Environmental Engineering Reference
In-Depth Information
The angular turn specifi ed by the designer provides the fi nishing tension and
results in fi nished inaccuracies of about 25
35%.
There has been huge progress in the past few years for pre-loading, locking and
inspecting fasteners used in large WT design. Companies such as ITH-GmbH [30]
offer a complete suite of bolt tensioning solutions using more accurate stretch
type-tensioning tools. Bolt stretching processes are used for clamp-length ratio of
1:3 or more and for pre-tensioning large size bolts (e.g. M24 and greater). The
clamp-length ratio is the ratio of the bolt diameter to the clamp length of the joint.
Stretching procedures are best when (1) a high degree of accuracy (5
−
10%) is
required or (2) when several bolts have to be pre-tensioned simultaneously.
Future large turbine structural bolted connection technology will probably not
be too much different from today.
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4.4.17 Fire detection system
Future large turbine fi re detection technology will probably not change much
from today, with the exception of better integration into the turbine control sys-
tem such that predictive capability may be able to prevent a fi re from happening
to begin with.
4.5 Electrical
The electric power system can be classifi ed into two main categories; (1) the tur-
bine including the MV transformer and (2) the collection system and substation
to the point of delivery to the grid. Future large turbine electrical system technol-
ogy may incorporate elements of high voltage DC (HVDC) collection, centralized
power conditioning and superconducting or quantum wire electricity transmission
(for the right cost).
4.5.1 Turbine - generator and converter
The generator is where electricity production and the customer's revenue stream
begin. As such, doing this effi ciently for a justifi able cost is of prime importance
and must be reliable and sustainable over the lifetime of the turbine.
Figure 33 presents the mass for the three main elements of today's typical WT
power system that operates at relatively LV level (i.e. 575
690 VAC) between the
up-tower generator and the down-tower power conditioning and MV step-up trans-
former. The mass for these components are in the same order of magnitude, with
the LV cable mass roughly 2/3 of the mass of the generator and converter. The
converter mass can vary widely depending on the particular converter topology,
which can have a big impact on the amount of reactor mass required (reactor mass
being copper and steel, and often dominating total mass).
Of all the 10-turbine analysis group component mass characteristics plotted as
a function of net rated power, the generator is the only one to exhibit a negative
squared term for the curve fi t (i.e. diminishing mass increase for larger sizes). The
10-turbine analysis group varies gearbox ratio in order to hold the generator shaft
speed constant. This is consistent with increasing generator torque rating and the
corresponding electrical loading of the machine. This loading (electric current per
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