THE SYNCHRONOUS MOTOR 325 



condenser generally results in a power factor of perhaps 

 .90 or .95. 



86. Phase Shifting of a Synchronous Motor, as the Load 

 is Varied. It has been shown that varying the excitation 

 of the synchronous motor does not affect its load and it will 

 be remembered that the same thing was shown in the case 

 of one alternator operating in parallel with another. In 

 discussing the parallel operation of alternators it was proved 

 that a change in the relative phases of the machine e.m.fs. 

 was required in order to change the load distribution. 



Phase Shift Necessary for Load Variation. We can 

 show that the same thing holds good for a synchronous 

 motor; the motor c.e.m.f. must change its phase with respect 

 to the tine e.m.f. if a change of load is to be accomplished. 

 Of course, actually, the change in the load is what happens 

 first; then the motor e.m.f. changes its phase in order to 

 produce a corresponding change in the electrical power 

 input. 



FIG. 213. Vector Diagram to Show Effect of Phase Shafting of the 

 Armature of a Synchronous Motor. 



Vector Diagram Showing the Effect of Phase Shift. Fig. 

 213 shows how this phase shifting produces a change in the 

 power input. It is supposed that the line voltage and the 

 motor voltage are just equal and opposite, as shown at 

 OEi and OE m . The resultant of these two is zero and hence 

 this is the condition for zero input to the motor. 



