Evening star., 1896-08-15
PROBLEMS OF ELECTRIC TRACTION.
What the Trolley Companies Have
Learned by Experienced.

From the Electrical Engineer
The transition from animal power to
electric power on almost all the street rail-
| ways In this country has taken place 80
| rapidly that railway engineers have found
| 1t difficult in the absence Of any precedents
to keep pace with the additional require
ments which are made necessary by the
Introduction Of electric traction. In order
to design and install a modern high-class
electric railway carriage system it is nee
essary to combine a considerable knowl-
edge Of electrical, mechanical and civil
engineering, and in each of these branches
the necessary knowledge has had to be ac-
CURED by experience growing out of early
FAILURES. In almost every detail of the sys-
TEN the size and strength of the various
parts were greatly underestimated, owing,
no doubt. to the much less rigorous re-
qulrements of horse roads, which were at
nrst the only guide to street railway prac-
tice. 1t is interesting to notice the addi-
lions and changes which have gradually
been brought about with advancing expe-
| rience. Mr.. Sprague started to equip his
earliest motor cars with two, seven and
one-half horse power motors each, and It
hrst sight ffteen-horse power would seem
amply to replace the power of two horses,
even with allowance for the additional
weight of machinery on the car, but it was
soon found necessary to double the ca
pacity Of the car motors and later the
standard equipment was increased to
two twenty-f1ve-horSe power motors, which
is the capacity Of most Of the trolley cars
In general use today
The line-wiring is another matter which
mas undergone very great change At
the start the return circuit through the
tracks and the ground was considered not
70 oner any resistance and the wiring was
calculated as though the entire resistance
OF the circuit was that of the overhead
line. AS a result of this, 1t was found that
IN a good many cases the station pressure
OF ooo volts was reduced to about 300 volts
at the ends Of long lines, and burn-outs of
the machines were of almost daily occur
renee. The resistance Of the return circuit
soon became very apparent evil, and ex-
ira bonding and the addition of grounded
wire to the tracks were increased grad
ually until the standard practice now is to
supply metallic return circuit Of carry
ing capacity equal to that of the overhead
lines he same change of practice has
been noticeable in regard to the size and
strength of rails employed in street rail-
way service. In the days of old horse car
rails weighing from thirty to forty pounds
per yard Were generally employed, and
these were always laid on stringers The
tread of these fiat rails was not more than
from an inch to two inches deep, and the
hange less than half an inch thick. With
the grinding action of the trolley car
wheels, and the greatly increased weight
of the cars, the tread of these rails was
soon worn so thin that the wheel fianges
came in contact with the rail fange and
pressed out all the rivets which held the
bonds; SO fiat rails had to be entirely aban-
doned. Practice has been constantly In
creasing the weight of the rails, which now
generally run from sixty to ninety pounds
per yard. and are always of the T or the
girder pattern.
Another point is now being forced upon
the attention of the owners of trolley
roads, which is of the greatest Importance,
and that Is, the subject of railway bridges.
With the horse car almost any bridge that
would carry ordinary wagon loads was
sufficient for the purposes Of street rail-
way, but with the advent of the electric
car with Its greatly increased speed and
weight, great many of the bridges form
erly used became entirely inadequate for
the new service. A writer in the Railroad
Gazette points out the fact that bridge ac-
c1dents on trolley roads are beginning to be
reported. there being no less than four
during the past six months. The most dis
at Victoria. B. c.. by which forty three
lives were lost Steam railroads have
learned by long and often unfortunate ex-
perience that bridge is the worst pos
slble place to skimp on material, and most
roads of any considerable size now employ
their own experts to not only design all
bridges on their lines, but to periodically
examine them; but 1t Is doubtful II any
trolley car companies have taken this pre-
caution yet. Such accidents, however,
should draw the Importance of this sub
1ect to the attention of those who are in
any way responsible for such bridges. In
building bridges for the use of trolley cars
the tendency is to underestimate the loads
which they will have to carry. 1t should
be remembered that the average load is
not the enc which is liable to prove dang
erous, but the adventitious loads which are
liable to occur at any time. 1t is also in
evitable that car having capacity of
fifty passengers will al some time be loaded
with one hundred and fifty passengers,
and 1t is for these exceptional cases that
the bridges should be designed. If the fact
is considered that there is very slight DIFF
ference in the cost of a good bridge and
that of poor one there is little excuse to
be found for the failure of bridge