FIELD DATA ON POWER-LINE ICING

Atmospheric icing is an important cause of damage to transmission line s and a major concern about their design and reliability. Dangerous ic e accretions can be glaze caused by freezing rain precipitations, rime caused by in-cloud icing, or wet snow. For the design and maintenance of power line networks and for the validation of numerical icing mode ls, it is very important to obtain field data pertaining to such icing events. For this reason, a natural icing test site was developed at M t. Valin (Quebec) Canada, which allows the observation, each year, of about fifteen significant icing events. The Mt. Valin experimental ins tallation consists of two instrumented test lines, meteorological inst rumentation and a data acquisition and transmission system. Field data on icing collected at the test site from November 1990 to May 1991 ar e presented and analyzed. Generally, an icing event comprises three di fferent phases: an accretion phase, a persistence phase and a shedding phase. During the 1990-91 icing season, the average duration of icing events was 34 hours for the accretion phase, 137 hours for the persis tence phase and 17.2 hours for the shedding phase. The results show th at icing and shedding rate mean values are higher for a 12.5-mm diamet er conductor than for a 35-mm diameter conductor. The corresponding ma ximum values observed during November 1990 on the 12.5-mm diameter cab le, were 157 g/(m.h) for the accretion phase and 743 g/(m.h) for the s hedding phase. Using a constant icing rate empirical model, the Mt. Va lin data give a correlation coefficient equal to 97% for the conductor s of the main test line. The analysis shows that the same type of mode l can be used for the shedding phase.