[jaidan]

The problem with long distance AC is the reactive power component caused by the capacitance, and the voltage rise caused by the Ferranti effect.

The reactive component has significant impact on the generation equipment and grids. It also causes the Ferranti effect, where the voltage along the cable rises. This can make managing the voltage within the cable difficult because at no load, the load end has a higher voltage than the source, and when loaded, the middle of the cable has a higher voltage than both ends.

During stable operation these effects can be managed with Statcoms, shunt reactors and voltage regulation tap changers. However during transient operation you will be relying upon the static protective devices such as surge arrestors, depending on how large the transient is.

DC transmission does not suffer from the same reactive power component and has less losses, but it does require large convertor stations at both ends.