Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 171

Table 9.3 The design load cases of the simple load model
Design situation Load

case

Description Type of

analysis

Power production A Normal operation Fatigue

B Yawing Ultimate

C Yaw error Ultimate

D Maximum thrust Ultimate

Power production plus occurrence
of fault

E Maximum rotational speed Ultimate

F Short at load connection Ultimate

Shutdown G Shutdown (braking) Ultimate

Parked (idling or standstill) H Parked wind loading Ultimate

Parked at fault conditions I Parked wind loading (maximum

exposure)

Ultimate

Transport, assembly, maintenance
and repair

J To be stated by manufacturer Ultimate

increase our currently poor knowledge. In this context, it is noted that the author
was the Australian representative on the maintenance team that produced IEC
61400-2 and shares the responsibility for the good and bad features of the standard.
This chapter is an expanded version of Wood [ 3 ].

9.2 The Simple Load Model

The SLM can be applied only to a horizontal axis turbine having two or more
cantilevered blades, and a rigid (non-teetering) hub. All IEC standards exclude
vertical axis turbines.
The first step involves the collection or assigning of the following parameters:

• Design rotational speed, X design
• Design wind speed, U design = 1.4U ave (U ave is the average wind speed)
• Design shaft torque, Q design
• Maximum yaw rate, x yaw,max and
• Maximum rotational speed, X max (Table 9.4 )
The design rpm is set by aerodynamic considerations whereas the maximum is
set by the overspeed protection, furling in this case. The design power, P design ,is
determined at the design wind speed with the nominal electrical load connected.
The design torque, Q design , is found using 3
Q design ¼ 30P design
gpX design

ð 9 : 1 Þ

3

(IEC 51).