Bessbrook and Newry Tramwayby D. Kinnear Clark
The following is transcribed from a reprint of Tramways - Their Construction and Working, by D. Kinnear Clark, with the kind permission of the publisher.
A line of electrical tramway was constructed between Newry and Bessbrook (Co. Armagh, Ireland) for the carriage of coal and flax from the wharves to the mills, as well as the down traffic of manufactured goods, the abundant water power available offering exceptional advantages for the line being worked electrically.
In the construction of the line the following conditions had to be met. Ten trains were to be run in each direction per day, providing for a daily traffic each way of 100 tons of minerals and goods, and capable of dealing with 200 tons in any single day, in addition to the passenger traffic :- the electrical locomotive to be capable of drawing a gross load of 18 tons on the up-journey, in addition to the tare of the car itself, and it full complement of passengers, at an average speed of 6 miles per hour, and a load of 12 tons at an average speed of 9 miles per hour.
The contract for the construction of the line was of a rather special character: the company agreed to place the line entirely at the disposal of Dr. Edward Hopkinson, to whom its construciton had been entrusted, for a period of time, and to purchase the electrical plant at a fixed sum, when the above conditions had been complied with, and it had been shown that the cost of working as evidenced by six months' trial did not exceed the cost of steam traction on a similar line.
The work was commenced in November, 1884, and the line opened for traffic in October, 1885; it was formally taken over by the company, as having fulfilled the conditions of the contract, in the following April. Since that time it has been in regular daily operation.
The total length of the line is 3 miles 2.4 chains, the maximum gradient is 1 in 50, and the average gradient is 1 in 86. The gauge is 3 feet. For illustrations of the way, see page 392.
The locomotive equipment of the line consists of two passenger cars, 33 feet and 21 feet 8 inches long respectively, each provided with a motor. The body of the car is carried on two four-wheeled bogies, with a wheel-base of 4½ feet, the motor being carried on the front bogie independent of the body of the car (Fig. 341). By this arrangement the cars are enabled to traverse the 55-feet curves at the termini with great facility, and also relieves the body of the car from the vibration due to the driving. The body of the longer car, Fig. 341, is divided into three comparments; the front one covers the motor; the second forms a second-class compartment, seating twenty-four passengers; and the third, a first-class compartment seating ten passengers, is separated from the second by a cross passage. The front bogie carrying the motor has an extended platfrom projecting 3 feet 7 inches beyond the body of the car, and communicating by a slide-door with the dynamo compartment, thus giving the driver direct access to all parts of the driving machinery, which are at the same time entirely boxed off from the passenger comparments. All four wheels are braked by a powerful screw-brake, worked from the front of the driving platform, on which is also fixed the switch-board controlling the motor. The wheels of the back bogie are braked by a chain brake, worked from the cross-passage, and are under the control of the conductor. The brake is also prepared for coupling to the wagons. The total weight of the car is 8¼ tons, distributed as follows :-
Tons. Cwt. Qts. Car body 3 6 1 Leading bogie 1 17 2 Trailing ,, 1 0 0 Dynamo bed-plate, armature, and accessories 2 1 1
8 5 0
The shorter locomotive-car is similar, but without the first-class compartments. There is also a third passenger-car of the same length as the first, accommodating forty-four passengers, and similarly carried on two four-wheeled bogies. This car weighs 5½ tons. The wagons, having flangeless wheels, are, with the way, described and illustrated [below].
The generating machinery is fixed at Millvale, a distance of 68 chains from the Bessbrook terminus. At this point, in close proximity to the line, there is an available fall of 28 feet in the Camlough stream, down which there is a guaranteed minimum flow or 3,000,000 gallons per day. The turbine is an inward flow vortex wheel with double buckets, working on a horizontal shaft extended into the dynamo shed, from which the dynamos are driven direct with belts. The capacity of the wheel is 1,504 cubic feet per minute, and when running at 290 revolutions per minute, should develop a maximum power of 62 H.P. It is worked with a tail draught of 13 feet. The admission of water is controlled by a shutter-valve, rebulating the flow uniformly through each bucket of the wheel, and acutated either by hand or by a centrifugal governer. The latter is not direct-acting, but when its balls rise of fall beyond certain limits, it couples one of a pair of right and left-hand bevel-wheels, driven by a wheel on the governor spindle to a small countershaft geared with the valve-spindle.
