542 THE COLLIERY GUARDIAN. March 12, 1915. resistance in the rotor circuit. Where power is trans- mitted from a distance, and a high-power factor is of importance in order to keep down the cost of trans- mission mains, the power of such drives can be improved by using an exciter connected to the slip rings on the Scherbins, Milch, or Kapp systems. The second case is of a far more difficult character, as the speed range required during the first few. years is large. The alternative drives in 'this case are :— (1) Temporary rope drive, using a small induction motor until the power and speed warrant the erection •of a permanent motor. (2) A continuous current motor. (3) A “ Cascade ” motor, giving two or three speeds. A typical instance of continuous current fan drive is shown in fig. 25, which illustrates the plant supplied for _____________________________________________________________________________________________________________________________________________________________________________ Rhymney V alley .—(Elliot Pit) : Three pumps, two driven by 950 b.h.p. motors and one by a 1,000 b.h.p. motor. A description of these is given later. (Bargoed Colliery) : Two pumps, each driven by a 800 b.h.p. motor. Head.................................... 1,660 ft. Capacity................. 60,000 galls, per hour Speed and type of pump ... Sulzer 8-stage, 1,4*0 r.p.m. (Brithdir Colliery) : Fig. 22 gives' the results of tests taken on these pumps on site. These tests showed an over-all efficiency of 65 per cent. Two pumps, each driven by a 475 b.h.p. motor. Head.................... 950 ft. Capacity................ 70 000 galls, per hour Speed and type of pump ... Sulzer 4-stage, 1,480 r.p.m. One pump driven by a 330 b.h.p. motor. Head.................... 880 ft. Capacity................. 48,000 galls, per hour Speed and type of pump ... Worthington 5-stage, 1,440 r.p.m. (Britannia Colliery) : tion of the field rheostat. Starting is effected by using series grid resistances,-portions of which are successively short circuited by switches of the. contactor type, so arranged that by closing a master control switch, the contactor switches close successively in an automatic manner, and prevent the starting current exceeding a predetermined amount. The stand-by motor in this case is of the induction type, the fan being rope-driven. Speed in r.p.m. ' Efficiency. Per cent. Per cent. 135 ........................ 89'5 101 ..........................88*7 75 ........................ 87’0....... (e) Compressors.—Owing to the necessity of pro- viding stand-by plant for each section, the difficulties due to grit in the compressor, the provision of the neces- sary cooling water, and of executing repairs under- No. Make. Size of motor. B.h.p. Head. Feet. Gallons per hour. 1 ... Sulzer ... 600 .. . 2,250 . ... 40,000 1 ... ... 300 .. . 1,560 ... 40,000 2 Mather and Platt... ... 550 .. . 1,260 ... 40,000 1 Sulzer ... 800 .. . 1,260 ... 75,000 The largest pumping station is at Elliot Pit, the pump room being situated at the foot of the upcast shaft and containing three Westinghouse-Sulzer centrifugal pump- ing sets; two of these are driven by 950 b.h.p. three- phase motors, and the third by a 1,000 b.h.p. motor, the following being the respective duties :— 950 b.h.p. 1,000 b.h p. Gallons per hour......... 81,000 ... 87,000 Head in ft. (manometric)... 1,690 ... 1,690 Full load r.p.m........... 1,475 ... 1,475 The following are the leading particulars of the 1,000b.h.p. pump :—The pump is of Messrs. Sulzer’s six-stage type, with special cast-iron casing and bronze impeller and guide wheels, and having the makers’ patent balance-disc method of taking up end thrust, dis- pensing with the necessity of a thrust block. 18"dia. .22x20' nW” Urge "40xIl£ 22x20‘conn. fdia.- Duel; CO < motorJ ^Filter screen ; on hinged frame 3- z ^'CHO55-SECTION ■ Showing ducts -to motors only ---h----n * ~ Z6did Odmpt c osec Longitudinal Section Arrangement of TWO n^FAH i DUCTS ATELUOT PIT feet 5__o 5 iQ /5 to___________Effect Fig. 23.—Ventilating Arrangement at Elliot Pit Pumping Station. Fig. 22.—Curves of Test Results, 800-b.h.p. Centrifugal Pumps, Bargoed. Rea motor i,8oo - 1,700 - 1,600 - ,E 1,500 - -01,400 k £ . 7op 33 ^69 668 .667 ~66 Revolutions per minute______________ ________N=14-80 1______________ 900^= 800--- j?oo— 6600L— O 800 900 1,000 1,100 1,200 Gallons per minute - 5 La- - x2 9 deep Motor , g-as pipe 6-stag'e pump Motor 6-stage pump gas pipe itfgas pipe Globe valve b-stag'c pump ;0il returns to tank , under 14" head Fig. 24.—Lay-out of Elliot Pit Pumping Station. The 1,000 b.h.p. motor is of the slip ring type, With liquid starter, the stator being built in a turbo-alternator frame. The windings are designed to give a tempera- ture rise not exceeding 35 degs. Cent, above the inlet temperature of the air, which passes through the pump room at the rate of 10,000 cu. ft. per minute. Owing to the confined nature of the pump room and the size of the pumping plant, the following system: of air filtering and ventilation. is used (fig. 23) Two 17| in. fans, one being in reserve, are erected in the passage way leading to the upcast shaft, and discharging into it. These fans are driven by 20 b.h.p. three-phase 500-volt motors, and maintain a Water gauge of from 4 to 6 in. in the air trunks. Incoming air is’brought through a special