Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 190

Using the calculated moment from Eq. 9.50 the equivalent stress in the main
shaft is;

r eq ¼ M shaft
W shaft

6 : 52
1 : 534 10 6 ¼ 4 : 25 MPa

¼ ð 9 : 65 Þ

9.5.6 Equivalent Stress for Case F: Short at Electrical
Connection

Load case F also considers a single load for both the main shaft and the blade root.
Again, the calculations for the equivalent stress are straightforward. For the blade
root:

r eq ¼ M xB
W xB

7 : 55
3 : 036 10 6 ¼ 2 : 49 MPa

¼ ð 9 : 66 Þ

using the result of Eq. 9.52 . For the main shaft:

p 22 : 64
2 1 : 534 10 6 ¼ 12 : 78 MPa

3

r eq ¼ 3

p M shaft
2W shaft

¼ ð 9 : 67 Þ

from ( 9.51 ).

9.5.7 Equivalent Stress for Load Case H: Parked Wind Loading

This case also considers one load on both the blade root and the main shaft.
The equivalent stress levels for the blade root are
r eq ¼ M yB
W yB

283 : 71
1 : 527 10 4 ¼ 1 : 86 MPa

¼ ð 9 : 68 Þ

using ( 9.53 ). Similarly, ( 9.54 ) leads to:

r eq ¼ F x shaft
A shaft

1754 : 89
4 : 909 10 4 ¼ 3 : 58 MPa

¼ ð 9 : 69 Þ

for the main rotor shaft.

9.6 Spreadsheet for the Simple Load Model

To simplify the use of the SLM, an excel spreadsheet, SLM_500.xls has been
developed. Figure 9.1 shows the first chart in the spreadsheet. The shaded cells
indicate values that must be input by the user in order to undertake the calculations