Environmental Engineering Reference
In-Depth Information
Chapter 7
Grid Integration and Power Quality
7.1 Basics of Grid Connection
7.1.1 General
The power curve of a wind turbine is the basic characteristic to describe its capabil-
ity, see 2.4.3. Besides, the standards require the following operational actions to be
tested:
Paralleling at cut-in wind speed,
Paralleling at rated wind speed,
Switching between generator stages, if applicable,
Switching of power factor compensation devices,
Service tripping from rated power,
Emergency tripping from rated power,
Unsymmetrical grid faults in each of the phases.
In order to obtain permission to parallel a wind energy system or a wind park to
the grid, the transmission systems operators (TSO) require the declaration of tech-
nical properties. A main requirement is the limitation of voltage deviation caused
by the wind systems at the point of common connection (PCC), for which 2% of
nominal voltage is a commonly established limit. The short-circuit power at PCC
is the crucial value for the permissible installed power ratings. Conventional reg-
ulations establish limits of frequency and voltage for normal operation. In the last
years further-going guidelines were published which require wind parks to behave
similar to conventional power stations regarding power factor, active power supply
at frequency deviation and short-circuit capability in case of grid faults. Eventually
harmonic and flicker limitation are power quality requirements.
7.1.2 Permissible Power Ratings for Grid Connection
WES generators are rated for low voltage, in Europe for 690 V or, less frequent,
for 400 V. A machine transformer transforms the power to medium voltage level,
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