. Electric railway journal . K^stopj^ . \7ESEC\ \ u STOP L\ 1 60 70 20 30 40Seconds 50 60 70 190160 170 160 150 140 130 120 110 100 90 60 70 60 50 40 30 20 10 0 Fig. 13—Operation with Motor No. Fig. 12—Operation with Motor No. 4SPEED-TIME AND POWER-INPUT GRAPHS FOR CARS EQUIPPED WITH TAPPED-FIELD MOTORS 508 Electric Railway Journal Vol. 52, No. 12. field-controlled motor is also less during this period, be-ing but 76 amp. as against 84 amp. for the non-field-controlled motor. The reasons for these economies areseen by comparing the motor characteristic curves forthese two motors. These
. Electric railway journal . K^stopj^ . \7ESEC\ \ u STOP L\ 1 60 70 20 30 40Seconds 50 60 70 190160 170 160 150 140 130 120 110 100 90 60 70 60 50 40 30 20 10 0 Fig. 13—Operation with Motor No. Fig. 12—Operation with Motor No. 4SPEED-TIME AND POWER-INPUT GRAPHS FOR CARS EQUIPPED WITH TAPPED-FIELD MOTORS 508 Electric Railway Journal Vol. 52, No. 12. field-controlled motor is also less during this period, be-ing but 76 amp. as against 84 amp. for the non-field-controlled motor. The reasons for these economies areseen by comparing the motor characteristic curves forthese two motors. These show that the speed of thefield-controlled motor, with tapped field is about thesame as the motor without field control, while its speedwith full field is about 25 per cent less. The full fieldis used in accelerating so the rheostatic losses will becut out quicker and thus greatly reduced. The tappedfield is used for running and so the car is able to attainthe same speeds as can be attained with the non-field-control motor. By the use of field-controlled motors a means is pro-vided for rapid acceleration with a minimum amountof loss in the starting rheostats. The maximum cur-rent peak is higher with the tapped-field motor due tothe swing that takes place when changing from full totapped field. The first cost of tapped-field motors isalso somewhat
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