ARMATURE WINDINGS. 445 



Now the various inductors which constitute a given current 

 path through a wave wound armature are distributed under all 

 of the field magnet poles, so that, in the wave winding, equal 

 electromotive forces are induced in all of the armature paths and 

 there is no perceptible tendency for the production of local cur- 

 rents through certain armature paths, and through the wires 

 which connect the brush sets. On the other hand the various 

 inductors which constitute a current path through a lap wound 

 armature lie under two adjacent field magnet poles and, there- 

 fore, an inaccurrate centering of the armature may lead to the 

 production of veiy considerable local currents through the cur- 

 rent paths and brush connections of a multipolar lap-wound 

 armature. 



These local currents may be prevented from flowing out through 

 the brushes and across the brush connections, by making perma- 

 nent low resistance cross-connections in the commutator (or in 

 the armature winding) between each given commutator bar, and 

 every other bar which passes at the same time under a positive 

 brush. These cross-connections are called equipotential connec- 

 tions for the reason that every set of commutator bars so connected 

 will be at the same potential (no electromotive force between them) 

 if the magnetic field is symmetrical. Equipotential connections 

 obviate the increased tendency to sparking due to the local cur- 

 rents, but at the expense of a slightly increased heating of the 

 armature. 



54. Modified multiplex wave winding - -The above mentioned 

 advantage of the wave winding over the lap winding, namely, that 

 the electromotive forces induced in the various paths of a wave 

 winding are always balanced and do not tend to produce local 

 currents, applies to multiplex wave windings as well as to simplex 

 wave windings. Now, one advantage of the lap winding over the 

 wave winding, for low electromotive force machines, is that a 

 multi-path lap winding does not require an excessive number of 

 commutator bars like the multi-path wave winding. The follow- 

 ing modification of the singly reentrant w-plex multipolar wave 



