AI/TERNATING MOTORS FOR RAILWAY WORK. 1389 
of the compound section of the transformer system to pro- 
duce the requisite go deg. phase difference, 2 and /, the 
parts of the compound transformer, and g % 7 j £ the 
segments of the secondary windings. Once given the two 
phase current, the shifting over to three phase 1is easy. 
The coil, 7, furnishes one phase, the resultant of & and £ a 
second, and the resultant of % and 7 the third, all of which 
are connected in the ordinary way to the motor, M. The 
result of this very ingenious combination is a very close 
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CO!}MF’OUND SECTION[OF TRANSFORMERE 
  
  
?IMPLE SECTION OF TRANSFORMER 
-4 
AAAANAM? WWW 
PN (g [MM 
  
  
  
  
  
  
  
  
  
  
  
Tt ot i 
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M 
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FIG. 104. 
  
  
approximation to a true three phase relation throughout a 
considerable range of load, both in starting and running. 
The use of three resultant phases tends to preserve a more 
uniform phase relation than would be obtained by utilizing 
the original two derived phases. 
The employment of a condenser, while it adds to the 
complication, tends to annul the inductance of the main 
circuit. At all events it can be made to give a very high 
power factor, better than that given by ordinary poly- 
phase motors. 
On the other hand, the condenser is an element of 
weakness in that it is of somewhat uncertain life, and un- 
less exposed to high voltage and used at rather high fre- 
quency, is both bulky and expensive. Its use involves