420 ELEMENTS OF ELECTRICAL ENGINEERING. 



stitute a closed circuit of wire. Such armatures are called open 

 coil armatures. The simplest form of open coil armature for a 

 direct current dynamo is represented in Fig. 21, Chapter II., 

 which shows a single turn of wire with its ends connected to the 

 segments of a two part commutator. 



Closed coil armatures always give a much steadier current 

 than open coil armatures, and they have a smaller tendency to 

 cause sparking at the brushes. 



41. Inductors. That portion of the element of an armature 

 winding which actually cuts the lines of force as the armature 

 rotates, and in which electromotive force is induced, is called an 

 inductor. Thus the inductors on a ring armature consist of the 

 wires which lie on the outside surface of the ring. The wires 

 which lie on the interior of the ring cut no lines of force, and are 

 therefore not inductors ; they serve only as return paths for the 

 electric current. In the drum armature the inductors are the 

 straight wires lying on the surface of the core parallel to the 

 shaft. The end connections between inductors, including those 

 portions of the straight wires projecting beyond the armature 

 core and pole faces (as in the case of barrel wound drums) are 

 not inductors. 



Armature inductors have been called armature conductors in 

 the previous chapters of this text, but in discussing armature 

 windings it is convenient to employ a term which cannot lead to 

 confusion. 



42. Armature coil. Element of a winding. That part of an ar- 

 mature winding which terminates at two commutator bars or seg- 

 ments is called a winding element or a winding unit. A winding 

 element consists usually of a single armature coil, but there may 

 be two or more coils in a winding element. The terms armature 

 coil and winding element are used synonymously hereafter. 



In so far as winding connections are concerned, the number of 

 turns of wire in an armature coil is a matter of indifference, and 

 therefore each armature coil may be treated as if it had one turn 



