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COMMERCIAL ELECTRICAL TESTING 



should be plotted, one curve for armature and one for 

 field, against times in hours as abscissae and degrees 

 centigrade rise as ordinates. Lines should be drawn 

 through zero and the plotted points corresponding to 

 the different loads, the intersections of these lines with 

 the line of 75 deg. C. rise giving the respective values of 

 time that the motor takes to attain 75 degrees rise 

 with that load. From these curves another curve 

 should be plotted with time as abscissae and amperes 

 load as ordinates. This is an ampere-time curve for 75 



Fig. 26. Connections for Load Running Test on Railway Motors 



deg. C. rise. On the same sheet on which the ampere- 

 time curve is plotted, a curve should be drawn with 

 time as abscissae and horse power as ordinates, the 

 horse power being calculated from the standard 75 deg. 

 C. characteristics. (Fig. 25.) 



In taking a load running test, as in the speed curve 

 test, two motors are geared together on the same shaft 

 (Fig. 26), one running as a motor at the rated voltage 

 and full load current and driving the other as a separately 

 excited generator. The separately excited field of the 

 generator is in series with the motor field, thus giving 