There are two generating dynamos of the Edison-Hopkinson type, shunt-wound, for a normal output of 250 volts, 72 amperes, at a speed of 1,000 revolutions per minute. Three times that amount may be necessary for starting a heavy train on a steep gradient.
The resistance of the field magnets is 74 ohms, and that of the armature is 12 ohms. Consequently, the electrical efficiency with the normal current is 92.2 per cent., and the commercial efficiency 90.4 per cent.
The conductor is of channel-steel, laid midway between the rails, and carried on wooden insulators nailed to alternate sleepers. The electrical connection is made independently by a strip of soft copper of such section that its conductivity is about the same as that of the steel. It is bent in a U form to allow for the expansion and contraction of the channel. These strips are riveted in the channel with double copper rivets, care having been taken that the hole in the channel was perfectly free from rust efore the riveting. At the several crossings of occupation roads, twelve in number, the electrical continuity of the conductor is broken by insulating a section of the channel, and the current is coneyed by a cable laid beneath the sleepers. The top of the channel being level with the rails, the intervening space can be paved or planked, thus making a good roadway without interfering with the mechanical continuity of the conductor. As none of these crossings exceed in width the length of the locomotive cars, the leading collector makes contact on one side the crossing before the back collector braks on the other. The cables are of stranded copper wire, consusting of 37 No. 14 B.W.G.: 1st, cotton lapped and varnished; 2nd, heavily covered with pure rubber; 3rd and 4th, double served with best rubber separator; 5th, covered with pute rubber; 6th and 7th, taped with double-served proof tape, the cable then vulcanized and made water-tight; 8th, lapped with thick serving and tarred help; 9th, braided over all and heavily compounded. In contructing a conductor of iron or steel it is of the utmost importance to specify the composition. Steel may be obtained with a specific resistance varying from 0.00001 ohm to 0.00007 ohm, according to the amount of carbon, silicon, and particularly manganese. The steel used in this case was manufactured by the Darlington Steel and Iron Company, and specified not to exceed in carbon 0.15 per cent.; silicon, 0.05 per cent.; manganese, 1.00 per cent. The actual composition, according to the makers' analysis, is, carbon 0.09 per cent., silicon 0.02 per cent., manganese 0.63 per cent,. and the specific resistance 0.0000121 ohm. The weight per foot of the conductor is 4.33 (6.46 kilograms per metre), and the section 1.367 square inch (8.817 square centimetres).
The insulators, which are of poplar wood, are 5 inches long. These are carefully dried and then impregnated with boiling paraffin. A block of dried poplar will absorb as much as 75 per cent. of its won weight of paraffin, which permeates through the whole mass. These blocks have proved efficient insulators, and they are apparantly standing well. The actual measured insulation of the conductor, under unfavourable circumstances as regards weather and when charged to a potential of 250 volts, is about 900 to 1,000 ohms per mile, approximately the same as the insulation obtained at Portrush. Such an insulation is sufficient for practical purposes. It represents a loss, through leakage, of ¼ ampere, or one-tenth of a horse-power per mile. The actual measured leakage current of the whole line in wet weather amounts to nealy four times the above amount, the excess being probably due to some slight fault in the cables and arrangements at the points and crossings.
The circuit is completed by the rails of the permanent way, which are uninsulated. As is the case with the conductor, the fish-plate connections are not sufficient, and they are therefore supplemented by flexible copper strips riveted to the under surface of the rails. The specific resistance of the steel rails (Barrow Hematite) is 0.0000166 ohm, and hence the total resistance of the four rails, having an aggregate area of 12.4 square inches, is 0.033 ohm per mile. The resistance of the conductor is 0.221, making the resistance of the cirecuit 0.254 ohm per mile. Allowing for the earth and for some contact resistance, probably 0.25 ohm represents the average resistance per mile (0.156 ohm per kilometre). The electrical connection of the rails of the permanent way is essential, since the earth conneciton is of little value, as the rails are practically insulated by the sleepers and dry ballast.
