brackets in such a way as to permit of an uninterrupted passage of an
upward pressing trolley wheel underneath it. The trolley wire itself
may be either round, grooved, or figure 8 in section. Where a round
wire is used, No. 00 B. & S. gauge is the most common size. Figure
8 wire, so called from its section, which is shown in Fig. 64, is
designed to present a smooth under surface to the trolley wheel, which
will not be interrupted by the clamps or ears used to support it.
Clamps are fastened to the upper part of the figure 8. The grooved wire
is rolled with grooves into which the supporting clamps fasten. This
wire also presents a smooth under surface to the trolley wheel.
[Illustration: Fig. 65. Trolley Wire Clamp and Ear.]
=Trolley-Wire Clamps and Ears.= The trolley is supported either by
clamps or by soldered ears. One type of clamp grasps the wire by virtue
of screw pressure. A soldered ear is shown at E, Fig. 65. This ear has
small projections at each end, which are bent around the wire to assist
the solder in holding the wire to the ear. Another form of ear, used to
some extent, holds the wire by virtue of having the edges of the groove
offset or riveted around the wire.
The ear or clamp screws to a bolt which is insulated from the metal
ear through which passes the span wire. A cross-section through a
common type of trolley-wire hanger is shown in Fig. 66. Here there is
an outer shell of metal, which is adapted to hook to the span wire. In
this shell is an insulating bolt, that is, a bolt surrounded with some
form of insulating material which is very strong mechanically and not
likely to be cracked by the hammering action of the passing trolley
wheel. Most of the insulating compounds used in making trolley-wire
insulators are trade secrets. Another kind of insulator called the “cap
and cone” type is shown at C, Fig. 65. In these insulators, the metal
part B which fastens to the span wire does not completely surround
the insulation C. Wood has sometimes been used for the insulation of
trolley-wire hangers.
[Illustration: Fig. 66. Cross-Section Trolley Wire Hanger.]
=Span Wires.= In city streets, the trolley wire is commonly suspended
from span wires stretched between poles located on both sides of the
street. These span wires are of ¼-inch or ⅜-inch galvanized stranded
steel cable. In order to add to the insulation between the trolley
wire and the poles at the side of the street, what is called a _strain
insulator_ is placed in the span wire. This is an insulator adapted to
withstand the great tension put upon it by the span wire. One of these
is shown in Fig. 67. Means are usually provided for tightening the
span wires as they stretch and as the poles give under the strain. The
insulator in Fig. 67 has a screw eye for that purpose.
[Illustration: Fig. 67. Strain Insulator.]
[Illustration: Fig. 68. Overhead Construction.]
=Brackets.= In the bracket type of overhead construction, a trolley
wire is fastened to brackets placed on poles near the track. This
construction is used on suburban and interurban lines where the
presence of poles near the track is not objectionable. It has been
found that a rigid connection of the trolley wire to a bracket is
likely to result in the breaking of the trolley-wire insulators. For
this reason the brackets now commonly used provide for a flexible
suspension of the trolley-wire hanger from the bracket. A bracket
employing such flexible construction, made by the Ohio Brass Company,
is illustrated in Fig. 68.
An example of standard straight-line bracket construction is shown in
Fig. 69.
=Feeders.= Where additional conductivity is needed beyond that
furnished by the trolley wire itself, feeders are run on insulators
along the poles at the side of the track. Such feeders are connected to
the trolley wire at regular intervals. Where span-wire construction
is used, the feed wire may be substituted for the span wire at the
pole where the connection between feed wire and trolley wire is made.
In such a case, of course, a trolley-wire hanger is used which has
no insulator, so that the current feeds directly through the hanger.
Another method is to run the feed connection parallel with a span wire
and a short distance from it.
[Illustration: Fig. 69. Standard Straight Line Construction.]
