264 ALTERNATORS. 



The second method of connection is indicated above as 

 being of more general application. The modifications 

 required in order to make the instructions applicable to the 

 first method will be readily seen on referring to the diagram 

 Fig. 123. 



Instructions. Make connections between the alternators 

 to be synchronised through a 2-pole switch. Make 

 connection to one high-tension winding of the synchroniser 

 from the terminals on one side of the switch, connecting the 

 other winding similarly to the other pair of switch terminals. 

 Connect the low-tension synchroniser winding to a lamp or 

 voltmeter*, or to both in parallel. 



In order to measure the circulating current between the 

 machines, insert an ammeter in series with one of the switches. 

 In the figure an ammeter is shown for each generator. This 

 enables simultaneous readings of the output of each machine 

 to be made. If the machines are to be loaded, connect a 

 resistance to the circuit in series with an ammeter and switch. 



Connect a voltmeter to each alternator. Excite the 

 machines from a source of continuous current with an inde- 

 pendent regulating resistance for each generator. 



If one alternator is already running at normal speed and 

 voltage, run up the second to about the correct speed, and 

 adjust its field current until the voltages of the machines 

 are equal. 



The lamp will probably blink rapidly. The speed must 

 now be adjusted in the direction giving less rapid flickering. 

 The lamp should then go completely out and light up brightly 

 more and more slowly. When the action is sufficiently 

 slow and marked, so that in the case of a small machine two 

 or three seconds elapse between each period of brightness, 

 close the double-pole switch as the lamps are brightest 

 (if this is the condition when in synchronism). Then note 

 the sudden throw of the ammeter in the circuit between the 

 machines, and after this has assumed its steady reading, 

 regulate the field of the alternator until the ammeter reading 

 is as low as can be obtained. For large machines it is 

 essential that the speeds should be practically identical 

 before switching in. 



After this, the switch in the load circuit may be closed, 

 and the machines tested undej load. 



* If the machines are of large size a voltmeter is a necessity, in order to 

 judge the synchronism sufficiently accurately. 



