Hollow conductors are used in the transmission lines to reduce corona loss. An electrical discharge is known as the corona discharge, often referred to as the corona effect, which is brought on by the ionization of a fluid, like the air surrounding a conductor that is electrically charged. 
The diameter of the hollow conductors are large as compared to the solid conductors. The corona loss is eliminated due to the large diameter. The skin effect of hollow conductors is less as compared to stranded conductors.
Hollow conductors reduce corona loss in transmission lines primarily due to their larger diameter and specific design characteristics.
Hollow conductors have a larger diameter compared to solid conductors of similar weight or cross-sectional area.
The larger diameter helps in spreading the electric field and reducing the intensity of the electric field at the surface of the conductor.
Corona discharge occurs when the electric field around a conductor becomes intense enough to ionize the surrounding air.
In a hollow conductor with a larger diameter, the electric field is distributed over a greater surface area. This distribution results in a lower electric field intensity at any specific point on the conductor's surface.
The reduced electric field intensity means that the air surrounding the conductor is less likely to undergo ionization and corona discharge.
With less corona discharge, there is a reduction in corona loss, which is the energy lost as a result of the ionization process.
The larger diameter of hollow conductors helps in achieving a more uniform voltage distribution along the surface.
A more uniform voltage distribution minimizes the likelihood of localized high electric fields that could lead to corona discharge.
The surface gradient, or the rate of change of electric field strength along the surface of the conductor, is lower in hollow conductors due to their larger dimensions.
A lower surface gradient further contributes to the reduction of corona loss.