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BATTERY AND CONDUCTOR SYSTEMS COMPARED. 289

verted in the motor into mechanical energy. The interposition of the battery between dynamo and motor must necessarily reduce the efficiency of the whole system, because we can never recover from the battery all the energy which has been put in. The extra weight which has to be carried is also a disadvantage. On the other hand, the loss of electric pressure occasioned by the resistance of the conductor may become very considerable, and the corresponding loss of energy may even exceed the energy which would be wasted in the battery. Thus the average resistance of the conductor at the Portrush Railway is 1 ohm, and when five cars are running distributed all over the line, requiring a total current of 200 amperes at 250 volts pressure, the loss of energy amounts to 37 horse-power. The power actually required for five cars is 68 horse-power, and therefore the efficiency of the conductor, even if its insulation be perfect, is

68

68 +37 = 65 per cent. If we add to this the loss due to the imperfect insulation of the line, which is dependent on the state of the weather, we find that in this case the conductor system is, after all, not more economical than would have been the battery system. The Portrush line is, however, an exceptional case, as the resistance of the conductor is rather great. In the Blackpool Electric Tramway the resistance of the conductor is only half an ohm, and the loss of pressure with six cars running—on the supposition that each requires an average of 18 amperes would be about 30 volts out of 200. In this case 15 per cent. of the energy is lost in the conductor. If this line were to be worked on the battery system the loss would probably be 10 per cent. greater.

But there is another consideration besides efficiency

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which must be taken into account when deciding between the two systems. In some cases the application of a fixed conductor along the line and above ground is inadmissible on account of the other traffic which may pass over the road. Such a conductor would not only interfere with all other traffic, but being always charged, and being of necessity unprotected by an insulating covering, so as to allow for the sliding contact, it would be a constant source of danger in our crowded streets. Mr. Holroyd Smith has overcome the difficulty by placing the conductor underground, and a description of this arrangement will be given presently. Where batteries are used, each car is perfectly independent from all the other cars, and this is a great advantage in working over a complicated net of tramroads. After this rapid comparison between the two systems, we may sum up by saying that the conductor system is better for lines running across country, where an overhead conductor and high electric pressure can be used without difficulty, and the battery system is better for tramways within the crowded streets of a town.

According to the nature of the conductor, the electric railways can be further classified as follows:

1. The rails are used as conductors, one conveying the outflowing and the other the returning current. In this case the rails must be insulated from the ground, and at the joints special connecting pieces must be used. The car wheels are insulated from their axles. An example of this kind is the short railway erected by Mr. Magnus Volk on the beach at Brighton, and the line, BerlinLichterfelde.

2. A separate conductor is used for the outflowing, and both rails are used for the returning current. The rails

BESSBROOK AND NEWRY ELECTRIC RAILWAY. 291

need not be insulated from the ground, but special connecting pieces must be used at the joints to insure good conductivity. The conductor may be above ground or under ground. Examples of this kind are the railways at Portrush, Newry, and Blackpool.

3. Separate conductors are used for the outflowing and returning current. These are carried overhead on poles, and consist either of slotted copper tubes on surface railways, or of angle iron on underground railways in mines. Examples of this kind are the railways at Mödling, Berlin, Frankfurt, Zankerode mine, and others.

4. Separate conductors are used for the outflowing and returning current. These are attached to poles, and so arranged as to form one single line, along which suspended trucks run. The only example of this kind is the Telpher line at Glynde.

The Bessbrook and Newry Electric Railway was opened for traffic in September, 1885. It is three miles in length, and was erected to facilitate the traffic between these two towns, which amounts to about 28,000 tons annually. The generating station is placed at about the middle of the line at Millvale, where ample water-power is available. A turbine capable of working up to 65 horse-power is used to drive two Edison-Hopkinson dynamos (see description on page 241), one of these being sufficient to work the traffic, the other being held in reserve. The pressure employed is 250 volts, and the current is conveyed along a channel iron conductor laid at the same level as the rails, and supported on wooden blocks, which are attached to the cross sleepers in the centre of the track. In a front compartment of each of the two passenger cars at present in use there is an Edison-Hopkinson dynamo acting as motor, and there is

a collector with contact sliding on the centre rail, both in front and rear of the car, in order to span the breaks at farm crossings and sidings, where the current is continued by means of an underground cable. At one point the line touches the public road, and since there the conductor on the surface would be objectionable, it is interrupted for a distance of 50 yards, and the gap is spanned by two overhead wires, supported on poles 15 feet from the ground, and a collector with sliding contact is fixed to the roof of the cars for the purpose of bringing the current to the motor whilst the car is on this part of the line. The passenger car, which performs at the same time the function of an electric locomotive, weighs 8 tons, and on the level attains a speed of 15 miles an hour. It is capable of accommodating 34 passengers, and of hauling at the same time a train of loaded waggons up an incline of 1 in 85, at a speed of 7 miles an hour. The gross weight of the whole train, including locomotive and passengers, is 26 tons, and the motor develops about 25 horse-power. The steepest gradient is 1 in 50, and the sharpest curve has 150 feet radius, but at the two termini there is a pear-shaped loop with a minimum radius of 56 feet 6 inches. This arrangement obviates the difficulty of having to turn the cars on a turn-table at the end of each journey. The cars are 35 feet long, and run on double bogies, having a gauge of 3 feet, and the ordinary flanged wheels. The goods waggons have flangeless wheels, 3 feet 44 inches gauge, and run on two flat rails placed outside of the car rails, and 3 inch below them. The car rails form thus a guide for the wheels of the goods waggons, and the latter can by reason of their broad flangeless wheels be at either terminus drawn off the track, and over the ordinary country roads. In the

BLACKPOOL ELECTRIC TRAMWAY.

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first four months after the opening of the line, a total of 25,000 passengers and 1,600 tons of goods was carried, and the total mileage was 5,200.

In the Blackpool Electric Tramway, which is two miles long, the conductor is placed under ground and consists of

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HOLROYD SMITH UNDERGROUND CONDUCTOR.

two semicircular channels of copper (Fig. 110), supported by, but insulated from cast-iron chairs. The conductor is split up into two parts in order that any dirt or other foreign matter which might fall through the slot in the roadway should also fall through the space between the two

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