POLYPHASE CURRENTS.

87

the condition of the field that produces it. The secondary orsupplemental poles b 7 o' are therefore availed of. There beingthirty degrees difference of phase between the currents in coilsn k, the magnetic effect of poles if o' should correspond to thatproduced by a current differing from the current in coils n or kby fifteen degrees. This we can attain by winding each supple-mental pole b 7 o' with two coils h h 7 . The coils h are includedin a derived circuit having the same self-induction as circuit u,and coils h 7 in a circuit having the same self-induction as circuite, so that if these circuits differ by thirty degrees the magnetismof poles b 7 c 7 will correspond to that produced by a current dif-fering from that in either n or e by fifteen degrees. This is truein all other cases. For example, if in Fig. (18 the coils n 7 e 7 bereplaced by the coils h h 7 included in the derived circuits, themagnetism of the poles b 7 c 7 will correspond in effect or phase,if it may be so termed, to that produced by a current differingfrom that in either circuit n or e by forty-five degrees, or one-eiglith of a period.

This invention as applied to a derived circuit motor is illustra-ted in Figs. TO and 71. The former is an end view of the motorwith the armature in section and a diagram of connections, andFig. 71 a vertical section through the field. These figures arealso drawn to show one of the dispositions of two fields that maybe adopted in carrying out the principle. The poles bbcc arein one field, the remaining poles in the other. The former arewound with primary coils i j and secondary coils i 7 .t 7 , the latterwith coils k l. The primary coils i j are in derived circuits, be-tween which, by reason of their different self-induction, there isa difference of phase, say, of thirty degrees. The coils i 7 k arein circuit with one another, as also are coils j 7 l, and there shouldbe a difference of phase between the currents in coils k and l andtheir corresponding primaries of, say, fifteen degrees. If thepoles b c are at right angles, the armature-coils should be con-nected directly across, or a single armature core wound from endto end may be used; but if the poles b c be in line there shouldbe an angular displacement of the armature coils, as will be wellunderstood.

The operation will be understood from the foregoing. Themaximum magnetic condition of a pair of poles, as b 7 b 7 , coincidesclosely with the maximum effect in the armature, which lags be-hind the corresponding condition in poles b b.