Grid Integration and Power Quality - Wind Energy Systems for Electric Power Generation - page 159

Fig. 7.16 Model of capacitive compensator with series inductor

In the example, for a required p = 0 , 07 and given f 1 = 50 Hz, the inductor must
be designed for L

10 − 6 / C (in H when C is in F). The frequency response
curves of the impedance referred to the capacitor impedance at

≥ 70 , 92 ·

ω 1 , with and without
series inductor are shown in Fig. 7.16; in the example the signal to grid frequency
ratio is ω 1 = 15. Note that in the model resistive components are neglected, and

inductive/capacitive reactances are of positive/negative value.

ω s /

7.5 Noise Emission

7.5.1 General

Sources of sound produced by mechanical systems such as wind turbines are:

- aerodynamic noise,
- magnetic noise,
- noise of bearings and slip-ring/brush contacts (if applicable).

These sources contribute in different magnitudes and frequencies to the sound emis-
sion.
The physical quantities most used in acoustics are expressed in logarithmic
notation:

Sound pressure level L p = 20 · lg( p / p o ) , dB

10 − 5 , Pa

with the reference p o = 2 ·

Sound power level L w = 10 · lg( P / P o ) , dB

10 − 12 W with the reference P o = 1 ·

The sound power from a source can be calculated from sound pressure levels,
measured on a suitably defined surface, e.g. a half-sphere, put up above the ma-
chine under test. Test conditions and averaging procedure are specified in relevant
standards. Using the measuring surface S , the relevant equation is:

S o = 1m 2

L w = L p + 10 lg( S / S o )

where