Abstract:The maximum allowable carryingcurrent capacity of overhead transmission lines highly depends on the meteorological parameters but traditionally the rigid and harsh setting of meteorological parameters makes the carryingcurrent capacity conservative. In order to make the carryingcurrent capacity setting satisfy the actual meteorological situation, this study utilizes the hourly data from 94 automatic meteorological stations over the southern Hebei to drive the wire energy balance equation for the analysis of carryingcurrent capacity. It helps to improve the transmission capacity of the transmission lines in the southern Hebei that the constant carryingcurrent capacity is changed into seasonally varied carryingcurrent capacity. Based on the analysis of the sensitivity of allowable maximum carryingcurrent capacity to the variation of ambient wind speed and air temperature, the study has determined the probability density distribution of ambient air temperature and wind speed, obtained the regional probability distribution of allowable maximum carryingcurrent capacity, and evaluated the transmission capacity at several safety operation levels. The results show that at the 95% safety operation level, the maximum carryingcurrent capacity of the LGJ400/35 transmission line in the southern Hebei can be set to 945, 774, 795 and 1012 A in spring, summer, autumn and winter, respectively, which is significantly higher than the traditional carryingcurrent capacity. Thus, currentcarrying capacity of the overhead transmission lines driven by actual meteorological data on the seasonal scales improves the transmission capacity of the lines.