Description - The Elementary Theory of Direct Current Dynamo Electric Machinery by Cyril Ernest Ashford
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 Excerpt: ...crosses show the directions of the induced E. M. F. in each case. Beginning with conductor No. 1, connect the front end to any commutator strip, say 'a, ' and from 'a' connect to either No. 8 or No. 10. Connection must not be made to No. 9, for this would put Nos. 1 and 9 in series, and as we have seen they must always be in parallel. It is necessary that the conductors to which No. 1 is connected shall 'change sides' as nearly as possible simultaneously with No. 1, hence Nos. 8 and 10 are chosen in preference to any others. If the connection is made from No. 1 to No. 8 in front it will be from No. 1 to No. 10 at back and vice versa. Since No. 8 is connected to No. 1 in front it must be connected to No. 15 at back and so on. The next step is to decide on the position of the brushes. Conductor No. 3 in the diagram is shown on the point of 'changing sides, ' that is to say it was cutting the magnetic field in one direction and is just about to cut the field in the other direction, and consequently the direction of the induced E. M. F. in No. 3 is also on the point of changing. Now in order to utilize the induced electromotive force to the best advantage the current must flow in every conductor in the same direction as the induced E. M.f., and therefore finally the commutator strip b must be under a brush. For symmetry the commutator strip f must be under the other brush. A moment's consideration will show that when the armature is running as a dynamo x is the positive brush. The two paths in parallel from brush to brush are distinguished by thick and thin lines. 34. Formula for E.M.F. generated in a Dynamo. To prove that in the armature of a dynamo the E.M.f. generated is given by NPn 2 W V where N is the total magnetic flux threading the armature, P is the tot...
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