Abstract
Abstract. Historically, as far as wet-snow loads were concerned, overhead line design was often based on experience or long-term applications with positive results. New standard like CENELEC EN 50341-1 (2012) take into account characteristic loads, i.e. 50-year return-period loads, for the overhead line design. This article proposes a method to estimate characteristic wet-snow loads based on meteorological data recorded at weather stations. The model used to calculate those loads is mainly inspired by a recent article written by Nygaard et al. (2013a) in which a new parameterization is proposed for the classical cylindrical wet-snow accretion model, as described in ISO 12494 standard (2001), annex C. After a complete description of the model and its parameterization adapted to French wet-snow events, the statistical issues are examined. Then, the model is used with the meteorological data of 87 weather stations in order to calculate wet-snow loads whose relevance has been positively tested according to real damages recorded in a complete wet-snow event database. At last, the characteristic loads of those 87 stations have been determined according to all the loads generated by the model and processed by a peak-over-threshold (POT) method. A practical method to determine the 90% confidence intervals of those characteristic values is given. As it is demonstrated that there is only one value of the ice class (IC) masses proposed by ISO 12494 in each confidence interval, characteristic loads can be easily expressed in terms of ICs. That method shows that ICs ranging from R1 (0.5 kg m−1) to R5 (5 kg m−1) could be used for overhead line design in France.
Highlights
The new CENELEC EN 50341-1 standard (2012 edition) proposes a complete method to calculate 50year wind loads on overhead line components, it only refers to ISO 12494 for wet-snow load determination, encouraging overhead line design engineers to use its ice classes (ICs) as 50-year loads
A recent article by Nygaard et al (2013a) proposes a new parameterization of the classical cylindrical wet-snow accretion model to be used with meteorological data simulated by the WRF model (Weather Research and Forecasting Model)
ICs can be determined based upon meteorological data together with the use of an ice accretion model, which is based on the classical equation given in the ISO annex: dM
Summary
The new CENELEC EN 50341-1 standard (2012 edition) proposes a complete method to calculate 50year wind loads on overhead line components, it only refers to ISO 12494 for wet-snow load determination, encouraging overhead line design engineers to use its ice classes (ICs) as 50-year loads. A recent article by Nygaard et al (2013a) proposes a new parameterization of the classical cylindrical wet-snow accretion model (described in ISO 12494, annex C) to be used with meteorological data simulated by the WRF model (Weather Research and Forecasting Model). This new parameterization has been successfully tested with real, severe and windy wet-snow cases in Iceland. The authors propose a method to adapt the previous model to meteorological data recorded at weather stations instead of simulated data They propose a parameterization adapted to countries like France, where wet-snow events are less windy and less severe than those in Iceland.
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