806 THE COLLIERY GUARDIAN. April 16, 1915. _________________________________________________________________________________________________________________________________________________________________________ by moving bis lever back and making connection with the opening arrangement. The disadvantage of this valve is that the throttle valve is usually some distance from the engine cylinder, and consequently when the valve is tripped there is still a certain amount of steam to be used up between the valve and the cylinder. One great advantage, however, is that as the valve is in constant use it will be free and easy in working, and when it is tripped there will be no fear of the valve sticking and failing to close. If, however, it should be desired to keep the main valve as a throttle valve only, then a se, arate trip- throttle valve connected direct to the overwinder may be used. When an overwind or over, peed takes place this valve is tripped, shutting off the steam without in any way affecting the main throttle valve; the brakes, however, must be applied at the same time, because the engineman, having lost control of his engine, due to the steam being cut off, is absolutely relying upon the brakes to bring the engine to rest. Whenever a separate trip throttle valve is used, it should be tested frequently, in order to see that it is free from any sticking, and will work satisfactorily. Another point which should be considered is that the overspeed gear on the overwinder should be capable of working effectively at two different speeds—that is, when winding coal and when winding men. It is essential that a certain speed should not be exceeded when the gear is winding men, and consequently the overwinder should be capable of being set for working at that speed, independently of the speed attained when winding coal. Electric Winding in South Africa.* By J. H. RIDER. ________________________ COAL TRADE BENEVOLENT ASSOCIATION. The New Chairman. The new chairman of the board of directors of the Coal Trade Benevolent Association is Mr. Thos. King Fox, of Broomfield House, Royston, near Barnsley, whose photograph we reproduce. Mr. Fox has been for the last 20 years commercial manager of the Micklefield Coal and Lime Company Limited, the owners of the Micklefield and Ledstone Luck Collieries, and few men are better known or more esteemed ■ on the coal exchanges of the United Kingdom. Previously Mr. Fox was salesman for the Old Silkstone and Dodworth Coal Photo] [Rosemont, Leeds. and Iron Company for 18 years. His official associa- tion with the work of the society of which he is now at the head is of comparative recent date. He became a director of the Yorkshire branch in February 1912, but his enthusiasm for the cause largely contributed to the formation of branches of the association at Hull, Leeds, and Sheffield, of which latter branch he is a past-president. The distinguished honour which has now been conferred upon him has been received with the greatest pleasure by his wide circle of friends, none the less by those in Yorkshire, with which part of the coalfield he has been so long and honourably connected. _____________________________ Sulphate of Ammonia as a Fertiliser.—The Sulphate of Ammonia Association have issued a timely series of leaflets and pamphlets recording the results of field tests conducted during 1914 in different districts in England, Scotland, Wales, and Ireland. Various crops have been treated, and the profits realised show in striking fashion the value of sulphate as a nitrogenous dressing. As a result of the war, the desirability of increasing crops has been impressed upon farmers, and this can only be done at short notice by the use of large quantities of artificial manures, and the shortage of potash and nitrates should direct greater attention to sulphate of ammonia, large supplies of which can be pro- duced in this country. Particulars are also given of the association’s patriotic root crop competition, handsome prizes being offered for the best returns from land devoted to mangels, swedes, or cabbage and potatoes respectively, and treated with sulphate. Directions as to the proper use of the fertiliser have been compiled, and will be supplied to [hose interested. The paper deals with the power (electricity and compressed air) supply given by the Rand Mines Power Supply Company Limited to those gold mining companies of the Central Mining Rand Mines group which have contracted with the power company for the whole of their power requirements, and treats the subject from the consumers’ point of view. These companies produce about 36 per cent, of the total gold output of the Transvaal, or about 14'5 per- cent of the total gold output of the world. Power Supply. When it was decided, in 1908, that the whole of the power requirements of the above mines should be taken from an outside source, it was stipulated that a separate supply company, to be called the Rand Mines Power Supply Company Limited, should be formed for that purpose. This power company owns the Rosherville and Vereenicing power stations, and the air-compressing station at Robinson Central Deep (a section of Crown Mines Limited). Its overhead and underground trans- mission and distribution systems are separate from those of the Victoria Falls Company, but have been and are at present (1914) interconnected. The history of the first three years of the supply under the contract teaches one outstanding lesson— namely, that it is only courting failure to attempt to give a permanent and reliable supply without a proper reserve of generating and transforming plant. It was not until August 1914 that the power company was able to supply the whole of the compressed-air load, and up to that date a number of the old steam compressors on the mines were still used. The author has little doubt, however, that some of the frequent breakdowns were ca used by nothing else than continuous overloading, in an attempt to give as large a supply as possible from the existing plant, before the spare plant was ready. A reserve of 25 per cent, is not by any means too much, particularly with such large generating units as are used in the power company’s stations. Experience has shown that the maximum individual demands of the mines for electricity supply have a diversity factor of about 1'14, while the power factor averages about 0'77. The load factor of the electrical system is about 75 per cent., and the annual consump- tion at the rate of about 310,000,000 units. Considerable economies have been made in the use of compressed air since 1913, and the maximum aggregate