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A BOLD NEW LOCOMOTIVE
For all the apparent conservatism in the selection of d.c. as the system of choice, the S-motor design was a bold departure from earlier electric locomotives. It was primarily the work of General Electric's Asa F. Batchelder, who patented four of the design's features. Most significant was a Batchelder innovation that produced the first successful use of bipolar gearless motors.
The lure of the gearless motor is the absence of gears, which by their very nature introduce friction (with its loss of operating efficiency) and require maintenance. In practice a gearless motor design is achieved by wrapping the motor armature around the driving wheel axle. This has the drawback of adding dead weight to the axle, which in turn lowers the locomotive's center of gravity, a detriment to good tracking. In an age of early motor design, placing the armature on the axle also limited the capacity of a motor by restricting its size to the space available between the wheels. Previous gearless designs usually placed the armature in a hollow quill that surrounded but did not contact the axle. The motor's fields were placed in the motor casing, which surrounded the quill and was attached to the locomotive frame. The quill ends were fastened to the drive wheels via springs or rubber to allow a flexible connection that reduced the unsprung weight of the motor and mitigated some of the stresses of starting and accelerating on the wheels and motors. The B&O; used a gearless quill drive in its historic locomotives of 1895 but chose geared drives instead for its second generation of locomotives in 1903. The New Haven also used gearless quills in its initial a.c. locomotive fleet of 1907 and likewise turned to geared quill drives for subsequent designs. But Batchelder chose a gearless drive that omitted the quills altogether. Such an attempt had only been tried on an "important" installation once before.[10] That was on the locomotives for the 1890 deep-tube electrification of the City & South London Railway in England. The C&SL; attempt was a disappointment, though, and the locomotives' pounding of the rails soon led to the use of multiple-unit motor cars in place of the locomotive-drawn trains. Thus Batchelder's initiative drew a good deal of attention throughout the industry.
----------------------- There were two significant differences between the C&SL; attempt and the Central's. First, the London installation was said to be very light, and the vibrations from running were readily "transmitted to and propogated in the surrounding soil of London clay in a way which could not be possible on a roadbed of the character of the New York Central."[11] Second, in the C&SL; design the entire motor was axle-mounted, which produced a relatively greater unsprung weight, a large contributor to rail-pounding. In the Batchelder design only the motor armature was mounted on the axle. The pole pieces were mounted on the truck frame. The resulting 11,000-lb dead weight of each axle, drive wheels and armature included, was "somewhat less than is customary with steam locomotives."[12] Since the most problematic element of the steam locomotive as regards wear on the track is the "impossibility of properly balancing the reciprocating motion of connecting and driving rods"[13] (completely absent in gearless designs), the concern for pounding the rails was heavily discounted. Engineers expected a twenty to thirty percent reduction in wear from that of a comparable steam locomotive.[14]
----------------------- Batchelder's innovation lay principally with his solution to the problem of maintaining a nearly fixed relationship between the frame-mounted field poles and axle-mounted armatures while permitting relative vertical movement of the axle. Batchelder solved the problem by providing only two field poles for each motor instead of the four customary in d.c. traction motors. This enabled him to place nearly-flat-faced iron pole pieces opposite each other in vertical planes parallel to the axle. The axle then was free to move up and down while the locomotive was moving. It also allowed the axle, drive wheels, and armature to be easily removed as a single unit when maintenance was needed.
Electrically, the magnetic flux was continuous from one end of the truck to the other, i.e., the fields were arranged in tandem so that the flux passed through all poles and armatures in series and then returned via the cast-steel side frames and two iron bars between the frames. The design, called "entirely novel" by the Street Railway Journal, effectively permitted each motor to act independently while remaining in circuit with the main flux.[15]
----------------------- Structurally, the Batchelder locomotive consisted of three components: 1) the main truck, 2) the pony trucks pivoted from each end of the main truck, and 3) the locomotive main frame and superstructure supported from below by the main truck and the pony trucks. The main truck included the four driving axles, motor armatures, and field poles. Each end of the truck frame was extended to provide a mounting for the coupler. A system of half-elliptic springs and equalizing levers suspended the locomotive main frame and superstructure, effectively providing cross equalization and three-point support for the load. The two pony trucks were single-axle, radial type, connected to and pivoted from each end of the main truck by a radius bar. An arrangement of linkages enabled these trucks to support the portion of the locomotive frame above them while retaining the ability to swing about their own centers. On straight track they also were self-centering. The design was reported by the Street Railway Journal to be "the standard construction adopted" by the Central for its steam locomotives.[16]
----------------------- With the motors placed around rather than above the axles, where they would encroach upon the superstructure, the designers were able to provide a roomy center cab for the engineer and train crew, as well as a center-aisle walk-through space from end to end of the locomotive. Contactors, rheostats, reversers, and such were placed in fireproofed steel boxes adjacent to the aisles. Since this equipment was small, the enclosure height could be kept low to afford the engineer excellent forward/backward visibility from the cab. The outer shape of the locomotive formed a neat, straightforward representation of the spatial arrangement within. Inside the cab, master controllers for multiple-unit operation and other equipment to be manipulated by the operator were provided at each end. The control system permitted three running connections: 1) four motors in parallel, 2) two groups of two motors in parallel-series, and 3) all motors in series. A motor-driven air compressor and, later, a small boiler to provide a limited amount of steam on passenger runs, were also placed in the cab.
