Grid Integration and Power Quality - Wind Energy Systems for Electric Power Generation - page 147

The shielded nacelle, the steel- or steel-reinforced tower and the cable-conduit form
LZ 1. The electric control system is situated in the electro-magnetically shielded
LPZ 2. Passing from one lightning protection zone to another, protection devices
must be connected between the leads and the potential equalization bus.

7.3 System Operator Regulations

7.3.1 General

In view of the steady increase of WES installations, utilities have published addi-
tional regulations since 2001 [Eon03]. They require wind energy systems to con-
tribute to a stable grid operation, and act similar to a conventional power plant. This
means fault ride-through properties and the ability to supply reactive power in case
of short-circuits.
First, the protective set-value requirements as reported in 7.4.1 are increased:

Limit Tripping time

Voltage decrease 0 , 80 U N 3 ... 5 s

Voltage increase 1 , 10 U N < = 100 ms

Frequency decrease 47,5 Hz < = 200 ms

Frequency increase 51,5 Hz < = 200 ms

Other requirements are mentioned as follows:

• Starting from any operation point, the WES must be capable to reduce the power

supply to a specified maximum value without disconnection from the grid; at
least by 10% of rated power per minute.

• A wind park must be capable to operate at a power factor of between 0,975 ind.

and 0,975 cap.

• In case of frequency deviations between 47, 5 and 51,5 Hz automatic breaking

is not permissible; rather a specified power supply must be possible for a certain
time interval.

•

In case of grid faults with voltage sags no automatic breaking is permissible
within a specified terminal voltage/time diagram.

• In case of short-circuit the wind parks must be capable of contributing to the

short-circuit power for a certain time interval.

Active and reactive power are considered in the consumer (motor) coordinate sys-
tem, where active and reactive power are assigned to the quadrants as in Fig. 7.6.
The following example guidelines are all for 50 Hz grids.