TRANSFORMERS 



313 



has the advantage over the other connections that, if one trans- 

 former burns out the system can still be operated with the two 

 remaining transformers connected in V but carrying a con- 

 siderable increase of load. The V connection is discussed in Art. 

 194 below. 



Delta-Delta Delta-Star Star-Delta Star-Star 



FIG. 289. Single-phase transformers on three-phase circuits. 



The AY arrangement is used at the generating end of high- 

 voltage transmission systems so that the voltage per transformer 

 may be as low as possible. The system has a neutral point on 

 the high-voltage side which may be grounded. The YA arrange- 

 ment is used at the receiver end of the line. 



The YY arrangement may be used in place of any of the above 

 and gives a neutral point on both the high-voltage and low-voltage 

 sides. 



194. "Open Delta" or "V" Connection. If one trans- 

 former of a A A system burns out, the system can still be operated 



FIG. 290. Open delta or "V" 

 connection. 



FIG. 291. 



with the other two transformers without any change in con- 

 nections. This arrangement of two transformers on a three-phase 

 system, Fig. 290, is called the "Open Delta " or "V "-connection. 

 Each transformer carries the full line current and therefore for the 

 same output from the system the current in the transformer 

 windings is increased in the ratio A/3 : 1 or 73 per cent. 



