In recent years, the phenomenon of wet snow accretion is becoming a serious problem for the Italian power grid causing long and prolonged electrical outages. The Transmission and Distribution operators require ever more accurate weather forecasts to deploy operational teams in the alerted areas and, at the same time, to adopt the most appropriate dispatching solution (e.g. the anti-icing currents). For this first need, RSE has developed a weather forecast system named WOLF (Wet-snow Overload aLert and Forecast) based on Numerical Weather Prediction (NWP) model combined with simple cylindrical accretion model for wet snow (ISO 12494 2001). The forecast system provides, 72-hours in advance, the snow load on the entire high voltage grid together with the estimation of anti-icing current in the expected weather conditions.

Another important topic for operators consists of a proper planning of the lines, taking into account the climatological snow loads on the territory. For this reason, RSE is developing a preliminary map of wet-snow loads through the MESoscale ANalysis system (MESAN) provided by Swedish Meteorological and Hydrological Institute. This gridded dataset has an horizontal resolution of 5km and provides the daily maximum and minimum temperature, cumulated precipitation and 6-hours wind intensity. These variables have been used to calculate the daily wet-snow loads by using Makkonen model for different typical conductors of transmission and distribution lines in the last 30-years (1985-2013).

For each grid point, the time series of yearly maximum ice load has been analyzed by GEV distribution in order to obtain the expected maximum values of wet snow loads on the power lines by setting a typical return period of power line’s lifetime (i.e. 50 years). To date RSE is verifying the preliminary results and in general a good agreement has been found between electric faults and the expected snow loads. Furthermore, a new test site named WILD (Wet-snow Ice Laboratory Detection) located in the West Alps has been developed by RSE. In the WILD station, some rotating test spans have been installed in order to weight the snow sleeves on different conductors. The station is equipped with advanced instrumentation able to supply measurements even under extreme weather conditions as the wet-snowfall.

The station measures allow to fine-tune the accretion model parameterization and to verify the thermal anti-icing model and the weather forecast. Finally, different innovative icephobic coatings are being tested to reduce the formation of the sleeve or to facilitate the shedding.