416 



ELECTRICAL EQUIPMENT 



windings or by one three-phase transformer, as shown in Fig. 259. 

 Primary winding may be connected either Y or delta and is in 

 no wise different from an ordinary three-phase winding. The 

 secondary, however, is provided with 15J per cent coils in two of 

 the phases and 15 J per cent taps in the other phase in such a 

 manner which are interconnected, as shown in Fig. 259. 



FIG. 259. 



b e ,a 





r v *i 



This may also be accomplished by means of two transformers 

 T connected as shown in Fig. 260. 



The choice between the two methods given above of obtain- 

 ing three-phase and two-phase on four wires depends for the most 

 part upon whether the three-phase or the two-phase load predom- 

 inates. Where the three-phase load is predominant, it is evident 



