444 ELEMENTS OF ELECTRICAL ENGINEERING. 



information needed for properly connecting the coils (of a simplex 

 winding) is the numbers of the commutator segments to which 

 the terminals of any given coil are to be connected. 



The matters above mentioned are illustrated in Fig. 61, which 

 represents a six pole drum simplex wave winding having 22 coils 

 of any given number of turns each, the half-coils being num- 

 bered from I to 44 as shown in the figure. The back pitch is 7, 

 inasmuch as half-coil No. 39 is connected across the back, as 

 shown by the dotted line, to half-coil No. 2, and half-coil No. I 

 is connected at the back to No. 8 and so on. The front pitch is 

 also 7, inasmuch as half-coil No. 2 is connected at the front end 

 to half-coil No. 9, as shown by the full line and so on. The 

 commutator pitch is also 7, inasmuch as the terminals of the com- 

 plete coil 1-8 are connected to commutator bars No. I and No. 

 8. The slot pitch or throw of the coils is 3. 



Any one pair of brushes A, B is sufficient for the wave wind- 

 ing shown in Fig. 61. The figure, however, shows three posi- 

 tive brushes A v A 2 and A z and three negative brushes B v B 2 

 and B y 



53. Further comparison of lap and wave windings. Equipo- 

 tential connections. In practice the armature of a dynamo 

 never is exactly centered in the field, but it is usually nearer to 

 one pole or poles than to others, especially after the bearings 

 have become worn. Inaccurate centering of the armature causes 

 more flux to enter or leave the armature at certain poles than at 

 others, so that greater electromotive forces are induced in the in- 

 ductors under certain poles than in the inductors under other 

 poles. These inequalities of electromotive force exactly balance 

 each other insofar as the closed circuit of the whole winding is 

 concerned, but if there are two or more positive brush sets and 

 two or more negative brush sets these inequalities of electromotive 

 force produce local currents through certain paths of the wind- 

 ing, and through the wires which connect the positive (or nega- 

 tive) brush sets together. These local currents increase the heat- 

 ing of the armature and they tend also to increase the sparking. 



