The effects of overlapping joints in laminated magnetic cores on the m.m.f. and power required for their a.c. magnetization

Formulae are deduced for evaluating the increase in m.m.f. and power due to the presence of overlapping joints in a magnetic core under a.c. magnetization conditions, assuming that the magnetic material is homogeneous, and that its permeability is a constant quantity. The effect of hysteresis is considered, and the formulae appear to be applicable at frequencies in, at least, the power- and audio-frequency ranges.The investigation shows that a certain value of mean flux density exists, under constant-frequency conditions, for which the percentage increase of both the m.m.f. and the power loss attains a maximum value. The maximum value and the values of mean flux density at which it occurs increase as the frequency is reduced.Experimental results for both Mumetal and 4% silicon-steel have been obtained, and they serve to verify the general validity of the formulae which have been derived in the theoretical investigation.