TransactionsPublished under the care of the General Secretary and the Treasurer . converter than in the ordinary converter, because at equalfrequencies the direct-current machine of the cascade converterobtains fewer poles and therefore a much larger pole distributionon the commutator at the same surface velocity. The difference 9. See also E. Arnold and J. L. la Cour, Der Kaskadenumformer SeineTheorie, Berechnung, Konstruktion und Arbeitaweise. 852 ARNOLD AND LA COVR: COMMUTATION. of voltage between two neighboring segments of the commutatorcan, for this reason, be kept considerably smaller i
TransactionsPublished under the care of the General Secretary and the Treasurer . converter than in the ordinary converter, because at equalfrequencies the direct-current machine of the cascade converterobtains fewer poles and therefore a much larger pole distributionon the commutator at the same surface velocity. The difference 9. See also E. Arnold and J. L. la Cour, Der Kaskadenumformer SeineTheorie, Berechnung, Konstruktion und Arbeitaweise. 852 ARNOLD AND LA COVR: COMMUTATION. of voltage between two neighboring segments of the commutatorcan, for this reason, be kept considerably smaller in the cascadeconverter than in the ordinary converters, which is of greatimportance in commutation. COMMUTATION OF ALTERNATING CUERENTS. 15. Polyphase Commutatoe us consider a three-phase commutator machine, Fig, 45,with a direct-current winding on the armature. If one suppliesto the stator winding a three-phase current, there is produced arotary field, which pulsates weakly. This rotary field is bestanalyzed into a sine-shaped fundamental field and into harmonic. riG. 45. Statob and Rotob Winding of aThree-Phase Commutator Motor. 60 c fields. The first rotates with synchronous speed nj)Z= revs, per Pminute; c is the frequency and p the number of pairs of poles inthe machine. Since the harmonic fields are ordinarily very small,these may be neglected in what follows. If we let the armaturebe driven by a current from an external source and rotate in thisfield with n revolutions per minute, there is induced in evei-y winding of the armature, composed of — wires, an propor-tional to {nj, — n) and of the frequency g _P {np — n)•~ 60 = c — c. C, =80 ARNOLD AND LA COUR: COMMUTATION. 853 is the frequency of the slip andc^ =^;—the frequency of the rota-tion of the armature. If the flux per pole is ^, there is inducedin every armature coil an effective er = —$!(;-* volts. If we add the induced in all the armature coils, and plotthe
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