Design and development of megawatt wind turbines - Wind Power Generation and Wind Turbine Design - page 218

as a function of the WT rated net power. On a cost per kg basis, the converter,
main bearing and pitch systems are the most expensive. At the other end of the
spectrum, the partial hub, tower, and foundation are the least expensive. The foun-
dation is considerably less expensive than any other component on a $/kg basis.
However, the foundation is by far the heaviest component - typically two to three
times the mass of the WT itself.
Accurate cost data for the actual component technologies under consideration
are crucial for making proper assessments in the value analysis methodology. The
best way to ensure the accuracy of this information is for the OEM's Sourcing
Department to provide these fi gures (normalized to eliminate the largest varia-
tions) and for routines to be established to store the data for the value analysis
program to automatically use the latest information.

4.3.2 Power performance calculations
The method used to calculate the performance of a WT is to use a power curve
together with the annualized wind distribution for a given project location. The
power curve plots the power produced by the WT as a function of wind speed. The
power production quoted by an OEM is typically given at either the low voltage
(LV) or high voltage (HV) terminals of the medium voltage (MV) transformer
depending on the supply scope for the customer. Losses from cables and converter
are more commonly included in the turbine losses along with other conversion
losses within the turbine OEM scope of supply. Sometimes an OEM may quote
output at the generator terminals, and additional losses for the LV cables, con-
verter, MV transformer, MV cables and wind plant collection and substation must
be properly accounted. The end goal is to ensure the accurate determination of
electricity production (i.e. “at the meter”) used to compute revenue.

4.3.3 Acoustics and vibrations
WT acoustic and vibration design falls into three major categories:

￿ WT rotor system acoustics

￿ Machinery structure-borne noise

￿ Machinery and airborne noise

The rotor blade and operating controls impact the rotor system acoustics. The
direct acoustic pressure radiation and the forces that drive vibrations in the machin-
ery structure contribute to airborne noise emission. Noise is an important factor
during the conceptual design of most new MW turbines, particularly for onshore
machines targeted for land-constrained markets. Today's 1

− 3 MW turbines are

designed to emit maximum noise in the range of 102 − 106 dBA at HH. This pro-

duces actual measurements of 35 400 m from the tower

base at ground level, similar to the background sound experienced in a bedroom at
night or quiet conversation around the dinner table.

− 45 dBA observed 300 −

4.3.4 Thermal management
Electrical components and sub-components housed in close quarters can quickly
lead to over-temperature and unnecessary production loss. MW WTs are subjected