. Electric railway gazette . oduce the same output, and thus we are en-abled to make slow-speed generators. The samemay be said of motors, and it will have been ob-served that all slow-speed motors, such as thegearless motors, are i^rovided with multipolarfields. The philosophj- of this, simply stated, isthat if a given current fed to a motor having twopoles will give it at any specified speed a givenpower, the same current acting upon a motor withfour poles would produce a motor practicallyequivalent to two machines of the bipolar type,and as the power of a motor is also dependentupon its spe
. Electric railway gazette . oduce the same output, and thus we are en-abled to make slow-speed generators. The samemay be said of motors, and it will have been ob-served that all slow-speed motors, such as thegearless motors, are i^rovided with multipolarfields. The philosophj- of this, simply stated, isthat if a given current fed to a motor having twopoles will give it at any specified speed a givenpower, the same current acting upon a motor withfour poles would produce a motor practicallyequivalent to two machines of the bipolar type,and as the power of a motor is also dependentupon its speed, a four-pole motor will produce thesame power at half the speed of a similar motorwith only two poles. Thus far we have said nothing as to how weget the magnetism in our field magnets. We haveassumed, however, that they are electromagnets,viz., that the field magnets are made of soft ironand have no magnetism of their own, but areconverted into magnets by passing electric cur-rents through coils of insulated wire properly. on the other half, as would be the case were this abipolar field and there were but two brushes. Referring again to Fig. 50, since In a four-polefield the opposite poles are alike, the colls on thearmature diametrically opposite to each other asthey sweep by these poles will always have elec-tromotive forces generated in them in the samedirection. This being the case, we can connectthe diametrically opposite coils with each other,either in series or In multiple, so that they prac-tically form but one coil, and by bringing theends of this coil to the proper commutator blocksagain reduce the number of brushes to two. Inthis case the brushes will be most convenientlylocated at right angles to each other, about halfway between a north pole and its two adjacentsouth poles, or between a south pole and itstwo adjacent north poles. It is evident that ifopposite coils be connected in series the electro-motive force generated will be doubled, while theresistance Is
Size: 2029px × 1232px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookidelectricrail, bookyear1895
