Question

why we prefer long distance transmission over high voltage?

Answer 1

Alternating current can be transmitted over long distances using step up transformers. The loss of energy is negligible. Direct current can not be transmitted as such.
In the transmission of a.c. over long distances. The loss of power in the transmission lines is I²R, where I is the strength of the current and R is the resistance of the wires. To reduce the power loss, a.c. is transmitted over long distances at extremely high voltages.