PROCEDURE IN DESIGN OF D.C. GENERATOR 211 



be tried. Bearing in mind that the maximum flux in the arma- 

 ture core is one-half of the total flux per pole, we have, 



Rd X l n X 6.45 X 15,000 = -~ 



whence 



6,970,000 



= 4 in. 



2 X 9 X 6.45 X 15,000 



Item (56): Weight of Iron in Core. The weight of a cubic 

 inch of iron is 0.28 Ib. and the total weight of iron in the core 

 below the teeth will therefore be 



0.28 X 9 X | [(17.5) 2 - (9.5) 2 ] = 428 Ib. 



Item (57): Weight of Iron in Teeth. 



0.28 X 1 X 0.521 X 9 X 57 = 75 Ib. 



Items (58) to (60): Iron Losses. Refer Art. 31. The watts 

 per pound are read off the curve of Fig. 34 on page 102; thus, 

 for the armature core we have, 



Bf _ 15,000 X 20 V 

 1,000 1,000 



whence watts per pound = 3; and total watts = 3 X 428 = 

 1,284. 



Similarly, for the teeth (item (59)) we get a loss with full- 

 load flux of 390 watts. The total iron loss of 1,674 watts, being 

 2.23 per cent, of the output, is rather higher than the average 

 as given in the table on page 104; but if the temperature rise 

 is not excessive, it will not be necessary to reduce the flux 

 densities. 



Item (61): Total Loss to be Radiated from Armature Core. 

 Refer Art. 34, page 109. The copper loss to be added to the 

 total iron loss is the amount of item (50). 



Items (62 to (64) : Cooling Surfaces. Refer Art. 34, page 107. 



Cooling surface item (62) = IT X 19.5 X 11 = 675 sq. in. 

 Cooling surface item (63) = TT X 9.5 X 11 = 329 sq. in. 



Cooling surface item (64) = \ [(19.5) 2 - (9.5) 2 ] X 4 = 1,820 

 sq. in. 





