Environmental Engineering Reference
In-Depth Information
during normal operation or extreme events in order to estimated the severity of
each fault on the turbine structure.
Bachynski et al. [
11
] studied the dynamic response of the floating wind turbine
subject to three different faults, the first fault is the blade seize where the pitch
actuator of one blade is blocked, the second one is the blade seize, recognized by
the controller and followed by shutdown (grid disconnection and aerodynamic
braking), and the last fault is the grid loss followed by shutdown. The faults are
assumed to be detected within a short period of the fault event. A utility-scale wind
turbine mounted on different floating platforms are used, and platform motions in
addition to the structural loading caused by fault events are compared to loads
encountered during normal operation and during selected extreme weather con-
ditions. The main results of this study indicate that the platform motions and
mooring loads are dominated by the extreme wave conditions and hardly affected
by the faults, while the tower bending moments are more affected by fault con-
ditions; moreover, they found that blade bending loads in flap-wise direction are
sensitive to the imbalance while in edge-wise direction are sensitive to shutdown.
This study, though it is limited to the actuator seize and the shutdown process
directly after it, gives a good idea about the floating system dynamic response to
the fault-induced imbalance in the rotor and its effects on the platform motions.
In another study, Etemaddar et al. [
12
] investigated the effect of the magnitude
of different faults on a land-based wind turbine where the faults are assumed to
proceed through the simulation undetected. While Bachynski et al. used a col-
lective blade pitch controller, Etemaddar et al. used an individual blade pitch
controller in their work. The sensitivity of each control method to faults depends
on the fault origin and type which should be taken into account when comparing
the results. The presented results by Etemaddar et al. indicate that the individual
blade pitch control can reduce the penalty term of pitch sensor and pitch actuator
faults on output power and thrust load; however, the main effect of pitch sensor
fault is on the shaft main bearing bending loads. Moreover, the study did not
mention the effect of the faults on the tower loading.
Nevertheless, modern wind turbine control systems are equipped with condition
monitoring and fault detection and isolation systems, once the fault is detected and
isolated the common approach is to deploy the condition monitoring system and
shut down the turbine. However, not all faults share the same severity on the
turbine, some faults change the characteristics of a component such as the slower
performance of the pitching system, this change in the performance can be adapted
if the turbine is equipped with a fault-tolerant control system, or it might be just
monitored without engaging any preventive procedure in case of well-known
effects of such fault. Most condition monitoring systems and fault detection sys-
tems in wind turbines are signal-based, which makes fault detection and isolation
more challenging knowing that different faults may show similar signals. This last
point draws particular attention to the undetected occurring faults in wind turbines
and their effects on its structure. This chapter examines the effects of undetected
occurring pitch system faults on floating wind turbines. These faults lead to an
imbalance in the aerodynamic loading over the rotor disk, which will affect not
