The effect produced on the permeance of a laminated pole-core by the insertion of a solid steel fixing-piece

The object of the paper is to discuss the effect produced on the permeance of a laminated pole-core which has been perforated with an axial circular hole into which a solid steel fixing-piece or plug is inserted to receive the holts which attach the core to the yoke. The theory of a core in which the plug fits perfectly in the hole is first examined, and curves for the permeance calculation are prepared. The theory is then extended to apply to a plug which fits loosely in the hole, the influence of imperfect fit being shown by a numerical example. The application of the theory in practical cases is shown, in general, to be satisfactory. In the extreme example of pole-coies used in water-wheel generators, where numerous secondary matters have to be considered, the discrepancy between theory and practice is explained. The utility of the theory in calculating the permeance of transformer limbs consisting of laminae clamped together by insulated bolts is shown, and uses in certain problems of current conduction, e.g. in a perforated busbar, are suggested.