446 



ELECTRICAL EQUIPMENT 



such precautionary measures that drying in most cases will be un- 

 necessary. Large transformers with properly constructed tanks, 

 provided with chloride breathers may be shipped with or without 

 oil. Small high-voltage transformers may be shipped filled with 

 oil using chloride breathers where necessary. With such ship- 

 ments careful examination, if shipped without oil, and oil tests if 

 shipped oil filled, are of utmost importance. The oil samples 

 should be taken both from top and bottom after the tank has 



FIG. 281. Thermometer with Electrical Connections for Use on 

 Water-cooled Transformers. 



stood for twenty-four hours, the required puncture strength of the 

 oil to be as previously given. 



Where transformers are shipped without the oil in the tanks 

 it is almost invariably necessary to dry them out first. This may 

 be accomplished in several ways, of which the "external" and 

 the " internal " heat methods are mostly used. 



The " external " method requires the circulation of heated air 

 through the transformer in its tanks. Dry air is forced at a tern- 



