Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 169

Chapter 9
Using the IEC Simple Load Model
for Small Wind Turbines

9.1 Introduction

The IEC safety standard for small wind turbines, IEC 61400-2 and the Germa-
nischer Lloyd guidelines, GL [ 1 ], 1 provide a major challenge and opportunity for
small wind turbine designers. It was mentioned in the first sentence of the Preface
that IEC 61400-2 defines a small turbine as having a rotor swept area of less than
200 m 2 which corresponds roughly to a rated power of less than 50 kW. The
standard makes a further provision for micro-turbines of rotor area of 2 m 2 or less;
they can be certified independently of their tower. For all other turbines, the tower
must be assessed with the turbine.
IEC 61400-2 allows the analysis of turbine safety through three mechanisms:

1. The ''Simple Load Model'' (SLM) which combines straightforward, and pos-
sibly simplistic, equations for the main loads with high safety factors. As its
name implies, it is the simplest design methodology and is the only one
described in detail in this chapter.
2. ''Aero-elastic'' Modeling involves (hopefully) more accurate computer mod-
eling of wind turbine loads in response to stochastic inputs such as changes in
wind direction and gusts. This method is routinely used for large wind turbines,
employing programs such as bladed, which is sold by the consultants Garrad
Hassan. 2 The equations for gusts and wind direction changes that are specified
in IEC 61400-2 for aero-elastic modeling are identical to those used for large
wind turbines, IEC 61400-1, and described by Burton et al. [ 2 ]. The main
problem with aero-elastic modeling would seem to be the high cost of the
software and/or the large amount of time required for its implementation. Aero-
elastic modeling is not commonly used for small wind turbines.

1

GL [ 1 ] is the first edition of the guidelines with specific information on small turbines.

2

http://www.gl-garradhassan.com/en/GHBladed.php , an educational version is available.