THE SYNCHRONOUS MOTOR 329 



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represents the power supply of the synchronous motor. 

 A clutch BB' represents the synchronizing switch, a fly- 

 wheel D represents the ' armature of the motor which is 

 connected by a thin flexible shaft, C, to the clutch B'B. 

 A pulley E, carrying a belt driving some load, represents the 

 load of the synchronous motor. 



Operation Analogous to Synchronizing. The half of 

 the clutch B is running all the time as this represents the 

 live line to which the motor is to be connected. Now 

 evidently the clutch BE' could not be thrown together 

 with the half B' stationary; something would break. So 

 B' must first be driven by some outside source of power 



B B 



Clutch 



FIG. 214. Mechanical Analogy of a Synchronous -Motor. A, driver; 

 B-B , clutch; C, flexible shaft; D, heavy balance wheel; E, pulley 

 with belt. 



until it reaches the same speed as B and then when the pins 

 on B' are opposite to the holes of B, the clutch may be 

 thrown together. This corresponds to closing the synchro- 

 nizing switch of the motor. 



Illustration of Phase Shifting. When the clutch is 

 thrown in, suppose a certain point P' on D is just hi line 

 with a point marked P on the driver A. We know that 

 when load is put on the belt and pulley E, the thin shaft 

 C will twist, the amount of twist depending upon the 

 load on E. But if the shaft C twists backward, the point 

 P' must fall behind the point P by a certain angle; 

 this angle we called a in Fig. 213. 



