78 ELECTRICAL MACHINERY 



simply conductors. The wires on the outer side of the 

 coil of a ring winding are inductors, because when the arma- 

 ture rotates these wires move through the magnetic field 

 and an e.m.f. is induced in them. Those wires which are 

 on the inside of the armature core and on the ends are merely 

 conductors. 



Superiority of Multiple Circuit Winding. One reason 

 why the multiple circuit winding is used so much more than 

 the two circuit winding will appear when we consider the 

 voltage generated by a given number of armature induct- 

 ors, first when connected so as to give a two path winding 

 and then when they are connected to give a multiple path 

 winding. 



Suppose we have a 12-pole generator having 1500 active 

 inductors on the armature altogether. The voltage gen- 

 erated per inductor might be 2 volts. If these inductors 

 were arranged in a wave winding all of them would have 

 to be used in only two paths, so that there would be 750 

 inductors in series in each path. The voltage generated 

 per path would be 1500 and this would be the voltage of 

 the machine. Now this would be much too high for an 

 ordinary c-c. generator, as the highest voltage ordinarily 

 used in c-c. service is 600, which is the voltage of an ordinary 

 railway system. 



Suppose now that the inductors were arranged in a 

 multiple circuit winding; as the machine has 12 poles there 

 would be 12 paths in the winding and therefore the number 

 of inductors in series per path would be 125. The voltage 

 per path, which is the same as the voltage of the generator, 

 would be 250 which would be right for a lighting generator. 



A machine of the size we have in mind could not use a 

 fewer number of inductors than 1500 because in that case 

 the inductors would have to be of such large cross-section 

 that they could not be bent readily and therefore the opera- 

 tion of winding the armature would be too difficult. Of 

 course the two windings would have the same capacity 



