208 POLYPHASE CURRENTS. [Exp. 



The most convenient and instructive method for studying the 

 electrical relations of these connections is to use three trans- 

 formers with the same ratio of transformation (say i: i), the 

 primaries and secondaries of which can be connected in any 

 desired manner. 



With three such transformers and with a 3-phase supply given, 

 make connections in the following six ways: 



With three transformers: 



(1) Primaries star-connected. Secondaries star-connected. 



(2) " " " " delta 



(3) " delta " " star 



(4) " " " " delta 

 With two transformers: 



(5) Primaries T-connected. Secondaries T-connected. 



(6) " V V 



In each case measure all electromotive forces and construct 



electromotive force diagrams, 

 comparing computed and meas- 

 ured results. 



The star- and delta-connec- 

 tions have already been dis- 

 cussed; the special relations of 

 the T- and F-connections, will 

 now be considered. 



24. T-connection. For the 



FIG. 15. Relation between currents -, ,. 



_ ./-connection, measure the volt- 



ana voltages in a T -connection. 



age OZ, Fig. 15, and note that 



it is 86.6 when XY is 100. For a balanced load, the three cur- 

 rents, /x, /Y, /z, are equal. For a non-inductive* load, Fig. 15, 

 the current in transformer XY is out of phase with the elctro- 

 motive force by 30 and the power factor (cos 30) is 0.866; 



* (243). For an inductive load, the currents take the positions shown 

 by dotted lines in Fig. 15; /x is now out of phase more than 30, and /y 

 less than 30. 



