Harmonic losses in a three phase transformer core

The iron loss of laminated cores is always greater than the nominal loss of the steel as measured in an Epstein Square or single strip tester. The extra loss is due to a number of factors. Flux harmonics have been measured locally in individual laminations of grain-oriented silicon-iron in a 3 phase transformer core and the loss associated with the harmonic components has been estimated. For the experimental core used, the loss associated with the harmonics in the yokes and limbs was 15% of the total loss, and corner loss accounted for 17% of the total. The calculated loss in the core accounted for over 80% of the measured loss, the difference being due to the effect of mechanical stress and also the errors in estimating the losses.