all day efficiency is ratio of energy output to the energy input taken over 24 hour period. design distribution transformer for max. efficiency occurring at the avarage output power. performance of distribution transformer represent by all day efficiency.
Skin Effect: tendency of the current to crowd near the conductor surface.
Skin effect is proportional to frequency, conductor diameter and permiability. Skin effect increases effective resistance of conductor. In DC, no skin effect.
EXAMIANS