TRANSFORMERS 



167 



long. Close the secondary switches and by touching 

 the frame of one of the transformers with the fuse wire, 

 determine whether voltage is on the transformer ; a small 

 spark indicates that the transformer is excited. Now 

 excite the alternator, gradually bringing it up to normal 

 potential. As soon as field is applied to the alternator, 

 the man handling the fuse wire should begin tapping 

 its loose end on the primary terminal of the other trans- 

 former; if no spark is seen the transformers will operate 

 in parallel. If a small spark appears, connect a volt- 

 meter in series and read the difference of voltage with 

 normal potential on the transformers. If this voltage 



UA/WWWW-n Primary 



Secondary 



Normal 

 Secondary 

 Voltage 



:WWVWVW\T Primary 



Seconafary 



Fig. 49 

 Connections for Parallel Run 



is more than one-fourth of 1 per cent of the rated voltage 

 of the transformer, the wrong coil should be located and 

 corrected. Instead of reading the voltage, the exchange 

 current may be read by connecting an ammeter in the 

 circuit instead of the voltmeter. This current should 

 not exceed 5 per cent of the normal current. Continue 

 the parallel tests as above, until all the transformers 

 have been run in parallel with the one selected as stand- 

 ard. 



If the transformer has two circuits that may be oper- 

 ated either in series or parallel, the parallel test should 

 be rrmde by connecting together the corresponding ends 

 of these coils on one side, completing the circuit by means 



