|
Main
- books.jibble.org
My Books
- IRC Hacks
Misc. Articles
- Meaning of Jibble
- M4 Su Doku
- Computer Scrapbooking
- Setting up Java
- Bootable Java
- Cookies in Java
- Dynamic Graphs
- Social Shakespeare
External Links
- Paul Mutton
- Jibble Photo Gallery
- Jibble Forums
- Google Landmarks
- Jibble Shop
- Free Books
- Intershot Ltd
|
books.jibble.org
Previous Page
| Next Page
Page 30
These experiments were originally directed mainly toward an endeavor
to increase the tractive adhesion of the driving wheels of locomotives
and other vehicles, and to utilize the electric current for this
purpose in such a manner as to render it entirely safe, practical, and
economical. It will be apparent at once that a method of increasing
the tractive power of the present steam locomotives by more than 50
per cent. without adding to their weight and without injury to the
roadbed and wheel tires, such as is caused by the sand now commonly
used, would prove of considerable value, and the same holds true with
respect to electrically propelled street cars, especially as it has
been found exceedingly difficult to secure sufficient tractive
adhesion on street railways during the winter season, as well as at
other times, on roads having grades of more than ordinary steepness.
As this, therefore, is probably the most important use for this
application of the electric current, it has been selected for
illustrating this paper.
I have here a model car and track arranged to show the equipment and
operation of the system as applied to railway motors. The current in
the present instance is one of alternating polarity which is converted
by this transformer into one having the required volume. The
electromotive force of this secondary current is somewhat higher than
is necessary. In practice it would be about half a volt. You will
notice upon a closer inspection that one of the forward driving wheels
is insulated from its axle, and the transformed current, after passing
to a regulating switch under the control of the engineer or driver,
goes to this insulated wheel, from which it enters the track rail,
then through the rear pair of driving wheels and axles to the opposite
rail, and then flows up through the forward uninsulated wheel, from
the axle of which it returns by way of a contact brush to the opposite
terminal of the secondary coil of the transformer. Thus the current is
made to flow _seriatim_ through all four of the driving wheels,
completing its circuit through that portion of the rails lying between
the two axles, and generating a sufficient amount of heat at each
point of contact to produce the molecular change before referred to.
By means of the regulating switch the engineer can control the amount
of current flowing at any time, and can even increase its strength to
such an extent, in wet or slippery weather, as to _evaporate any
moisture_ that may adhere to the surface of the rails at the point of
contact with the wheels while the locomotive or motor car is under
full speed.
It will be apparent that inasmuch as the "traction circuit" moves
along with the locomotive, and is complete through its driving wheel
base, the track rails in front and rear of the same are at all times
entirely free from current, _and no danger whatever can occur by
coming in contact with the rails between successive motors_. Moreover,
the potential used in the present arrangement, while sufficient to
overcome the extremely low resistance of the moving circuit, is too
small to cause an appreciable loss of current from that portion of the
rails in circuit, even under the most unfavorable conditions of the
weather. In practice the primary current necessary is preferably
generated by a small high speed alternating dynamo on the locomotive,
the current being converted by means of an inductional transformer. To
avoid the necessity for electrically bridging the rail joints, a
modified arrangement may be employed, in which the electrical
connection is made directly with a fixed collar on the forward and
rear driving axles, the current dividing itself in parallel between
the two rails in such a manner that, if a defective joint exists in
the rail at one side, the circuit is still complete through the rail
on the other; and as the rails usually break joints on opposite sides,
this arrangement is found very effective. The insulation of the
driving wheels is very easily effected in either case.
As the amount of additional tractive adhesion produced depends upon
the _quantity_ of current flowing rather than upon its pressure, the
reason for transforming the current as described will be apparent, and
its advantages over a direct current of higher tension and less
quantity, both from an economical and practical standpoint, will for
this reason be clear. The amount of heat produced at the point of
contact between the wheels and rails is never large enough to injure
or otherwise affect them, although it may be quite possible to
increase the current sufficiently to produce a very considerable
heating effect. The amount of current sent through the traction
circuit will of course vary with the requirements, and as the extent
to which the resistance to slipping may be increased is very great,
this method is likely to prove of considerable value. While in some
cases the use of such a method of increasing the tractive power of
locomotives would be confined to ascending gradients and the movement
of exceptionally heavy loads, in others it would prove useful as a
_constant_ factor in the work of transportation. In cases like that of
the New York elevated railway system, where the traffic during certain
hours is much beyond the capacity of the trains, and the structure
unable to support the weight of heavier engines, a system like that
just described would prove of very great benefit, as it would easily
enable the present engines to draw two or three additional cars with
far less slipping and lost motion than is the case with mechanical
friction alone, at a cost for tractive current that is insignificant
compared to the advantages gained. Other cases may be cited in which
this method of increasing friction will probably be found useful,
aside from its application to railway purposes, but these will
naturally suggest themselves and need not be further dwelt upon.
Previous Page
| Next Page
|
|