Effective magnetic path length in Epstein frame test of electrical steels

The effective magnetic path length lm for a 25 cm Epstein frame test is studied on the basis of a relevant demagnetizing model and determined by a comparative measurement of dc and ac hysteresis loops at each value of peak flux density Bp, with the field recorded by H-coils placed above the mid-section of the limbs or calculated from the magnetizing current. The obtained Bp and frequency dependences of lm for testing core loss Ps and peak field Hp of an electrical steel are explained in terms of differential susceptibility along the measured loops and demagnetizing and eddy-current effects on local magnetization processes.