The Electrification of Coal Mines

Progress, Volume VIII, Issue 2, 1 October 1912, Page 92

The Electrification of Coal Mines

By W. Leonard Parker, B.E.

(Continued from page 38) Some nineteen miles up the coast is the quiet little township of Ngakawau, a settlement which has grown since the opening of the Stockton Colliery in 1905. The conspicuous object of the town is a long white building with a tall black chimney. This indeed is the power-house of the Stockton mine, from whence energy is sent six miles inland to the substations on the hilltops directly over the mine itself. Behind this building and nestled under the hill is the great coal bin, with that semi-circular roof which makes it look like a garrison hall on stilts. It is here that the coal is deposited when brought from the mine, and from ■ beneath this structure issues a stream of waggons, laden with "Stockton" on its way to the shipping depot at Westport. The Power House is built of ferro-concrete, and accompanied by a steel stack 120 ft. high. The main engine room contains two generating sets of equal size, and there is room (in case of extension) for two more. The units are each 300 kw. alternators by the British Thomson-Houston Company, and are directly connected to triple expansion Bellis-Morcom steam engines, which run at 400 r.p.m. Though situated in wild surroundings those machines are of modern design, being fitted with automatic compound governors. They are supplied by four Babcock and Wilcox boilers. On the electrical side of this equipment, the alternators are excited by two steam driven dynamos, which is transmitted through slip rings to the rotating fields. Power House lighting and workshops power is provided for by a motor-generator set running off the 6600-volt mains, and generating 100-kw. direct current at 250 volts. ' The bins are fitted with conveyors and screens for handling the coal, and all are separately driven by direct current motors. Immediately behind the bins and connected therewith by a short bridge is the entrance to the Ngakawau tunnel, in which a third of a mile of single track pieces the first range of foot hills. The grade is one in sixty, sloping towards Ngakawau.

At the tunnel mouth is an electrically driven winding engine, by which the coal, in races of 25-tubs, is convoyed through the tunnel to the bin tips. Thus coal can be conveyed through the tunnel at the rate of 250 tons per hour. A brief walk through the tunnel brings us out suddenly at the bottom of a deep gully, across which is a short bridge. Up the opposite side through a long ribbon of cleared bush, stretches a double track cable road. At the base where we stand we hear the clang of clip-chains as the rope boys busily detach coal from the “full” road, and send up empties on the other track. In this manner a stream of loaded tubs is being collected, and sent through the tunnel, while the rope is replenished by empties sent back in return. The incline is 33 chains in length, and has a grade of one in three. From the foot it runs straight up to the sky line, where the long row of tubs, lookingsmall in the distance, disappears over the brow. The locality is surrounded by splendid bush, and to the left can be seen, nestled in the shade, a saw mill for cutting the mine timber. But the cable road has no eye for scenery, and goes straight on, past this spot, soon diving into a tunnel speckled with glow-worms. A short run (or climb, for the grade is one in five) brings us out into daylight again, with bush on either side, and Top Brake just out of view over the next ridge. This latter part of the incline is 40 chains long, and the summit is 1000 ft. above sea level. At this point the rope road connects with an electric railway, which winds up over the flat tussock-covered tableland by a tortuous route, with grades usually regarded as unworkable by pure traction. The' gauge is 36", and 65-lb. rails are used, there being a centre rail for the Fell Brake, which is used when descending. This line extends for five miles further inland to within the mine workings. There are three sub-stations connected with the 6600-volt three-phase transmission line from Ngakawau. These are situated along the railway line, and each contains a motor-generator set consisting of a squirrel-cage induction motor of 290 h.p., and a six-pole direct current generator developing 200 kw. at 250 volts. A quarter of a mile from the Top Brake No. 1 sub-station is supplemented by a running shed with workshops and smithy. It forms the head quarters of the line, and in the running shed are facilities for the regular overhaul of the electric locomotives. Thus they are rendered very reliable, and trouble caused by breakdowns is seldom, if ever, heard of, in spite of the severe treatment to which the motors are subjected. The locomotives themselves are of the type peculiar to mines, made by the General Electric Company. The frame is of rigid iron castings, fitted closely together, and carrying the four axle boxes. It contains two motors each of 100 h.p, controlled by the Sprague system. The draw-bar pull at 8 m.p.h. is 75001b5. These motors do splendid work against grades of one in ten, and erratic curves, on mountain railway the like of which it would be difficult to find in New Zealand. Being intended for work underground, they are built low and stand 39" above the rail, and the total weight

40,0001b5. Besides three such locomotives for the main line, there are two smaller ones exerting’ onethird of the tractive effort, and used for feeding and shunting in the mine workings. While the larger locomotives are fitted with Fell Brakes, these are not, but each carries the usual hand-brake, and is fitted with a large fiat reel of cable, lying horizontally on the top of the locomotive frame. When entering any section in which no overhead wire is

fitted, this cable is trailed behind as a substitute for the trolly wire. It may also be re-wound automatically on the return of the locomotive.

{To he Continued)

The total quantity of Portland cement produced in the United States last year was 78,528,637 barrels, equivalent to 13,321,822 tons, the value of which was 4.97 dollars per ton.