7-A] POLYPHASE TRANSFORMATION. H5 



motor load with 50 per cent, drop, while A has a lighting load 

 with, say, 2 per cent, drop, unaffected by the starting and stop- 

 ping of the motors on B. They are absolutely independent of 

 each other. 



9. Composite Transmission. If the phases A and B, Fig. 3, 

 were generated and utilized separately, it would not be necessary 



for B to differ from A 

 3j| by ninety degrees; B 

 M could have any phase, 



i even the same phase as 

 * A. Again A and B 



FIG 3. Two-phase generator and receiving m ight be of different 

 circuits with 3-phase transmission. 



frequencies ; in fact they 



can be treated as two independent transmission systems* whether 

 of the same or of different frequencies. In the same way a direct 

 and alternating current can be combined with economy of copper 

 and independence of regulation. 



10. Test. First note the single-phase transformations which 

 can be made with the transformers to be used, and determine 

 whether or not the transformers are suitable for the purpose. 

 Connect the transformers so as to transform from a 2-phase 

 system to a 3-phase system and make measurements of the 

 primary and secondary line voltages, and the voltage of the 

 T-connected coil, checking all by computation. 



Make corresponding transformation from a 3-phase to a 

 2-phase system. 



If the transformers are provided with two sets of coils, for 

 parallel and series connection, make the polyphase transforma- 

 tions with all possible voltage ratios. Compute the volt-ampere 



*(90- Various methods of composite transmission will be found in 

 the following: Elect. World, February 28, 1903, pp. 347 and 351, Vol. XLL, 

 No. 9; Am. Electrician, April, 1903, pp. 189 and 177, Vol. XV., No. 4; 

 Elect. Review (New York), March, 1903, p. 362, Vol. 42, No. n; Elect. 

 Age, March, 1903, p. 179, Vol. XXX., No. 3; Mill Owners, April, 1903, 

 p. 14. 



