Design and development of megawatt wind turbines - Wind Power Generation and Wind Turbine Design - page 244

4.6.4 Grid transient response
WT grid transient response relates to the operation control and protection of the
transmission and distribution networks, interconnects, generators and loads. This
is a very broad topic that has a number of specifi c points to consider from the
WTG perspective. These include the fundamental frequency response and protec-
tion of the transmission and distribution system to faults that are also based on grid
transients. The WT and the WPP must be able to absorb voltage spikes caused by
lightning or switching events. This is addressed with proper grounding, overvoltage
and lightning protection of the equipment.
4.7 Siting
There are many considerations when deciding where to site a WPP. Installation for
fl at terrain will often provide more favourable wind conditions and project eco-
nomics, while irregular or diffi cult terrain has more diffi cult WT placement and
increased installation cost. Turbine local geotechnical conditions are key when
designing WT foundations. The amount of energy produced for a given project
site is vital, but in many cases, more important are the regional electricity demand
and pricing structures that will determine the overall WPP profi tability. Land use,
environmental regulations and permitting is the key when siting the individual
WTs, and accounting for these requirements early in the new product development
cycle will avoid costly miss-steps during production application.
4.7.1 Site-specifi c loads analysis
Turbines are often designed to one of the IEC TCs [13]. Specifi c sites may require
more detailed analyses to ensure design adequacy. Some permitting agencies may
require analyses certifi ed by a licensed professional engineer for a specifi c turbine
applied to the actual site conditions.
4.7.2 Foundations
Foundations are a crucial integral part of the overall MW WT design. They must
account for the highly variable geotechnical conditions encountered in normal
practice without adding unnecessary base cost. Foundations affect the natural fre-
quency of the overall WT design. Many OEMs chose not to include the foundation
in their scope of supply, but this does not mean that the foundation design can be
ignored from the overall turbine design (Figs 37 and 38).
Figure 39 aggregates the major components of WTs into a single average tech-
nology trend derived from the 10-turbine analysis group. Against this backdrop the
nominal foundation mass and combined WT and foundation mass trends are plot-
ted with increasing WT size. The mass for some known foundations track reason-
ably well with the calculated “foundation only” trend. For a 10 MW machine these
results project nearly 6000 tonnes for a monolithic foundation. However, a design
goal of 4000 tonnes or below should be possible, especially considering numbers
of smaller individual foundations supporting a multi-leg tower structure instead of
a monolithic foundation. From Fig. 39, a good fi rst estimate for the monolithic