The Electric Railway - 7

The Electric Railway - 7

 As a matter of fact, Edison retained a very lively interest in electric-railway progress long

after the pregnant days at Menlo Park, one of the best evidences of which is an article in

the New York Electrical Engineer of November 18, 1891, which describes some

important and original experiments in the direction of adapting electrical conditions to the

larger cities. The overhead trolley had by that time begun its victorious career, but there

was intense hostility displayed toward it in many places because of the inevitable

increase in the number of overhead wires, which, carrying, as they did, a current of high

voltage and large quantity, were regarded as a menace to life and property. Edison has

always manifested a strong objection to overhead wires in cities, and urged placing them

underground; and the outcry against the overhead "deadly" trolley met with his instant

sympathy. His study of the problem brought him to the development of the modern

"substation," although the twists that later evolutions have given the idea have left it

scarcely recognizable.

[15] See 61 Fed. Rep. 655.

Mr. Villard, as President of the Edison General Electric Company, requested Mr. Edison,

as electrician of the company, to devise a street-railway system which should be

applicable to the largest cities where the use of the trolley would not be permitted, where

the slot conduit system would not be used, and where, in general, the details of

construction should be reduced to the simplest form. The limits imposed practically were

such as to require that the system should not cost more than a cable road to install. Edison

reverted to his ingenious lighting plan of years earlier, and thus settled on a method by

which current should be conveyed from the power plant at high potential to motorgenerators

placed below the ground in close proximity to the rails. These substations

would convert the current received at a pressure of, say, one thousand volts to one of

twenty volts available between rail and rail, with a corresponding increase in the volume

of the current. With the utilization of heavy currents at low voltage it became necessary,

of course, to devise apparatus which should be able to pick up with absolute certainty one

thousand amperes of current at this press- ure through two inches of mud, if necessary.

With his wonted activity and fertility Edison set about devising such a contact, and

experimented with metal wheels under all conditions of speed and track conditions. It

was several months before he could convey one hundred amperes by means of such

contacts, but he worked out at last a satisfactory device which was equal to the task. The

next point was to secure a joint between contiguous rails such as would permit of the

passage of several thousand amperes without introducing undue resistance. This was also

accomplished.

Objections were naturally made to rails out in the open on the street surface carrying

large currents at a potential of twenty volts. It was said that vehicles with iron wheels

passing over the tracks and spanning the two rails would short-circuit the current, "chew"

themselves up, and destroy the dynamos generating the current by choking all that

tremendous amount of energy back into them. Edison tackled the objection squarely and

short-circuited his track with such a vehicle, but succeeded in getting only about two

hundred amperes through the wheels, the low voltage and the insulating properties of the

axle- grease being sufficient to account for such a result. An iron bar was also used,

polished, and with a man standing on it to insure solid contact; but only one thousand

amperes passed through it--i.e., the amount required by a single car, and, of course, much

less than the capacity of the generators able to operate a system of several hundred cars.

Further interesting experiments showed that the expected large leakage of current from

the rails in wet weather did not materialize. Edison found that under the worst conditions

with a wet and salted track, at a potential difference of twenty volts between the two rails,

the extreme loss was only two and one-half horse-power. In this respect the phenomenon

followed the same rule as that to which telegraph wires are subject--namely, that the loss

of insulation is greater in damp, murky weather when the insulators are covered with wet

dust than during heavy rains when the insulators are thoroughly washed by the action of

the water. In like manner a heavy rain-storm cleaned the tracks from the accumulations

due chiefly to the droppings of the horses, which otherwise served largely to increase the

conductivity. Of course, in dry weather the loss of current was practically nothing, and,

under ordinary conditions, Edison held, his system was in respect to leakage and the

problems of electrolytic attack of the current on adjacent pipes, etc., as fully insulated as

the standard trolley network of the day. The cost of his system Mr. Edison placed at from

$30,000 to $100,000 per mile of double track, in accordance with local conditions, and in

this respect comparing very favorably with the cable systems then so much in favor for

heavy traffic. All the arguments that could be urged in support of this ingenious system

are tenable and logical at the present moment; but the trolley had its way except on a few

lines where the conduit-and-shoe method was adopted; and in the intervening years the

volume of traffic created and handled by electricity in centres of dense population has

brought into existence the modern subway.