Using the IEC Simple Load Model for Small Wind Turbines

Abstract

This paper describes the application of the “Simple Load Model” of the new IEC standard for the safety of small wind turbines to a three-bladed, 2m diameter, 500 W turbine with a permanent magnet generator and a furling tail fin. The two most important load cases are discussed in detail along with the determination of the component stresses from these loads. A spreadsheet is presented that allows rapid calculation of the loads and stresses for all ten cases in the Simple Load Model. The spreadsheet can be used for any small turbine. A number of inconsistencies and inaccuracies in the standard are identified; the prime one being the lack of a thrust term in the equation for the blade root bending moment. Important aspects of small wind turbine behaviour are still not well understood: these include yaw behaviour, in particular the maximum yaw rate that determines the gyroscopic moment on the blades and main shaft which is usually the dominant load on a small turbine.