244 PHASE CHANGERS, ETC. [Exp. 



6. This method of transformation is reversible ; *. e., if a 

 3-phase system be connected (see Fig. i) to XYZ as primary, 

 2-phase circuits may be taken from A A' and BB' as secondary. 

 7. Double Transformation. In Fig. 3 is shown a double 

 transformation, from the 2-phase gener- 

 atmg circuits A, B to the 3-phase trans- 

 mission circuits X, Y, Z, and from 

 these to the 2-phase receiving circuits A, 

 B. The receiving circuits, A and B, 

 may be used together, as for operating 

 FIG. 2. Voltage and cur- po lyphase motors, or separately as for 



rent relations. . 



lighting. 



8. As a further explanation of the T-connection, referring 

 to Fig. 3, suppose the connections OZ', OZ' were left out and 

 that, instead, a fourth wire s' (not shown) were used to connect 

 Z' and Z* '; each phase would then have its independent 2-wire 

 transmission circuit, wires xy for phase A and 22' for phase B. 

 In making the T-connection of Fig. 3, the fourth wire 2* is 

 omitted* and in its place use is made of the two wires x and y, 

 acting in parallel as a single conductor. The current from the 

 coil ZZ' flows to O and divides, passing through OX and OY 

 differentially, so as to have no magnetizing effect on the core 

 of XY. With respect to the current from Z', the two parts of 

 the coil XY are wound non-inductively. They should be inter- 

 spaced so as to have the least possible magnetic leakage and con- 

 sequent leakage reactance, which would give poor regulation on 

 phase B. This precaution is necessary in winding any T-con- 

 nccted transformer. 



The regulation of phase A and of phase B are as independent 

 of each other with three wires (Fig. 3) as they would be with 

 four wires making separate circuits ; phase B may have a heavy 



*(8a). There is obvious copper economy in this case in changing 

 from a 4-wire 2-phase to a 3-wire 3-phase transmission; see Appendix III., 

 Exp. 6-A. 