=Section Insulators.= Section insulators are usually placed in the
trolley wire at regular intervals. Such a section insulator is shown
in Fig. 70. Its purpose is to insulate one section of trolley wire
from the next, so that in case the trolley wire of one section breaks,
or is grounded in any other manner, that section can be disconnected
and the other sections on either side kept in operation. In large
city street-railway systems, each section of trolley wire usually has
its own feeder or feeders, independent of the other sections. This
feeder is supplied through an automatic circuit breaker at the power
house. In case a certain section of trolley wire is grounded the large
current that immediately flows will open the circuit breaker supplying
that section; but, unless the ground contact is of an extremely low
resistance, it will not affect the operation of the other feeders.
Should it be of sufficiently low resistance to cause all the generator
circuit breakers to open, it would, of course, interrupt the entire
service temporarily; but usually the circuit breaker on any individual
feeder will cut that feeder out before all the circuit breakers will
open.
[Illustration: Fig. 70. Section Insulator.]
=High-Tension Lines.= Where high-tension alternating-current wires are
run, as in the case where the road is of such length as to require the
establishment of several substations, these high-tension circuits are
usually carried some distance above the 500-volt direct-current trolley
and feeders. An example of interurban overhead construction is shown
in Fig. 69. Here the high-tension wires are carried on large porcelain
insulators of a size necessary for 26,000 volts. These insulators
are placed 35 inches apart. High-tension wires are kept so far apart
because of the danger that arcs will in some way be started between the
lines, as the high-tension current will maintain an extremely long arc.
The blowing of green twigs across the lines, or birds of sufficient
size flying into the lines, is likely to establish arcs which will
temporarily short-circuit the line. The greater the distance apart of
the wires, the less danger that such things will occur.
Both glass and porcelain insulators are successfully used on lines of
very high tension. Glass is the cheaper and porcelain has the greater
mechanical strength.
High-tension wires are usually of hard-drawn copper or of aluminum made
up in the form of a cable of several strands. Aluminum is lighter for
a given conductivity than copper; and, at the market price controlling
at the present time, is cheaper. It is, however, more subject to
unevenness of composition, which leaves weak spots at certain points
in the wire; and that is the reason why aluminum is now always used
in the form of a stranded cable rather than as a single conductor.
Aluminum, being considerably softer than copper and melting at a lower
temperature, is more likely to be worn through as a result of abrasions
or to be melted off by a temporary arc. These slight objections are
balanced against its smaller first cost as compared with the cost of
copper.
The calculation of the proper amount of feed wire for a given section
of road is somewhat similar to the calculation of electric light and
power wiring as already outlined. It is first necessary to estimate
approximately the amount of current required at different portions of
the line. The amount of drop to be allowed between the power house and
cars must be decided arbitrarily by the engineer. A drop of 10 per cent
is probably the one most commonly figured upon in designing feeding
systems. The resistance in ohms of the copper feeders required to
conduct a given current with a given loss in volts, can be calculated
by dividing the volts lost by the current, according to Ohm’s law. By
the aid of a table which gives the conductivity of various sizes of
wire according to the methods outlined in connection with “Electric
Wiring,” the proper number and size of the feeders can be determined.
The most difficult thing to determine is the load that will be placed
upon any section of the line. Of course, there will be times when cars
are bunched together owing to blockades. It is out of the question
to provide enough feeder copper to keep the loss in voltage within
reasonable limits at such times. The ordinary load upon any feeder is
used as the basis of calculation in most cases. The amount of current
required per car depends on the weight of the car and the character of
the service. This will be taken up later under the head of “Operation.”
THIRD RAIL.
[Illustration: Fig. 71. Third-Rail Insulator.]
=Location.= The third-rail system of conducting current to electric
cars, as most commonly employed in the United States, follows the
example set by the Metropolitan West Side Elevated Railway of Chicago.
All the elevated roads in the United States are now operated by means
of third rails located at one side of the track. The third rail is
an ordinary T-rail and is located with the center of its head 20
inches outside of the gauge line of the nearest track rail, and 6³⁄₁₆
inches above the top of the track rail. On a few interurban roads this
distance has been increased in order to accommodate certain steam
railroad rolling stock which must at times be operated over the line.
