9 6 



ELEMENTS OF ELECTRICAL ENGINEERING. 



by impregnating the fibrous insulating 

 material, and partly to facilitate cooling 

 by carrying the heat from the core and 

 coils to the containing case. Especial 

 provision must be made for cooling very 

 large transformers. For this purpose 

 passage ways or ducts are left through 

 the core and coils, and the oil circulates 

 through these ducts and is itself cooled 

 by a coil of water pipe placed in the top 

 Fig - 164 - of the containing case. In some cases 



a blast of air is driven through the transformer by a fan-blower. 



Fig. 165. 



