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.
For reduction of harmonics method is given below:
integral slot winding
larger air gap
Sr≠Ss : avoid cogging
Sr-Ss≠P,2P,5P avoid synchronous cusps
Sr -Ss ≠ 3P avoid magnetic locking
here, Sr is number of rotor slot, Ss is number of stator slot