Superconductor ‘SeaTitan’ Wind Turbines Represent Quantum Leap in Offshore Wind Power Market
Among the greatest challenges to developing larger wind turbines have been the practical size and weight limitations of the wind turbine generator. The power density advantage of superconductors, however, is now being applied to wind turbine generators to maximise the ‘power per tower’ of multi-megawatt turbines, while at the same time overcoming size and weight barriers – and reducing overall project costs. Utilising superconductor direct drive generators, SeaTitan wind turbines are being designed to produce 10MW or more of power, which would make them the world’s largest and most powerful wind turbines.
By Martin Fischer, Vice President of American Superconductor, General Manager of AMSC Windtec
The offshore industry, which accounted for just 2GW of the world’s total 158GW of wind power installed at the end of 2009, is expected to enter a period of rapid and prolonged growth beginning within the next few years. For example, industry research firm Emerging Energy Research currently projects that global offshore installed capacity will increase to approximately 20GW by 2015 and rise sharply to 104GW by 2025. The development of higher capacity wind energy systems will be required to fully capitalise on this vast clean energy resource.
Superconductor Turbines for the Offshore Environment
Offshore wind energy has many advantages over its onshore counterpart, including higher wind speeds with less intermittency, greater availability of space, aesthetic advantages, and closer proximity to population centres. The size of the resource is huge. However, offshore wind is still about 50% more expensive than onshore wind on a first-cost basis and, thus, there is a concerted focus to improve economics. Part of the cost premium is due to less than optimal ‘adaptation’ of conventional technology with ad hoc design modifications such as sealed nacelles and special access platforms for maintenance purposes. Because the majority of costs associated with offshore wind are related to installation and the subsea support structures, the most effective way to reduce costs is by maximising the power output of each turbine, such as is achieved by using superconductor generators.
Power Density of Superconductors to Enable Power Ratings of 10MW and Beyond
Wind turbines being employed today for the offshore market are currently limited to power ratings of approximately 5MW in capacity, partly due to the fact that the drive trains for these conventional multi-megawatt turbines are very heavy and have unresolved reliability issues. Allowance for tolerances and deformations in large generators reduces the effectiveness of permanent magnet (PM) generators. What is needed to fully capitalise on the vast opportunity presented by offshore wind is the design of special purpose machines with inherent high efficiency and lower maintenance requirements. The generator developed by AMSC achieves this by using the company’s Amperium high temperature superconductor (HTS) wire, which is capable of conducting more than a hundred times the electrical current (‘amperage’) of copper wire of the same dimensions. The resulting power density of these systems compared to conventional generators constructed with copper wire will break this existing power rating barrier and enable smaller-sized turbines that are capable of producing more power per tower.
New Technology Paradigm on the Horizon
By eliminating copper in the turbine rotor and using superconductor rotors instead, the wind generator is not only much smaller and lighter, but more efficient and less expensive than conventional large-scale wind turbine generators. Efficiency is further enhanced – and manufacturing and maintenance costs reduced in the SeaTitan wind turbine design – by using a direct drive generator, thus eliminating the complex turbine gearbox, which tends to be the most maintenance-intensive wind turbine component. This further reduces costs. Superconductor technology has already been proven numerous times in many applications, including large-scale power cable projects and rotating machine platforms such as large ship propulsion motors. In fact, a 36.5MW superconductor ship propulsion motor designed and manufactured by AMSC for the US Navy successfully completed the Navy’s full-load power testing in January 2009. These machines are now ready for deployment.
Reducing Weight and Complexity is Key
The weight savings attributable to HTS technology allow the SeaTitan generator to be placed directly above the tower, enabling improved mainframe design and direct load transfer from the hub to the tower offering. In most existing offshore wind turbines, a major failure mode is caused by the deflections of the rotor shaft. To reduce damage, the housing of the gearboxes or generators could be decoupled from the mainframe, but only in a complex way. This is not needed for the superconductor generators because their large airgap can absorb all deflections, allowing the generator housing to be directly integrated in the wind turbine mainframe. This factor, combined with the significantly smaller generator diameter, is the primary contributor to the strength, light weight and small size of the SeaTitan wind turbine design. Further, the SeaTitan wind turbine requires only one main bearing configuration.
