FIELD DATA ON POWER LINE ICING

Atmospheric icing is an important cause of damage to transmission lines and a major concern about their design and reliability. Dangerous ice 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 models, it is very important to obtain field data pertaining to such icing events. For this reason, a natural icing test site was developed at Mt. Valin (Québec) Canada, which allows the observation, each year, of about fifteen significant icing events. The Mt. Valin experimental installation consists of two instrumented test lines, meteorological instrumentation and a data acquisition and transmission system. Field data on icing collected at the test site from November 1990 to May 1991 are presented and analyzed. Generally, an icing event comprises three different 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 persistence phase and 17.2 hours for the shedding phase. The results show that icing and shedding rate mean values are higher for a 12.5-mm diameter conductor than for a 35-mm diameter conductor. The corresponding maximum values observed during November 1990 on the 12.5-mm diameter cable, were 157 g/(m.h) for the accretion phase and 743 g/(m.h) for the shedding phase. Using a constant icing rate empirical model, the Mt. Valin data give a correlation coefficient equal to 97% for the conductors of the main test line. The analysis shows that the same type of model can be used for the shedding phase.