December 31, 1915. THE COLLIERY GUARDIAN 1339 feeders from the power station to only half the sub- stations, each of these in turn feeding one of the remaining sub-stations. This involves graded overload gear, and a faulty feeder may shut down both the sub- stations in connection with it, and will probably shut down one of them; it is therefore only permissible ■where continuity of supply is not of such vital importance. For the purpose of the comparison a typical case is assumed of an area of 25 square miles, with the power station at the centre and a sub-station with a maximum load of 500 k.w. at 0*8 power factor and a load factor of 30 per cent, situated at the centre of each square mile, the distribution being effected by underground mains at 6,000 volts. It is assumed that owing to the diversity between the various sub-station loads the power station load factor will be 50 per cent., and the average feeder load factor on an interconnected system 40 per cent. The average maximum feeder currents are therefore deduced by assuming the sub-station maximum demand to be reduced in the ratio of the sub-station load factor to the average feeder load factor. This only holds for the interconnected system, but in the first instance the same reduced sub-station demands will be taken for other types of system, i.e., the advantage which an inter- connected system gains from its utilisation of diversity is neglected. Table 1 gives the comparison, while the diagrammatic lay-outs of the three types of system are shown in fig. 2 (a), (b), and (c). Table 1. Inter- Simple Series connected, radial. radial. Reference to figs............. 2(a) ... 2(b) ... 2(c) Number of switches ............ 64 ... 96 ... 96 Mileage of mains.............. 32'0 ... 93*7 .. 6i‘2 Annual costs (£) ............ 4,752 ... 7,664 ... 6,075 Percentage increased cost over interconnected system — ... 61’3 ... 27’8 In certain cases where momentary interruption of supply is not of great importance a “ tee ” system has (*) («) Substations shown thus Power station shown thus Fig. 2.—Diagrammatic Lay-outs of Distribution Systems. been used, arranged as shown in fig. 2 (d). Each sub- station is normally given a non-duplicate supply from one of the feeders, and arrangements are made for the sub-station to be changed over to the other feeder in emergency, thus involving a complete temporary inter- ruption in the supply to all the sub-stations fed by the faulty feeder. In a modification of -this system both tees into the sub-station are normally closed through switches equipped with time-limit gear, but the sub- station busbars are sectioned by a special switch. The sectioning swutch may be either left open or it may be closed and equipped with instantaneous overload gear, so that it will immediately trip in case of a feeder fault. In either case supply is automatically maintained to half the sub-station busbars, and by opening the faulty feeder switch and closing the sectioning switch com- plete supply to the sub-station can be resumed. Table 2. Inter- Semi- Change- con- duplicate over nected. “ tee? “ tee ” Reference to figs 2 (a) ... 2(d) .. ■ 2(d) Number of switches 64 ... 80 .. . 56 Mileage of mains 32*0 ... 48*0 .. . 48-0 Annual costs (<£) Percentage increased cost 4,752 ... 5,478 .. . 5,216 over interconnected system — ... 15*3 .. . 9’8 Table 2 gives a comparison of these systems with the interconnected system, and it is interesting to note that the latter is still cheaper, in spite of the great sacrifices in security entailed by the “ tee ” systems. The foregoing comparison proves that the intercon- nected system is the most economical for the particular case which has been selected as typical; but in order to make the investigation complete it is necessary to show that this superiority still holds under other con- ditions, and accordingly the interconnected system will be compared with the cheapest system giving reasonable security of supply—the series radial system—under various modified conditions which may obtain in practice. These are :— (1) The same number of sub-stations distributed one mile apart in a ring round the power station, or in line one mile apart with the power station at the centre, as shown in fig. 2 (e), (/), (g), and (h). (2) The area of supply extended or decreased with the same number of sub-stations and the same total load on the system, i.e., the sub-stations situated at the increased and decreased spacings of one per 4 square miles and four per square mile respectively, instead of one per square mile, the load per sub-station remaining the same. (3) The area of supply extended to, say, 49 square miles with the same density of load and a correspond- ingly increased number of sub-stations supplied from the central power station, as shown in fig. 2 (i) and (;). A further extension of the area of supply to 81 square miles has also been worked out, but it has not been