TRANSFORMERS 



397 



Delta-delta. With the delta-delta system the leads of three 

 single-phase transformers are connected to the mains as shown 

 in Fig. 241. The e.m.f.'s and currents differ in phase 120 

 electrical degrees, and the line voltage is equal to the individual 



FIG. 241. 



transformer voltages. This voltage is commonly denoted the 

 " delta-voltage " to distinguish it from the " star or Y- voltage " 

 in the star-connected combination. Similarly the line current 

 must be distinguished from the current flowing in the closed delta 

 winding. 



The voltage and current relations are easily explained by 

 referring to the vector diagram in Fig. 

 242. 



If we denote: E = delta-voltage, or volt- 

 age between phases; 

 e = Y- voltage, or voltage 

 between phases and 

 neutral; 



7 = Y-current or line cur- 

 rent; 



FIG. 242. 

 i = delta-current or current in delta winding; 



then: 



and 



E=eV% or e = =, 



or = 



-=. 

 V3 



