GE's Power Conversion business (NYSE: GE) has taken an important step in testing a viable way of producing large amounts of electricity from renewable resources using superconductors running at relatively high temperatures.
The inner rotor of GE’s breakthrough high temperature superconducting technology, Hydrogenie. Running at 50 Kelvin the superconductive technology offers significant advantages in efficiency as well as size, mass and weight reductions compared with conventional machines.
(Photo: GE Power Conversion: GEPCPR148)
The company has successfully completed trials of Hydrogenie, a power generator incorporating ground breaking technologies that enable highly efficient production of electricity in a small space. Hydrogenie makes use of superconductors instead of copper for the rotor windings on the motor, operating at 43 Kelvin, or -230°C. It was tested late last year up to and well beyond its full rated load 1.7MW spinning at 214 rpm, and met expectations and design predictions. The tests were carried out at a GE Power Conversion facility in Rugby, England.
Until recently, superconductivity could only be achieved at around 4K (-269°C). But new “high temperature superconductors” (HTS) exhibit the phenomenon at much higher temperatures. Such machines will need less complex insulation systems and less powerful cooling than used hitherto on devices such as medical MRI magnets.
Latest superconductors are made by depositing a superconducting layer of ceramic onto a relatively cheap base metal. They have virtually no resistance to electrical current when cooled to very low temperatures, so windings can be made with wires having a cross section around 2% that of a conventional copper wire winding.
More windings can be fitted into electromagnet coils, resulting in a higher power magnet that is substantially smaller or lighter than before. Superconductivity offers significant advantages in efficiency, and significant weight reductions compared with conventional machines. The greatest benefits in terms of size and mass reduction are for applications where high torque machines are typically used, most likely as a direct drive application in installations such as wind turbines, ship propulsion or run-of-river hydro plants.
GE has overcome significant technical challenges relating to the cryogenic cooling and thermal insulation required to keep the superconductors at the required temperature. Extremely cold helium gas is piped through a rotating coupling into the machine rotor and then circulated around the individual coils. “It’s rather like trying to keep ice cubes frozen on a rotisserie in a very hot oven,” says Ingles. “Except that our rotisserie is rather high tech.”The rotor is located inside a vacuum, but still has some direct contact, via its shaft, with the outside world. This creates issues relating to the massive temperature differences along the shaft.
The machine incorporates a patented method for transferring torque from cold HTS coils to the machine rotor. Low resistance thermal joints and assemblies ensure that low cooling power is required to cool the coils. In fact, the machine demonstrates all of the technologies required to make HTS machines a commercial reality. GE’s Power Conversion business did much of the development of the Hydrogenie 1.7 MW 214 rpm HTS generator as part of the EU Framework Programme 6 funded project that ran between 2006 and 2010.
The successful completion of the Hydrogenie project will set the framework for continued research and development in the study of superconducting machines. One specific area that may potentially benefit in the future is the upgrading of older run-of-river power plants. Coupled with running the machine/turbine at variable speed the benefits could allow efficiency improvements of up to 12% at part load.
The technology building blocks developed as part of the project will also be used in other businesses where high torque and slow speed machines are in use. The most immediate areas of demand are in wind power generation and in marine propulsion.
A superconducting wind turbine generator may permit significant reductions of mass mounted on the tower, thus helping to reduce the cost for the tower itself and its foundations. Recent studies conducted for GE Power Conversion show that the lifetime energy saving for a superconducting wind turbine compared to a conventional machine could be as much as 20%, for offshore or desert machines above 10MW.
On ships, HTS technology combined with DC or variable AC systems can result in up to 4% fuel savings, while the reduced size of the motors will be attractive to naval architects leaving more space for payload or passengers.
Other partners in the EU Framework Programme 6 funded project, “Development and field testing of a compact HTS hydro power generator with reduced investment costs, lowered environmental impacts and strongly improved performance to reduce the price per KWh,” were: Zenergy Power; KEMA Nederland; Stirling Cryogenics & Refrigeration; Silesian University of Technology; Cobham CTS; E.On Wasserkraft.
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