. Electric railway review . -turns and the cross ampere-turns. The backampere-turns, included in the angle, b. Figure -1, directlyoppose the field flux, and the cross ampere-turns, included inthe angle, a, act at right angles causing a distortion of the lield Mux. This phenomenon is known as armature reactionand is proportional to the current in the armature. To consider more fully the effects of armature reactionrefer to Figure 5, which is a diagrammatic representation ofan armature winding. It will be seen that the current entersthe i>ositive brush (only one of which is shown) divides at
. Electric railway review . -turns and the cross ampere-turns. The backampere-turns, included in the angle, b. Figure -1, directlyoppose the field flux, and the cross ampere-turns, included inthe angle, a, act at right angles causing a distortion of the lield Mux. This phenomenon is known as armature reactionand is proportional to the current in the armature. To consider more fully the effects of armature reactionrefer to Figure 5, which is a diagrammatic representation ofan armature winding. It will be seen that the current entersthe i>ositive brush (only one of which is shown) divides at a,b and c, and leaves at the negative brushes. It is also ap-parent that as each coil passes under a brush it is short cir-cuited as shown at a, and when leaving the brush the currentflows through the coil in a direction opposite to that when thecoil is approaching the brushes. The backward lead of thebrushes brings the short-circuited coils under the influence ofthe field so that an electromotive force is generated in them. Interpole Motors—Figure 4. in the same direction that the impressed electromotive forcewill assume when the coils pass the brushes. If no currentwere generated in the short-circuited coils their inductiveresistance would cause the current to arc from the toe of thebrush to the segment passing from under it, resulting inserious sparking. This condition would be still more exagger-ated if the brushes were given a forward lead, as an electro-motive force would be generated in the short-circuited coilsthat would directly oppose the impressed electromotive forceas the coil passed from under the brush. In railway motors the brushes, of course, are stationary,the design being such that armature reaction is compensatedfor to a greater or less degree under ordinary conditions ofoperation, but it is plain, as the armatviie reaction increaseswith the armature current, that a point will be reached inperiods of overload at which excessive sparking will occur. In Figur
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