For several years past some of our large manufacturers have used fractional pitch windings, for induction motors to a con siderable extent, and for alternators to a lesser extent. It was the original purpose of this investigation to develop by theory and experiment a method by means of which the effects of such windings may be calculated; and although this purpose has been successfully carried out as far as time allowed, there is still a very interesting part of the subject which must be left

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... r another time; namely, the relation of fractional pitch windings to squirrelcage motors. THEORY The theoretically ideal induction motor would have a very large number of symmetrically placed phase windings of full pitch on both primary and secondary structures, the primary windings being supplied with the same number of equal, sym metrical, simple harmonic electromotive forces. In this case the flux density across the air-gap, the primary current, and the secondary current would be distributed sinusoidally around the gap periphery at any instant, and these distributions would re volve smoothly around the periphery at synchronous velocity. The chief difference between this ideal machine and the actual is that the number of phases in the latter is small and there must, therefore, be several adjacent conductors or slots carrying the same current at the same instant, thus forming what may be termed a belt of conductors in which the current increases and decreases as a unit. On either side of this belt is another, the current in which differs in phase from that in the first by a considerable angle, 60° in a three-phase and 90° in a two-phase 1245