG&E’s Sunrise PowerLink will play a major role in bringing renewable generation from the Imperial Valley into southern California, even though one of its primary reasons for existence is system reliability and load growth.  According to the Renewable Energy Transmission Initiative, the Imperial Valley region has potential for 6,870MW solar, 3,495MW wind and 2,000MW geothermal power generation.

·       LS Power’s Southwest Intertie will move renewable power from Wyoming and Montana to substations near Las Vegas, using combinations of AC and possibly high voltage DC transmission. 

·       Another LS Power project, called Overland Transmission, will apply either high voltage AC or DC circuits across 560 miles to move renewables-fueled generation between eastern Wyoming and southern Idaho.

Although there are multiple major transmission projects underway or nearing construction in the U.S., they are by far not enough to support RPS requirements. The two key impediments for the expansion of the renewable power transmission capacity are:

·       The fragmented and time consuming regulatory approval process and

·       The absence of an integrated renewable generation and transmission strategy

To get an idea of what the future could look like in U.S. transmission, let’s take a quick look at a couple of examples of recent transmission successes in Europe and China.

Europe: Visionary governments, regulators pave way for offshore wind power

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An ABB engineer tests HVDC Light valves to be used for the connection of a remote offshore wind farm north of Germany in the North Sea.

In the North Sea, 81 miles off the coast of Germany, the world’s largest offshore wind farm is connected to the grid using advanced HVDC technology.  With HVDC cables lying both underwater and underground, the environmental impact of the project is minimized and the regulatory and siting procedures have been swift. The project connects the wind generators and transmits the power to a new substation on the coast of Germany that is then connected to the existing transmission grid. 

The BORWIN 1 offshore wind farm demonstrates how HVDC can effectively accumulate power generated in remote locations and transmit it to load centers. Through the use of HVDC and wind generation, Transpower, the project owner, expects to avoid CO2 emissions of 1.5 million tons per year by replacing fossil fuel generation. 

Additionally, several European countries are currently discussing ways to build up a renewable generation DC Grid in the North Sea linking multiple offshore wind farms with hydro power generation from Norway to create a firm renewable power source.

Coming Soon: An 800MW Offshore Wind Farm

Just this summer, an even larger project off the coast of Europe was launched.  ABB is working with the transmission grid operator, Transpower, to supply an 800 megawatt (MW) power link. This project will involve HVDC Light technology to transmit power from the 400MW Borkum West II wind farm and other wind farms to be developed nearby. The wind farms will be connected to an offshore HVDC converter station which will transmit electricity to the onshore HVDC station at Dörpen, on the northwest coast of Germany via 165km of underwater and underground DC cables. The Dörpen/West converter station will in turn feed AC power to the mainland grid. At 320-kilovolts, this will be the highest voltage level of extruded cable ever used for HVDC.

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In Europe: Visionary governments and regulators pave the way: E.ON Borkum 2 Wind Farm applies HVDC to move generated wind power off the coast of Germany.

State-of-the-art transmission technologies like these are integrating renewable energy sources efficiently, ensuring grid reliability and stability, and lowering environmental impact.  HVDC Light transmission systems offer numerous environmental benefits, such as neutral electromagnetic fields, oil-free cables and compact converter stations. It is an ideal solution for connecting remote offshore wind farms to mainland networks, as well as connecting remote renewable energy sources to load centers far away with underground cable transmission.  These technologies overcome distance limitations and grid constraints and ensure minimal electrical losses.

This offshore wind project is scheduled to be operational by or before 2013, and is expected to avoid three million tons of carbon dioxide emissions per year by replacing fossil-fuel based generation. Germany currently meets about eight percent of its electricity requirements with wind power, and expects to double that by 2020.

Several other HVDC offshore wind projects are underway in Europe. Sweden is, for example, implementing this same HVDC Light technology off the island of Gotland, the same island where the world’s first HVDC line was installed in 1954. Again this advanced technology is used to carry wind power from the coastal areas onshore to load centers on the mainland.