Reducing Maintenance Costs and Ensuring Availability
The SeaTitan wind turbine additionally incorporates a number of design solutions that ensure redundancy of its operation. For example, the cryogenic cooling system for the HTS generator achieves high reliability by employing n+1 modular, single-stage Gifford McMahon (GM) coolers and long-life seals in its helium transfer coupling. In fact, in AMSC’s experience with cooling transfer systems in both HTS transmission and large rotating machines, the reliability of this component has proven to be excellent. The SeaTitan system design, which is equipped with more than one cryogenically cooled surface, promotes efficiency and eases maintenance. Firstly, more than one cryogenically cooled surface in series allows each surface to work less to lower the temperature of the cryogenic fluid. In addition, if one cryogenically cooled surface malfunctions, the redundancy in the system will be able to overcome the loss. The refrigeration system also has no unusual environmental requirement or impact due to the required cryogenic cooling components for an HTS generator. In fact, most serviceable components are placed at the bottom of the tower for easy access. These accessible components include power converters, compressors for cryogenic cooling, the control cabinet and switchgear.
Other Key Operational Issues Addressed by Superconductor Generators
Superconductor generators offer many technical benefits, including:
In addition to the SeaTitan wind turbine, AMSC Windtec provides a variety of licences and customised designs for onshore and offshore turbines. More than a dozen wind turbine manufacturers today are using AMSC Windtec’s suite of conventional wind turbines with power ratings up to 6MW. The company also provides extensive customer support services through manufacturing scale-up as well as advanced electrical control systems for each wind turbine that its customers produce.
In the near future, AMSC expects to select its first SeaTitan wind turbine licensee. It will then work with this customer to establish a full supply chain for this wind turbine, including a manufacturer for the SeaTitan generator. The SeaTitan will have an initial design capacity of 10MW with a 190-metre rotor. The tower can rest on conventional jacket foundations and deep-water foundations of various types. AMSC plans to field a first SeaTitan prototype in the 2013 timeframe and enter full-volume production by mid-decade.
Conclusion
Maximising the potential of offshore wind power sites will require new technical approaches in turbine design to increase power density, reduce weight and lower maintenance costs. Having been proven in large ship propulsion motors and other electric utility applications, superconductors offer a unique solution to achieving these goals. Due to the power density advantage of superconductors, the SeaTitan wind turbine will dramatically reduce system size and weight and, ultimately, significantly lower offshore wind development and maintenance costs. Coupled with AMSC Windtec’s design engineering expertise, the SeaTitan wind turbine also represents a path forward to achieving power ratings beyond the 10MW range.
SeaTitan, AMSC Windtec and Amperium are registered trademarks of AMSC.
Biography of the Author
Martin Fischer holds a Master of Science degree in Electrical Engineering from the Delft University of Technology in the Netherlands. He joined Windtec GmbH in September 1995 as Project Manager, Electrical Power Systems. (AMSC acquired Windtec GmbH in early 2007 forming its wholly owned AMSC Windtec subsidiary.) Fischer has been promoted to multiple positions since then. Most recently in 2008 and 2009 respectively, he was promoted to the positions of Managing Director, AMSC Windtec GmbH, and to his current position of Vice President, American Superconductor and General Manager of AMSC Windtec.{/access}
Among the greatest challenges to developing larger wind turbines have been the practical size and weight limitations of the wind turbine generator. The power density advantage of superconductors, however, is now being applied to wind turbine generators to maximise the ‘power per tower’ of multi-megawatt turbines, while at the same time overcoming size and weight barriers – and reducing overall project costs. Utilising superconductor direct drive generators, SeaTitan wind turbines are being designed to produce 10MW or more of power, which would make them the world’s largest and most powerful wind turbines.By Martin Fischer, Vice President of American Superconductor, General Manager of AMSC Windtec
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}American Superconductor (AMSC) is developing the SeaTitan wind energy system by combining the company’s world-renowned wind turbine engineering experience with its leadership in the superconductor arena. The superconductor generators to be used in SeaTitan wind turbines are based largely on proven superconductor ship propulsion motors and generator technology developed by AMSC for the US Navy. The unique power density of superconductors will enable a 10MW SeaTitan wind turbine to be similar in weight and size to a conventional 5MW system.
