7V/ A' TRANSFORMER 199 



Figure 186 shows a Type H transformer assembled, but re- 

 moved from its case. 



88. Cooling of Transformers. All the energy lost in a trans- 

 former must be dissipated as heat. Although this energy is but 

 a small proportion of the total energy undergoing transformation, 

 it becomes quite large in amount in the larger capacity trans- 

 formers. The larger the transformer the more difficult it be- 

 eomes to dissipate the heat, for the kilowatt capacity of the 

 transformer increases jnuch faster than the radiating surface. 



Kii.. IsO.- Type II transform'- I " ' s ~- \Vamier oil-filled, self- 



,,MI tank. cooled, three-phase. distril>utioii-type 



transformer. 



irmen are divided into two self-cooled type* 



and artiticially-couled types, 'Tin- >elf-eooled typrs are usually 

 immersed in oil. The oil within the windings and core becomes 

 heated and. because of the lesser deiinty of the heated oil, it rises 



to the top Of the Case, where it becomes cooled. The cooled oil 

 has a greater density than the warm oil and so tlows downwards, 



in Close Contact with the case, where it i- further conled. 



it reaches the bottom of the Iran-former it again ri>es, passing 



up through the windings. In addition to carrying heal awa\ 



the \\indingsand OOTB, theoil i> an excellent in.-ulat orand dielect i ic. 



