154 THE DESIGN OF STATIC TRANSFORMERS 



a leak. As the tubes are well separated from one another, 

 and as the air consequently circulates very freely among them, 

 the efficiency of the radiating surface is considerably higher 

 than for the ordinary corrugated case. Self-cooled oil- 

 immersed transformers are very appropriate for sub-stations 

 wherever water for cooling purposes is either not available or 

 else expensive, or where it is of special importance that the 

 transformers shall require but little attendance. 



The Westinghouse Electric and Manufacturing Co. has 

 recently built twelve 1000-kva 100 000-volt 60-cycle trans- 

 formers of the above-described type for the Southern Power 

 Co. Fig. 87 is an illustration of the design. Of the 

 twelve supplied, three are for outdoor service, and nine are 

 installed indoors. 



In Fig. 88 is shown, out of its case, a three-phase, self- 

 cooled, oil-immersed, 50-cycle transformer recently designed by 

 the author for Messrs. Johnson & Phillips, and of which two 

 are now in service at the generating station of the Aston 

 Manor Corporation. The transformer is for 600 kva at a 

 primary pressure of 6300 volts and a secondary pressure of 

 356 volts. The periodicity is 50 cycles per second. 700 

 gallons of oil are used in this transformer. 



