THE INDUCTION MOTOR 



CHAPTER I. 



The General Alternating Current Transformer. 



1. The problem of problems, in the solution of which the electrical 

 engineer is deeply interested, and which underlies all others, is set be- 

 fore us in the form of the alternating current transformer possessing 

 considerable leakage and a relatively large magnetizing current. 



2. A transformer with an open secondary takes from the primary 

 mains just so much current as is necessary to produce a magnetic 

 field which can balance the primary voltage. This current neglect- 

 ing for the moment hysteresis and eddy currents lags behind the 

 primary voltage by a quarter of a phase ; hence the work done by this 

 current is zero, and the magnetizing current is therefore a "wattless" 

 current. This consideration is true only for a transformer without 

 leakage. The magnetizing current need not be a wattless current in 

 the sense in which this term is generally used. We shall learn more 

 about this in Chapter VIII. 



3. If you throw a non-inductive load upon the secondary, that is to 

 say, if the secondary of the transformer be closed through a resist- 

 ance, then the impedance represented by the action and reaction of the 

 primary and the secondary system of the transformer, is diminished, 

 permitting a larger current to flow. If, for didactic purposes, we 

 make the assumption that the whole magnetic flux of the pri- 

 mary is transmitted without loss into the secondary, and vice versa, 

 then the vector of the primary current must be composed of two 

 vectors, the one representing the magnetizing or wattless current, 

 lagging behind the terminal volts by a quarter of a phase, and the 

 other representing the watt irrent and being in phase with the ter- 



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