THE SYNCHRONOUS MOTOR 



319 



resultant of OE m ' and OE is OR'. This resultant voltage 

 will cause a current to flow (through the two armatures 

 and line) which will lag nearly 90 behind OR' as the arma- 

 tures are highly inductive. This current is shown at 

 OI f in Fig. 207. This current is mostly reactive and it 

 leads the line voltage, ~OE g . Now if the motor voltage is 

 decreased to OE m " the resultant voltage becomes OR" 

 and the current through the circuit 01". This again is 

 reactive current and it lags behind the line voltage, OE . 



Power Factor Depends Upon Load and Field Current. 

 When the motor is already drawing from the line an active 



EM 



R' 



FIG. 207. Effect of Increasing or Decreasing the Field Current of the 

 Synchronous Motor. 



current (to supply the power for whatever load it is carrying) 

 and the field current is varied, then the total armature cur- 

 rent is made up of the active current and the reactive 

 current; the resultant power factor depends upon the rela- 

 tive magnitudes of the two. This fact accounts for the 

 results given in Fig. 205 which show higher power factors 

 for the full-load run and half-load run than for the no-load 



run. 



At light loads it is sometimes impossible to make the 

 power factor equal to unity, no matter how the field current 



