Niagara Falls 



1894 come up over one hundred and forty feet out of the wheel pits 

 from the rotating water wheels, which make two hundred and 

 fifty revolutions per minute. In order to obtain direct driving — 

 that is, without the intervention of toothed or friction gearing, or 

 belt or rope driving — the revolving portions of the generator 

 are arranged to rotate in a horizontal instead of, as is usual, a 

 vertical plane. 



A dynamo of any type whatever consists, as is well known, 

 essentially of two portions, one of which possesses motion with 

 respect to the other, viz., the armature and the field magnets. 

 Since the field magnets are almost invariably much heavier and 

 much less compact than the armature, the latter is usually chosen 

 as the moving part. In the case under discussion the contrary 

 has been decided on, the armature being fixed and the field mag- 

 nets rotating. This gives certain advantages in the matter of less 

 complicated electrical connections and of dispensing with the 

 armature's rubbing collectors altogether; it also gives the advan- 

 tage — much more important in this case than with smaller 

 machines — that, since the revolving magnets are arranged on a 

 ring and point inward, the attraction between them and the arma- 

 ture core tends toward neutralization of the strains of centrifugal 

 force. The greatest advantage, however, attained by this method, 

 and again one which is of far greater value in the present case 

 than in ordinary practice, is the high degree of insulation possible 

 with fixed armature coils and connections. The requirements 

 that had to be met in the way of limiting the centrifugal strains 

 were that the product of the sum of the weights of the revolving 

 parts in pounds and the square of their velocities in feet per second 

 should not exceed eleven hundred million. The weight of the 

 moving parts of each dynamo was also limited to eighty thou- 

 sand pounds, while the weight of the turbine and its shaft amounts 

 to seventy-two thousand pounds. 



This whole weight of seventy-six tons acts in one vertical 

 line — i. e., that of the turbine shaft — and revolves two hundred 

 and fifty times per minute. It would have been very difficult to 



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