Publication: Western Electrician
Chicago, IL, United States
Electrical Mine Equipment of the C. &
C. Shaft at Virginia City, Nev.
BY LEON M. HALL.
When the mining properties on the Comstock Lode were first developed operations were carried on by means of steam-generated power, wood being used as the fuel. This was very costly on account of the scarcity of wood. The milling was, until quite recently, done at a distance of some 15 miles from the mine, at a point on the Carson River where cheap waterpower could be obtained. About two years ago the question of electrical transmission for the purpose of supplying power for deep mining operations on the Comstock Lode was taken up, and since then intensive hydraulic developments have been carried out at Floriston, Cal., on the Truckee River. Power is now transmitted 35 miles to the mines in Storey County, and a dozen or more of the properties have been equipped with electrical machinery. Among these is the C. & C. shaft of the Consolidated California and Virginia Mining Company, which has a world-wide reputation as a bullion producer.
The power plant on the Truckee River is about two miles east of Floriston. The river is dammed just below the Floriston Pulp and Paper Mill, and the water is conveyed about 600 feet through a canal, and then 8,600 feet through a wooden flume six feet eight inches high and 10 feet wide, to a point directly above the generating station. It is then conducted through two wooden stave pipes, 160 feet long and six feet in diameter, to the wheels, upon which there is a head of 84 1/2 feet. There are two pairs of 27-inch horizontal McCormick turbines, direct-connected to Westinghouse, three-phase, 60-cycle generators of the revolving-armature type. These generators are separately excited by two 22 1/2-kilowatt, direct-current machines. The wheels will each develop 1,400 horsepower at 400 revolutions per minute, with the above bead of water. They are regulated by two type-B Lombard governors. A view of this station is shown in Fig. 1.
Current is generated at 500 volts and is raised to 24,000 volts by means of six 300-kilowatt oil-insulated transformers, at which potential it is transmitted 33 miles over a double circuit of No. 4 hard-drawn copper wire, to the sub-station at Virginia City. The line is composed of square redwood poles 30 feet in length, with pine cross-arms and locust pins, upon which are mounted 7 1/2-inch Locke insulators. The telephone circuit is carried on the same poles by oak brackets with pony insulators. At the sub-station at Virginia City the potential is lowered to 2,300 volts by means of six 450-kilowatt, Westinghouse, oil-insulated transformers, and at this potential current is distributed to the various mining companies. The distribution circuits are composed of weatherproof wire, and are designed for four per cent. drop under full load. The generating station at Floriston is constructed of brick, with a galvanized-iron roof, and the sub-station at Virginia City is entirely covered with corrugated galvanized iron. Fig. 3 gives a general view of the shaft and buildings of the Consolidated California and Virginia Mining Company and shows the sub-station at the left.
The plant has been in continuous operation since October 20, 1900. The Truckee River General Electric Company sells power to the various mining companies at $7 a horsepower a month, the amount used being based on a maximum-peak load of two minutes duration. This, with other conditions, has made advisable the installation of machinery of the very highest grade and the introduction of some features which are rather unique in character. In the C. & C. shaft at Virginia City every precaution has been taken to secure thorough reliability and the highest efficiency.
The electrical machinery in operation on the surface comprises a 200-horsepower, 2,200-volt, three-phase induction motor, geared to a balanced electric hoist. This machine is shown in Fig. 5 and will be described later. A 100-horsepower, 2,200-volt induction motor is belted to a 16 1/2 by 30-inch, single-stage air compressor, and other motors consist of a 30-horsepower, 440-volt motor, operating circular saws, a 15-horsepower motor, driving tools in the machine shop, and a 10-horsepower motor, operating a Blake rock-breaker at the ore bin. The transformer equipment consists of three 15-kilowatt, indoor-type transformers, stepping down from 2,200 volts to 440 volts, and one five-kilowatt lighting transformer, transforming from 2,200 volts to 110 volts. These transformers are shown in Fig. 2. Illumination is supplied by two Manhattan arc lamps and 50 incandescent lamps, the remainder of the electrical apparatus on the surface consisting of the necessary lightning arresters, fuse blocks, cut-outs and switches.
The motor apparatus underground consists of the following: A 15-horsepower induction motor, operating at 440 volts and driving a fan on the 250-foot level; two 10-horsepower motors, driving fans on the 1,950-foot and 2,150-foot levels (the latter showing in Fig. 4); three 225-horsepower motors, operating at 2,200 volts, and geared to three duplex double-acting Riedler pumps located on the 2,150-foot level. On the 1,750-foot level are three 10-kilowatt transformers, transforming from 2,200 to 440 volts, and a three-kilowatt lighting transformer, transforming from 2,200 volts to 110 volts. On the 1,950-foot level are installed three 15-kilowatt transformers, transforming to 440 volts; two 15-kilowatt lighting transformers, transforming from 2,200 volts to 110 volts; three 15-kilowatt transformers, transforming to 440 volts, and a five-kilowatt lighting transformer, transforming to 110 volts. These transformers supply the motor and lighting circuits within the mine. All the motors and transformers are of the Westinghouse type.
