With increase in the transmission voltage size of the conductors is reduced (Cross section of the conductors reduce as current required to carry reduces).
As the reduction in current carrying requirement losses reduces results in better efficiency
Due to low current voltage drop will be less so voltage regulation improves
Disadvantages:
With the increase in the voltage of transmission, the insulation required between the conductors and the earthed tower increases. This increase the cost of line support
With increase in the voltage of transmission, more clearance is required between conductors and ground. Hence higher towers are required.
With increase in the voltage transmission, more distance is required between the conductors. Therefore cross arms should be long
