Observation Study on Properties of Cloud and Fog in Ice Accretion Areas

Ice accretion on conductors from freezing rain or glaze is a common meteorological disaster in Guizhou mountainous areas, causing serious damages with the warped wire, the collapsed pole and/or tower and broken circuit. For example, the severe ice accretion in 1984 in Guizhou brings the blackout in the local electricity transport network. The security of electricity transport is threatened by ice accretion on conductors. The glaze forms from freezing rain on conductors near surface with the air temperature between 0 ℃ and 6 ℃ in Guizhou. It is found in experiment that ice frozen between 0 ℃ and 6 ℃ is difficult to fall off with its great density, which is a main cause for Guizhou's ice accretion with the extreme danger. In Liupanshui of western Guizhou the site especially for observation of ice accretion on conductors is built by national power company. In this site and two other ice accretion areas in northern and central Guizhou the field observations are conducted with the elevations of 2128 m, 1780 m and 1659 m respectively. The growth rate of conductor ice accretion is closely associated with the cloud-and fog-conditions. The major observation factors include cloud droplet size distribution, water content in cloud and fog, air temperature, wind direction, wind speed, long and short diameters of ice accretion on conductors. The cloud droplets and water content in cloud and fog are colleted with the method of integration suction. The ice accretion is measured in the specific stands in both east-west and north-south directions. In three observation areas there are no significant differences for cloud droplets on both the concentration of 140—312 droplets/cm³ and the average diameters with arithmetic mean diameter of 7.5 μm, cube root diameter of 11.3 μm and median volume diameter of 20 μm; although the number concentration of cloud droplets with the diameter bigger than 14 μg are 12.5% of the total concentration, water content contributed by them is as high as 78% due to the dominant contribution to water content considering the high collision efficient of these large cloud droplets on conductors, the distribution of large droplets is a key factor involving ice accretion; the water content with the average value of 0.20 g·m^-3 in cloud and fog decreases with air temperature from 0 ℃ to -6 ℃; more ice accretes on conductors of north-south than east-west direction caused by prevailing northeast wind in the surface levels during the stationary front period in winter; the growth rate of ice accretion is proportional to the water content in cloud and fog and the wind speed, especially of more obvious direct ratio with the wind speed over 3 m·s^-1.