Does it Feel as Though Life is Moving at Warp Speed? Do you have trouble keeping current with technology? Are newer technologies being introduced before the last ones are installed? This is a pretty common thread in society today. As soon as that new computer is purchased, it is obsolete. Ray Kurzweil's thought-provoking book The Singularity is Near makes an interesting argument about technology. The premise is that “human-created technology is accelerating, and its powers are expanding at an exponential pace.” Kurzweil contends that, going forward, knowledge doubles approximately every 10 years.
Our intelligent transmission grid technology is following this concept all too well. The first 60 to 70 years were on a gentle slope. There were advances, but not so rapid that an individual could not keep up with them. In the 1980s, we hit the knee in the technology advancement. And today, we see advances coming at us at hyper speed.
High-temperature superconducting (HTS) technology certainly followed this accelerating trend. Superconductivity was discovered in 1911, and Southwire Co. was credited with the first industrial cable application in 2000, after installing three 30-m (98-ft) superconducting power cables at its Carrollton, Georgia, U.S., manufacturing plant.
First-generation (1G) cable HTS projects are being installed on utility transmission grids in ever-increasing numbers today, and second-generation (2G) HTS cables are now out of the laboratories. SuperPower Inc. (Schenectady, New York, U.S.) installed a 34.5-kV, 800-A HTS cable between two National Grid substations in Albany, New York, which has operated for more than 7000 hours with only routine maintenance and no problems. It successfully withstood a system fault in November 2006 when a nearby substation breaker experienced a flashover.
The project has a pretty interesting twist. Cable-manufacturer Sumitomo Electric Inc. (Osaka, Japan) produced the 1G HTS cable in two sections, a 320-m (1050 ft) section and a 30-m section. The 30-m section was later replaced by a 2G HTS cable. Another HTS cable system was installed at American Electric Power's (AEP) Bixby substation in Columbus, Ohio, U.S., leveraging wire from American Superconductor (AMSC; Westborough, Massachusetts, U.S.). This 200-m (656-ft) 13.2-kV, 3000-A HTS cable system uses Ultera's (a joint venture between Southwire and nkt cables) Triax HTS cable.
According to Chuck Stankiewicz, AMSC executive vice president, Triax incorporates all three phases through one cable. “This dramatically reduces the cost of superconductor systems for distribution voltages and brings the technology much closer to commercial viability,” says Stankiewicz.
A third HTS project is going in on the Long Island Power Authority's system connected at the Holbrook substation. Through this project, managed by AMSC, a Nexans HTS cable rated for 138 kV will carry 574 MVA. At 600 m (1968 ft) in length, it will be the world's longest HTS cable, and it will be the first in-grid deployment of a transmission-voltage HTS system. Commissioning is scheduled for late 2007 or early 2008.
TIME TO DOWNSIZE
In North America, the eastern interconnection is approximately 600,000 MW and the western interconnection is about 130,000 MW. Any problem on one side of an interconnection is felt on the other side, possibly leading to a widespread blackout.
For years, George Loehr, former executive director of the Northeast Power Coordinating Council, has been saying these interconnections are too big. He has proposed reducing the size of these grids while increasing their number, so we would have more manageable interconnections. Loehr has suggested using high-voltage dc (HVDC) back-to-back converter stations to separate the grids at an estimated conversion cost of US$8 billion to $10 billion. Considering the 2003 blackout cost roughly $6 billion, this idea is more attractive, especially when power semiconductor technology advancements are making HVDC and flexible ac transmission systems (FACTS) more affordable.
ABB (Zurich, Switzerland) introduced the HVDC Light scheme, which is making HVDC transmission affordable down to tens of megawatts. ABB is using insulated gate bipolar transistor (IGBT) technology, which is less costly than conventional thyristor architecture. When used in voltage-source converters, the design can be configured into a wide range of power-quality devices to address problems ranging from voltage flicker, harmonics, power factor, voltage sags and interruptions. ABB reports success with these schemes in projects like the Cross Sound Cable project, a 40-km (25-mile) 330-MW transmission link between Connecticut and Long Island near New York City. The Murray Link is a 180-km (112-mile)-long 200-MW project in southern Australia. The Eagle Pass Converter Station in Piedras Negras, Texas, is a back-to-back HVDC light system. It is an asynchronous connection rated for 36 MW between Mexico and the United States.