----------------------- On the roof, a small pantograph known as a dc shoe was placed near each end. These enabled the locomotive to receive power from overhead conductors to be installed where complicated trackwork, as in Grand Central, would result in excessively long gaps in the third rail. In operation the dc shoe was extended to the overhead rail and held there by the engineer's pressing and holding the DC SHOE UP button. Upon release of the button, gravity would return the dc shoe to its down position. The first formal testing of the prototype for the Central's new electric locomotive took place on November 12, 1904. The event, which was open in the morning to railway officials and in the afternoon to the press, and locomotive number 6000, the object of everyone's attention, were well covered by the Street Railway Journal in its November 19 issue the following week. Appropriately, the testing took place on an experimental six-mile electrified section of track in nearly the same location that the early steam trials had been conducted by DeWitt Clinton some seventy years before. Commenting on number 6000's design, the Journal noted:
----------------------- The Journal observed that in spite of any effect the dead weight of the motor on the axle might have on the roadbed, there was none to be felt while riding in the cab. Moreover, it said:
----------------------- The Journal also compared the recent acceleration test of number 6000 with that of a steam locomotive two years earlier. The steam locomotive had been designed specifically to achieve high acceleration for suburban use. Both locomotives pulled 265-ton trains, locomotive and tender weights included, in the tests. The startling results recorded the new electric locomotive and train as reaching 30 mph in 37.5 seconds versus 55 seconds for its competitor. In its description of number 6000, the Journal noted that the "total rated capacity of the locomotive is 2200 hp, although for short periods, a considerably greater power may be developed, making it more powerful than the largest steam locomotive in existence."[19] The Journal noted also that with its multiple-unit control, the locomotive could be operated simultaneously with additional units to increase the effective pulling capacity:
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----------------------- In its competition with other forms of motive power, electric locomotives are particulary good at starting and accelerating heavy train loads. In heavily trafficked trunk lines, the electrics can handle longer trains and maintain shorter operating schedules than steam or even diesel-electric. They can literally save a railroad from having to install additional track where traffic would otherwise require it. The secret of the electrics lies 1) in their ability to exert a steady tractive force through their drivers, as opposed to the steam locomotive's intermittent traction-defeating bursts, 2) in the inherent characteristics of electric motors, and 3) in their effective use and placement of on-board equipment to achieve maximum power-to-traction efficiency. One distinguishing characteristic of the electric motor is its ability to deliver maximum torque at zero rpm (exactly the opposite of the internal combustion engine). Another is the electric motor's ability to deliver greater-than-normal horsepower for short durations. Electric motors rise to the demand, that is, they deliver the power called for until they overheat, at which time their insulation melts and their wires short or burn out. Electric motor horsepower ratings are thus given as functions of time, usually as one-hour and continuous. A rating for one-hour may be 50 to 60 percent higher than for continuous, and a rating for several minutes may be many times higher than that. The limit to an electric locomotive's starting a large load, then, is not so much the horsepower rating as the limits of adhesion between drive wheels and rail. Here again the electric locomotive has an advantage because a greater percentage of its weight can be carried by drive wheels than for a steam locomotive, which normally carries its fuel supply in a tender. By not having to generate its own power, the electric locomotive, unlike the steam or diesel-electric, can have every piece of apparatus on board used to direct power supplied from a distant power plant to the motors. In 1906, with testing of number 6000 completed, the Central ordered 34 more identical locomotives and took delivery later in the year. The new locomotives were numbered 3401 through 3434. Number 6000, the prototype, was renumbered 3400 and all were designated by the Central as Class T motors. In December electric operations from Grand Central began, thus concluding the first step of the project brought on by that fateful Park Avenue tunnel accident nearly five years earlier.
This is the third part of an article written in 1992 for Electric Lines magazine, just before it ceased publishing. |
