. A text-book of electrical engineering;. resistance R of each doublebranch be 0-05 ohm. What will be the current in each branch when thetotal current is 100 amperes? Since the terminal pressure is the same for each branch, we have E^ - I^R = £, - I^R = 115 - A-o-05 = 114 - Wherefore /^ - /^ = 20. As the total current is 200 amperes, we have/j = 60 amperes,12 = 40 amperes. AAAAAA ^. ^^AAAAAl Fig. 117 /, 49- Series-parallel Ring-zoinding 133 The greater load and therefore the greater currents under some pole-pairs may lead to destructive sparking at the commutator. It is thereforeb
. A text-book of electrical engineering;. resistance R of each doublebranch be 0-05 ohm. What will be the current in each branch when thetotal current is 100 amperes? Since the terminal pressure is the same for each branch, we have E^ - I^R = £, - I^R = 115 - A-o-05 = 114 - Wherefore /^ - /^ = 20. As the total current is 200 amperes, we have/j = 60 amperes,12 = 40 amperes. AAAAAA ^. ^^AAAAAl Fig. 117 /, 49- Series-parallel Ring-zoinding 133 The greater load and therefore the greater currents under some pole-pairs may lead to destructive sparking at the commutator. It is thereforebest to provide such armatures with equalising connections by means ofwhich these differences between the currents in the different branches areequalised within the armature itself, and the same current is carried by eachbrush. The difficulty can, however, be overcome to a large extent by usingArnolds series parallel windings. Each branch of the armature winding isdistributed around the whole armature, so that any inequality between the. poles acts in a similar manner on every branch. The winding progresses inone direction only, and, after finishing a coil, passes to the correspondingcoil under the next pair of poles. Up to this point the winding does not differ from the series windingsalready described. These latter were, however, two-circuit windings, where-as Arnolds winding has more than two parallel paths. This result isobtained by so arranging the winding that, after going once round thearmature, we arrive at the coil next but one, or next but two, as the casemay be, to the coil from which we started; in the two-circuit winding wearrived at the next coil. To make this plain, we shall consider a bipolar machine and examine theeffect of winding successively every other coil, so that it is necessary to gotwice round the armature to complete the winding. This is shown in Fig. 118, 134 Electrical Engineering where the step is 2, and the number of coils 15. U and y have no comm
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