Each locomotive-car is fitted with an Edison-Hopinson dynamo-motor. As previously mentioned, the motor is fixed on the leading bogie, and is entirely independent of the body of the car. The armature shaft carries a double helical toothed steel pinion, 0.05 inches in diameter, gearing into a steel wheel 21.08 inches diameter, carried on a small countershaft running in bearings fixed on the bed of the motor. This shaft also carries a chain pinion-wheel of steel, 8.8 inches diameter, on the extended boss of which the helical toothed wheel is keyed. The chain pinion drives with chain gear on to a wheel 21 inches in diameter, keyed on to the back axle of the bogie, the wheels of which are 28 inches in diameter. This gives a ratio of gear of 8.3 to 1; hence a speed of 1 mile per hour corresponds to 100 revolutions per minute of the dyncamo axle. To give the necessary adhesion the axles are coupled with outside connecting-rods.
The motors are series-wound with such a number of convolutions that the magnets are nearly saturated with 12 amperes, which is also the notrmal current for the armature. The resistance of the magnets is 0.113 ohm, and of the armature 0.112 ohm; hence if the potential between the terminals be 220 volts, the electrical efficiency with the normal current is 92.6 per cent., and the commercial efficiency 90.7 per cent., the power developed being nearly 20 H.P. In actual work the power of the motor frequently exceeds this amount. To transmit this power with the car running at, say, seven miles per hour, the tension of the chain would be 1,430 lbs., and with the car running at the maximum rate, the speed may reach 1,300 feet per minute.
A steel chain based on the well-known tricycle form was employed. The tubes are keyed as well as riveted in the inner links, and the pins in the outer links.
The current is conveyed from the conductor by two collectors fixed on the bogies. These form a good rubbing contact on the upper surface of the conductor. From them the current passes to the reversing and regulating switch fixed on the splash board of the leading bogie. To avoid throwing the full load suddenly on the generator and motor dynamos, a series of resistances are first thrown into circuit and cut out one by one. After passing through the armature and magnets, the current returns through the axle boxes and wheels to the rails.
The potential allowed by the Board of Trade is 300 volts, byut the actual potential employed is only 250 volts.
The trains are commonly composed of one locomotive car and three or four trucks, but frequently a second passenger car is coupled, or the number of trucks increased to six. Thus a gross load of 30 tons is constantly drawn at a speed of 6 or 7 miles per hour on a gradient of 1 in 50.
The cost of the electrical equipment of the Bessbrook and Newry line is summarized as follows:--
£ s. d. Turbine, pen-trough, and driving gear 330 0 0 Two generator dynamos, measuring instruments, and driving belts 450 0 0 Conductor at £200 per mile 600 0 0 Two locomotive cars, including their entire electrical equipment 1,120 0 0
£2,500 0 0
The cost of each of the above items includes delivery and erection.
The cost of haulage was carefully ascertained over a period of five months, from November 21st, 1885, to April 22, 1886, and is given as follows:--
£ s. d. Wages of driver and attendant at generator station 32 7 6 Sundry repairs 6 1 0 Oil, grease and waste 5 4 10 Rental of water-power 59 16 0 Dynamo brushes, renewals of driving chain and commutators 14 11 6
118 0 10
Train mileage, 8,652
Hence cost per train mile, 3.3d.
For the six months ending June 30th, 1887, during which period there had been a goods traffic of 8,000 tons over the line, a much larger amount than in the period referred to above, the cost per train-mile was something greater, as follows:--
£ s. d. Wages 50 18 0 Sundry repairs and alterations, including the cost of changing the winding of four armatures of the dynamos 34 14 3 Oil, grease and waste 10 0 0 Rental of water-power 71 15 0 Dynamo brushes and sundry renewals 12 5 10
£179 13 1
Train mileage, 10,276
Hence cost per train mile, 4.2d.
The above amounts do not include anything for depreciation or for general supervision.