There are 250 16-candlepower incandescent lamps scattered through the workings underground. A No. 6 B. & S., three-conductor, lead-covered cable armored with iron wire extends from the surface to the 2,150-foot level, and a No. 0, three-conductor cable runs to the pumps on the same level. The weight of the No. 6 cable is six tons and of the No. 0 cable 10 tons. The cables were lowered down the shaft by means of the hoisting rope and then securely clamped to the wall plates. At each station a water-tight junction box is used, and the lead covering sweated into a tight-fitting sleeve located in the side of the box.
The power is brought into the works over two separate circuits, each of which is provided with a single-pole switch at the entrance of the building, and also a Westinghouse integrating wattmeter with its transformer. The pump circuit is further equipped with an ammeter, a frequency-indicator, a power-factor indicator and a static ground-detector. Oil- break switches are used on the cable circuits and upon all of the 2,200-volt motors. The smaller motors, both on the surface and underground, are equipped with auto-starters, quick-break switches and slate-base fuse blocks. Some of these machines are located in warm places and operate under severe conditions.
The entire installation is wired with lead-covered cables or with rubber-covered copper wire, mounted on glass insulators or porcelain knobs. The greatest care was used in installing the wiring, with the result that it is safe and gives absolutely no trouble. Candles have been entirely discarded, incandescent circuits having been carried directly to the working faces and into the slopes. The current is taken into the mine at a potential of 2.200 volts, through the cables above mentioned, and the potential is lowered in the mine by transformers, which are located as near as possible to the points of consumption.
The compressed-air plant on the surface, supplying air for drilling, for a number of underground hoists and for the hydraulic pump, consists of a 16 1/2 by 30-inch Rand & Waring, single-stage air compressor, driven at 73 revolutions per minute by a 100-horsepower motor. The motor speed is 580 revolutions per minute, which is reduced by a countershaft with wooden-rim pulleys and rubber belting. No automatic regulator is used at the present time, as the compressor is working to its full capacity, and the motor is developing 96 horsepower.
The electric hoist is a decided departure from usual practice in deep-mine hoisting plants, and embodies what is commonly known as the balanced, continuous or tail-rope system. This was adopted in order to reduce the cost of operation, and also the size of the motor to the lowest size compatible with the duty required — viz., to hoist 500 tons daily from the 2,500-foot level by means of double-deck cages carrying 3,600 pounds of rock. The hoist consists, essentially, of a main driving drum and an idler, around which is wrapped a 1 1/8-inch plow-steel wire rope. The rope passes down one compartment, around a movable tail sheave and up the other. One cage is inserted between the ends of the rope and the other fastened to it by means of heavy iron clamps. The main driving drum is geared to a 200-horsepower, type-F, variable-speed, Westinghouse, three-phase induction motor (Fig. 5), which operates at a maximum speed of 580 revolutions per minute, moving the cages through the shaft at 1,250 feet per minute. The speed of the motor is readily controlled by means of variable resistances inserted in the secondary winding, but external to the motor itself. The variation of the resistance is accomplished by the use of a special controller, resembling an ordinary street-car controller; the primary circuit is controlled by means of an oil-break switch. The hoist is equipped with heavy post brakes, hydraulically operated, and the machine is handled with remarkable ease. In tests that have been made these hoists show a net efficiency of about 75 per cent., counting all electrical and frictional losses.
The pumping plant consists of three duplex, double-acting 6 11-16 by 24-inch Riedler pumping engines, located on the 2,150-foot level, as shown in plan and elevation in Fig. 6. These pumps take their water supply from a tank on the east side of the shaft, just below the 2,150-foot station. Each pump is separately driven by a. 220-horsepower, 2,200-volt induction motor, and has a capacity, at 110 revolutions per minute, of 1,500 gallons per minute to the height of 450 feet, or to the Sutro tunnel level. The motors run at a speed of 495 revolutions per minute, the necessary reduction being obtained by the use of cut gearing with stepped teeth. The total capacity is 4,500 gallons per minute, and it is intended to take the water from the hydraulic elevator as long as it is used as a sinking pump.
The pumps are located in a station 30 feet north of the shaft. This station is cut from the solid rock, and is 18 by 17 feet eight inches in section and 110 feet long. It is timbered with 14 by 14-inch pine timbers with three-inch planking. A