162 



ALTERNATING CURRENTS 



by a potential winding connected across one phase of the gen- 

 erator, usually through a potential transformer. The plunger 

 of this magnet acts upon one end of a pivoted lever. On Ilic 

 other end of the lever there is an adjustable counter weight and 

 the lower contact of the main contacts. 



The direct-current magnet is operated by a winding connected 

 across the exciter terminals. The plunger of this magnet acts 

 upon another pivoted lever. On the other end of this lever there 

 is the upper contact of the main contacts, so that these main 

 contacts are not fixed but are " floating." A spring on the con- 

 tact end of the lever tends to keep the main contacts closed. 



Main Contacts 



Compensating Current 



Winding. Transformer 



D.C. Control 

 .Magnet 



Fia. 161. Elementary connections of alternating- voltage regulator. 



There is a differential relay magnet just as in the direct-current 

 regulator. One coil of this magnet always is connected across 

 the exciter terminals and the other coil is connected across the 

 exciter terminals when the main contacts are closed. A series 

 resistance limits the current in each to its proper value. The 

 armature of this relay magnet, when released, is pulled upward 

 by a spring and closes the relay contacts. These relay contacts 

 short-circuit the exciter field rheostat. A condenser is shunted 

 across these contacts to minimize arcing. 



The field of the exciter is first adjusted so that the alternator 

 voltage is about 65 per cent, below normal. This weakens both 

 control magnets so that the floating main contacts are closed. 

 This closes the circuit of the second winding on the relay magnet 

 which opposes the other winding. The relay armature is there- 

 fore released and the relay contacts closed. These contacts 



