THE ALTERNATOR. / 



armature of a 5,000 kilowatt alternator manufactured by the 

 Westinghouse Electric and Manufacturing Company. This alter- 

 nator is mounted on the crank shaft of a 7,000 horse-power steam 

 engine having a speed of 75 revolutions per minute. 



Alternators of very large capacity, but comparatively small in 

 size on account of the high speed of driving, are now extensively 

 used in conjunction with steam turbines. These alternators are 

 always of the revolving-field type and their peculiar features are 

 the small number of field magnet poles, the wide gap space be- 

 tween armature core and field poles, and the extreme solidity of 

 the field magnet structure. Thus Fig. 12 shows, to a scale of 



Fig. 9. 



about i to 20, the revolving field magnet of a 5,000 kilowatt al- 

 ternator which is mounted on the shaft of a 7,500 horse-power 

 steam turbine and driven at a speed of 500 revolutions per minute. 

 Besides the revolving armature type and revolving field type, 

 there is a third type of alternator, called the inductor alternator 

 in which the iron field structure alone rotates, both the field wind- 

 ing and the armature being stationary. The rotating iron struc- 

 ture NNSS, Fig. 13, is called the inductor, and it is magnetized 

 by a large stationary coil BB which encircles it. The magnetic 

 flux produced by this coil passes from the polar projections 

 NNNN into a laminated structure AA, through the iron rods 

 RR to the other laminated structure AA, and thence to the polar 



