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导线积冰的云雾特征观测研究
Observation Study on Properties of Cloud and Fog in Ice Accretion Areas
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摘要: 导线积冰在贵州山区是常见的气象灾害, 导线积冰增长率与气象云雾因子密切相关。研究选择贵州西部、北部、中部3个积冰区进行了专门外场观测, 观测项目有:云滴谱、含水量、气温、风向、风速、导线上积冰的长径、短径。观测分析表明:贵州云滴浓度、特征平均直径没有显著性地区差异; 云滴平均浓度140~312个/cm3, 云滴算术平均直径、均立方根直径、中值体积直径分别为7.5 μm, 11.3 μm和20 μm; 14 μm以上大云滴浓度平均占云滴总浓度的12.5%, 但对含水量的贡献高达78%, 大滴与导线碰撞效率高, 大滴是导线积冰的关键因子; 云雾含水量平均0.20 g/m3; 在0~-6 ℃之间, 含水量随温度的降低而降低; 南北向导线积冰比东西向的积冰多; 导线积冰增长率与含水量的大小成正比, 风速超过3 m/s时, 积冰增长率与风速有较明显的正比关系。Abstract: 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.
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图 1 各云滴尺度对含水量的贡献百分率
(阴影部分是14 μm以上云滴对含水量的积分值)
Fig. 1 Contributing percent of different cloud droplet scale with water content
(more than 14 μm of integral value for cloud droplet to water content with shaded)
图 2 马落菁1991年2月2—4日积冰过程
Fig. 2 Ice accretion process over Maluojing from Feb 2 to 4 in 1991
表 1 贵州重冰区过冷云雾的微观特征
Table 1 Micro Characteristics of super-cooling cloud fog in heavy ice region
表 2 云雾滴谱表达式
Table 2 Cloud and fog droplet formulae
表 3 含水量W特征值
Table 3 Eigenvalue of water content W in different area
表 4 不同高度温度区间内的含水量分布 (单位:g/m3)
Table 4 Distribution of water content in different height and temperature (unit:g/m3)
表 5 不同风向、风速条件下Kd平均值
Table 5 Mean Kd with different wind condition
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