heading driven into the downcast shaft. The air filter, consisting of cloth stretched on wooden frames, is erected at the incoming end of the pump room, and suitable dampers are provided at each motor for controlling the supply of air. The general lay-out of the plant is shown in fig. 24. The system of forced lubrication employed for the pumps and motors is shown in fig. 24, and consists of oil tanks fitted with submerged “ spur wheel ” pumps, chain-driven by small three-phase motors mounted on the covers of the tanks, and supplying oil to the various bearings. Each pump is fitted with an oil filter, which can be withdrawn and cleaned while the pump is in action. The switch- gear is of the totally enclosed cast iron type. Duplicate feeders and busbars are used, arranged so that any feeder or pump motor can be connected to either feeder. The water is discharged to the surface through two .rising mains in the upcast shaft, the mains being of 6 in. and 8 in. diameter respectively, and worked in parallel, or else through one 12 in. main in the down- cast shaft. The over-all efficiency of the above set tested at full duty was 71-9 per cent. (d) Ventilation.—-Up to a few years ago the general colliery practice was to use low-speed fans; latterly a considerable number of centrifugal high-speed fans have been employed. All the principal fans of the Powell Duffryn Company have duplicate motors as a stand-by, to allow for cleaning and repairs. These fans are driven by induction motors, and in order to give flexibility in the volume of air, the fans are rope-driven to allow the pulley ratio to be varied. In deciding the size and speed of the motors, two distinct problems have to be faced :— (1) Replacing or supplementing existing steam drives working at full power. " (2) Opening out a new colliery. In the first case any variation in speed that may be required is small, which can be met by inserting FAN MOTOR ROTARY CONVERTER AIR COMPRESSOR ANO DRIVING MOTOR Fig. 25.—Fan-drive, Britannia Colliery. TRANSFORMER PIT EF., ~tu Io o bi the new Britannia Colliery. The fan employed is designed for the full air output for ventilating the work- ings when the latter are fully opened out, but until this time has arrived it will run at speeds to suit the develop- ment. The electrical equipment consists of a rotary converter and continuous current motor, the latter being direct-coupled to the fan shaft. The rotary converter mentioned under “ Compressors ” is used for driving the fan motor. The fan motor has a maximum output of 550 b.h.p., with a speed range from 75 up to 135 revolutions per minute. It has 16 main poles, and is provided with commutating poles and a compound winding. Speed variation is obtained by hand regula- ground, the Powell Duffryn Company erect the main compressor plant in the winder house, so that it can supply all requirements, the separate air systems being inter-connected so as to reduce the percentage of reserve plant. As the air requirements are intermittent, it is desirable to run the electrically-driven compressor or, when the demand is large, a part of the compressing plant equivalent to the load variation, at a variable speed. Large variable speed compressors are at present only operated by continuous current motors, and if induction motors are used, it is necessary either to sacrifice efficiency and increase the amount of wear and tear by running at constant speed, the air compressor being con- trolled. by an unloading device, or alternatively to use two- or three-speed “ Cascade ” motors, with an unload- ing device when the motor reaches its minimum speed. Where the fans and the compressor drives are both in the same house, an efficient and satisfactory drive can be obtained from the alternating current system for both purposes by using a rotary converter. The compressing plant at Britannia Pit consists of three electrically-driven compressors, two running at constant speed driven by induction motors :— Cubic feet of free air per minute .. 2,500 .. 3,500 Motor r.p.m______________. ____ 243 ... 240 Brake horse-power ............ 410 ... 550 The compressors are by Messrs. Beiliss and Morcom, and are fitted with an unloading device, which operates when the air pressure exceeds 701b. per sq. in. A further compressor plant capable of dealing with 5,000 cu. ft. of free air is being added, driven by a continuous current motor. The latter will be supplied from a 1,100 kw. six-phase rotary converter, which runs at 500 revolutions per minute. The converter is fitted with compound winding and commutating poles, and is started by a squirrel cage motor, which is connected for self-synchronising. When starting, the windings of the starting motor are in series with the armature windings of the converter, and with normal supply voltage the rotary converter gradually gains speed until it reaches synchronism, the windings of the starting motors being then short circuited. The output of the converter is 2,500 amperes at 500 volts, and it will supply power for driving variable speed continuous current motors for the compressor and the fan drive. . The compressor motor is mounted on the same shaft and between the cylinders of a Robey air compressor of the cross compound type. The speed variation is from 58 to 105 revolutions per minute at 850-horse power. The motor has 16 main poles, and is provided with