The effect of the joints in the plates of a laminated iron core on the d.c. ampere-turns required for its magnetization

The effect of joints in a laminated core has been investigated experimentally (e.g. H. BOHLE: Journal I.E.E., 1908, vol. 41, p. 527), but the authors know of no theoretical treatment except that given by Moullin (¿The Principles of Electromagnetism,¿ p. 175). Allowance is there made for the gaps between the faces of the plates, but only on the basis of constant permeability in the iron. This method is now extended to calculate the effect of the gaps for any particular sample of iron under d.c. magnetization; the method is applicable for mean flux densities up to half the saturation value. When once the calculation has been made for a particular material it is available for plates of that material of any size and thickness. The calculations have been verified by d.c. tests with a fluxmeter. A suggestion is made for reducing the effect of the joints by cutting the plates at an angle less than 90° to the axis of the core. Experimental results are given in support of this suggestion.