TransactionsPublished under the care of the General Secretary and the Treasurer . the additionalcurrent 4 rnax> the coefficient of stray induction S, and the surfacevelocity Vk on the commutator. The additional current igmanbecomes smaller the harder are the brushes and the greater theresistances ^,. of the connecting wires between armature windingand commutator. The resistance B, of the armature coils may ARNOLD AND LA COUR: COMMUTATION. 843 not be increased in order to improve the commutation, becausethen the armature gets too hot and the degree of efficiency of themotor too poor. This is
TransactionsPublished under the care of the General Secretary and the Treasurer . the additionalcurrent 4 rnax> the coefficient of stray induction S, and the surfacevelocity Vk on the commutator. The additional current igmanbecomes smaller the harder are the brushes and the greater theresistances ^,. of the connecting wires between armature windingand commutator. The resistance B, of the armature coils may ARNOLD AND LA COUR: COMMUTATION. 843 not be increased in order to improve the commutation, becausethen the armature gets too hot and the degree of efficiency of themotor too poor. This is true, also, in part, of the resistances E„ 12. Design of Direct-Current Machines to Obtain GoodCommutation. As the first condition for good commutation, we have foundthat the , which is inditced between the laminations lyingunder the brush tips, should be as small as possible. This induced by the armature field and the slot field. a). In order to keep this as small as possible it is neces-Bary to make the slot field and the armature field in the commu-. FiG. 37. Cast-Steel PolbOF Ganz & Co. iating zone as small as possible. The first is brought about byconstructing the slots relatively wide and not too deep. In orderto make the armature field small, the pole-tips and the arma-ture teeth ought to be so far saturated as may be made compatiblewitli expense of the copper on the field. In Figs. 37 to 39 arerepresented three typical pole constructions. b). In order to coiii])(iisat( tlie A e completely, it is neces-sary to induce in the short-circuited coils an which isequal and opposite in direction to the induced by the slotfield and the armature field. This can be effected according tothe proposal of Menges ( 34465, 1884) by placing thebrushes in the neutral zone and disposing between the main poles 844 ARNOLD AND LA COUR: COMMUTATION. auxiliary or compensating poles excited by the armature current,see Fig. 40. The necessary amp
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