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ELEMENTS OF ELECTRICAL ENGINEERING. 



TABLE. 



VOLTAGE RATIOS OF TWO-RING AND THREE-RING CONVERTERS (55o-volt type). 



The values of E and E 6 are not included in this table inas- 

 much as the alternating voltage of a four-ring converter is usually 

 specified as the effective voltage between opposite rings which is 

 the same as E 2 , and the alternating voltage of a six-ring con- 

 verter is usually specified either as the voltage between opposite 

 rings (= E 2 ) or the voltage between a given ring and the next 

 ring but one, between rings I and 3 for example (= 3 ). 



Voltage control of the synchronous converter. It is evident from 

 the above table that the direct voltage E Q of a synchronous con- 

 verter is very nearly constant if the alternating supply voltage E n 

 is constant. Therefore it is not possible to alter E Q at will if E n 

 is constant. If the field excitation of a synchronous converter is 

 reduced, the machine takes lagging wattless current * from the 

 alternating -current supply, and the effect of this wattless current 

 in the armature is to help the field flux and make up almost 

 completely for the decrease of direct-current field excitation ; if 

 the field excitation of the machine is increased, the machine 

 takes the leading wattless current, the effect of which in the arm- 

 ature is to oppose the field flux and counteract almost com- 

 pletely the increase of direct-current field excitation. If, how- 

 ever, an inductance is connected in the alternating-current circuit 

 outside of the machine, the lagging wattless current in the first 

 instance causes a considerable drop of alternating voltage, or the 

 leading wattless current in the second instance causes a consider- 

 able rise of alternating voltage, and the direct voltage of the con- 

 verter is decreased or increased correspondingly. To be able to 



* The statements here made are worded to apply to the single-phase converter. 



