THE CONTINUOUS CURRENT MOTOR 



161 



Comparison of Speed-load Curves. In Fig. 101 are shown 

 the speed-load curves for three motors having the same full- 

 load speed; curve A is that for a shunt- wound motor, curve 

 B is for a series and curve C is for a heavily compounded 

 motor. The shunt motor has a definite no-load speed and 

 the speed drops somewhat as the load is increased; on the 

 average shunt motor the drop from no load to full load may 

 be between 5% and 15% of the no-load speed. The amount 



2 4 6 8 10 12 14 16 18 20 22 24 



Armature current 

 FIG. 100. Comparative Current-torque Curves 



of decrease in speed depends upon the armature resistance; 

 the greater the resistance the greater the decrease in speed. 



The curve for the compound motor has the same shape 

 as that for the shunt motor but the speed decrease with 

 increase of load is much more marked. 



The series motor decreases its speed very much as its 

 load is increased; as the load is decreased the speed 

 increases rapidly and at very light loads the motor runs 

 at speeds which are far above the safe speed. If all load 



