Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 195

Fig. 9.5 The fifth sheet of
the SLM spreadsheet

Calculation of the Equivalent
Stresses
Description Equivalent Stress (MPa)
Load Case A - Fatigue Loads on Blades and Rotor Shaft
Blades 3.51
Shaft 15.53
Load Case B - Blade and Rotor Shaft Loads during Yaw
Blades

0.27

Shaft 40.29

Load Case C - Yaw Err or Load on Blades
Blades 2.77

Load Case D - Maximu m Thrust on Shaft
Shaft

0.65

Load Case E - Maximu m Rotational Speed
Blades 1.14

Shaft 4.25

Load Case F - Short at Load Connection
Blades

2.49

Shaft 12.78

Load Case G - Shutdo wn Braking
Blades n/a
Shaft n/a
Load Case H - Parked Wind Loads during Idling
Blades 1.86

Shaft 3.58

described in this paper facilitates the analysis. Addressing the limitations of the
standard will greatly add to our knowledge of small wind turbine behaviour.
It should be apparent from the previous sections that designing small turbines to
IEC 61400-2, and then demonstrating that the turbine is safe is not simple. The
SLM calculations of the 500 W turbine highlight the critical role of the turbine's
yaw behaviour. The largest load was due to the Coriolis acceleration on the
rotating and yawing blades.
Part of the reason for the single failure was the poor state of knowledge of the
shaft material and it would be more than worthwhile to improve this situation. It is
also possible that the standard over-estimates the Coriolis component of the shaft
load because of the mandatory formulation of the maximum yaw rate and the
requirement that this be combined with the design rotor speed.