Technical criteria for wind farm power stations connected to the transmission system - Wind Power Integration: Connection and System Operational Aspects - page 281

within statutory limits as specified under CC 5.4. A WFPS
shall continuously control voltage at the Connection Point
within its Reactive Power capability limits. If when set in
Power Factor or Reactive Power control the voltage exceeds
the specified band, the Power Factor control or Reactive
Power control must revert to Voltage Control . The control of
voltage, Power Factor and Reactive Power Dispatch must
ensure stable operation over the entire operating range of the
Controllable WFPS . In the event that action by the Con-
trollable WFPS Active Power and Reactive Power control
functions is unable to achieve a sustained voltage within the
statutory limits, the Controllable WFPS must detect this and
immediately shut down.

(b) Other Voltage Control schemes may be possible but

agreement between the Generator and the TSO must be
reached at the application stage for Connection about their
suitability. If Voltage Control is implemented for the
Controllable WFPS , rather than on individual Generating
Units , then the range of Power Factor available should not
be less than that which would have been available if Voltage
Control had been on individual Generating Units . Voltage
Control schemes based upon Equipment located on the
TSO's side of the Connection Point may be possible, but
such schemes are considered special, and the details,
responsibilities and cost schedule must be agreed between
the Generator and the TSO in the Connection Agreement
or other agreement.

(c) In order to deal with Controllable WFPSs inducing power

fluctuations, an additional control loop must be provided by
the Generator to ensure that the Generating Unit control
system, wind turbulence or other factors in the Controllable
WFPS cannot produce power oscillations between 0.25 Hz
and 2 Hz. It should be designed and operated to ensure that
the total peak-to-peak MW oscillation within this Fre-
quency range is less than 1% of the Registered Capacity of
the Controllable WFPS .

CC.S2.5.4

The TSO may specify the requirement for tap changing facilities
on the Site transformer(s) for WFPSs . Where a suitable Site
transformer does not exist, the requirement may be applied to
individual Wind Turbine Generator Transformers . The tap-
ping range and the step sizes will then be specified in the
respective Connection Agreement or other agreements.