Ferranti Effect

The answer is (1) both 35 KM overhead line and underground cable or (2) only the 35 KM overhead transmission line. This is based on which side of the transmission line the cable is located.

(1) Normally the capacitive charging current for cable is more than the overhead line. So, if the cable is located at the load end side, the charging current drawn by the cable is passing though the overhead line and it is causing more negative voltage drop (voltage increase effect) in the overhead line. In this case, both overhead line and underground cable are causing this Ferranti effect.

(2) If the cable is located at the supply end, the charging current drawn by the cable is not passing through the long transmission overhead line and so the cable has negligible effect to the Ferranti effect. So, in this case mostly the 35 KM overhead line is contributing the voltage increase effect.

This effect will be eliminated once you have load at the receiving end.

See the links for more clarification:

http://tkne.net/downloads/power/transmissionlines1/transmission%20lines/_Ferranti%20Effect.pdf

- MS