. Electric railway journal . of this time forthe different motors while operating on the same-lengthrun, are due to having the free running speed the samefor all motors. The average voltage per motor variesfrom 410 to 493. Field-Controlled Motors Most Economical for City Service To determine the advantages that field-controlled mo-tors might have over the motor selected, I have chosentwo additional motors for consideration. Motor No. 4is the same as No. 2 except that it is arranged for fieldcontrol, and motor No. 5 is a tapped-field motor of thesame size but built by a different manufacturer.
. Electric railway journal . of this time forthe different motors while operating on the same-lengthrun, are due to having the free running speed the samefor all motors. The average voltage per motor variesfrom 410 to 493. Field-Controlled Motors Most Economical for City Service To determine the advantages that field-controlled mo-tors might have over the motor selected, I have chosentwo additional motors for consideration. Motor No. 4is the same as No. 2 except that it is arranged for fieldcontrol, and motor No. 5 is a tapped-field motor of thesame size but built by a different manufacturer. Thecharacteristic curves of these motors, arranged to meetthe service conditions we are considering, are shown inFigs. 10 and 11, and speed-time, power-input, heating- g GO 30 50 3 25o r 30; 20 5 10 MOTOR NO. 4 ■ /u 8540 DiAv aramLine ^Ol t A/heVoH o 14els£age «v/ -J */ */ \ % w f- ra\- t v3iA te 4 / % f V; > & -A w & I MOTOR NO. 5 | Gear Ratio 15:66= 26 Av. Line Voltage 540 40 60 120Amperes 180. 10—Motor No. 4—55 hp. at600 volts 60 120 IfcOAmperes 11—Motor No. 5—55hp. at 600 volts \CTERISTIC CURVES OF MOTORS ARRANGED FORFIELD CONTROL current and voltage graphs using these motors are givenin Figs. 12 and 13. In order to compare their perform-ance with motor No. 2 more readily I have tabulatedthe results in Table II. Both motors will perform theservice satisfactorily without overheating, and bothshow a decreased power consumption over that of motorNo. 2. Motor No. 4 is the more efficient, however, andshows a decrease in power consumption over motor of about 5 per cent. A comparison of the graphs shown in Figs. 8 and 12indicates the advantages of field control for reducing therheostatic losses during the acceleration period. Therate of acceleration is the same in both cases. Withthe tapped-field motor the rheostats are entirely cut outat a speed of , in five and one-half secondsfrom the starting of the car, while with the non-
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