减小输电线路铁塔塔窗尺寸对降低工程整体投资有重要意义。分析了影响输电铁塔塔窗尺寸的因素，提出了中相采用T 型串的设计方案。输电铁塔中相采用T 型串减小了铁塔的塔窗尺寸、降低塔重，减少了地面电场强度和走廊拆迁宽度，提高了线路的耐雷水平和输送容量，建议地形条件较好的输电线路采用T型串以减小工程投资。

Reducing the transmission tower’s window dimension is important for lowering the overall project investment. The paper analyzes the factors that determine the transmission tower’s dimension and proposes a designing scheme of T-shaped insulator string in middle phase. The use of T-shaped insulator string has reduced the tower’s window dimension and weight, and decreased the electric field intensity and the transmission corridor width, subsequently improving the anti-lighting level and transmission capacity of transmission lines. So it is recommended to use the T-shaped string under better ground conditions to minimize the project investment.