ARMATURE WINDINGS. 423 



winding always gives two paths between the brushes whatever the 

 number of field poles may be. 



The simple ring winding when used with a multipolar field 

 magnet offers a number of paths between the brushes equal to 

 the number of field poles as explained in Art. 29, Chapter II., 

 and the simple ring winding corresponds in this respect to the 

 lap wound drum. 



The windings of a ring armature, when used with a multipolar 

 field magnet, may be grouped in coils, and these coils may be 

 interconnected in such a way as to give a symmetrical closed 

 coil winding which presents two paths between the brushes what- 

 ever the number of field poles may be. Such a ring winding 

 corresponds to the wave wound drum. 



The following discussion of lap and wave windings is limited 

 to drum armatures. 



From the fundamental equation of the dynamo, equation (21) 

 Chapter II., it is evident that a multipolar dynamo with a wave 

 wound armature (/' = 2) gives a greater electromotive force for 

 a given number of armature inductors, than the same dynamo 

 with a lap wound armature (/' =/). High voltage dynamos 

 (especially those of small current output) are usually therefore 

 provided with wave wound armatures, and low voltage dynamos 

 usually have lap wound armatures. 



The lap wound armature must have as many brush sets as field 

 poles if every current path in the armature is to be utilized. The 

 wave wound armature needs only two brush sets to bring into 

 service every armature inductor, as pointed out in Art. 50. 



45, Lap winding. Starting at commutator segment No. i, 

 in Figs. 52 and 53, if we proceed by front end connection to in- 

 ductor No. i, then along inductor No. I towards the back (or 

 pulley end) of the armature, then across the back (by dotted line 

 in Fig. 52) to inductor No. 6, thence along inductor No. 6 

 towards the front (or commutator end), then by front end con- 

 nection to commutator segment No. 2, we shall have completed 