VFT — THE ALTERNATE TECHNOLOGY
Paralleling HVDC technology for asynchronous transmission connections is another advanced technology that is pushing the technology curve. GE Energy (Atlanta, Georgia, U.S.) developed the variable frequency transformer (VFT), which is essentially a continuously variable phase-shifting transformer. The first VFT was installed at the Langlois substation on the Hydro-Québec system in Canada (see Transmission & Distribution World, November 2004). The second was installed at the Laredo Power Station on the AEP system in Texas (see T&D World, August 2007). Both of these installations connect asynchronous systems.
Now GE's engineering staff has come up with a new application that uses the VFT technology to control power flow between synchronous systems, which lets the VFT behave as a continuously variable phase-angle regulator. The first use of the VFT as a phase-angle regulator will be in the Northeastern United States, where the VFT will transmit 300 MW of power from the Pennsylvania/Jersey/Maryland (PJM) Interconnection to the NYISO grid serving the New York metropolitan area. GE is installing a VFT “three pack” at its 900-MW Linden, New Jersey, cogeneration power plant on the PJM grid to Consolidated Edison Company of New York's (Con Edison) Goethals substation in New York City's Staten Island. Construction started earlier this year, with completion expected in 2009.
GRID SHOCK ABSORBERS
Dr. Stan Attcity, a senior member of the technical staff at Sandia National Laboratories (SNL; Albuquerque, New Mexico, U.S.), reports that we have passed the knee of the technology curve with the development of the emitter turnoff (ETO) thyristor. Developed at North Carolina State University, the ETO thyristor is made up of inexpensive components readily available from several manufacturers, which keep the price down since the thyristor is not proprietary to one manufacturer. The ETO thyristor is very fast (5 kHz) and can handle high currents (4 kA) and high voltages (6 kV), making it ideal for use in FACTS controllers and HVDC converters.
The Electric Power Research Institute (EPRI; Palo Alto, California, U.S.) is leading a team comprised of SNL, the U.S. Department of Energy (DOE), Tri-State Generation and Transmission Association Inc. (Westminster, Colorado, U.S.), the Tennessee Valley Authority (TVA; Knoxville, Tennessee, U.S.) and the Bonneville Power Authority (BPA; Portland, Oregon, U.S.) to develop a static synchronous compensator (STATCOM) based on this ETO technology. The ETO-STATCOM will be installed at the Condon Wind substation on the BPA system.
Dr. Abdel-Aty Edris, technology manager of EPRI Power Delivery and Markets, says that approximately 50% of the cost of converter-based FACTS controllers is in the power electronics. Projects like the ETO-STATCOM will have a ripple effect across the spectrum of equipment. With the advancements being developed currently, Edris points out that EPRI has a project it calls the “Grid Shock Absorber.”
Much like Loehr's vision, EPRI, in collaboration with Digital Control Inc., proposed a strategy of a segmented power grid made up of asynchronously operated ac sectors linked by grid shock absorbers (new technology HVDC facilities). Being asynchronous, the segments would not collapse due to a problem in a neighboring segment. This would prevent cascading failures in large transmission interconnections. Edris says the 2003 blackout did not propagate to the Hydro-Québec interconnection because it is interconnected by HVDC transmission.
FAULT CURRENT CONTROL
Rising fault currents are now reaching levels at which utilities are required to consider equipment replacement. But perhaps this expense could be curtailed if, instead, we installed a fault current limiter (FCL), which allows utilities to avoid upgrades. Earlier this year, AMSC and Siemens (Erlangen, Germany) produced and successfully demonstrated a medium-voltage FCL.
To further the development of FCL technology, the DOE is funding three projects:
AMSC will lead one team — made up of Southern California Edison (SCE; Rosemead, California), Siemens, Nexans (Paris, France), the University of Houston and the DOE's Los Alamos National Laboratory (LANL; Los Alamos, New Mexico) — to install its SuperLimiter 3-phase, 115-kV low-impedance coil, using AMSC's 2G HTS 344 superconductor on SCE's transmission system.
SuperPower will lead another team — comprised of members from AEP, Sumitomo Electric, Nissin Electric Co. Ltd. (Kyoto, Japan), The BOC Group Inc. (Munich, Germany) and the DOE's Oak Ridge National Laboratory (Oak Ridge, Tennessee) — to install a 138-kV FCL, featuring a 2G HTS matrix design, using Sumitomo Cable on the AEP transmission grid.
