This was just one of a number of conclusions looking at the problem of SWT collapses. This size of wind turbine is defined by IEC 61400 Part 2 standard 11 as “wind turbines with a rotor swept area smaller than or equal to 200 m2 , generating electricity at a voltage below 1000 V ac or 1500 V dc for both on-grid and off-grid applications”are often privately owned or used to supply agricultural farms or small enterprises whereby only surplus electricity is exported to the national grid. In the HSE recently published report RR1081 “Review of small wind turbine construction instructions and specifically for structural supports and foundations” a review of a number of failures also highlighted that whilst the sources of failure differ in each case contributory factors appear to have included:
- Local topography adding to turbulence and wind shear loading not accounted for in the design
- Reliance on components and structural details which are inherently poor in fatigue
- Potential mis-application of design standards including use of the simplified load model outside the bounds of its stated applicability leading to under-prediction of design loads
- Deviations from the prescribed installation process preventing bolt tension and compression in the surrounding concrete and grout being developed, exposing the rods to fatigue for which they were not designed, by inter alia:
- inclusion of additional support nuts (beyond the number specified) under the tower flange during construction
- Poor quality grouting under the tower flange using cosmetic not structural grade grout.
To read the complete report please go to the HSE website at http://www.hse.gov.uk/research/rrpdf/rr1081.pdf where the report can be downloaded.
