Grid Integration and Power Quality - Wind Energy Systems for Electric Power Generation - page 145

7.2 Standard Requirements

7.2.1 Safety-Relevant Set Values

Systems with asynchronous or synchronous generators must be equipped with pro-
tective devices, with set values to allow adjustment of lower and upper limits of
voltage and frequency. Recommended tripping values are given as follows (50 Hz
rated frequency assumed):

Limit Tripping value

Voltage decrease 0 , 70 U N 0 , 8 U N

Voltage increase 1 , 15 U N 1 , 06 U N

Frequency decrease 48 Hz 49,5 Hz

Frequency increase 52 Hz 50,5 Hz

7.2.2 Reactive Power Compensation

The active factor cos , in literature often called the power factor, should be ad-

justed according to agreement. Usual recommendations require values between 0,9
cap. bis 0,8 ind. Use of capacitor banks is the conventional way to compensate in-
ductive load. In grids where audio-frequency transmission devices are installed, the
WES frequency response curve must be adapted by an appropriate inductive choke
(see 7.6.3).
To obtain a specified cos

ϕ

value at the point of connection (POC), it may be nec-
essary to provide a significantly higher reactive power in the wind park. Consider
the example in Fig. 7.4 of a wind park with rated power 50 MW. A cos

ϕ

of 0,9 (ca-
pacitive) at the POC on the 110 kV HV side means that a 36,2 Mvar reactive power
must be supplied on the wind turbine generator level, due to the inductive (magne-
tizing) currents for the LV/MV and MV/HV transformers, respectively. Capacitive
contributions from assumed cable connections are only of minor influence.

ϕ

7.2.3 Lightning Protection

It is necessary to provide wind turbines with lightning protection equipment. To this
end non-metal blade tips are carrying interception apparatus, from where lightning
currents are conducted to the hub by means of appropriate connectors. From the hub
the lightning current is conducted to the metal tower construction and from there to
the earthing system.
Since these measures are not sufficient to protect the electric and electronic sys-
tems, lightning protection zones (LPZ) are defined to create coordinated EMC-
condition areas, see example in Fig. 7.5. The complete WES is situated in LPZ 0.