62 



COMMERCIAL ELECTRICAL TESTING 



The shunt in the commutating pole field is then 

 adjusted to give the best commutation at full load, 

 the amount of current shunted through the commutating 

 pole field being measured. The amount of this shunted 

 current should always be recorded. 



Fig. 20. Series Characteristic 



The open circuit tests, already described, are some- 

 times taken on commutating pole generators. 



The building up of a series generator is a more com- 

 plicated operation. The load increases with the voltage 

 and, therefore, great care should be taken in obtaining 

 the correct external resistance to prevent the load from 

 increasing rapidly. As it is practically impossible to 

 decrease the external resistance enough (i.e., put the 

 blade of the water box in far enough) to allow the 