High Capacity Wind Turbines Needed for Nascent Offshore MarketThe offshore industry, which accounted for just 2GW of the world’s total 158GW of wind power installed at the end of 2009, is expected to enter a period of rapid and prolonged growth beginning within the next few years. For example, industry research firm Emerging Energy Research currently projects that global offshore installed capacity will increase to approximately 20GW by 2015 and rise sharply to 104GW by 2025. The development of higher capacity wind energy systems will be required to fully capitalise on this vast clean energy resource.
Superconductor Turbines for the Offshore Environment
Offshore wind energy has many advantages over its onshore counterpart, including higher wind speeds with less intermittency, greater availability of space, aesthetic advantages, and closer proximity to population centres. The size of the resource is huge. However, offshore wind is still about 50% more expensive than onshore wind on a first-cost basis and, thus, there is a concerted focus to improve economics. Part of the cost premium is due to less than optimal ‘adaptation’ of conventional technology with ad hoc design modifications such as sealed nacelles and special access platforms for maintenance purposes. Because the majority of costs associated with offshore wind are related to installation and the subsea support structures, the most effective way to reduce costs is by maximising the power output of each turbine, such as is achieved by using superconductor generators.
Power Density of Superconductors to Enable Power Ratings of 10MW and Beyond
Wind turbines being employed today for the offshore market are currently limited to power ratings of approximately 5MW in capacity, partly due to the fact that the drive trains for these conventional multi-megawatt turbines are very heavy and have unresolved reliability issues. Allowance for tolerances and deformations in large generators reduces the effectiveness of permanent magnet (PM) generators. What is needed to fully capitalise on the vast opportunity presented by offshore wind is the design of special purpose machines with inherent high efficiency and lower maintenance requirements. The generator developed by AMSC achieves this by using the company’s Amperium high temperature superconductor (HTS) wire, which is capable of conducting more than a hundred times the electrical current (‘amperage’) of copper wire of the same dimensions. The resulting power density of these systems compared to conventional generators constructed with copper wire will break this existing power rating barrier and enable smaller-sized turbines that are capable of producing more power per tower.
New Technology Paradigm on the Horizon
By eliminating copper in the turbine rotor and using superconductor rotors instead, the wind generator is not only much smaller and lighter, but more efficient and less expensive than conventional large-scale wind turbine generators. Efficiency is further enhanced – and manufacturing and maintenance costs reduced in the SeaTitan wind turbine design – by using a direct drive generator, thus eliminating the complex turbine gearbox, which tends to be the most maintenance-intensive wind turbine component. This further reduces costs. Superconductor technology has already been proven numerous times in many applications, including large-scale power cable projects and rotating machine platforms such as large ship propulsion motors. In fact, a 36.5MW superconductor ship propulsion motor designed and manufactured by AMSC for the US Navy successfully completed the Navy’s full-load power testing in January 2009. These machines are now ready for deployment.
Reducing Weight and Complexity is Key
The weight savings attributable to HTS technology allow the SeaTitan generator to be placed directly above the tower, enabling improved mainframe design and direct load transfer from the hub to the tower offering. In most existing offshore wind turbines, a major failure mode is caused by the deflections of the rotor shaft. To reduce damage, the housing of the gearboxes or generators could be decoupled from the mainframe, but only in a complex way. This is not needed for the superconductor generators because their large airgap can absorb all deflections, allowing the generator housing to be directly integrated in the wind turbine mainframe. This factor, combined with the significantly smaller generator diameter, is the primary contributor to the strength, light weight and small size of the SeaTitan wind turbine design. Further, the SeaTitan wind turbine requires only one main bearing configuration.
