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The Electric Tram System.

Captain Griffin recently read a paper on ‘ Electric Street Railways ’ before the Boston Society of Arts. After having described the methods of working the tramway by the Thoinsou-Houston system, the lecturer proceeded as follows ;

There are two general methods of using electricity for the propulsion of street cars: the direct method, by conductors extending from the dynamo along the track ; and the indirect method, by the use of storage batteries, secondary batteries, or accumulators. In the direct method the conductors mav bo overhead, underground, or on the surface. In the conduit system the conductors are placed in a conduit between the rails or between the tracks. The wires must be bare, and yet must be thoroughly insulated from the ground—a condition very difficult to obtain under such circumstances. A slot about five-eighths of an inch wide gives access to the conductors by means of a contact plough, but unfortunately also permits the flow of water, slush, mud, etc., into the conduit. The overhead wire is suspended from poles by brackets or from cross wires which span the street between poles on either side. When the street is of sufficient width, poles are placed in the centre of the street between the two tracks, with, bracket arms carrying the conducting wires. These poles are placed about 125 ft apart, and from actual experience arc found to present little or no obstruction to traffic. Tho wires may be single or double. When single wire is used, the rails are utilised for the return current. When two wires are used, one wire carries tiie outgoing, and one the return current. Contact is obtained with the wire by an overrunning or an under-running trolly. The over - running trolly is a light carriage with one or more wheels resting on the wire. A flexible conductor carries the current down to the car. The trolly is pulled along by the flexible conductor. The objections to the over-running trolly are that it is difficult to keep tho trolly on the wire, it is difficult to replace tho trolly when it comes off, and any automatic system of switching on to a turn-out, branch, or Y is impossible. The latter is such a serious objection that, except in special cases, the over-running trolly will never be used. In the underrunning trolly a light arm of the requisite length is mounted on the top of the car, reaching up to the wire. A wheel on the end of the arm is pressed up against the wire by means of springs at tho other end, and the current is carried from the wheel down through the arm itself, if made of metal, or through wires if the arm is made of wood. The arm i? usually called the contact liar. The under-running trolly is automatic in its action at curves, turnouts, etc,, and follows the direction of the car. It turns on a swivel on an entire circle and moves through au arc of 9(T in a vertical direction. In the storage system a battery of about 120 cells is carried on the car, and the motors arc driven by the current from this battery. The advantages of this system are ; the cars can run on any track; no wires, cither overhead or underground, are required ; each car is more independent than is the ease in other systems. The disadvantages are: The extra weight of about two "tons on each car, and the power to drive this dead weight in addition to that required to drive cars required by the other met hods ; the lack of inefficiency in the batteries (the highest effioienry claimed is 82 per cent., while the actual practic'd efficiency is stated by many authorities as about 70 percent.); storage cars cannot be regularly operated on guides exceeding 5 or 6 per cent., while the power required on grades makes too great a demand on the batteries, the expense, the cost of two sets of batteries per car, being about 3,000dol; and the cost of maintenance, batteries not yet having been made of sufficient durability to be operated economically. There are four qualities which the electric motor must be shown to possess before it will be generally adopted for street car work. These are efficiency, economy, durability, and re liability. As to efficiency: The steam engine" is not au efficient machine. If we can utilise 15 per cent, of tho units of energy stored iu the coal we are fortunate. In other words, we must expect a loss of 85 per cent, of the heat units in converting the other 15 per cent, into mechanical power. The dynamo electrio machine, on the other hand, possesses a high degree of efficiency. No good generator runs below 92 per cent, efficiency. The loss in tho line depends upon the amount of copper used in proportiou to the current to be carried. The size of the conductor is generally calculated for a loss of 10 per coat. The efficiency of the motor, under favorable circumstances, lias been shown to bn but little below the generator ; in actual tests running as high as per cent. In practice it would not probably be tiken higher than 35 per cent. Starting, then, with 100 horse-power in the steam engine, we lose 8 per cent, iu the dynamo in converting the mechanical into electrical energy. The output of the generator is then 92 horse-power. In the line we lose 10 percent., and deliver 82.S horse-power to the motor. Here we lose 15 per cent., and on tho final reconversion into mechanical energy on the ear we have 74 horse-power out of tho original 100 horse-power. By no other known method could tiiis power be transported to such a distance with so little loss. Economy : This is perhaps a quality which appeals more directly to the railway officials than any other—what will it ccsb ? An electric railway connects Omaha with Council Bluffs across the new bridge. lam credibly informed that to run twenty cars per day they consume five tons of slack, for which they pay Idol 14c per ton. This is 28Ac per day for fuel. These cars are scheduled at fifteen miles per hour, and the average daily mileage per car is over 100 miles. Where natural gas or water is available fuel may bo even cheaper. On many different roads, from numerous measurements, it has been found that where the grades are slight tho power required averages from 5 to 8 horse power per car. Tho consumption of coal varies from Sib to Gib per horse-power, according to the style of the engine and its more or less economical operation?. Of course a road operating only one or two cars would show abnormal results in every way, ard these averages are only true of roads operating a number of cars—ten or more. The wear and tear in the generating plant does not exceed 3 per cent, The depreciation on line work does not exceed, or even equal, 10 per cent. On some roads, under very favorable conditions, the cost of renewals and repairs to electrical apparatus has been but little below one dollar per clay per car in actual operation. On other roads, under very favorable conditions, the cost of maintenance has been less than 25 cents per day per car. A copy of the reports obtained from eleven roads iu actual operation, under different conditions, shows a daily cost of operation of less than 2dol 50e per oar, not including drivers and conductors. Experience has shown that it is well within limits to put tho savings of electric over horse power at 25 per cent. In some cases a saving of 50 per cent, has been shown. Tho secretary of the Des Moines Broad Gauge Railway Company, under date of January 3, 1889, writes as follows: “The receipts from four cars electrically propelled are four times more than five cars by horses.”

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Bibliographic details

The Electric Tram System., Issue 7982, 10 August 1889, Supplement

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The Electric Tram System. Issue 7982, 10 August 1889, Supplement

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