490 THE COLLIERY GUARDIAN. March 5, 1915. cells in lead-lined teak boxes. The accumulators in each barge, which are capable of a discharge of 150 amperes for about seven hours, weigh 18 tons. The accumulators on one boat will be charging whilst the other set is working in the tunnel. A special basin has been made close to. the power house for the boats to stand in whilst the accumulators are being charged, and iron piles were driven into the canal at-the Hare- castle end of the tunnel to form a wide curve so that the boats will leave the tunnel easily. By means of this scheme about 30 boats, most of them with 20-ton loads, can be hauled through at one ■■ "MS! ■'•Sa 1 * ' ■' * Fig. 4.—Anchorage and Tension Gear. trip at the rate of about two miles per hour, but the usual load is from 15 to 18 boats. At present the plant is worked only 18 hours daily, six trips being made in each direction. The Old Canal tunnel is closed for traffic purposes, but used as a by-pass for circulation of the water displaced by the towage through the new tunnel. Ultimately, it is intended to take out the towing path from the new tunnel, thus providing an unrestricted waterway 14 ft. in width throughout its length. Grimsby Coal Exports. — Returns for the week ending February 26, show that the coal shipped from Grimsby con- sisted of the following :—Foreign : To Aalborg, 1,379 tons; Aarhus, 1,759; Copenhagen, 2,161; Dieppe, 751; Gothen- burg, 5,011; Odense, 105; Oxelosund, 4,301; and Rotter- dam, 528 tons. Coastwise : To Gravesend, 160 tons; total, 15,995 tons foreign, and 160 tons coastwise, against 20,199 tons foreign, and 377 tons coastwise during the correspond- ing week of last year. Immingham Coal Exports.—Returns for the week ending February 26, show that the coal exported from Immingham was as follows:—Foreign: To Boulogne, 1,035 tons; Dieppe, 1,593; Malmo, 1,261; Odense, 1,961; and Rotter- dam, 521 tons. Coastwise: To London, 850 tons; total, 6,371 tons foreign, and 850 tons coastwise. Total for the corresponding period last year was 25,671 tons foreign, and 3,440 tons coastwise. Institution of Mining and Metallurgy. — At a members’ dinner held on Wednesday last at the CaK Monico, occasion was taken to express to Mr. T. A. Rickard the recognition by the members of his services to the profession, and their regret at his impending departure from London to reside in San Francisco. There was a good attendance of the members of the institution, Dr. F. H. Hatch, the president, being in the chair. Although in consequence of the war the customary annual dinner of the institution has been aban- doned for the present year, the proceedings on Wednesday were of more than ordinary interest. “ The Institution of Mining and Metallurgy ” was proposed by Sir Robt. A. Hadfield in an excellent speech, in which he referred to the progress of the institution and to the satisfactory conclusion to’ which its efforts to obtain a Royal Charter had been brought. The president acknowledged the toast, and proceeded to the main business of the evening — the presentation to Mr. T. A. Rickard of an address, accompanied by a piece of plate— in which he was supported by Mr. F. H. Hamilton in an excellent speech in eulogy of the recipient’s high qualifications, both as a journalist and as a mining engineer. Mr. Rickard, in thanking the members for their kind wishes, expressed his regret at leaving London, where he hoped his work for the last six years had achieved the object he had always kept in view, viz., the interests of the profession of the mining engineer. Mr. H. L. Sulman then proposed the toast of “ The Chairman ” in an interesting speech, full of pleasant reminiscences of bygone days. Dr. Hatch suitably responded, and the proceedings terminated, the company singing “ God Save the King." Electricity Applied to Mining.* By C. P. SPARKS. (Continued from page 436.) Transmission System. (a) Distribution Above Ground. — Experience has proved the reliability of overhead transmission with bare conductors for colliery supply. Apart from the saving in first cost, the main risk through the use of cables is avoided, namely, subsidence. To secure safety it is advisable to screen the overhead conductors at all points where they cross traffic. The efficiency of screen- ing is dependent on reliable earthing, which is best secured by a continuous stranded earth wire of sub- stantial section, the section having a definite ratio to the Merz Price pilot flood bdttrni ever — earth-wires (drth-wire rd/vamzed N°55.H.G. 'Ivanized iron fi°5 S W G." Fig. 7.—10,000-volt Transmission Lines. Pole carrying one set of lines. Fig. 6.—10,000-volt Transmission Lines. A = pole carrying two sets of lines. Duplicate tearsmsnn wire; bound together every iu ft. 1 3/4'dia wire rope Bracing iH'xA'anjIe iron Fig. 8.