7-AJ 



POLYPHASE TRANSFORMATION. 



247 



Reverse the primary or the secondary coil of one transformer ; 

 the secondary voltages now form an open delta, making very 

 nearly an equilateral triangle, and hence forming a nearly sym- 

 metrical 3-phase system. Compute these voltages and verify by 

 measurement. This method was used for 

 obtaining polyphase current for operating 

 3-phase motors upon what was initially a 

 single-phase circuit with a so-called " tea- 

 zer" circuit (b 2 ) added. It was introduced 

 by Steinmetz; the name indicated a pul- 



FlG . 



sating (monocyclic) flow of energy instead tion from 



(XOF) to 

 (AOB). 



T ransforma- 

 3-phase 

 2-phase 



of a non-pulsating (polycyclic) flow. The 

 transformation is instructive, even though 

 its introduction has been discontinued. 



13. Miscellaneous Transformations. Several other trans- 

 formations are here indicated. Try these by experiment, so far 

 as time and facilities permit. Compute for each case the excess 

 of volt-amperes over watts ; see 24, Exp. 6-A. 



14. Fig. 4 shows a method for transforming from 3- to 2- 

 phase, with three transformers. The primaries are connected to 

 a 3-phase supply. The secondaries of the first 

 \^ two transformers are OX and OF. The third 



transformer has two secondaries, whose vol- 

 tages are AX and YB. What must be the 

 values of these, in order that AOB will give 

 true 2-phase voltages? 



15. Fig. 5 shows a method, occasionally 

 of laboratory use, of using three auto-trans- 

 formers for 3-phase transformation from 

 XYZ to xyz. What ratio of transformation 

 will be obtained by using three auto-transformers with a middle 

 tap? 



1 6. Fig. 6 shows two F-connected auto-transformers for 

 3-phase transformation from XYZ to Xyz. This is a method 



z 



FIG. 5. 

 formation 



Trans- 

 from 3- 



phase (XYZ) to 3- 

 phase 



