324 PRINCIPLES OF ELECTRICAL DESIGN 



CALCULATIONS. Continued 



115. Numerical Example. Calculations. Items (1) to (11). 

 With a frequency of 60 cycles per second and a speed of 1,800 

 revolutions per minute, the number of poles is 



P 



2 X 60 X 60 

 1,800 



= 4 



At a peripheral velocity of 18,000 ft. per minute, the diameter 

 of the rotor would be - - = 38.2 in. 



l,oUU A, IT 



Since the air gap is not likely to-be less than 1 in., let us decide 

 upon an internal diameter of the armature D = 40 in. (item (10)), 

 and determine the exact dimensions of the rotor after the air 

 gap has been decided upon. 



The line current (item (4)) is 



8,000,000 

 A/3 X 6,600 



700 amp., 