=Insulators.= The third rail is supported every fifth tie on an
insulator. These insulators on first construction were made of wooden
blocks boiled in paraffine, but at the present time more substantial
forms of insulation are being used.
One form of third-rail insulator, known as the “Gonzenbach,” has a
base of cast iron resting on the tie. Over this is placed a cap of
insulating material similar to that used in strain and trolley-wire
insulators. Over this insulating material is another cast-iron cap upon
which the third rail rests. The weight of the third rail holds it in
position, and there is no clamping together of the various parts of the
insulator.
Another form of third-rail insulator is made of what is called
“reconstructed granite,” and another of vitrified clay. Fig. 71 shows
one of the latter.
=Switches.= Where the third rail is used, a contact shoe is placed on
each side of both trucks of the motor car. At switches it is necessary
to omit the third rail for a short distance on one side of the track,
and place a short section of third rail on the other side of the track
so that the current supply to the car will be uninterrupted.
=At Highway Crossings.= Where the third-rail system is employed on
interurban surface lines, it is necessary to omit a section of it at
every highway crossing. If the crossing is too wide to be bridged
across by a car, the car must have sufficient momentum to drift over
such crossings when it comes to them. To connect across the break in
the third rail at such points, an underground cable is generally used.
This cable must be thoroughly protected against leakage of moisture
into the insulation where it comes to the surface for connection to the
third rail.
Another form of third rail, laid several years ago on some of the lines
of the New York, New Haven & Hartford Railroad, was of an inverted
V-shape, and was laid midway between the track rails with its top 1
inch above them and its bottom only 1⅝ inches above the ties. It was
supported on wooden blocks. This location of the third rail has never
been popular, because of the poor insulation with the rail located so
close to the ties between the rails.
=Conductivity.= The conductivity of a steel rail varies considerably. A
rail of the ordinary composition used on steam railroads is too high in
carbon to give the best conductivity. Such a rail has about one-tenth
the conductivity of the same cross-section of copper. Steel can easily
be obtained, however, which will have one-seventh the conductivity of
copper, and the additional cost of obtaining such special steel is
quite low, so that the majority of roads installing the third-rail
system have seen fit to pay the extra cost and thereby secure a softer
rail than that usually employed in track rails.
=Cost.= The cost of the third-rail system is less than an overhead
trolley system, provided enough copper is placed in the trolley feeders
to make the conductivity of the trolley system equal to that of the
third-rail system. It is very seldom, however, that a trolley system is
so constructed on an interurban road; and hence the trolley system, as
usually constructed, is cheaper than the third-rail system, because it
is not of equal conductivity to a third-rail system.
=Advantages in Operation.= Where very heavy cars or trains are to
be operated, the third-rail system is decidedly an advantage, for
two reasons. In the first place, it affords the cheaper method of
conducting a given heavy volume of current; and in the second place,
the contact shoes that conduct the current from the third rail to the
moving car or train are built to carry a much larger volume of current
than the trolley wheel, which has only a small area of contact on
the trolley wire. Ordinarily there are two of these contact shoes in
multiple for every motor car.
Another advantage of the third rail over the trolley is that the
trolley may leave the wire at high speeds or in passing switches.
On well-constructed roads, where the trolley wire is kept in good
alignment and the track is smooth, there is little trouble from this
source; but it is undoubtedly a convenience to be able to operate cars
or trains without giving any attention to a trolley pole.
[Illustration: Fig. 72. Cross-Section of Conduit.]
CONDUIT SYSTEMS.
The underground conduit system, in which the conductors conveying the
current to the cars are located in a conduit under the tracks, is in
use in two cities of the United States—New York City and Washington,
D. C. The cost of this system, and the danger of interruption of the
service where the drainage is not excellent, have prevented its more
extensive adoption.
The New York type of conduit is a good example of this construction.
The conductors consist of T-bars (CC) of steel supported from porcelain
cup insulators located 15 feet apart in the conduit. A cross-section
of the conduit is shown in Fig. 72. At each insulator a handhole is
provided (Fig. 73), so that access may be had to the insulator from the
street surface. Manholes are provided at intervals of about 150 feet,
so that the dirt which collects in the conduit can be scraped into
these manholes and removed at intervals. The manholes also serve as
points of drainage to the sewer system.