Subjoined are tables showing distribution of the power employed:--
|Total water power||30.4||20.63||13.9|
|Total electrical power developed by generator||18.1||10.86||4.71|
|Net power of motor||12.6||7.82||3.62|
|Loss in generator||1.68||0.88||0.40|
|Loss in line resistance||1.82||0.65||0.14|
|Loss in leakage||0.71||0.52||0.39|
|Loss in motor||2.07||0.90||0.165|
|Sum of electrical losses||6.31||2.95||1.10|
|First journey.||Second journey.||Third journey.|
|Gross load||Tns. Cts. Qrs.
28 12 3
|Tns. Cts. Qrs.
21 18 0
|Tns. Cts. Qrs.
8 16 0
|Mean speed in miles per hour||5.7||7.2||11.3|
|Total energy of water in foot lbs.||60,291,000||40,860,600||27,522,000|
|Total electrical energy developed by generator in foot lbs.||35,871,000||21,516,000||9,332,400|
|Net mechanical energy developed by motor in foot lbs.||24,928,200||15,493,500||7,170,900|
|Sum of electrical losses in foot lbs.||12,493,800||5,841,000||2,174,700|
|Loss in generator in foot lbs.||3,343,000||1,735,800||801,900|
|Loss in leakage in foot lbs.||1,420,300||1,029,600||775,500|
|Loss in resistance of line of foot lbs.||3,613,500||1,296,900||287,100|
|Loss in motor in foot lbs.||4,098,600||1,791,900||326,700|
|Total work done against gravity||11,867,400||7,356,800||2,858,300|
|Total work done against friction||13,060,800||8,136,700||4,312,600|
|Mean tractive effort exclusive of gravity in lbs. per ton||28.9||27.4||37.1|
|First journey.||Second journey.||Third journey.|
|Of the water power.||Of total power of generator.||Of the water power.||Of total power of generator.||Of the water power.||Of total power of generator.|
|Net motor power||41.3||69.4||37.9||72.0||26.1||76.8|
|Loss in generator||5.5||9.3||4.2||8.0||2.9||8.6|
|Loss in leakage||2.3||3.9||2.5||4.8||2.8||8.3|
|Loss in line resistance||6.0||10.6||3.2||6.0||1.0||3.1|
|Loss in motor||6.8||11.4||4.4||8.3||1.2||3.5|
|Loss in motor||6.8||11.4||4.4||8.3||1.2||3.5|
The line has been regularly worked since October, 1885. The following table shows the traffic on the line in successive years:--
The cost of haulage for the year 1891 was as follows:--
£ s. d. Wages (drivers, guards, and dynamo engineer) 123 12 6 Maintenance and repairs of electrical machinery--materials 60 6 4 Maintenance and repairs of electrical machinery--wages 23 18 9 Oil, grease, and waste 9 6 2 Water rent 128 11 0
£345 14 9
Train mileage, 23,468
Hence cost per train mile, 3.94d.
Authors footnote: The material for the notice of this undertaking has been derived from Dr. Edward Hopkinson;s paper on "Electrical Tramways," in the Minutes of the Proceedings of the Institution of Civil Engineers, vol. xci., 1887--88.
Wagons used on the line can be adapted for use on the ordinary public road, so obviating transhipment, loading goods at the wharves, drawing them to the line by horses, and delivering them at any part of the mill premises. This system was originally suggested, in 1880, by Mr. Alfred Holt, and was worked out by Mr. Henry Barcroft for the Bessbrook and Newry Tramway. The wheels of the wagons, Figs. 272 and 273, are without flanges, with tyres 2¾ inches wide, for running on common roads. The tram rails are of steel, 41¼ lbs. per yard, and outside these second rails, 23¾ lbs. per yard, are laid at a level 7/8 inch below that of the way, on which the plain wheels run, the ordinary rails forming the inside guard. The wheels are loose on the axles, and these work loose on journals. The wagon is supported on a fore carriage with a central coupling, which engages in a jaw in the fore carriage, to guide it when not pinned. Shafts are attached to the fore carriage when the wagon is to be used on ordinary roads. The wagon weighs, without the shafts, 23¼ cwt., and is constructed to carry 2 tons.