GENERATING ELECTRICITY COMMERCIALLY 193 



231. Armature and Core. The armature, of a dynamo 

 ^Fig. 84) consists of a steel or iron shaft on which are mounted 

 a large number of thin circular iron disks held together by 

 bolts. This arrangement makes a cylinder with a groove 



MICA INSULATI 



FIG. 84. Armature. 



cut in it, running parallel to the armature shaft. Insulated 

 wire is wound around the core and laid in the grooves, which 

 are lined with mica or some other insulating material. The 

 wires are painted over with shellac. Binding wires are 

 wound on the outside to hold the armature coils in place. 



The iron core or shaft is used in the armature to concen- 

 trate the lines of force and to keep them from escaping. 

 The electric current is generated by the rotary motion of 

 the armature between the poles of the magnets. 



232. Action of a Dynamo. A dynamo, then, is a machine 

 for transforming mechanical energy (which is the energy that 

 rotates the armature) into electrical energy, and for forcing 

 the current of electricity through the wires. 



A dynamo, when in action, may be considered as a pump, 

 which raises electricity from a low level or pressure to a high 

 level. When the dynamo is in action the electricity flows 

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