[Illustration: Fig. 73. Handhole.]
=Contact Plow.= Current is conducted to the car through a pair of
contact shoes commonly called a _plow_ (Fig. 74). This plow has the
two shoes insulated from each other, and from the frame of the plow.
They are provided with flat springs that hold the shoes against the
conducting bars in the conduit. The shank of the plow is thin enough
(⁹⁄₁₆ inch) to enter the slot of the conduit. The conductors pass up
through the middle. These plows can, of course, be removed only when
the car is over an open pit.
=Cost.= A conduit system of this kind is very expensive to build
because of the fact that a very deep excavation must be made in the
street to accommodate the conduit. The track rails, slot rails, and
sheet-steel conduit lining are held in alignment by cast-iron yokes
placed 5 feet apart. The entire space around and underneath these yokes
is filled with concrete in order to give rigidity and a permanent
track. Three expensive items, therefore, enter into the construction
of a conduit road—namely, the deep excavation, which may call for the
changing of other underground pipes or conduits in the street; the
large amount of iron and steel needed for the yokes and slot rails; and
the large amount of concrete needed.
On American conduit roads the slot and conduit are placed under the
middle of the track. Some of these roads are simply reconstructed
cable-conduit roads in which the old cable conduit has been used for
electrical conductors. In the conduit road at Buda-Pest, Hungary, the
slot is placed alongside one of the track rails.
=Current Leakage.= The leakage on an underground conduit road is
considerable, because the insulators are necessarily located in a damp,
dirty place, which causes leakage over the surface of the insulators.
This leakage, however, is not prohibitive so long as the conductor
rails are not under water. If on account of poor drainage the conductor
rails become submerged, the leakage becomes so great that it is
impossible to operate the road.
[Illustration: Fig. 74. Contact Plow.]
It will be noticed that the conduit system as illustrated here employs
two conductor rails—one for the positive side of the circuit and the
other for the negative. The track rails, therefore, are not used
as conductors, and one side of the circuit is not grounded as in
the ordinary trolley system, although the leakage to ground may be
considerable from one or both conductor rails.
TRACK CONSTRUCTION.
=Girder Rail.= A great variety of track rails are used in electric
railways. The most common at one time was the girder, a typical section
of which, with joint, is illustrated in Fig. 75. This is an outgrowth
of the old tram rail used on horse railways. It has a tram alongside
of the head, on which vehicles may be driven. Its chief advantage from
the standpoint of the railway company is that there is plenty of room
for dirt and snow to be pushed away by the flanges of the cars. If the
company maintains the paving, it may be to its advantage to have teams
use the steel track rather than the paving, although this advantage in
maintenance is probably more than compensated for by the delay of cars
through the regular use of the track by teams.
[Illustration: Fig. 75. Girder Rail.]
=Trilby Groove Rail.= A modification of the girder rail, known as the
_Trilby_, and sometimes as the _grooved girder_, is shown in Fig. 76.
A rail similar to this is used in several large cities of the United
States. It has a groove of such a shape that the flanges of the car
wheels will force snow and dirt out of it instead of packing it into
the bottom of the groove, as in the case of the regular European
narrow-grooved rail. A narrow-grooved rail in which the grooves
correspond closely to the shape of the car-wheel flanges is sure to
make trouble in localities where there is snow and ice, as the grooves
become packed and derail the cars.
[Illustration: Fig. 76. Grooved Rail.]
=Shanghai T-Rail.= In some systems a T-rail is used. Where the T-rail
is to be used with paving, the popular form is the Shanghai T, shown
in Fig. 77. This rail is high enough to permit the use of high paving
blocks around it.
[Illustration: Fig. 77. Shanghai T-Rail and Joint.]
=Common T-Rail.= The T-rail used by steam railroads is known as the A.
S. C. E. standard T-rail, because it follows the standard dimensions
recommended for T-rails by the American Society of Civil Engineers.