air demands now vary in the neighbourhood of 18,000 lb. per minute. The diversity factor is also very variable but averages about 1'13, so that the maximum demand upon the compressed air system is about 15,800 lb. per minute, or 37,900 kw. The load factor is about 34 per cent., and, as an air unit represents 27'441 lb. at 100 lb. gauge pressure, the annual consumption is about 103,000,000 air units. A flat price is paid for the electric and air unit, and is subject to special rebates, depending on the working costs of the power company and the cost of railway carriage of coal. The whole of the transforming and extra-high-tension control apparatus at each point of supply on the mine properties is provided by the power company. The transformer and switch houses, however, are provided by the consumer. The normal declared electric pressures at each point of supply are 2,100 volts and 525 volts, and the consumer is entitled to receive its supply at these pressures in any proportions which it may require from time to time, There are altogether 23 transformer houses at the various points of supply. The arrangements for measuring the various supplies have been the subject of very careful consideration by both parties. The number of units of electricity supplied to the consumer is ascertained by three inter- grating watt-hour meters placed in series and connected in circuit at each point of delivery on the low-tension side of the transformers. One complete set of motors is installed for each pressure of supply. The first meter of each set is the property of and kept in repair by the power company ; the second is the property of and kept in repair by the consumer; and the third is the property and kept in repair at the joint expense of the con- sumer and the power company. The number of units of compressed air supplied to the consumer is ascertained by an air meter or meters of a type to be approved by the consumer, provided by and maintained at the expense of the power company and connected in the air-pipe line at the point of delivery. The pressure and temperature of the air supplied are measured by the power company’s meter or meters at the outlet end. The air meter used by the power company is of the Venturi type, while that used by the consumer is of the swinging-gate type. The “ gate ” meter has a much wider range than the Venturi meter, and will read with accuracy down to 2 per cent, of the full flow. The Venturi meter is not accurate below 10 per cent, of the full flow. Electrical Equipment. With trifling exceptions, all the power requirements of the mines in the Central Mining Rand Mines group are supplied by means of electric motors. The number of motors installed (1914) is about 1,500. They vary in size from 2 h.p. to 2,000 h.p. (R.M.S. rating), and the total horse-power- is about 142,300, made up as follows:— Horse-power. Winders ........................ 57,340 Pumps ......................... 30,330 Stamp mills .........:................... 13,890 ..... ...................... ...................... Compressors .................... 11,700 Tube mills ...................... 10,170 Hauling and conveying........... 5,290 Crushers.........................___ 5,350 Workshops......................... 2.110 Ventilating____ ..................... 1,370 Miscellaneous .................. 4,750 Total.................... 142,300 Three- phase. Totals. 2 4 :. H13 19 31 :: 8 9]9 5 : :: Ip There are at the present time 38 shafts in use on the mines of the group, many of which have underground winders for the lower depths, in addition to surface winders. For the purpose of winding, shafts may be divided into three classes, viz. (a) incline shafts, which approxi- mately follow the dip of the reef; (&) vertical shafts, which strike the reef at its lower depths; and (c) com- pound shafts, which descend vertically until the reef is struck and then follow on the incline. A few of the compound shafts are still served by single-stage winders, the skip or cage first descending the vertical portion, then turning the corner, and finally descending the incline; but the majority now use a sepaiate winder for the incline portion. The deepest shaft of any mine in the group is No. 3 Shaft, Village Deep, Ltd , which is 4,144 ft. deep in the vertical. An incline shaft has already been sunk at the bottom of the vertical for a distance of about 1.200 ft., and will be continued for an additional 5,000 ft., which will make the total length of vertical and incline over 10,000 ft. The incline shaft is at an angle of about 35 degs. to the horizontal, and will probably be served by two winders on different levels, in addition to the surface winder which deals with the vertical only. When t>>e general electrification scheme was decided upon, it was resolved, for financial reasons, to use as many of the existing steam winders as possible, by removing the connecting rods and connecting up the motors to the drum shafts, either directly or through gearing. At the end of 1914 there were 69 electric winders in use or on order, as enumerated below. Type. Ward- Surface. Leonai d. New— Direct-coupled ... 7 Geared.......... — Converted— Direct-coupled... — Geared.......... — Underground. New— Direct-coupled ___ — Geared.......... 1 Converted— Direct-coupled ... 1 Geared__________ — 9 The figures do not include small winches, &c. Out of the total number of winding motors now in use, 54 of the 3-phase type and 4 of the Ward-Leonard type were ordered before the advent of the author on the Rand at the end of 1910. The policy which guided his prede- cessor in deciding to use 3-phase motors in such large numbers for winding was that of saving fresh capital outlay, as is indicated in a paper by Mr. H. J. S. Hea her.j" in which the theory of the control of such motors is investigated. Systems of Winding. Generally speaking, it must be admitted that the 3-phase winding motors on the Rand are working quite satisfactorily. Whether their use is justified, however, under all conditions, and whether Ward-Leonard sets would not have proved more economical in working in many cases, are debatable points. A 3-phase winding motor per se is a much simpler machine than a continuous-current winding motor, with its necessary adjunct on a 3-pha e system of supply, the motor-generator, but its control is n< t nearly so simple. The control apparatus is apparently, and actually, much simpler- than the complicated resistances, switches, and connections required by the Ward-Leonard system. In practical operation, however, the Ward- Leonard winder is much the easier to control, and for the following reasons (