Question

In a localized capacitance method for a Long transmission line what could be consider a drawback from it? Also when a long transmission line is open circuited on its receiving end, would there be any current at the sending end?

Answer 1

In a localized capacitance method for a Long transmission line.If you have heard of a thing called Ferranti Effect, thats the result of Capacitive nature of transmission lines. If we consider a unit length of conductor as a capacitor plate and Ground as another plate, separated by the air medium, it forms a small capacitor. And upon traversing the entire length of the line, we can see that its nothing but many such small capacitors connected in parallel. Since we know, capacitance increases when connected in parallel, there is a voltage build up due the capacitance and voltage at receiving end becomes more than that of sending end. This is Ferranti Effect. This effect is commonly seen in long transmission lines. For short ones, the total capacitance is negligibe to cause any voltage build up. Reactors are generally employed to reduce this effect.

In a long transmission line there would be sending end current which is equal to charging current at no load

With the increase in length of the transmission lines, the line charging currents and the shunt admittance become more and more dominant, hence due to this line capacitance the magnitude of receiving end voltage at no-load or lightly loaded conditions becomes greater than the magnitude of sending end voltages.