TRANSFORMERS 373 



The regulator then cannot hold a higher voltage than 135, 

 and should the voltage reach this value and tend to go higher, the 

 regulator would maintain a constant exciter voltage of this value 

 of 135; but the A.C. voltage would necessarily drop due to the 

 fact that it would be requiring a higher exciter voltage than 

 this value in order to maintain the A.C. voltage for which the reg- 

 ulator might be adjusted. The above value of 135 is selected only 

 as a matter of convenience and the regulator may be set for 

 whatever value it is safe to operate the condenser fields. If 

 they could be operated to as high as 145 volts the regulator should 

 be adjusted at 145 instead of 135. 



For a further study of the subject of " Synchronous Condenser 

 Regulation," the reader is referred to an article by F. W. Peek, Jr., 

 in the General Electric Review for June, 1913. 



6. TRANSFORMERS 1 



Fundamental Principles. A constant potential transformer 

 consists essentially of an iron core upon which are wound two 

 windings, a primary and a secondary. When one winding is 

 connected to an alternating-current supply of power, an alternating 

 magnetic flux is excited in the iron core and an alternating voltage 

 is induced in the secondary winding, as its turns are surrounded by 

 the same flux as the primary. If the now secondary winding 

 is closed through a resistance or other load a current will flow 

 therein. 



In an " ideal " transformer, power would be transmitted 

 from primary to secondary without any loss. In actual practice, 

 however, this is not quite possible on account of the losses which 

 take place in the iron core and the windings. Similarly, in an 

 ideal transformer, the ratio of primary to secondary voltage 

 would be equal to the ratio of the number of turns in the respective 

 windings. In a real transformer there is, however, also a voltage 

 drop caused by the resistance and leakage reactance of the wind- 

 ings. This reactance is due to the leakage flux which links with 

 the turns or part of the turns of one winding only. 



The action of a transformer can best be understood by means 

 of a vector diagram (Fig. 224). Consider first the open-circuit 



1 Part of this section is taken from an article on " Transformer Connec- 

 tions " in the General Electric Review by one of the authors and Mr. L. F. 

 Blume. 



