Loadbearing structures and detailed design - Concrete Structures for Wind Turbines - page 126

safely and optimally, that is efficiently, without malfunctions. The safety system has to
guarantee that in the event of a malfunction, the offshore wind turbine can be
transferred to a fail-safe condition [11].
The range of normal operating conditions embraces rotational speeds between the
“minimum” and “maximum” rotor r.p.m.(n 1 n n 3 ). The “rated speed” (n r )is
established at the “rated wind speed” (V r ). Once the “cut-out speed” (n 4 ) is reached,
the wind turbine is shut down by the control system. Upon reaching the “activation
speed” (n A ), the safety system must shut down the turbine immediately. The
“maximum overspeed” (n max ) may never be exceeded. Figure 4.12 shows the relation-
ships between the various rotor and wind speeds.
The “rated power” (L r ) is the maximum continuous electrical power (effective power)
produced at the output terminals of the offshore wind turbine. Reaching the “over-
power” (L T ) triggers an intervention by the control system. Once the “activation power”
(L A ) is reached, the wind turbine is shut down immediately by the safety system.
The “cut-in wind speed” (V in ) is the lowest wind speed at hub height (normal wind
speed model, NWP) at which the offshore wind turbine starts to produce power. The
“rated wind speed” (V r ) is the lowest average wind speed at hub height at which the
offshore wind turbine produces its “rated power” (L r ). The “cut-out wind speed” (V out )
is the maximum wind speed at hub height at which the wind turbine must be shut down.
The turbine must be shut down immediately if the “short-term cut-out wind speed”
(V A ) is exceeded only momentarily.
Fig. 4.12 Range of normal operating conditions [11] 2.2.2.5