380 



ELECTRICAL EQUIPMENT 



the heat. They may be built for large capacities, but the voltage 

 rarely exceeds 30,000 because of the difficulty of insulating them 

 properly. 



Oil immersed self-cooled or water-cooled transformers are gen- 

 erally used with hydro-electric power developments, the latter in 



Single-Phase 



Three-Phase 



Core Type 



Horizontal 

 View 



Shell Type 



Combination 

 Core & Shell 

 Type 



FIG. 225. Different Types of Transformer Core Construction. 



the generating station, while either type may be used with the sub- 

 stations, depending upon the availability of cooling water. Both 

 types are built for the largest capacities and the highest voltages. 

 Self-cooled oil immersed transformers have the core and coils 

 immersed in a tank of oil, the tank usually being corrugated so as 

 to increase the surface available for dissipating the heat generated 