Reducing Maintenance Costs and Ensuring Availability
The SeaTitan wind turbine additionally incorporates a number of design solutions that ensure redundancy of its operation. For example, the cryogenic cooling system for the HTS generator achieves high reliability by employing n+1 modular, single-stage Gifford McMahon (GM) coolers and long-life seals in its helium transfer coupling. In fact, in AMSC’s experience with cooling transfer systems in both HTS transmission and large rotating machines, the reliability of this component has proven to be excellent. The SeaTitan system design, which is equipped with more than one cryogenically cooled surface, promotes efficiency and eases maintenance. Firstly, more than one cryogenically cooled surface in series allows each surface to work less to lower the temperature of the cryogenic fluid. In addition, if one cryogenically cooled surface malfunctions, the redundancy in the system will be able to overcome the loss. The refrigeration system also has no unusual environmental requirement or impact due to the required cryogenic cooling components for an HTS generator. In fact, most serviceable components are placed at the bottom of the tower for easy access. These accessible components include power converters, compressors for cryogenic cooling, the control cabinet and switchgear.
Other Key Operational Issues Addressed by Superconductor Generators
Superconductor generators offer many technical benefits, including:
- High turbine power density: The superconductor field winding produces magnetic fields higher than those of conventional machines, resulting in much smaller size and weight.
- High partial load efficiency: Superconductor generators have higher efficiency at part load, which results in a potential efficiency advantage of 10% or more at low speeds.
- Low noise: Superconductor generators have lower sound emissions than conventional machines.
- Harmonics: Superconductor generators have better power quality and are free of harmonics.
- Maintenance: In addition to negating the need for a gearbox, direct drive superconductor generators will not require the rotor overhaul, rewinding or re-insulation that is required with conventional generators.
- Simple mainframe: No decoupling between generator stator and mainframe housing is needed, because rotor deflections are absorbed by the large airgap.
- Increased personal safety: A superconductor generator rotor can be easily demagnetised during wind turbine maintenance or potential wind turbine repairs. This significantly increases the personal safety of service employees compared to wind turbines with PM generators.
In addition to the SeaTitan wind turbine, AMSC Windtec provides a variety of licences and customised designs for onshore and offshore turbines. More than a dozen wind turbine manufacturers today are using AMSC Windtec’s suite of conventional wind turbines with power ratings up to 6MW. The company also provides extensive customer support services through manufacturing scale-up as well as advanced electrical control systems for each wind turbine that its customers produce.
In the near future, AMSC expects to select its first SeaTitan wind turbine licensee. It will then work with this customer to establish a full supply chain for this wind turbine, including a manufacturer for the SeaTitan generator. The SeaTitan will have an initial design capacity of 10MW with a 190-metre rotor. The tower can rest on conventional jacket foundations and deep-water foundations of various types. AMSC plans to field a first SeaTitan prototype in the 2013 timeframe and enter full-volume production by mid-decade.
Conclusion
Maximising the potential of offshore wind power sites will require new technical approaches in turbine design to increase power density, reduce weight and lower maintenance costs. Having been proven in large ship propulsion motors and other electric utility applications, superconductors offer a unique solution to achieving these goals. Due to the power density advantage of superconductors, the SeaTitan wind turbine will dramatically reduce system size and weight and, ultimately, significantly lower offshore wind development and maintenance costs. Coupled with AMSC Windtec’s design engineering expertise, the SeaTitan wind turbine also represents a path forward to achieving power ratings beyond the 10MW range.
SeaTitan, AMSC Windtec and Amperium are registered trademarks of AMSC.
Biography of the Author
Martin Fischer holds a Master of Science degree in Electrical Engineering from the Delft University of Technology in the Netherlands. He joined Windtec GmbH in September 1995 as Project Manager, Electrical Power Systems. (AMSC acquired Windtec GmbH in early 2007 forming its wholly owned AMSC Windtec subsidiary.) Fischer has been promoted to multiple positions since then. Most recently in 2008 and 2009 respectively, he was promoted to the positions of Managing Director, AMSC Windtec GmbH, and to his current position of Vice President, American Superconductor and General Manager of AMSC Windtec.{/access}
