. Report of the Electric Railway Test Commission to the president of the Louisiana Purchase Exposition . power to the motorside of the motor-generator set and the frequency of the gen-erator was adjusted by varying the speed of this motor bymeans of its field rheostat. The alternating current was takenfrom the generator side of the motor-generator set, connectionbeing made to the high pressure winding of the General Electrictransformer through an oil switch. The low pressure side ofthis transformer was short-circuited directly through the rail ALTERNATING CURRENT LOSSES 395 under test in serie
. Report of the Electric Railway Test Commission to the president of the Louisiana Purchase Exposition . power to the motorside of the motor-generator set and the frequency of the gen-erator was adjusted by varying the speed of this motor bymeans of its field rheostat. The alternating current was takenfrom the generator side of the motor-generator set, connectionbeing made to the high pressure winding of the General Electrictransformer through an oil switch. The low pressure side ofthis transformer was short-circuited directly through the rail ALTERNATING CURRENT LOSSES 395 under test in series, with an ammeter shmit and the non-inductive resistance described below. Later it was found unnecessary to run the rotary converteron all tests at the higher frequencies, as the direct current mainsand the direct current motor-generator set could be used toadvantage in this connection, as shown in Fig. 113. Here the250 volt power circuit was placed in series with the armatureof the 250 volt generator, and power was supplied to the motor- 6600 ToltMains )il sWitcl ttansformer Transformers «W1»|J^. S^vitch Fig. 112. —Diagram of Connections for A. C. Tests. generator set at 500 volts. In other respects the connectionswere the same as in Fig. 112. In the tests where the frequencies were 30, 25, 20, 15, and 10cycles per second, the armature of the driving motor was sup-plied with power from the 250 volt direct current generator,while the field of this machine was excited from a circuit inwhich the pressure was obtained from the 250 volt powermains and the driving generator connected in series. By thisarrangement the driving motor was given a strong magneticfield and the pressure across the armature could be reduced toa low value, with a resultant decrease in speed. The con-nections were the same as those in Fig. 113, except that the 396 ELECTRIC RAILWAY TEST COMMISSION armature of the 500 volt motor was connected directly acrossthe brushes of the 250 volt generator. By proceed
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