THE TRANSFORMER 



215 



transformer be is called the main transformer and ad the teaser 

 transformer. 



Figure 205 (c) shows the voltage diagram. The three-phase 

 supply is assumed to be 100 volts across lines and the transformers 

 have a one-to-one ratio. 



The \ ,1 1 a ues# dr and E db are each equal to 50 volts and are 180 

 apart, since coil dc and coil db are both on the same magnetic 



(a ) \ Main Transformer - x 

 Primary and secondary voltages 



Teaser 

 Transformer 



' ' 



Method of rormprtiiiu: transformer coils. Vector diagram. 



.. 205. T-c-oimei-teil transformers. .'l-phasf to .'{-phase. 



circuit. Each side of the equilateral triangle, Fig. 205 (c), is 

 equal to 100 volts. The voltage Eda is the altitude of the equi- 

 lateral triangle and is, therefore, equal to 100\/3/2 or 86.6 volts. 



line relations hold in the secondary coils, SO that </'//. 

 symmetrical t hrec-phase system. The full capacity of the trans- 

 formers is not utili/ed, however. The teaser transformer oper- 

 ates at only 86.6 per rent, nf its rated vnltage and in the coils lnl 

 and dc the current lags 30 in one and leads 30 in the other at 

 unity pov, i. This uivcs a power-factor of 0.8<r> in the 



md is therefore equivalent to the transformer- 

 operating at only 86.6 por cent, of their rated kv-a. capacity. 



