6-A] GENERAL STUDY. 209 



in transformer OZ the current is in phase with the voltage, 

 giving unity power factor. For a current of 100 amperes, on 

 non-inductive load, we have 



Volt- 

 E I Power Factor. Watts. amperes. 



Transformer XY 100 100 0.866 8,666 10,000 



Transformer OZ 86.6 100 i.oo 8,666 8,666 



"17^333 18,666 



This shows that the power output of each transformer is the 

 same ; for non-inductive load the two transformers require about 

 8 per cent, more transformer capacity (volt-amperes) than watts 

 power transmitted. For delta- and star-connection, on non- 

 inductive load, no excess of transformer capacity is needed. 



The T-connection is discussed further under Polyphase Trans- 

 formation, Exp. 7~A, where it is shown (8) that, for good 

 regulation, the windings OX and OY on one transformer must 

 be interspaced so as to reduce the magnetic leakage between 

 them. 



The neutral point in a T-connection can be obtained by a tap 

 at N in the coil OZ (see Fig. 9, Exp. 7~A), dividing the coil into 

 4 and f . 



25. V-connectlon or Open Delta. Draw a diagram similar 

 to Fig. 15, for the F-connection, and from the power factor of 

 each transformer show that for non-inductive* load this connec- 

 tion requires 15 J per cent, more transformer capacity than power 

 transmitted. Obviously a F-connection can be replaced to ad- 

 vantage by a T-connection ; even using the same two transform- 

 ers, there will be an advantage in the change, for there will 

 be less voltage on one of the transformers and hence less core 

 loss. 



It is seen that, as a general principle, apparatus in which cur- 

 rents and voltages are out of phase require greater volt-ampere 



* (253). Note that an inductive load will cause the power factor for 

 one transformer to become more and for the other less than cos 30, which 

 will make the regulation better on one and worse on the other. 

 15 



