ALTERNATORS. 



263 



This arrangement has the advantage that an ordinary low- 

 pressure voltmeter may be used, while its dial may be 

 graduated so as to indicate the full pressure of the alternator, 

 since the actual voltage at the voltmeter terminals is always 

 a definite fraction of that generated by the alternator. 



Special forms of synchronisers, indicating whether the 

 alternator runs too fast, or too slow, are also employed, but 

 their description hardly comes within the scope of this book. 



EXPERIMENT XL. To SYNCHRONISE AN ALTERNATOR 

 WITH ANOTHER ALREADY RUNNING. 



DIAGRAM OF CONNECTIONS. 



FIG. 126. 



m v m.> Source of direct current. 



G V G 2 Alternator armatures. 



F v F z Alternator field windings, 



R^ R., Field regulators. 



R Variable resistance in load circuit. 



A Ammeter in load circuit. 



A v A 2 Ammeters reading output of each generator, 



Fj, F 2 Voltmeters reading voltage of each generator. 



S T Synchroniser transformer. 



L Synchroniser lamp, 



$j /S 2 Paralleling switches. 



S Switch in load circuit. 



Connections. These will necessarily depend upon the 

 nature of the machines and upon the nature of the per- 

 manent connections, if the machines are connected to a switch- 

 board. 



Supposing the machines to be without permanent 

 connections to a board, the method of running to be adopted 

 may be that indicated in Fig. 123, for low-tension machines, 

 or that shown in Fig. 124, if the pressure is higher. 



