Observation of Ice Shed from wind turbines

Contact: Markus Drapalik

March 2012 – March 2016

The insufficient knowledge of the actual risk of ice shed from wind turbines leads to unnecessary uncertainty both among residents and the competent authorities. This is probably due to the existing observing campaigns, which do not differentiate between falling distances of pieces of ice due to ice throw and icefall due to the operating conditions of the facilities.In most European countries, shutting down iced wind turbines is not compulsory. This means that pieces of ice not only fall off during deicing while the rotors are stationary, but they can also be thrown over considerable distances because of the considerable centrifugal force of the fast moving rotor blades.The computational models developed on this inadequate observational database and used by some review institutions provide shed distances, however, in the manner of “black boxes” in ways that are hardly comprehensible to outsiders, or using very strong generalizations The ISR has therefore developed a provisional risk assessment method, on the basis of initial experiments in which specimens were dropped from realistic heights. This method is valid for the lowlands in eastern Austria and already allowed for a certain relaxation of the situation in the permitting procedures for these areas. However, the method does not yet cover all the problem areas and in any case cannot be applied to the whole of Austria, because the meteorological conditions in other parts of Austria may differ considerably from those of the above-mentioned lowland and those encountered in the experiments. For the assessment of the risk of icing of wind turbines, a sufficient database with regard to the fall distends, shape, weight and density of the ice cubes for a given plant size and known meteorological parameters is necessary. To generate a representative statistic, real ice shed events have been observed and documented. This is done on the one hand in the form of systematic surveys with the aim of high data accuracy at defined wind turbine sites in Burgenland, in the Alpine foothills and in the Alps. On the other hand, service personnel of Austrian wind farms use prefabricated forms to record ice shedding events. Furthermore, the existing meteorological model for the estimation of icing frequencies was improved.

In this project, four events with risk-relevant icing were observed. In addition to the degree of icing of the rotor blades, fall distances and geometries of the ice fragments were determined. In total, 384 fragments were documented in terms of their location relative to the wind turbine tower and their dimensions. Furthermore, the weight and the density of selected fragments were investigated. By using stereo photogrammetric methods, several trajectories of falling fragments were reconstructed three-dimensionally.

The results of this project, with the great support of Windenergie Burgenland, can be found in the following publications:

Drapalik, Markus: Risiken der Vereisungproblematik bei Windenergieanlagen unter besonderer Berücksichtigung der Situation in Österreich. PhD Thesis, Universität für Bodenkultur Wien, 2017, http://www.risk.boku.ac.at/download/pub/2017/Drapalik_Diss_2017.pdf

Bredesen, R. E.; Drapalik, M. & Butt, B.: Understanding and acknowledging the ice throw hazard – consequences for regulatory frameworks, risk perception and risk communication. Journal of Physics: Conference Series, 2017, 926, 012001, http://iopscience.iop.org/article/10.1088/1742-6596/926/1/012001/meta

Furthermore, this project forms the basis for the further experimental investigation of WEA icefall in the project Experimental Investigation of Ice Shed from WEA.

Universität für Bodenkultur Wien