266 



ELECTRICAL MACHINERY 



circuit made up of the two armatures and the two lamps 

 ail in series. When the two e.m.fs. act together (in phase) 

 the lamps will glow, but when the two e.m.fs. are in 

 opposite phase (the condition required for synchronizing) 

 there will be no resultant voltage acting in this circuit, 

 as the two will just neutralize each other. If there is no 

 voltage in the circuit no current will flow through the 

 lamps and they will be dark; hence when the lamps are 

 dark it signifies that the two e.m.fs. are in phase opposition. 

 Lamps Used with High-voltage Machines. When the 

 machines are of high voltage, lamps cannot be used directly 



Synchronizing 

 Switch 



Xino 



Lamp 



FIG. 162. A Possible Connection for Using Low Voltage Lamp on 

 High-voltage Circuit. 



on the line, but small transformers must be used. Fig. 162 

 shows one scheme for using one transformer and one lamp 

 The coils on the outside legs of the transformer core are so 

 connected that when the two e.m.fs. are in phase oppo- 

 sition, no flux goes through the center leg, hence the lamp 

 is dark and, when the two e.m.fs. are 180 out of their 

 proper phase relation, the flux from both outside legs goes 

 through the center leg and so the lamp glows. 



Sequence of Operations in Synchronizing. To synchronize 

 the incoming machine, then, the proper sequence of opera- 

 tions is the following: The alternator is brought up to 

 approximately its proper speed and then its excitation 



