TRANSFORMERS 391 



may have a capacity up to 30,000 or 40,000 kilowatts, depending 

 on the voltage, and inasmuch as it is now possible to build single- 

 phase transformers for one-third this capacity, the arrangement 

 is entirely feasible; otherwise it would be possible to install 

 two banks in parallel for each line. 



Connections. Among the great variety of transformer ma- 

 nipulations in power and general distribution work, either for 

 straight voltage transformation or for phase transformation, the 

 following are the most generally used: 



Voltage transformation: 

 Single-phase; 

 Two-phase; 



Three-phase, delta-delta; 

 Three-phase, delta- Y, and vice versa; 

 Three-phase, Y-Y; 

 Three-phase, open-delta; 

 Three-phase, T. 



Phase transformation: 



Two- or three-phase to single-phase; 

 Two-phase to six-phase; 

 Three-phase to six-phase. 



Voltage Transformation . Single-phase. The windings may be 

 divided into sections and variously connected to meet different 

 requirements. So, for example, are most standard distributing 

 transformers made with two low-voltage coils. 



Fig. 230 represents the straight connection of two trans- 



I I 



FIG. 230. 



formers to 1000-volt mains, the transformer consisting simply of 

 single high- and low-voltage windings. 



Figs. 231 to 233 represent different connections of transformers 



