power carrying capacity of ac/dc lines

double circuit ac line power, Pac = 6EpIlcosφ
dc line power, Pdc = 6VdId

k = dc withstand voltage/ac withstand voltage (rms)
k1 = ac insulation level/rated ac voltage
k2 = dc insulation level/rated dc voltage

when the lines are loaded to their thermal loadings, and Vd=k*(k1/k2)*Ep

Pdc = 6(k(k1/k2)EpIl)
= k(k1/k2)*(Pac/cosφ)

taking k=1, k1=2.5, k2=1.7 (very conservative assumptions)

therefore, Pdc/Pac=1.47/cosφ

power transmission is at least 47% higher

losses is decreased by 1/1.47 = 68%

edit: i think electrical engineers can confirm that the power transmission and loss decrease can be higher than that, plus the skin effect wasn't taken into account.

This post has been edited by spursfan: Dec 3 2009, 09:00 AM