SC Power Systems Inc. (San Mateo, California) is leading another team — comprised of members from SCE, Con Edison, LANL, Air Products and Chemicals Inc. (Allentown, Pennsylvania, U.S.), Cryo-Industries of America Inc. (Manchester, New Hampshire, U.S.), Delta Star Inc. (Lynchburg, Virginia, U.S.) and Trithor GmbH (Rheinbach, Germany) — to develop and install a 138-kV saturable reactor-type FCL.
In addition to the DOE HTS projects, the U.S. Department of Homeland Security has announced its “Project Hydra,” which the department will direct in cooperation with Con Edison, AMSC and Southwire. Project Hydra will combine the power-transfer capability of HTS cable with AMSC fault-limiting HTS cable technology. It contains a high-resistance stabilizer in the cable design. Under normal conditions, current is carried in the HTS layer, but when a fault takes place, the high-resistance layer comes into play, blocking the fault. Once the fault has passed, the HTS is conductive again.
AMSC's Stankiewicz says the idea is to connect substations with this special HTS cable. “Like the mythical Greek monster that grew back heads when one was severed, multiple paths for electricity flow will be created in power grids to ensure system reliability if circuits were to be disrupted,” says Stankiewicz. Project Hydra will use Southwire's Triax cable system.
WIND AND VARS CONTROL
Wind power is one of the fastest-growing sources of electrical generation on the bulk power grid, and it is bringing both benefits and problems. American Wind Energy Association projects that wind generation in the United States in 2007 will be 14,603 MW. With all this generation comes voltage regulation, voltage stability and VAR-consumption problems, which are ideal territory for FACTS applications.
The S&C Electric Co. (Chicago, Illinois, U.S.) has developed a FACTS controller that is a fast-compensating (approximately one-quarter of a cycle) reactive power source it calls the PureWave D-STATCOM. The power electronics uses IGBT dc-ac inverters to produce either leading or lagging reactive current, as required by the installation. S&C installed two 6-MVAR D-STATCOMs at the Aragonne Mesa Wind Farm near Santa Rosa, New Mexico.
According to Darren Du Vail, Aragonne Mesa's operations manager, the wind farm provides 90 MW of New Mexico-produced wind power to the Arizona Public Service bulk transmission system over the bulk transmission system of Public Service Company of New Mexico. Du Vail says the D-STATCOMs are located on the wind farm's 34.5-kV collector system, coupled with four mechanically switched capacitor/reactor banks (three 26 MVARs and one 13 MVAR).
Gerry Keane, S&C's manager of projects and product management, says S&C developed special software to anticipate the utility's bulk transmission VAR condition based on the output of the wind farm. The D-STATCOM provides a smooth VAR curve with the IGBT electronics and the mechanically switched capacitor/reactor units, allowing it to operate over wide swings in the utility system conditions. Keane says this is a very cost-efficient method to cover the wide range of VAR support required by the 90-MW wind farm. The D-STATCOM provides VAR support, permitting the wind farm to be a good neighbor on the utility's bulk transmission system.
AMSC has developed a FACTS device, called D-VAR, to provide dynamic reactive compensation for a wide range of operational needs, such as those found on wind farms. The D-VAR uses IGBT inverter power modules to provide leading and lagging VAR support. Stankiewicz reports that AMSC has sold systems to support approximately 5.7 GW of wind power worldwide (33 wind farms at last count). And according to Stankiewicz, AMSC's customers are using the D-VAR to provide voltage regulation and power-factor correction, along with post-contingency assistance to prevent voltage collapse on the power grids where the wind farms are connected.
The technology of the intelligent grid has started out slowly, but the growth is deceptive, as Kurzweil points out, because we tend to accept the limits of our vision. When we focus on technology as a whole, it shocks us, it seems to be explosive, it appears to be overwhelming, and it is. HTS, HVDC and FACTS are just the tip of the iceberg, but are fairly representative of the technology advancements of our industry. It took almost 100 years from the discovery of superconductivity to the first power-cable applications, but today there are many projects including HTS cable, transformers, motors and FCLs. In 1936, GE used the mercury-arc valve for a 30-kV dc transmission line between Mechanicville and Schenectady. Today, Siemens is using light-triggered thyristors for the 800-kV ultra-HVDC projects in China. The GTO and the IGBT are facing the first appearance of the ETO. The advances continue, the pace increases and new solutions to old problems make the grid smarter in the process.