. L'avvolgimento di campo dell'ingegnere americano e della ferrovia . y è collegato in serie con l'armatura e produce un effetto magnetizzante che è proporzionale alla corrente dell'armatura. Le bobine ausiliarie sono posizionate il più vicino possibile alla superficie dell'indotto e le loro spire sono concentrate in quel punto. Questa disposizione si aggiunge materialmente all'esecuzione del motore, in quanto applica le influenze correttive dell'avvolgimento ausiliario nei punti in cui l'ef-fect distorcente della corrente di armatura è più forte. Questa disposizione,è molto più efficace di dove Th
1548 x 1613 px | 26,2 x 27,3 cm | 10,3 x 10,8 inches | 150dpi
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. American engineer and railroad journal . y field winding is connected in series with thearmature and produces a magnetizing effect which is propor-tional to the armature current. The auxiliary coils areplaced as close to the armature surface as mechanical con-siderations will permit, and their turns are concentrated at that point. This arrangement adds materially to the perform-ance of the motor, as it applies the corrective influences ofthe auxiliary winding at the points where the distorting ef-fect of the armature current is strongest. This arrangement, is much more effective than where the ampere turns are dis-tributed along the length of the auxiliary poles. The mag-netic field of the auxiliary winding acts in direct oppositionto that produced by the armature current. The resultant fieldis made up of three components—that due to the shunt wind-ing, that due to armature reaction, and that due to the aux-iliary windings. The field distortion usually produced byarmature reaction is therefore overcome, and the shape of the. AUXII.IARY-lOI.E DIRECT (TRREXT MOTOR. magnetic field at the point of commutation is maintained asformed by the main poles, and good commutation is madepossible over a wide range of speed. Type SA motors are shunt wound, and thus have a definitespeed for each point of the controller which is nearly con-stant for all loads. Heavy overloads may be momentarilydeveloped without injurious sparking. The motors are re-versible without danger and without readjustment of thebrushes. As the armature and auxiliary windings are con-nected permanently in series, it is only necessary to changethe external armature connections to reverse the directionof rotation. These motors develop their full rated outputthroughout the entire range of speed. They will carry full 114 AMERICAN ENGINEER AND RAILROAD JOURNAL. rated load at any speed within their range for six hours witha temperature rise not exceeding 40 deg. C. in armature andfield, and not exceeding 45 deg.
