Environmental Engineering Reference
In-Depth Information
The two shaded regions shown in Fig. 34 are for DD and geared (i.e. high speed)
type generators. The lower bound represents the expected mass assuming historical
technology progress with increasing MW rating, and the upper bound is for straight
scaling of today's technologies. The shaded symbols at the 10 MW rating refl ect
recent public announcements and are unproven at this time. With respect to Fig. 34:
DD generators using today's conventional wire-wound construction are more
than fi ve times heavier than the geared generator alone.
The linear fi ts projected from industry mass data form the bottom edge of the
shaded ranges. These mass trends should be achievable for continued technol-
ogy advancements with increased MW rating (i.e. new technology is needed to
avoid mass increase for straight scaling of today's technology originally
developed at lower MW ratings).
When the mass for the gearbox is included with the geared generator (a
fairer comparison), the DD and geared confi guration have the same order of
magnitude mass.
The geared confi guration (i.e. GB + Gen) is lighter than DD below 5 MW and
heavier above 5 MW.
For a 10-MW size WT, an advanced DD using a projection of technology
improvement from today's wire wound know-how, is at fi rst a reasonable choice
of about 150 tonnes. High temperature superconducting (HTS) DD generators
(shaded circular symbols) are reported to be on the order of 20% lighter and
advanced superconducting (shaded triangular symbols) are reported to be 50%
lighter still, bringing them to almost the same mass as the best high-speed
generator alone (i.e. without the GB accounted).
4.5.2 Turbine - electrical transformer
Should the electrical transformer be located up-tower or down-tower? The
up-tower advantage is higher voltage and lower current for a given power level
which translates into lower cost (i.e. smaller diameter) cable in the tower. The
downside is that a higher voltage level results in more stringent design and envi-
ronmental health and safety (EHS) requirements. Many turbines today employ
relatively LV (e.g. 575
690 V) between the generator and a MV transformer.
A down-tower transformer can be located inside the tower or installed on a con-
crete pad just outside the base of the tower. The vast majority of MW WTs installed
in the U.S. utilize the later design.
MV/LV transformers are a key component of wind plant. Traditionally WT and
MV/LV transformers have been protected using fused switches on and MV side and
circuit breakers on the LV side. This solution has worked well with rated
powers up to around 1.5 MW. WT ratings have grown well above 2 MW and WT
distribution voltages up to 36 kV, normal for offshore, are now gaining interest for
onshore application. Switch solutions have reached their limit for these higher volt-
age levels due to the nominal current ratings of the available fuse elements. There
are advantages for using circuit breakers for the protection of MV/LV transformers.
The use of modern digital protection relays associated with circuit breakers have
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