Probabilistic model of combined wind and ice loads on overhead power line conductors

Abstract

There is evidence that extreme ice loads combined with moderately high winds may cause catastrophic damage to overhead power lines and prolonged periods of electrical power outage. In this paper, a probabilistic model for combined wind and ice loads was developed for establishing realistic and conservative criteria for design and normalization. The proposed model combines icing of extreme thickness with a moderate wind speed, Vice, reduced by a reduction factor, kr, with respect to the extreme wind speed, Vmax. The evaluation of kr, which is the main purpose of this paper, is done by means of statistical analysis of samples taken from the same initial distribution of hourly wind speeds, Vh. The size of samples corresponds to the average annual icing persistency period, Tipp, observed in the climatic conditions of Quebec. This period, which was established in an earlier study by the authors using statistical analysis of data from the Hydro-Québec passive ice meter (PIM) network, is evaluated to be on average 144 h/year. It was found that kr ranges from 0.4 to 0.7, mainly as a function of the coefficient of variation (COV) of the initial distribution of wind speeds and the return period prescribed for extreme climatic loads.Key words: combined wind and ice loads, probabilistic model, overhead transmission lines.