168 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
series commutating motor only at starting, it becomes 
capable of doing excellent work. Such a combination has 
recently been exploited by the Fort Wayne Company, and 
is worth describing as a type capable of being developed 
even for certain classes of railway work. 
The principle of the machine is quite simple. It con- 
sists of a double wound armature in a laminated field. 
The main winding is an ordinary monophase winding in 
slots on the armature core. Over this completed structure 
is wound a continuous current drum winding connected to 
an appropriate commutator. ‘The machine starts as an or- 
. dinary series wound motor, the commutator serving tem- 
porarily to rectify the alternating current. When up to 
speed the alternating current is thrown over into the inner 
winding and the outer winding with its commutator sim- 
ply furnishes the necessary exciting current. 
Fig. 92 shows the general appearance of the stationary 
motors constructed in this manner. “The small commuta- 
tors used in starting and for excitation is at one end of the 
armature, at the other end are two collecting rings for the 
alternating current and a centrifugal contact maker in con- 
nection with the pilot light, to show when synchronous 
speed has been attained. When this point has been 
reached a double throw switch is thrown over, transferring 
the transformer leads from the commutator to the collect- 
ing rings and simultaneously connecting the field wind- 
ing to the commutator. ‘The machine then operates as an 
ordinary synchronous alternating motor. 
It is capable of starting under its normal load with a 
current about fifty per cent greater than that required for 
the same torque when running in synchronism. Of course, 
the field may be so adjusted as to secure a very high 
power factor at all ordinary loads, say, .93 average power 
 factor from quarter load to full load, but in starting and at 
very light loads there is necessarily considerable lag. * As 
to efficiency, it is not essentially different from that of any 
other alternating machine of similar size, except that the 
duplex winding is obviously disadvantageous. A motor of 
    
    
  
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