CHAPTER I 



GENERAL PRINCIPLES OF SYNCHRONOUS MOTORS 



Construction. Synchronous motors have the same construction 

 as alternators. The few special features relative to the production 

 of the direct current necessary for their excitation will be treated sepa- 

 rately, later. It will be assumed 

 that the reader is already familiar 

 with the general details of con- 

 struction of alternators. 



There are motors having mov- 

 able armatures and stationary fields, 

 or vice versa, and also motors with 

 revolving iron masses in which all 

 the windings are stationary. These 

 machines are similar to the gen- 

 erators of the same types; for 

 example, Fig. i indicates, diagram- 

 matically, the principle of construc- 

 tion of a two-phase synchronous motor, with a ring armature and mov- 

 able fields, receiving an exciting current through the brushes b\ and &2- 



These motors are designed like generators, the essential condition 

 to be fulfilled being to have a low armature-reaction and powerful 

 inducing fields, in order to obtain good stability. 



Although it is more difficult to increase the number of poles 

 for small powers than for large powers, the construction of small 



FIG. i. 



