PARTS OF A DYNANO-ELECTRIC MACHINE 77 



extensively for arc lighting. The armature had three 

 coils only, and these coils were connected to each other 

 and to the commutator as shown in the figure. This is 

 called an open circuit winding in contrast to (6), which 

 shows an eight-coil, ring armature with all of the eight 

 coils connected in series with each other, forming by them- 

 selves a closed circuit. Such is called a closed circuit 

 winding. The winding shown in (a) quite evidently does 

 not form by itself a closed circuit, in fact as the armature 

 revolves each coil is out of the circuit entirely twice per 

 revolution. 



Wave and Lap Windings. The next classification is 

 made according to the number of paths by which current 

 can flow through the armature winding to the external 

 circuit. In one type of winding, called the two circuit 

 or wave winding, there are two paths through the armature 

 no matter how many poles the generator may have. This 

 type of winding is used principally for railway motors; 

 it is seldom used for generators designed for lighting, power 

 purposes, etc. 



In another type of winding there are as many paths 

 through the armature winding as there are poles on the 

 generator; this is called the multiple circuit or lap winding. 

 By far the greatest percentage of machines are equipped 

 with this type of winding. 



From this classification we see that the most important 

 type of winding for c-c. armatures is the closed circuit, 

 drum, multiple path winding and we shall later give two 

 or three examples of this type. When the generator is 

 bipolar, the lap winding and the wave winding have the 

 same number of paths, namely, two. Two paths is the 

 smallest number which can be obtained with a closed cir- 

 cuit winding. 



In discussing armature windings we shall call any con- 

 ductor in which an e.m.f. is induced an inductor; the rest 

 of the conductors making up the winding we shall call 



