First, the complete calculation includes 3 parts: Ampacity [IEEE 738], Mechanical part-resistance, sag, foundation and so on, voltage drop and stability. My calculation it is for voltage drop only.
1) The standard tower [for simply support, dimensions] it is as attached.
2) The average distance [Siemens]Dm=(d12*d23*d31*d1ii*d2III*d3I/(d1I*d2II*d3III))^(1/3)=6.3572 m
3) The equivalent radius of the bundle [Siemens] r=(rt*nc*(sag/2/SIN(PI()/nc)^(nc-1)))^(1/nc) where rt=radius of one wire, sag= the distance between wire[400 mm]
nc=number of wires in the bundle. [mm]
4) the resistance[electrical] as per catalogue [a.c. 75oC ohm/km] divided by no. of wires in a bundle, number of lines on the same tower [1-2], number of parallel lines [1-6].
5) the inductive reactance: 4*pi()*f/10^4*ln(Dm/r) [ohm/km] divided by number of lines on the same tower and number of parallel lines.
6) capacitance =2*pi()*εr*εo/ln(Dm/r) [F/km] multiplied by number of lines on the same tower and number of parallel line.
εr-relative dielectric constant (in air: εr = 1)
εo=dielectric constant (8.854 nF/km)
7) γ=√[(r+jx)*j2*pi()*f*Cap] Cap in F/km
8) Zo=√[(r+jx)/(j2*pi()*f*Cap)]
9) g=γ*length
10) Us=Ur*cosh(g)+Ir*Zo*sinh(g)
Us=source voltage
Ur=receiver voltage[required] Ur=138/√3
Ir=required current Ir=Sr/√3/138
if Sr=600 Ir=2.51[cos(ϕ)-jsin(ϕ)]
Is=Ir*cosh(g)+Ur/Zo*sinh(g)
Ss=3*Us*conjugate(Is)
That’s all, I think.