China: World’s longest and most powerful transmission link up and running

China continues to set the example and lead the way in developing advanced transmission technologies that tap the power of renewable energies without many of the state or national obstacles faced in the U.S. or Europe.  For example, ABB recently worked with the State Grid Corporation of China (SGCC) to create the world’s first Ultrahigh-voltage direct current (UHVDC) transmission link for commercial operation. This represents both the world’s longest and the world’s most powerful transmission link.

The ±800kV Xiangjiaba-to-Shanghai UHVDC link has the capacity to transmit up to 7,200 megawatts (MW) of power from the Xiangjiaba hydropower plant in southwest China to Shanghai, the country's leading industrial and commercial center, about 2,000 kilometers away in eastern China. The new link is able to meet the electricity needs of about 24 million people, and sets a new benchmark in terms of voltage levels and transmission capacity, superseding the 600kV (kilovolt) Itaipu transmission line in Brazil, which was also developed by ABB.

The high-capacity power link comprises a single overhead line and occupies less space than the existing system. Moreover, transmission losses on the new line are under seven percent, again, considerably less than the existing 500kV system. The electricity saved is equivalent to the power needs of around one million people in China.

UHVDC transmission is a new and expanded development of HVDC. This technology with an advanced control system represents the biggest capacity and efficiency leap in power transmission systems in more than two decades. It is particularly suitable for vast countries like China and India, where consumption centers are often located far from power sources, including renewables.

United States: Regulatory, political obstacles can be overcome

While in other parts of the world, governments, regulators, utilities and industries are working towards common goals, many transmission projects in the United States have not yet overcome regulatory hurdles.

The good news is that there is proof that things can be done differently. In Texas, unique cooperation between utilities, multiple regulatory agencies, generation companies, and reliability councils are executing a Public Utility Commission order effectively, timely and fairly.  Hallmark to this activity is the PUC-driven coordination between transmission and generation stakeholders.  When completed by the end of 2013, this Texas CREZ initiative should realize incremental addition of more than 5,000 miles of high voltage AC transmission, reliably moving 18GW of renewable generation from west Texas into Dallas, San Antonio, and Austin.

Multiple scenarios were developed and studied by ERCOT in consultation with other regional transmission organizations, independent organizations, independent system operators, and utilities. The Texas Department of Wildlife provided impact analysis.  Based on ERCOT recommendations, the Commission chose one out of four CREZ scenarios and ordered its development in the State.

Simultaneous guidelines and protocols were provided to generation stakeholders to assure that neither generation nor transmission investment will be “stranded,” and that generation stakeholders produce sufficient assurance such that wind generation is built.

To comply, wind generators have been busy.  Nearly 11GW of wind are installed, there are 450 megawatts of new wind under construction, and nearly 13GW of wind are in development.

The bottom line in Texas: these projects got off the ground in a matter of years, not decades. 

What is needed to resolve key obstacles delaying renewable energy and related transmission build out across the U.S. and other nations grappling with this issue are: Swift regulatory and siting procedures; fair cost allocation; and political courage to execute.

If there’s a progressive PUC in place, as there is in Texas, and if there is cooperation between the various regulatory agencies that have agreed on common goals and executed the reviews and permits needed to keep schedules on track, then there is the real possibility for successful breakthroughs.


Idaho Governor C.L. Otter recently said, “The recent economic recession has slowed the growth in demand for electricity, but we cannot squander this opportunity to address future needs. It is clear that coordination among states, the federal government, all segments of the industry and non-governmental organizations is essential for the region to meet its clean energy needs.” 

The Texas CREZ is an excellent example of how things can get done in the U.S. A visionary PUC with political support, a coordinated regulatory process, and the courage by everyone involved combines for a favorable environment for sustainable renewable power growth.  This model can, and hopefully soon will be, applied across the United States as it is elsewhere.

Only when a fast track, integrated renewable power and transmission strategy is set in motion, will the United States meet its RPS targets and be in position to take full advantage of these rapidly-growing transmission technologies, systems and capacity already being built and implemented throughout Europe, China, and several other countries around the world.