28 COMMERCIAL ELECTRICAL TESTING 



i*lE* (72-70=0.00017 Wr* (S^-S, 2 ) or 

 = 0.00017 W *^~ Sf) ft. Ibs. per sec. 



1 2 1 1 



, 0.00017 WV 2 (Si 2 - S 2 2 ;> 746^ 1 



Therefore, kw. . ^_^ X Q X 



23Q8 W* (5i 2 -5 2 2 ) 



If 7 3 and T 4 are respectively the times at which the 

 speeds Si and S 2 occur with no field on the machine, 



2308 Wr* (S! 2 -S 2 2 ) 

 then kw. in this case = ^- =r ~ 



J- 4 J 3 



The kw. core loss is then the difference between the 

 kws. obtained by the formulae given above. 



If the kw. running light has been obtained, 



2308 Wr* (Si 2 - S 2 2 ) -.Wf* (Si* - S 2 2 ) 

 kw. running light = =K- 



A11 .... K Wr* (S! 2 -S 2 2 ) 

 Also kw. friction = -- v JL 

 ^4^/3 



Or substituting for Wr 2 



j^ _ y 



Kw. friction = ^ =^Xkw. running light. 

 ^ 4 ^3 



Hence knowing "running light," the friction can be 

 calculated and the core loss separated from the ' ' running 

 light." 



In making "deceleration core loss" tests, the same 

 data should be recorded that are required in connection 

 with the "belted core loss" method. Tables II and III 

 show the standard method of calculating test results, 

 open circuited and short circuited, taken by the "belted 

 core loss" method. Table IV shows the method em- 

 ployed in calculating results of deceleration "core loss" 

 by using either the value of the moment of inertia of 

 rotating parts, or by "running light" test. 



