Operation of power systems - Wind Power Integration: Connection and System Operational Aspects - page 195

control. Alternatively, points B and C could be coincident such that a contribution
is provided. Within this deadband region, the wind turbine output is limited to a
defined fraction of the available wind resource, following the methods described
earlier. Hence, should the frequency fall below point B, the wind turbine is required
to increase output (a low frequency response) following a governor droop char-
acteristic (default 4%), while for a frequency below point A the active power
response should be maximised, irrespective of the governor droop setting. At sys-
tem frequencies above point C, the power output should gradually be reduced
(a high frequency response), again following a governor droop characteristic
(default 4%), until at point D the power output is reduced to the minimum operating
level. For frequencies beyond f E the wind turbines should disconnect.
At present, for many utilities, points A-D are set at 100 per cent of actual power,
i.e. neither low or high frequency reserve is provided and the wind turbine does not
participate in load-frequency regulation. Instead, only the capability of providing a
frequency response is required. In the future, however, as wind penetration levels
increase, one or indeed all of the three ancillary services will be required. Instead, at
present, only the capability (rather than the actuality) of supplying these services is
required. In Great Britain, from January 2006, all new wind turbines must be capable
of contributing to frequency control. Similarly, in Ireland, while newer wind turbines
are required to fulfil the defined power and frequency ranges listed in Table 5.1, the
normal requirements are that P A ¼ P B ¼ P C ¼ 100 per cent, with some, but not all,
wind farms presenting a high frequency droop above 50.2 Hz, and a disconnection
frequency of 50.8 Hz. In Germany, wind turbines are required to provide a high
frequency response (region C-D in Figure 5.31). In E.ON, above a system frequency
of 50.5-51.5 Hz, turbines should possess a 40 per cent droop characteristic (see
Figure 5.5 and Table 4.4). The capability should also exist to reduce output at a rate
of 5 per cent of rated output per second above 50.5 Hz. When the frequency has
stabilised, the restoration ramp rate must not exceed 10 per cent of the rated output
per minute.
Individual TSOs will define the locations of points A-D differently, and
their exact position may depend on wind farm location and/or system conditions,
e.g. high wind/low demand versus low wind/high demand. For example, SONI
(N. Ireland) utilises a similar capability chart (Figure 5.31) to that for EirGrid, with

Table 5.1 EirGrid load-frequency control requirements

System frequency (Hz) Power output (% available power)

WF > 5MW

f A 47-49.5 P A 50-100

f B 49.5-50 P B 15-100

f C 50-50.5 P C 15-100

f D 50.5-52.0 P D 15-100

f E 50.5-52.0 P E 0