The flux density was measured in a typical tooth of a 500-MV A synchronous generator. Peak flux densities of 14.3, 16.9, and 21.2 kG were observed in an open circuit test at 80%, 100%, and 125% of rated voltage. The search coil voltage waveforms were rich in odd harmonics tending toward a square wave. These voltages were reproduced in an Epstein test frame for the purpose of measuring the core loss in the generator material (M-14), a singly oriented and a cube-textured material. When the turbogenerator tooth flux density waveform was reproduced in the Epstein frame, the measured losses were less than the loss under sinusoidal conditions at all values of induction for all three materials. The less oriented the test material, the greater the relative decrease in losses under the observed tooth flux density wave form. These results are in agreement with an earlier work which established that a square waveform of rate of change of induction produces a minimum core loss.1