Environmental Engineering Reference
In-Depth Information
the platform stability. An index value larger than one means that the fault
excites the corresponding motion.
• Tower fore-aft, side-side, and torsional moments fatigue DEL: the damage
equivalent loading index for the tower moments shows the fault effect on the
tower loading. An index value larger than one means the rotor imbalance
increases the dynamic loading over the tower and reduces the useful average
lifetime.
• Low speed shaft (LSS) non-rotating bending fatigue DEL at the shaft tip at 0
direction (vertical) and at 90 direction (horizontal): this index shows the fault-
induced rotor imbalance effect on the low speed shaft (LSS) bending moment.
An index value higher than one means higher dynamic loading on the LSS.
• Blade root flap-wise and edge-wise bending moment DEL: this index monitors
the fault-induced loading over the blades in flap-wise and edge-wise directions.
An index higher than one means increase of the blade loading moment.
11.5.2 Blade Pitch Bias Fault
The bias in blade pitch angle causes rotor imbalance which affects the LSS and the
tower bending moments. The GSPI controller performance is not affected that
much with this bias as the collective blade pitch angle is used for gain scheduling
only, which means minor deviations in the reference pitch angle. The bias fault has
most effect at EC2 (Table
11.2
) where the thrust force over the rotor disk is close
to its maximum value (Fig.
11.10
). As the GSPI pitch controller switches between
the full and partial load control methods which means disabling the pitch control in
the partial load region, this reduces the fault effects at EC1, yet the high thrust
force. The fault effect also depends on the bias magnitude but not the sign. Fur-
thermore, the blade flap-wise and edge-wise moments in addition to tower fore-aft
and side-to-side moments show negligible response to this fault.
2.5
2.5
2.5
2
2
2
1.5
1.5
1.5
1
1
1
EC1 EC2 EC3 EC4 EC5
EC1 EC2 EC3 EC4 EC5
EC1 EC2 EC3 EC4 EC5
M1
M2
M3
M4
Fig. 11.10 Fault: blade pitch sensor bias. Normalized DEL (NDEL) of tower torsional and LSS
moments. High DEL at maximum bias (absolute) and at EC2
