138 ARMATURE CONSTRUCTION 



thereby induced in the conductor, and the current flowing when 

 the circuit is closed, will be directed away from the observer. 



In the present chapter the arrow-heads will always indicate 

 the direction of the induced electro-motive force, i.e. the direction 

 of both electro-motive force and current for the case of a dynamo. 



The diagram in Fig. 164 differs from that in Fig. 163 only in the 

 addition of (1) the brushes as there shown diagrammatically inside 

 the circle representing the commutator surface, (2) arrow-heads 

 showing the direction of the current, and (3) diagrammatic repre- 

 sentations of the pole faces. These latter are sketched at the very 

 outer edge of the diagram in order not to confuse the rest of the 

 diagram by additional lines. It will be seen that the typical turn 

 (represented by heavy lines), consisting of conductors 1 and 34, as 

 well as five other equally spaced turns (33-66, 65-98, 97-130, 

 129-162, and 161-2), is Vitfo provided with arrow-heads. Ivns is 

 because, at the instant considered, these six turns are passing 

 through the position of short circuit under the six brushes, which 

 are shown resting upon the twelve commutator segments connected 

 to the twelve ends of these six turns. The direction of motion is 

 clockwise, as shown by the large arrow at the centre of the diagram. 



Increased familiarity with armature windings may be obtained 

 by constructing so-called " developed " diagrams. A recent sugges- 

 tion for the arrangement of "developed" diagrams is that of 

 Stembridge. 1 In Fig. 165 is shown, arranged in accordance with 

 this method, a diagram of a 6-circuit winding with 60 conductors. 

 The winding pitches are given by the formula 



whence 



In a diagram drawn according to the Stembridge method, the 

 two ends of the armature are shown exactly the same size with 

 the end connections precisely as they might appear on the actual 

 armature. The cylindrical surface is shown " developed " or rolled 

 out flat on the paper, between the two end drawings, and the 

 conductors are shown jointed to their end connections by thin 

 lines, which, of course, unlike the other lines, do not represent 



1 "A Simple Method of representing Armature Windings," E. K. 

 Stembridge, Electrical Wvrld and Engineer, vol. xlvii. p. 265, 3rd February 



1 'JOG. 



