The impact of freezing weather on the grid is increasing with the continuing deterioration of global climate. Previous existing studies about icing on the transmission line only considered the impact of climate condition according to the weather temperature, rainfall rate, air humidity, wind speed and other impact factors to calculate the ice load, and did not consider the ice-melting effect of the current thermal effect. In this paper, the ice-melting effect of the current thermal effect is considered in the original icing model, and the icing process is divided into the critical icing process, icing process and icemelting process, and it is established an integrated icing model of the lines. Through an example, it analyzed ice-melting effect on the line, the current value of ice-melting and thawing time, and calculated an integrated ice load value trend of the transmission line in the freezing weather. Keywordfreezing weather ； ice load; current thermal effecte; integrated icing model

Solved differential equations of the power system by Euler method programs, calculated the fluctuation of frequency and voltage resulted by the operation on the network during the restoration period. And continuous power flow method, which based on continuous load increase was used to calculate voltage margin during the network operation steps here. Established objective function, steady-state voltage margins as its variables, combined dynamic simulation programs to check whether there were exceeding limits phenomenon in the dynamic process, to select best order of the line reconnections, providing certain evidence for system restoration. Comparison among results of Simulation on IEEE 14 bus system with 5 generators proved the effectiveness of the method.

Abstract. Reclosing technology is widely used in EHV transmission system of China. In Shanxi 220kV power grid, the reclosing delay time is commonly set to 0.5s, while there used to be several reclosing failures in recent years. This paper focuses on this problem, the transmission system as well as transmission lines are modeled, and factors that may influence secondary arc are investigated. In addition, suggestions on auto-reclosing time setting for Shanxi 220kV power grid are proposed.