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point of view, which directly affects the COE of an offshore plant. Advanced
means of control for handling grid-faults and low/zero-voltage ride through as
well as modular converter topologies that enable part-load/full-load operation
and optimization of ratings of the protection equipments such as circuit-breakers
along converter system need to be studied.
6 Other noteworthy innovations and improvements in technology
This section describes other key improvements that need to be achieved by the
offshore wind industry.
6.1 Assembly-line procedures
Unlike today's construction method, i.e. building unique one-of structures, the
future offshore projects will utilize assembly-line procedures to maximize cost
control in a mass production manner.
6.2 System design of rotor with drivetrain
Current commercial wind turbines utilize a three-blade confi guration. However,
two-blade designs which incorporate alternative hub structures may see a rise in
popularity because they allow turbines to reach higher rotor speed without visual or
noise constraints. Upwind confi guration might be preferred as it allows less dynamic
loads and has less rhythmic noise effects. Detailed investigations need to be carried
out on the blade defl ections and resonant modes under turbulent wind loading.
The WindPACT rotor study [18] was designed to explore many of these con-
fi gurations and attempt to determine their impact on overall turbine operation and
COE. The study has found that several loads in the fi nal two-bladed downwind
machine were higher than the corresponding loads in the baseline design. The
downwind two-bladed rotors also experience strong harmonic loading from the
tower shadow, which may excite natural frequencies. In the future offshore wind
projects detailed investigations need to be carried out on the relative advantages
and disadvantages of a two-bladed upwind with the corresponding three-bladed
version. The real benefi t of two-bladed design with unconstrained tip speed is
simplifi ed gearbox and more optimal direct-drive drive train. Preliminary studies
conducted by GE Global Research Center indicate that the rated speed of the wind
turbine has a large impact on the direct-drive cost. Considering aerodynamic power
only, the rated speed for a two-bladed turbine could be up to 30% higher than a
three-bladed turbine. In which case a direct-drive drive train for a two-bladed tur-
bine rated at 19.1 rpm would cost substantially less than one for a three-bladed
turbine rated at 11.7 rpm for a 5 MW system. However, energy capture will likely
to be less than an equivalent three-bladed wind turbine of the same diameter and
hub loading needs to be investigated as both tower and hub will require reinforce-
ment due to the two per rev loads. The suggestion in the WindPACT study to
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