160 



SYNCHRONOUS MOTORS 



The physical explanation of this is that the armature current 

 reacts upon a flux produced wholly by said armature current. Ordi- 

 narily this self-produced flux would be perpendicular to the plane of 

 the coil, and would therefore have no component in the plane of the 

 coil upon which the current could react to produce a torque; but in 

 this case the unsymmetrical reluctance of the magnetic circuit results 

 in a flux not in the same direction as the M.M.F., and the motor 

 will actually run without excitation at very light load. The arma- 

 ture current is, of course, excessive. 



FIG. 81. 



Mechanical Analogue 



The approximate diagram of Fig. 81 lends itself readily to the 

 explanation of a very interesting mechanical analogue to the synchro- 

 nous motor. 



Consider two shafts, a driver and a driven, placed end to end in 

 the same line and connected together by an elastic coupling consisting 

 of an elastic string or band, the two ends of which are connected to 

 two crank pins on the two adjacent ends of the shafts in question. 

 Assume further that the tension of the elastic band is directly pro- 

 portional to the distance between the two crank pins which lie in 

 the same plane perpendicular to the shafts. In Fig. 82 is shown a 





