322 



ELECTRICAL MACHINERY 



Now let us suppose a circuit made up of a resistance R, 

 paralleled by a condenser (7, and we evidently have a cir- 

 cuit which, by properly proportioning R and C, may be 

 used to represent the synchronous motor. In Fig. 211 the 

 line current / is evidently equal to the vector sum of /' and 

 /". But I" corresponds to the energy current of the motor 

 and /' corresponds to the leading component of the motor 

 current. 



Also as we know I" = E/R and r = E2irfC, it is seen that, 

 by choosing proper values of R and C, I" and /' may be 



X X' 

 Field Current 



FIG. 209. Phase Characteristic and Power-factor Curves. 



made to take any values we like. Hence the circuit of 

 Fig. 210 is the exact equivalent of the synchronous motor 

 provided we so select R that the energy dissipated in it is equal 

 to the power supplied to the motor and the condenser has such 

 a capacity that its charging current is just equal to the reactive 

 component of the motor current. 



An increase in motor excitation (above normal) would 

 be represented in Fig. 210 by an increase in the capacity 

 of the condenser C, and an increase of the motor load would 

 be represented by a decrease in the resistance R. 



