The magnetic field of the dynamo-electric machine

The first portion of the paper is for the most part written around the subject of the reluctance of the magnetic circuit, particularly of the air-gap and teeth. Other matters are, however, referred to, such as that of the shape of the curve of flux traversed by the armature conductors, and that of the flux variation along the pole-face. Much of the analysis was indeed originally developed with other ends in view, such as the determination of harmonics in the e.m.f. wave, of losses in the pole-face and elsewhere, or the investigation of the cause of noises and like incidental effects of the magnetic changes. These are for the most part particular applications of the analysis. The determination of the reluctance of the gap is made to depend on two factors ; one, an equivalent length, which has, in the normal portion of the gap, the same reluctance per unit area as the actual gap ; the other, an equivalent area, made up of the area of the radial projection of the normal gap on the cylindrical surface midway between armature and field, with additions for the fringe effects at the boundaries, and, where necessary, reductions to take account of ducts and band recesses. The magnetization of teeth is also discussed. The second part of the paper deals particularly with slots in which conductors carrying currents are located. The subjects of distributed excitation and of the reaction of the load on the exciting field are here discussed. Finally the reactance of the imbedded conductors is investigated. A number of Appendices deal with details of the calculations.