158 



ELECTRICAL ENGINEERING 



According to the manner of exciting the magnet fields, direct- 

 current machines are divided into magneto machines in which the 

 flux is produced by permanent magnets; separately excited ma- 



FIG. 121. Shunt or self 

 excitation. 



Source 

 Power 



FIG. 122. Separate excitation. 



chines (Fig. 121) in which the flux is produced by a winding sup- 

 plied with current from some source outside the machine; shunt 

 machines in which the field winding is connected across the arma- 



(a) (b) 



(a) Long Shunt (6) Short Shunt 



FIG. 123. Series excitation. FIG. 124. Compound excitation. 



ture terminals and receives a small current at the full-machine 

 voltage (Fig. 122); series machines in which the field winding is 

 connected in series with the armature and carries the full arma- 



