Environmental Engineering Reference
In-Depth Information
The incipient faults are introduced gradually to the system between simulation
time TOF and TOF + T
i
where TOF is the time step at which the fault is intro-
duced, and T
i
is the time duration at which the fault propagates from the fault-free
case to the faulty condition. The value of T
i
does not represent the actual value as
some faults, e.g., the pitch sensor bias, will develop slowly such as ±1deg/month
which could be considered as zero rate compared to the simulation time of 10 min.
The time duration T
i
is used to increase the development rate of the fault, which
will not affect the results, as most of the important effects of the faults are
introduced after the fault reaches the set magnitude. T
i
= 50 s is considered in all
simulations of incipient faults and this time is considered within the recorded
simulation time.
In addition to the previously illustrated faulty cases with their magnitudes, the
fault-free system is simulated at the above-mentioned environmental conditions,
these fault-free cases are used as reference to estimate the severity of the fault on
the normal operation of the turbine.
11.5 Results Discussion and Analysis
11.5.1 Performance Indices
To quantify the effects of each fault at each operating condition and at each fault
magnitude, a set of performance indices are used to monitor the key components of
the wind turbine. The performance indices involve two types of calculations, the
root mean square (RMS) and the damage equivalent load (DEL) values. The cal-
culation of the DEL requires using the rain flow counting algorithm [
21
], the fatigue
DEL is calculated at a reference frequency of 1 Hz. All calculated indices are
normalized to their corresponding fault-free values, then averaged over all simu-
lations. A brief description of each performance index is given in the following
• Generator power error: the normalized RMS is calculated for the generator
power error in order to study the fault effect on the output power as the GSPI
controller follows a constant output power strategy in the above-rated region. A
value larger than one for this index means that the fault will increase the error
in the generated power.
• Blade pitch rate: the normalized RMS of the blade pitch rate is calculated in
order to monitor the effect of the fault on the actuator usage. The index is
calculated for the first blade where the fault is induced, and for the second
blade which will be along with the third blade working as fault-free blades,
however, they will be affected by the faulty first blade. A value larger than one
for this index means higher actuator usage.
• Platform motion: the normalized RMS indices are calculated for platform
rotational motions, roll, pitch, and yaw in order to monitor the fault effects on
