Calculation and analysis of the broken line tension of the suspension tower in the medium ice area are conducted.The broken line tension of five-span and seven-span transmission lines in medium ice area is calculated under various conditions including icing rate
span
and insulator string length.The effects of icing rate
span
string length and sub conductor splitting number on the breaking tension are analyzed and compared with the values in the current regulations.Suggestions for the percentage of breaking tension of suspension towers in ultra-high voltage direct current transmission lines in medium ice area were proposed.