THE TRANSFORMER. 



22 9 



supply ; and it is desired to deliver three-phase currents at 240 

 volts between mains. Each side of the equilateral triangle pqr, 

 Fig. 197, therefore, must represent 240 volts, so that each of the 

 secondary coils a and b, Fig. 198, must generate 120 volts 



and have 120 turns of wire; and the secondary coil <:, Fig. 

 198, must generate 1/3/2 times 240 volts or 208 volts and 

 have 208 turns of wire. The coils a and b constitute one 

 continuous winding of 240 turns of wire, with a lead coming out 

 from its middle point. 



Dephasing action of the Scott transformer. When two transformers are used 

 for three-phase transformation as described in Art. no, the currents in the transformer 

 coils are not in phase with the induced voltages even when the receiving circuits are 

 non-inductive. The mutual action of the two transformers which causes the currents 

 a and b to differ in phase from the voltages E l and E v Fig. 188, and which 

 lowers the power rating of the two transformers in the ratio of I to 0.866 is called 

 dephasing action. There is a somewhat similar dephasing action in one of the two 

 transformers which together constitute a Scott transformer. Thus, when the Scott 

 transformer delivers current to balanced non-inductive receiving circuits, the currents 

 in the three coils a, b and <r, Fig. 198, are represented by lines drawn from the 

 center of the equilateral triangle pqr. Fig. 197, towards the apices r, p and q 

 respectively. That is, the current in coil a is 30 behind the induced voltage in a f 

 and the current in coil b is 30 ahead of the induced voltage in b. 



