Ice shedding from cables

Abstract

The shedding of atmospheric ice accreted on cables is responsible for impact forces, overloads, vibrations and, in the case of electrical conductors, short-circuits. On the other hand, ice shedding can reduce overall maximum load on cables. Despite these important effects, and while ice accretion on cables is a well-documented phenomenon, very little is known about ice shedding from cables. Three physical mechanisms are expected to induce ice mass reduction or ice shedding: ice melting, ice sublimation, and mechanical ice breaking. Each mechanism can be characterized from atmospheric parameters and ice shedding rate from cable. This paper presents conditions and examples of the three cable ice shedding mechanisms, as well as a signal-processing method developed from statistical analysis in order to dismiss unreliable data. A more detailed analysis of eleven shedding events by mechanical ice breaking, recorded at our Mt. Valin icing station located near Chicoutimi (Québec), Canada, is also presented. This shedding mechanism is the most frequent observed in the Mt. Valin data base, and also the most complex to analyze. The factors considered in this analysis are the mean values of air temperature and perpendicular wind velocity during accretion and shedding periods, the cable ice load at beginning of shedding, the shedding events duration, and the shedding rate. The study shows that the two factors having the highest correlation with the shedding rate by mechanical ice breaking are the normal wind velocity during ice shedding and the initial cable ice load.