Power Engineering

Superconducting Generator Under Development

By Steve Blankinship, Associate Editor


Oak Ridge National Laboratory's Bill Schwenterly stands next to the 1 MVA single phase superconducting transformer produced by ORNL with Waukesha Electric Systems and IGC-SuperPower. Photo courtesy of Oak Ridge National Laboratory.
Click here to enlarge image

A team led by General Electric Corporate Research and Development proposes to produce a 100 MVA superconducting generator in less than four years. The proposal is one of two high temperature superconductivity projects to receive new funding by the Department of Energy (DOE) aimed specifically at power generation. The other power generation proposal receiving DOE funding is for a superconducting flywheel system. The remaining five projects would have applications for transmission and distribution and for the chemical and medical industries.

The superconducting generator proposal would receive DOE funding totaling about $12 million. Other team members include the New York State Energy Research and Development Authority, PG&E National Energy Group, American Electric Power, Praxair Specialty Ceramics, and Oak Ridge National Laboratory in Tennessee. The proposed generator is intended to have improved efficiency, higher capacity, and improved reactive power capability compared to conventional technology. The award calls for additional private funding of $14 million.

Traditional metallic superconductors made of NbTi or Nb3Sn must be operated in liquid helium at about 4 K (-452 F), not far above absolute zero (-459 F). When used within the context of superconductivity, the term "high temperature" can be misleading to the layman. It still means very cold, in the vicinity of liquid nitrogen (77 K or -321 F). Maintaining temperatures hovering near absolute zero that are needed to achieve total lack of resistance to electric current consumes as much or more energy than superconductivity saves.

But the breakthrough discovery in 1986 of a ceramic compound that became superconducting at far higher temperatures (30 K) ushered in the era of high temperature superconductivity. It was later discovered that with the addition of lead, some oxide superconductors could conduct electricity with almost no electrical resistance at a temperature as high as 110 K. Under highly controlled conditions including high pressure, the limit has been raised to 138 K measured on a molecule of mercury.

Heike Kamerlingh Onnes, who in 1908 had become the first person to liquefy helium, discovered superconductivity in 1911. The liquid helium gave him the ability to expose various materials to ultra-cold temperatures (4 K), and in the process, discovered that electrical resistance virtually disappears at temperatures approaching absolute zero.

Applications of superconductivity started in the 1960s when it became clear that strong magnetic fields could be created in large volumes using the zero resistance properties of superconducting wires. MRI imaging systems, the large particle accelerator at places like Fermilab, and the widespread use of superconducting magnets in scientific instrumentation are examples of the maturing of this technology during the 1970s and 1980s.

Building on its extensive research into HTS materials and generators, GE has proposed a program to move the technology to full commercialization in three and a half years. In addition to producing major improvements in the efficiency and reactive power capability of new generators, the program intends to develop capability to retrofit the new technology into existing generators.

While retaining the stator design that is today's industry standard, the proposed generator will introduce a new rotor design and HTS winding which GE says will be unprecedented in its simplicity. GE says recent progress made by HTS wire manufacturers have helped pave the way for the development of an HTS generator with the potential for competitive cost, high reliability, rapid market introduction and a high probability of acceptance by the power industry.

A paradoxical complication associated with designing superconducting generators is the fact that generators require a magnetic field to produce electricity, but the presence of a magnetic field degrades the performance of the HTS wires. Because the wires GE will use are superconducting at about 110 K with no applied magnetic field, the generator will be designed to operate at temperatures between 20 and 77 K in order to achieve desired currents in the HTS wires.

"We believe the timing is right for the introduction of HTS technology into power generation equipment, and that we are presented with a unique opportunity to accomplish this technology milestone in the U.S.," said Jon Ebacher, vice president of power generation technology for GE Power Systems.

Concept designs indicate that new superconducting generators can achieve significant efficiency gains that translate into life cycle energy savings of approximately $500,000 over the life of a 100 MVA generator, and up to $10 million for a 1200 MVA unit. This drastic reduction in generator losses will increase overall power plant energy efficiency, creating the potential for annual energy savings of several billion kilowatt hours while also leading to significant annual reductions of CO2 emissions.

The proposed program will include the production and testing of a 1.5 MVA proof-of-concept model for the rotor, cryorefrigeration and HTS subsystems. Those results will be scaled to a 100 MVA prototype generator that will be fully tested under load.

American Superconductor will be the primary HTS wire supplier. Advanced refrigeration components will be developed in cooperation with Sumitomo Heavy Industries and Praxair. The National High Magnetic Field Laboratory at Florida State University and the Oak Ridge National Laboratory will conduct special studies as part of the development program.

The second superconductivity power generation technology receiving DOE funding is a superconducting flywheel power risk management system submitted by a team led by Boeing Phantom Works. Other team members are Praxair Specialty Ceramics, Ashman Technologies, Mesoscopic Devices, Boulder Cryogenics, Southern California Edison, and Argonne National Laboratory.

The 35 kWh system uses low loss superconducting bearings to provide an efficient device that manages both cost and reliability risks. It has potential applications for zero-emission, silent, efficient, electricity generation (when charged) in distributed energy systems as well as for power quality control at end-user facilities. DOE funding is about $7.3 million and private funding is $7.4 million.

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