EXAMPLE OF ALTERNATOR DESIGN 



331 



where there are 10 holes per slot, each 1J4 in. in diameter, 

 making a total of | (1.25) 2 X 10 X 48 = 589 sq. in. 

 The weight of iron in core (item 30) is 



0.28 X 46.8 X [7r(38.125 2 - 24.125 2 ) - 589] = 28,000 lb., approxi- 

 mately. 



The weight of the iron in the teeth (item (31)) is 

 0.28 X 46.8 X [7r(24.125 2 - 20 2 ) - (48 X 1 X 4.125)] = 4,9001b. 



Taking the approximate flux densities as previously calculated 

 (items 27 and 28), and referring to the iron-loss curve, Fig. 34, 



Fia. 136. Armature stamping of 8000 k.v.a. turbo-alternator. 



page 102, the iron loss per pound for carefully assembled high- 

 grade armature stampings is found to be 6.1 and 3.2 watts in 

 teeth and core respectively. The loss in the teeth is therefore 



6.1 X 4,900 = 30,000 watts, and in the core below the teeth, 



3.2 X 28,000 = 90,000 watts, making a total of 120 kw., or 1.5 

 per cent, of the rated output, which is not excessive although 

 quite high enough for a machine of 8,000 k.v.a. capacity. 



Items (33) to (36). In a machine of so large an output as the 

 one under consideration, the weight and cost of copper should be 



