请为我解决这道题吧---一、 额定电压为 110kV 的双回输电线路，长度为 80km，采用 LGJ-150 导线，其单位长度参数为: $r_1 = 0.21 \Omega/km, x_1 = 0.416 \Omega/km, b_1 = 2.74\times10^{-6} S/km$。变电所中装有两台三相 110/11kV 的 变 压 器 ， 每 台 的 容 量 为 15MVA ， 其 参 数 为 $P_0 = 40.5kW, P_k = 128kW, U_k\% = 10.5, I_0\% = 3.5$。母线 A 的实际运行电压为 117kV，负荷功率: $S_{LDb} = 30+j12MVA, S_{LDc} = 20+j15MVA$，当变压器取主抽头时，求取母线 c 的电压。 **Diagram Description:** * **Type:** Single-line diagram representing a power system. * **Main Elements:** * Three vertical lines representing busbars, labeled A, B, and C from left to right. * Horizontal lines connecting busbars A and B, representing a transmission line. * Two transformer symbols (circles representing windings with a core) connected between busbar B and busbar C. * Voltage ratio label "110/11kV" placed above the transformers. * Voltage level label "10kV" placed to the right of busbar C, below the transformers. * Arrows pointing away from busbar B and busbar C, indicating loads connected at these buses.