422 



ELECTRICAL EQUIPMENT 



groups, depending upon the angular displacement between high- 

 voltage and low-voltage windings. These groups are given in 

 Fig. 267, which shows that the delta-delta connection and the Y-Y 

 connection are similar, both capable of being connected so as to 



Group I 



Angular 

 Displac 



Group II 



Angular 



Displacement 



180 



Group III 



Angular 



Displacement 



>U P I X A ? 



gular /\ /\ 

 icement / \ / \ 



o L_\ Z_A X\ X\ 



A B X Y A BX ^ 



C Y X C Y X 



AV 



A B Z 



C Z 



>up in A 



gular A \y^ 



icement / \ ) 



30 / \ / 



A B Z 



C Z 



B X 



FIG. 267. 



give an angular displacement of zero degrees between high voltage 

 and low voltage, or an angular displacement of 180 degrees between 

 high and low voltages. Group 3 consists of the delta-Y or Y-delta 

 bank, in which the angular displacement is 30. 



Three-phase transformer banks will not operate in parallel 

 unless the angular displacements between high and low voltages 

 are equal. The operative parallel connections are as follows : 



TABLE XLVIII 



OPERATIVE PARALLEL CONNECTIONS 



