LA80RATC 



_,ED SCIENCE. 



RE G ftirATldN ^I*EST S 



51 



read at several intermediate points, the voltage being 

 held constant at all loads. A curve is then plotted 

 with speed as ordinates and amperes as abscissae. No 

 load and full load points of the cold speed curve should 

 also be taken. Fig. 17 shows the general shape of the 

 curve. Some motors with considerable armature 

 reaction give a speed curve which rises as the load 

 increases. 



Lo&cf 



Fig. 17. Speed Curves D-C. Motors 



When speeding up motors with increasing load, the 

 brushes must never be shifted far enough to produce 

 sufficient armature reaction to weaken the field. Care- 

 less shifting of brushes under load has sometimes 

 caused runaways ; hence care should be exercised when 

 attempting this operation. 



A test of the voltage regulation of alternating current 

 generators is sometimes made, but more frequently 

 the regulation is calculated from the saturation and 



