260 



ALTERNATORS. 



swinging too much, and if its moving parts are light and 

 free enough to follow rapidly the variation of voltage. 



It is important to notice that in the direct form of syn- 

 chroniser just described, parallelism is indicated by zero 

 reading on the voltmeter or darkness of the lamp. A single- 

 pole switch and single lamp are shown in Fig. 123. Usually 

 a double-pole switch with a lamp across each break in the 

 circuit would be employed. The lamps would, in this case, 

 be in series with one another, and would, consequently, only 

 receive half as much voltage, i.e., the full voltage of one 

 alternator as a maximum. 



Synchronisers Employing a Transformer. If the pressure 

 of the alternator is too high to make possible direct connection 

 to a lamp, a transformer may be used, the primary winding 

 taking the place of the lamp shown in Fig. 123, and the 

 lamp being connected in series : with the secondary, in 



FIG. 124. DIAGRAM OF SYNCHRONISER. 



order to reduce the pressure applied to the lamp. The action 

 is exactly the same as that just described, since the current, 

 passing round the transformer, will be nil when the alternators 

 are in phase, and the lamp will not glow under these conditions. 



The above methods both have the peculiarity that a 

 lamp is required for each pole of the switch, and that the 

 lamp ceases to glow when synchronism is attained, unless 

 the lamps are connected from one switch to the other, instead 

 of in parallel with the switch. 



The following modification (see Fig. 124) is of more 

 general use, as a 2-pole switch may be used with a single 

 lamp or voltmeter, and the iamp can be made to glow at 

 coincidence or at opposition in phase as desired. 



