THE INDUCTION MOTOR. 



the current if we assume that the drop through ohmic resistance in 

 the primary amounts for point 4' to 10% of O E. Finally the 

 ordinates of the curve i* 2" 3" 4" represent the amount of watt-com- 

 ponent of the current that is available in the secondary circuit. It 

 would be superfluous here to say anything about the manner in which 

 these curves have been plotted, as everyone familiar with polar dia- 

 grams will readily understand it from the lines in the figure. 



It is of importance to note that, though the primary resistance was 

 assumed to have a value which exceeds about five times the real value 

 in practice, yet the curves L i' 2' 3' 4' D and I 2 '3 4 deviate compara- 

 tively little from each other. If OD were zero, then they would not 

 deviate at all. In reality, OD +- LD is almost always considerably 

 smaller than it is in our figure. If, however, OD is large in compari- 

 son with LD, and if the primary resistance is considerable, we have 

 to draw a diagram like Fig. 5. This will be the exception and not the 

 rule. 



16. Thus we have learned that the influence of the ohrnic resistance 

 upon the locus of the current is, in most practical cases, negligible; 

 but the energy dissipated in the resistance, is in all cases to be taken 

 into account ; this can be done by deducting the watt-component cor- 

 responding to the ohmic loss from the ordinates of the semi-circle 

 LD. We thus arrive at a curve similar to i" 2" 3" 4". 



GENERAL CONCLUSIONS AND SUMMARY. 



17. We are now enabled, with the help of the diagram, to solve any 

 question pertaining to the alternating current transformer. We shall, 

 in a later chapter, discuss in detail for a concrete case the many prob- 

 lems of interest which this diagram permits us to solve; here we 

 shall merely summarize the main conclusions at which we have ar- 

 rived. 



In Fig. 6 OA represents the primary current ti, OD the magnetiz- 

 ing current to, and AD is equal to v l z' 2 2 in which HI and n* are the 



7?j 



number of turns in the primary and the secondary, respectively. 



8 