considered necessary to complicate fig. 2 with details of this, as the lay-outs are similar to those for the 49 square miles. There is no need to consider a reduction in the area of supply, as this is already quite small. (4) The original distribution of sub-stations, but with increased or reduced loads per sub-station, the alterna- tive loads considered being 250, 1,000, and 2,000 kw. The arrangement of feeders remains the same for the series radial system, as a cable capable of dealing with the load of two 2,000 kw. sub-stations in emergency is not too large to be handled. For the interconnected system it is necessary .to run more feeders from the power station to deal with the heavier loads, the feeder arrangments which would be adopted for the 1,000 and 2,000 kw. for sub-stations being shown in fig. 2 (k) and (I) respectively. The details of the comparison are given in Table 3. The outstanding features of this comparison are :— (a) The economy of the interconnected system is generally maintained; (b) the saving effected by an inter- connected system rapidly increases as the area of supply is enlarged. This is important, as only relatively restricted areas have been considered; (c) the saving is greatest for lightly loaded sub-stations, and decreases as the sub-station loading increases. In the case of the most heavily loaded sub-station it would appear at a first glance that while the interconnected system may have other advantages, its direct economy is very small. This is only apparent, for in the first case the saving due to diversity has been ignored, and secondly it will be found on investigation that a point has been reached at which distribution at so low a voltage as 6,000 is uneconomical. The question of the most economical distribution voltage will be considered further at a later stage, but it may be noted now that with a sub-station loading as high as 2,000 kw. the distribution system costs 37’1 per cent, more at 6,000 volts than it would at 11,000 volts, while if a pressure of 11,000 volts were adopted the interconnected system would show a saving of 21*8 per cent, compared with a series radial system at the same voltage. The possible further savings which may be effected if diversity is taken into account have been considered, and without going into details of the calculation it may be taken as adding something of the order of 4J- per cent, to the cost of a simple radial system, and rather less to the cost of a series radial system. When comparing an interconnected system with other types, two further points must also be borne in mind. (1) It is a very difficult matter exactly to forecast sub-station maximum loads or, as in the case of railways, definitely to fix the allocation between the various sub- stations. If the sub-stations are fed independently it is obvious that in proportioning the feeders to them allowance must be made for the assumed maximum loads being exceeded or varied, while if the sub-stations are interconnected the particular distribution between the sub-stations does not greatly matter so long as the total system load is unaltered. (2) The greater part of -the saving effected by an inter- connected system is in the trunk feeders, and in conse- quence it is more marked the farther the power stations are removed from the centres of load. In the above comparisons the power station has been taken at the electrical centre of gravity of the load, and therefore at the least favourable position for the interconnected system. So far the investigation has been limited to the com- paratively low voltage of 6,000; but, speaking generally, the higher the system voltage the greater is the economy to be obtained by interconnection. This is obvious if it is remembered that :—(a) The higher the voltage the less is the proportionate cost of the protective devices, which is practically independent of the voltage; (b) the higher the voltage the smaller is the section of the mains for given loads, and consequently the greater advantage offered by interconnection in reducing the total length of mains and increasing their average capacity. At the first ordinary general meeting of the Wankie Colliery Company in London last week, Mr. Edmund Davis stated that the company supplied large coal at 9s. per ton for all supplies as far as Norton siding, which was 488 miles from the colliery, and 8s. 6d. per ton beyond. The price of nuts was 7s. 6d. per ton. These prices were exclusive of railage. The Inland Revenue authorities give notice in the London Gazette that every person chargeable with Excess Profit Duty in respect of the excess, over the statutory pre-war standard of profits, of the profits arising from any trade or business to which the duty applies in any accounting period which ended after August 4, 1914, and before July 1, 1915, must inform the Commissioners of Inland Revenue thereof before January 31. A well-known Welsh-American, Col. R. A. Phillips, of Scranton, has just resigned the post of general manager of the Delaware, Lackawanna, and Western Company’s Collieries. He began work when only 12 years of age, and rose step by step until he attained the highest official position in one of the largest coal fields in America. The concern of which Col. Phillips was general manager gives employment to some 30,000 miners. BOOK NOTICES. Coal Distillation, Gasification, and By-Products. By J. E. Christopher. 