ACTUAL LOAD TESTS 



37 



Overload heat runs require considerable attention. 

 Where an overload is applied for one or two hours, it 

 should be certain that normal load temperatures have 

 been reached before applying the overload. The over- 

 load must be carried only for the specified time, since, 

 in many cases, the temperature rises rapidly throughout 

 the whole period of the overload. Hence lengthening 

 or shortening the overload period a few minutes may 

 make several degrees difference in the overload tem- 

 peratures obtained. To avoid continuing an overload 

 run for a longer time than that specified, arrangements 

 for a sufficient number of thermometer and resistance 

 measurements must be made well in advance of the 

 end of the run. 



Fig. 11. Connections for Loading a D-C. Generator on a Water Box 



During the heat run all conditions should remain 

 normal, and the machine should be watched carefully 

 for any undue heating of bearings or field spools, or 

 for the appearance of defects. The wiring, holding 

 down bolts, belt lacing, etc., must also be watched. 



In making heating tests two methods may be used; 

 i.e., actual load tests and equivalent load tests. Several 

 different means for obtaining actual load tests may 

 be employed, such as "water box," "circulating," "feed- 

 ing back," "shifting the phase" and "induction gener- 

 ators." 



The "water box" method, as the name implies, 

 consists in driving the machine by either a motor or 

 engine and loading it upon a "water box," or rheostat. 

 (Fig. 11.) This method entails considerable expense, 

 since all the power generated is lost. To obviate this 



