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GE has successfully tested a high temperature superconducting power generation device that could deliver significant advantages inefficiency as well as size, mass and weight reductions compared with conventional machines.
The Hydrogenie power generator offers a viable way of producing large amounts of electricity from renewable resources using superconductors running at relatively high temperatures. The technology makes use of superconductors instead of copper for the rotor windings on the motor, operating at 43 Kelvin, or -230°C. GE said that tests carried out at its Rugby facility in the UK were carried out at well beyond the full rated load of 1.7MW spinning at 214 rpm, meeting expectations and design predictions.
Until recently, superconductivity could only be achieved at around 4K (-269°C). But high temperature superconductors (HTS) exhibit the phenomenon at much higher temperatures. GE said that such machines would need less complex insulation systems and less powerful cooling than used on devices such as medical MRI magnets.
“This technology is a true breakthrough,” said Martin Ingles, Hydrogenie project manager at GE Power Conversion. “It could radically improve the efficiency of equipment producing electricity from water and wind and may also be suitable for further applications down the road.”
The latest superconductors are made by depositing a 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. The greatest benefits in terms of size and mass reduction will be 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 said that it had 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,”said Ingles. “Except that our rotisserie is 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.
GE says its latest demonstrator includes 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 1.7MW 214 rpm HTS generator as part of an EU funded project that ran between 2006 and 2010.
The Hydrogenie team will continue to develop superconducting machines in areas such as the upgrading of older run-of-river power plants and 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, helping to reduce the cost for the tower itself and its foundations, said GE. 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.