35 



THE THEOKY OF THE DYNAMO 



[Report of the Electrical Conference at Philadelphia in November, 1884, pp. 72-83, 90, 91, 

 104-107, Washington, 18S6 ; Electrical Review (N. Y.), November 1, 8, 15, 22, 1884] 



I will now proceed with the discussion of ' The Theory of the 

 Dynamo-Electric Machine.' I only claim in the skeleton of the theory 

 which I have here prepared to give a few points which may be of inter- 

 est and possibly of value to those who are constructing these machines. 



The principal losses of the machine I put down under the following 

 heads: (1) Mechanical friction; (2) Foucault currents in the armature; 

 (3) energy of the current used in sustaining the magnet; (4) self-induc- 

 tion of the coils; (o) heating of the armature. 



Of course the efficiency of the machine would be equal to the whole 

 work of the machine minus the different losses divided by the work, 

 namely : , 



JJT w LL efc. 



/ 



w 



Thus, when the losses are known, the efficiency of the machine is 

 known. 



The mechanical friction I shall not discuss. 



With respect to Foucault currents in the armature, by dividing up 

 the armature in the proper way, we can get rid of most of these. It is 

 very often effected in the Siemens armature by dividing up the arma- 

 ture into discs. 



I have purposely omitted the loss due to change of magnetism in the 

 armature as the armature revolves. 1 drew attention to this fact sev- 

 eral years ago. It has been recently experimented upon and found 

 that, although there is some heating effect, it is very small indeed. 



With respect to the energy used in sustaining the magnet, if the 

 magnet were of steel there would, of course, be no loss. The only 

 reason for not using a steel magnet is that the field is comparatively 

 weak. The field of a steel magnet is, I suppose, less than one-third of 

 the field due to a good electro-magnet; the two could not be made 

 equal by any possible means. Therefore, in most dynamo machines, 

 the magnet is produced by the current. 