A standard 65-pound T-rail of this kind is shown in Fig. 78. Other
weights of this rail have the same relative proportions. Such a rail
is used for interurban roads, and for suburban lines in streets where
there is no block paving. The high rails are used to facilitate paving
with high paving blocks.
[Illustration: Fig. 78. Standard A. S. C. E. Rail and One Joint Plate.]
=Track Support.= The greater portion of track is laid on wooden ties.
These ties, in the most substantial wooden tie construction, are 6
inches by 8 inches in section, and 8 feet long. They are spaced two
feet between centers. Sometimes smaller ties, spaced farther apart,
are used in cheaper forms of construction; but the foregoing figures
are those of the best construction known in American railway practice.
In paved streets, ties are usually employed, although sometimes what
is known as “concrete stringer” construction is used instead of ties
to support the rails. A strip of concrete about 12 inches deep is
laid under each rail, and the rails are held to gauge by ties or tie
rods placed at frequent intervals. Sometimes the concrete is made
a continuous bed under the entire track. In most large cities the
concrete foundation is used under all paving; and consequently, when
concrete is used instead of ties to support the rails, this concrete is
simply a continuation of the paving foundation. Where ties are used,
they are laid sometimes in gravel, crushed stone, or sand, although
frequently, in the largest cities, they are embedded in concrete.
Sometimes this concrete is extended under the ties, and sometimes it is
simply put around the ties.
=Ballast.= A ballast of gravel, broken stone, cinders, or other
material which is self draining and which will pack to form a solid bed
under the ties, should be used to get the best results under all forms
of tie construction, whether in paved streets or on a private right
of way, as on an interurban road. Of course, if concrete is placed
under the ties, the gravel or rock ballast is not necessary. If ties
are placed directly in soft earth, which forms mud when wet, they will
work up and down under the weight of passing trains, and an insecure
foundation for the track will be the result.
=Joints.= The matter of securing a proper joint for fastening together
the ends of rails so as to make a smooth riding track without
appreciable jar or jolt when the wheels pass a joint, has been given
much study by electric railway engineers. A section through an ordinary
bolted angle-bar joint is shown in Fig. 75. This joint is formed by
bolting a couple of bars, one on each side of the rails. The edges of
these bars are made accurately to such an angle that they will wedge
in between the head and base of the rail as the bolts are tightened;
hence the name _angle bars_. This is the form of joint generally used
on steam railroads and on electric roads in exposed track, or in track
where the joints are easily accessible, as in dirt streets. In paved
streets, the undesirability of tearing up the pavement frequently to
tighten the bolts on such joints, has led to the invention of several
other types, which will be described later. Nevertheless very good
results have been obtained in recent years with bolted joints laid in
paved streets where care has been given to details in laying the track,
and where the joints have been tightened several times before the
paving is finally laid around them.
=Welded Joints.= Several forms of welded joints are in use. All these
welded joints fasten the ends of the rails together so that the rail
is practically continuous—just as if there were no joints—so far as
the running surface of the rail is concerned. It was thought at one
time that a continuous rail would be an impossibility because of the
contraction and expansion of the rail under heat and cold, which, it
was thought, would tend to pull the rails apart in cold weather and to
cause them to bend and buckle out of line in hot weather. Experience
has conclusively shown, however, that contraction and expansion are not
to be feared when the track is laid in a street where it is covered
with paving material or dirt. The paving tends to hold the track in
line, and to protect it from extremes of heat and cold. The reason
that contraction and expansion do not work havoc on track with welded
joints, is probably that the rails have enough elasticity to provide
for the contraction and expansion without breaking.
It is found that the best results are secured by welding rail joints
during cool weather, so that the effect of contraction in the coldest
weather will be minimum. In this case, of course, there will be
considerable expansion of the track in the hottest weather, but this
does not cause serious bending of the rails; whereas occasionally, if
the track is welded in very hot weather, the contraction in winter will
cause the joint to break.
[Illustration: PORTABLE CUPOLA FOR CAST-WELDING JOINTS OF STREET CAR
RAILS.]