Environmental Engineering Reference
In-Depth Information
disappears. Furthermore, the effect of constant output power as control strategy is
more pronounced in the higher part of the full load region, where the positive or
negative bias leads to similar change in rotor speed and generator torque compared
to the normal operating conditions.
11.5.3 Blade Pitch Gain Fault
The gain fault does not affect the blades root moments, neither the tower fore-aft
and side-side moments. However, the fault effect is clear on the tower torsional
moment and the LSS moments DEL which increase with the mean wind speed and
the absolute magnitude of the fault (Fig.
11.12
). The reduced effects of the fault on
the EC1 are due to the switching between the operating regions. The effect
increases with the wind speed as the measured pitch angle will increase for higher
wind speeds, and the gain fault is becoming bigger. Therefore, the same gain fault
for small measured pitch angles (such as in EC1 and EC2) does not produce higher
effect on the structural response even though the aerodynamic thrust over the rotor
disk is at its maximum value at EC1.
The gain fault also introduces minor effects on the RMS power error, and the
platform motions. The effect seen by the bias fault at EC1 and EC2 in the gen-
erator power error and platform roll motion is not present here as there is no delay
in switching between the operating regions, in addition to that, at EC1 the mea-
sured pitch angle is small, which means small fault due to the change in pitch
sensor gain, and the resulting rotor imbalance is marginal (Fig.
11.13
).
11.5.4 Actuator Performance Degradation
Only the third magnitude M3 of the performance degradation fault has an effect
on turbine structure as it has slower response compared to the other magnitudes
1.3
1.3
1.3
1.2
1.2
1.2
1.1
1.1
1.1
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
EC1 EC2 EC3 EC4 EC5
EC1 EC2 EC3 EC4 EC5
EC1 EC2 EC3 EC4 EC5
M1
M2
M3
M4
Fig. 11.12 Fault: blade pitch sensor gain. Normalized DEL (NDEL) of tower torsional and LSS
moments. DEL increases with the wind speed and the absolute value of the gain error
