old american electric locomotive

CHICAGO, LAKE SHORE & SOUTH BEND RAILWAY FREIGHt tRAIN HAULED BY A 72-TON LOCOMOTIVE equipment to work without overloading the substationis well illustrated by the following case: A trailing load of 240 tons was to be started on a3 per cent grade located at a substation of 300-kw.continuous capacity and capable of 100 per cent mo-mentary overload. With 25 per cent adhesion a loco-motive weighing 45 tons was required. If this locomo-tive had been equipped with high-speed motors: A,Fig. 2, the starting current would be 1280 amp., thusloading the substation to 768 kw. oV in excess of its parallel. In this, the motors are permanently con-nected in two groups of two motors in parallel. Instarting, these two groups are first connected in seriesacross the line with a variable series resistance andthen the two groups are connected in parallel. Withseries-parallel control, there are two economical run-ning points.

This method of operationresults in greatly reduced efficiency. It must be bornein mind also that the motor output at half voltage isapproximately half the output at full voltage. The adaptability of the low-speed freight handling even number of motors. Most freight equipments havefour motors. The following fundamental explanationof the operation of the control apparatus applies to600-volt, four-motor equipments. Placing all four motors in parallel across the linewith sufficient resistance in the circuit to limit the firstrush of current to a safe value is a most uneconomicaland an obsolete method of starting any car or locomo-tive equipment. The gradual cutting out of this seriesresistance holds the current, and hence the torque,within relatively close limits as the locomotive accel-erates. Control of this type is called rheostatic.