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Q. What would be the speed, running free on a level with maximum tonnage?

A. Fig. 402 shows it to be 17 m. p. h.

Q. Why is the necessary tractive force greater on up grades?

A. The locomotive, besides overcoming the various resistances, is practically raising its own weight and that of the trailing load, up a hight equal to the difference of elevation between the foot and the head of the grade.

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Q. How much pull would be necessary to lift each net ton of the train (including engine weight) on a grade of one foot per mile?

A. 2,000-5,280-0.3788 lbs.

Q. On a grade expressed in per cent.?

A. 20 lbs. for each per cent.

Q. To what is the total train resistance on a grade equal?

A. To the grade resistance (or weight lifting) plus the train resistance (or friction resistance) on a level.

Q. How are American track curves expressed?

A. In degrees, noted by the deflection from the tangent at points 100 feet apart; that is, the number of degrees corresponding to a 100-foot chord.

Q. In American railway practice, to what radius does each degree of curvature correspond?

A. 5,730 feet.

Q. How can the shortest curve (that is the one with the shortest radius) be determined, that a locomotive or a car with a given rigid wheel base can round?*

A. This calls for considerable mathematical knowledge, and engineers use for that purpose either tables or diagrams such as Fig. 402a.

*The expression "negotiate" is a vulgarism, and not warranted.

CHAPTER LXXXIV

ELECTRIC LOCOMOTIVES

Q. Describe the electric locomotives on some wellknown American system?

A. On the N. & W. road each unit consists of two like parts; the main trucks hinged on the Mallet system, each having two driving and one guiding axle, and being placed back to back, making the wheel system 2-4-4-2. Drivers are 62 inches, guide wheels 30; total weight 270,000; on drivers, 220,000 lbs. Length over all, both units, 105 ft. 8 in. Rigid wheel base, 11 ft.; total wheel base, 83 ft. 10 in. In each unit, four three-phase, adjustable-speed motors. Maximum accelerative tractive effort of the two units together, 125,000 lbs. ; one-hour tractive effort 87,000 lbs.; continuous, 68,000 lbs.

Q. What gives especially smooth handling of long electric trains with pushers?

A. They can stand at full tractive effort for a minute or more before the road engine has pulled out enough slack to let the pusher move; conversely, when a train is coming to a stop on a heavy up grade, and the road engine shuts off and brakes, the pusher can keep moving until the cars are bunched.

Q. What is a special advantage of the liquid rheostats? A. They permit adjusting the load to the individual motors, so that the driver, by watching his ammeters, can develop maximum tractive effort without burn-out. Q. Where is this of especial worth?

A. On a heavy grade with bad rail, as each motor can be loaded up to the slipping point, regardless of differences of driving-wheel diameters or of the local track conditions.

Q. How is the regenerative control handled?

A. As the engine goes over a summit, the driver watches his ammeter; when the current drops he shuts off the controller, opens the regenerating switch, then reopens the controller to "running."

Q. What happens then?

A. In a few seconds the current is 300 or 400 amperes; the train is at synchronous speed plus slip. It works up hill at synchronous speed minus slip, down grade at that speed plus slip.

Q. How is braking done on down grades?

A. By air alone, all through; because time is needed to change the phase-converter connections after synchronous speed has been reached, and in that time train control might be lost by the speed causing the wheels to slide back to "synchronous," when regenerative braking would be impossible.

Q. What can be said of the electric locomotive's capacity for sustaining overloads?

A. It can do so over much longer periods than the steam locomotive without difficulty.

Q. What is the effect of increased load on electric engines with series characteristics?

A. It slows them down.

Q. Of what types is this true?

A. The single-phase and the direct-current.

Q. What is the greatest advantage of the electric engine over the steam locomotive?

A. It utilizes its weight much better.

Q. Which average the least time in the round-house; the electric or the steam locomotive?

A. The electric.

Q. How long is the average steam freight locomotive making say 3,000 miles a month, in the round-house?

A. About 45 per cent. of the time on the road, 30 in the round-house, 25 in the yard awaiting orders, etc.* *Wm. McClellan.

Q. What two characteristics determine the value of an electric locomotive, other things being equal?

A. The degree to which it is self-contained, and the greatest power that can be got into the space allotted to the motors.†

Q. What frequency is favorable for electric locomotives?

A. 25 cycles, not only for the locomotives (on account of the better ratio of tractive effect to weight on drivers) and the great speed-range adjustment, but also for convenient and effective incandescent lighting of yards and shops, and operation of induction motors in shops.

Q. How are higher speeds attained with the singlephase locomotive?

A. By higher voltages from transformer to motor terminals.

Q. What is the capacity of a single-phase motor of 15 cycles, as compared with one at 25?

A. About 30 per cent. operation.

Q. Which approaches more nearly the efficiency of the direct-current motor?

A. That of 15 cycles:-in most sizes above 90 per cent. throughout its entire load range.

Q. What type does not slow down much with increased load or up grades?

A. The three-phase alternating current.

Q. If at 1,500 H.P. normal output the motors of a given three-phase locomotive have 2 per cent. slip, what will be the slip at five times the normal tractive effort? A. 10 per cent.

Q. What will the speed drop be?

A. About eight per cent.

Q. How much overloading can a good three-phase induction motor of say 750 H.P. stand?

A. Maximum torque of 6 to 7 times full load torque. J. B. Whitehead.

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