Ice classes
IEA Wind and ISO 12494 have presented tables of icing severity i.e. ”ice classes” of a site, which can be used, depending on the application, to evaluate production losses and ice loads that have to be considered in the structural design. The crucial factors in these classifications are duration of the icing event, its severity and annual frequency of the event. The different ice classes according to IEA Wind are presented in the table IEA Wind´s ice classification system.
IEA Wind’s ice classification system
Meteorological icing denotes the duration of the icing event i.e. the ice accretion time on the wind turbine. Instrumental icing is the time that ice stays on the surface. Ice class is measured with icing of the unheated anemometer. The time that anemometer is disturbed by icing corresponds the meteorological icing values. Based on these measurements the production losses can be estimated. According to IEA’s suggestions the anti- or de-icing is cost-effective solution, when ice class of the site is 3 or higher.
ISO 12494- standard
ISO 12494- standard “Atmospheric icing of structures” has also classified icing severity on different structures, such as towers, mast, cables etc. Although it does not concern icing of overhead transmission lines, whose withstanding of the ice is evaluated in the IEC 60826 “Design criteria of overhead transmission lines”. ISO 12494- standard presents ice classes for both rime and glaze ice accretion, because their density differs.
In order to recognize valid ice class for the site, there are options; 1) collect meteorological data as an input data for ice accretion model to assess ice loads like in these studies, 2) measure accreted ice masses on the site (kg/m).
Icing severity map
The map shows icing severity utilizing the IEA’s ice classes. The in-cloud icing data is collected over 20 years from 4000 observation station. Altitude increases icing severity and this map shows the situation at 350 m.
Ice classes for glaze ice (900 kg/m3) figure left and for rime (figure to the right).
Ice class for glaze ice accretion can be determined whether by measuring the thickness of accretion or by measuring ice load (weight on distance, kg/m). For rime ice it is vital to take on account the role of density on the weight of ice accretion. Wet snow accretions are considered in this table for rime, because its density is in same range than rime ice. These classification systems require either reliable meteorological data for ice accretion models or measurement on the site. Site assessment is a critical step when the engineering structures are built in the icing climates.
[4] [5] [6] [7] [8] [9] [10] [11] [12]
References
- ↑ I. Baring-Gould, R. Cattin, M. Dustewitz, M. Hulkkonen, A. Krenn, T. Laakso, A. Lacroix, E. Peltola, G. Rönsten, L. Tallhaug, T. Wallenius, Wind Energy Projects in Cold Climates, IEA Wind 13.task, 2012 43 p. Available: https://www.ieawind.org/index_page_postings/June%207%20posts/task%2019% 20cold_climate_%20rp_approved05.12.pdf.
- ↑ V. Lehtomäki & E. Peltola, Blade Protection Systems and Their Performance Under Cold Climate Conditions, Optimizing Wind Farms in Cold Climates, presentation, Helsinki, Finland, 2014.
- ↑ ISO-12494, Atmospheric icing of structures, 2001, 56 p.
- ↑ Properties of icephobic surfaces in different icing conditions. Stenroos Christian. Master of Science Thesis. TAMPERE UNIVERSITY OF TECHNOLOGY. October 2015. Online.
- ↑ L. Makkonen, Modeling power line icing in freezing precipitation, Atmospheric Research, vol. 46, no. 1–2, 1998, pp. 131–142.
- ↑ E. A. Podolskiy, B. E. K. Nygaard, K. Nishimura, L. Makkonen, E. P. Lozowski, Study of unusual atmospheric icing at Mount Zao, Japan, using the Weather Research and Forecasting model, Journal of Geophysical Research: Atmospheres, vol. 117, no. 12, 2012 pp.1-24.
- ↑ L. Makkonen, P. Lehtonen, M. Hirviniemi, Determining ice loads for tower structure design, Engineering Structures, vol. 74, 2014 pp. 229–232,.
- ↑ L. Makkonen & M. M. Oleskiw, Small-scale experiments on rime icing, Cold Regions Science and Technology, vol. 25, no. 3, 1997, pp. 173–182.
- ↑ N. Dalili, A. Edrisy, R. Carriveau, A review of surface engineering issues critical to wind turbine performance, Renewable and Sustainable Energy Reviews, vol. 13, no. 2, 2009, pp. 428–438.
- ↑ O. Parent & A. Ilinca, Anti-icing and de-icing techniques for wind turbines: Critical review,” Cold Regions Science and Technology, Vol. 65, No. 1, 2011, pp. 88–96.
- ↑ S. Fikke, P.-E. Persson, B. Wareing, J. Chum, L. Makkonen, G. Ronsten, A. Heimo, S. Kunz, M. Ostrozlik, J. Sabata, B. Wichura, T. Laakso, K. Säntti, COST 727: Atmospheric Icing on Structures Measurements and data collection on icing: State of the Art, MeteoSwiss, 75, 2007, 110 p.
- ↑ F. Lamraoui, G. Fortin, R. Benoit, J. Perron, C. Masson, Atmospheric icing impact on wind turbine production, Cold Regions Science and Technology, vol. 100, 2014, pp. 36–49.