The power losses in magnetic sheet material at high flux densities

From an examination of the results of a number of investigators it is shown that while there is general agreement as to the validity of Steinmetz´s expression ¿Bx, where x is a constant index, for the hysteresis loss at flux densities up to about 10 000 C.G.S. units, there are considerable divergences between the results of different experimenters at flux densities above that value, particularly in tests on sheet material. Some find Steinmetz´s law to apply closely up to the highest flux densities at which tests could be carried out, whilst others record more rapid variations of hysteresis loss with B in the region of B = 10 000¿16 000. The extent of the departure from Steinmetz´s law also varies considerably, some observers finding a maximum exponent of approximately 2.0 and others obtaining values as high as 3.2. In the paper a series of tests, both by a.c. and ballistic methods, on a wide range of sheet materials is described. The results of this appear to confirm the increase in the exponent of B in the expression for the hysteresis loss at values of B between 10 000 and 15 000. They also show comparatively little difference between the various specimens of sheet material tested. The construction of a new Lloyd square for tests at still higher flux densities, and a further, more detailed, series of tests, both a.c. and ballistic, on a representative specimen of each type of material, making use of this square, are then described. These tests were carried up to B = 17 000 or 18 000 and, while confirming and extending the previous results of increased exponents of B for values up to 16 000, they indicate a rapid decrease in the exponent at the highest values of B employed.