Capacitance of 3-Phase Line with more than One Circuit

Consider the arrangement of conductors shown in the Fig. 1.

Fig. 1

      
The voltage between phases a and b is given by,

      We have,  V_ab + V_ac = 3 V_an

           q_a + q_b + q_c = 0
.^..         q_b + q_c = - q_a 

       Capacitance per phase will be nothing but 2 C_an