—Railway Crossing of 20,000-volt Line. ft Strips ci porcelain r-4'i’ H (4*’* i lsjl Li section of transmission lines protected, the earth wire being effectually earthed at each end and connected to intermediate earth plates every 300 or 400 yds. In order to minimise risk, all main conductors round the pit head should be run as armoured cable. All collieries in the Aberdare Valley are now supplied by a system of-3,000-volt ring mains, protected on the Merz-Price system. The section of the main feeders of hard-drawn copper has been increased to 0’15 sq. in. (19/12 S.W.G.), the wires being grouped in a triangle, for single circuits 3 ft. 6 in. vertically and 4 ft. 6 in. horizontally, with double circuits the conductors are carried on'three cross arms, the circuits being spaced 4 ft. horizontally and the phases 3 ft. vertically apart. The pilot wires for the Merz-Price system consist of either one or two three-core 7/21 S.W.G. paper insu- lated lead-covered cables, suspended from galvanised steel catenary wire, 7/14 S.W.G., by raw hide suspenders, these conductors being carried at the extremity of a fourth cross arm fixed about 4 ft. below the main conductors. The average length of span is 100 ft. Little depreciation is noticeable at the base of the creosoted wood poles, which have been erected over 10 years. The overhead wires radiating from the Middle Duffryn power station have been displaced by three-core * From a paper read before the Institution of Electrical Engineers. J . paper insulated lead-covered armoured cables to a point well clear of the power station, washery, and railways. The overhead wires branch from brick towers, in which the choking coils and horn gap lightning arresters with liquid resistances are placed. The Rhymney Valley 10,000-volt transmission lines run from Penallta to Bargoed, a distance of 31- miles. Duplicate circuits are run between Penallta and Pengam on the same "A” and “ H ” poles, and between Pengam and Bargoed on separate poles, the two pole lines being about 30 ft. apart. This allows the Britannia Colliery, which is completely electrified, to be supplied from either of two power houses by two sets of duplicate transmission lines, grouped on three independent pole lines. Wood poles are employed 36 ft. long, the maximum diameter at the base being ll|in., and at the top 7-J-in., and the pole being buried in the ground 5 to 6 ft. The conductors are hard drawn copper, 0’25 sq. in. section (37/13 S.W.G.). The phases are spaced vertically above one another, 15 in. apart, the two sets of transmission lines between Penallta and Pengam being 4 ft. 6 in. apart (figs. 6 and 7), and the average span being 100 ft. The insulators of the double petticoat pin type are carried on three channel irons of section 4 in. by 2^ in. bolted to the poles, each insulator being subjected to a test pressure of 55,000 volts under standard precipitation, and a pressure of 75,000 volts when dry. Each circuit is protected on the Merz-Price system. Earth plates are connected to the catenary wires every tenth span by protected copper earth con- nections. The overhead transmission lines are connected to the generating station and substations by three-core paper insulated lead-covered and armoured cables 250 yds. in length. These cables terminate at brick towers, in which are placed choking coils and horn gap lightning arresters, with oil immersed resistances connected to earth. On the 3,000-volt lines two duplicate sets of 0’2 sq. in. hard drawn copper (37/0’082 S.W.G.) connect Bargoed with Elliot Pit and New Tredegar. The average span is 100 ft. These conductors are also protected on the Merz-Price system. As the demand increases, the pressure on these lines will be raised to 10,000 volts. The distance between the Middle Duffryn power station of the Aberdare Valley and the new Britannia Colliery, which is a central point of the Rhymney Valley undertaking of the company, is approximately nine miles. The transmission line will be constructed for a working pressure of 30,000 volts. In the first instance, however, the line will be worked at 20,000 volts, supplied through three 2,200 k.v.a. single-phase oil insulated water cooled step-up transformers designed for 30,000-volt operation, and connected so as to give 3,000 volts mesh to 30,000 volt star, and 30,000 volts star to 10,000 volts mesh. The transmission line will be con- trolled by switchgear on the 3,000 and 10,000-volt systems, the transformers being connected direct to the transmission lines through isolating switches. When working with transformers mesh to mesh, supplemen- tary star transformers with the neutral earthed will be used to operate the protective system, the Merz-Hunter split-phase control being used, and the switchgear being actuated in the event of a line fault by balanced trans- formers connected in series with the split-phase con- ductors. Time limit overload relays will be used to protect the 3,000 and 10,000 volt systems. The power factor and the pressure drop on the trans- mission line when supplying from one end will be con- trolled by hand regulated static boosters star connected on the 3,000-volt system at Middle Duffryn. The transmission lines will consist of six 0’073 sq. in. stranded conductors, each comprising 7/11 S.W.G. hard drawn copper wires arranged on normal spans, with the phases 5 ft. apart vertically, the split phases being -at 4 ft. horizontal centres. The conductors will be carried on pin-type insulators mounted on three channel irons, 4in. by 21 in., these being protected by