ICE SHEDDING FROM CABLES

The shedding of atmospheric ice accreted on cables is responsible for impact forces, overloads, vibrations and, in the case of electrical co nductors, short-circuits. On the other hand, ice shedding can reduce o verall maximum load on cables. Despite these important effects, and wh ile ice accretion on cables is a well-documented phenomenon, very litt le 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 c able. This paper presents conditions and examples of the three cable i ce shedding mechanisms, as well as a signal-processing method develope d from statistical analysis in order to dismiss unreliable data. A mor e detailed analysis of eleven shedding events by mechanical ice breaki ng, recorded at our Mt. Valin icing station located near Chicoutimi (Q uebec), Canada, is also presented. This shedding mechanism is the most frequent observed in the Mt. Valin data base, and also the most compl ex to analyze. The factors considered in this analysis are the mean va lues of air temperature and perpendicular wind velocity during accreti on and shedding periods, the cable ice load at beginning of shedding, the shedding events duration, and the shedding rate. The study shows t hat the two factors having the highest correlation with the shedding r ate by mechanical ice breaking are the normal wind velocity during ice shedding and the initial cable ice load.