Direct drive superconducting wind generators - Wind Power Generation and Wind Turbine Design - page 328

As the performance of the HTS wire improves over the lifetime of the product,
it is expected that the design will evolve. The improvement in wire performance
could be used to increase in the operating temperature of the HTS coils, possibly
to as high as 65 K, thereby considerably reducing the cooling power required.
Alternatively the improvement in performance could be used to reduce the amount
of HTS wire by operating at a higher current, although this change would require
careful mechanical analysis of any resulting increase in forces on the coils.
Further developments are also expected in cryocooler technology. Pulse tube
cooler, with no cold moving parts, are beginning to reach the power levels at the
temperatures required in the HTS wind generator. Pulse tube will offer cooler with
less maintenance and greater reliability, with the potential to locate the entire cryo-
genic cooling system on the rotor, removing the need to transfer cold fl uid through
a rotating seal.
8 Other HTS wind generator projects
In 2007 AMSC announced the start of a $6.8 million project to design a 10 MW
class HTS direct drive wind generator. AMSC are working in partnership with
TECO Westinghouse and with partial funding from NIST. The 30-month project,
like the Converteam project, is also targeting the offshore wind power market. The
project scope is similar to the concept and full size detailed design stages in the
Converteam project.
A design study examining HTS direct drive wind generators at ratings of 2 MW,
21 rpm and 8 MW, 12 rpm was carried out in Japan [41]. Many conclusions were
similar to those in the Converteam study. The HTS generator designs were reported
as 1/3 to 2/3 of the size on non-superconducting machines, with effi ciency gains
of 1% at full load to 10% at part load. The optimum pole number was found to be
between 16 and 20.
9 Conclusions
The new generation of HTS wire coming to the market is predicted to be available
in volume at a cost low enough to make HTS motors and generators cost competi-
tive with conventional copper and PMGs. The signifi cant size and mass advan-
tages make direct drive HTS generators an enabling technology for the very large
10 MW class turbines that will help reduce the cost of offshore wind energy.
Leading players have substantial developments completed and in demonstra-
tion, and wind power system developers and operators are being invited to appreci-
ate the great potential in superconducting generators.
R eferences
[1] Global Wind 2007 Report; Global Wind Energy Council (GWEC), www.
gwec.net