90 pp. 8 in. x 5 in., with 41 illustra- tions and diagrams. Wigan : Thomas Wall and Sons Limited; 1915. Price, 2s. 6d. This is a reprint of two series of articles, which appeared in The Science and Art of Mining, written mainly for mining students. We share the author’s opinion that the increased attention which is now being given to the by-products and derivatives of coal distilla- tion are a sufficient justification for collecting these articles in book form. There are nine chapters in -the book. The subjects discussed are coal distillation, manufacture of coal gas, coke manufacture, manufacture of producer gas, by-products, tar, ammonia, benzol, and by-products from blast furnaces. The author treats these subjects in a clear and interesting manner. We note his remarks about coke ovens, over one-third of which are still of the non-recovery type. This, at the present juncture, seems to be almost criminal. In a country possessing so much fuel of various kinds, we ought not -to have to import benzol in any form. Yet the author tells us that, assuming all coal to be carbonised in by-product ovens, w’e should make only 38 million gallons of benzol per annum, whereas we import about 100 million gallons. We can recommend this book to all who wish to obtain an intelligible account of -the various processes connected with coal distillation. The Testing of Machine Tools. By George W. Burley, Wh. Ex., A.M.I.Mech.E. 231pp. 7J in. x4jin., with 110 illustrations. London : Scott, Greenwood and Son; 1915. Price, 4s. net. The author, who is on the staff of Sheffield University, has had in view the requirements of engineering teachers and others who have charge of classes in machine tool testing. In an excellent introduction, he classifies the different kinds of tests, and he states that the object of these tests is to acquire knowledge and information likely to be of use both to the designer and user of machine tools, so that improvements may be made in them. He then proceeds to describe what he terms accuracy tests, such as bed levelling tests by spirit-level, hydrostatic level, and pendulum level. Amongst the latter the Norton pendulameter is described and illus- trated. A diagram is given of an optical method of -testing a lathe bed for general horizontality, by means of a water surface, which is ingeniously used as a plane of reference, by means of a microscope attached to an arm which can be moved over the bed of the l-athe. Local bed levelling tests by straight edges and testing plates, as well as by wires under tension, are then described. Then we have -the consideration of headstock tests, upon which depends the accuracy of the machining. For these tests either measuring or non-measuring indicators can be used, the former being represented by the micro- meter screw gauge head, and the latter by various forms of test indicators, which are here figured and described. Then -the author proceeds to discuss driving headstock spindle tests, loose headstock• mandrel tests, slide rest tests, and finished lathe tests. This chapter also includes the consideration of turret lathes, milling machine, drilling and planing machine -tests. In the third chapter we have speed and feed tests for machine tools. This involves a description of tacho- meters or speed indicators, of which several types are figured. The question of speed involves some mathematical considerations, which are treated at some length in an analytical way, which engineering students will certainly appreciate. The subject is rather too complex to refer to at any length in this place, and we can only say that it is adequately treated by the author. The next chapter is devoted to efficiency tests of machine tools, including input determinations, by means of either the electric motor method or by some form of dynamometer. Then follows output determinations by means of a Prony brake or other appliance, and the efficiency can thus be determined as the ratio of the input to output. Cutting force tests by various dynamo- meter methods are then described, and chapters are given on output and power consumption tests, compara- tive tool testing, and commercial machine tool testing, while an appendix contains a specimen lathe test report. We commend this book especially for the prominence given to the description of methods and instruments. The work forms volume xviii. in The Broadway Series of Engineering Handbooks, to which it is a notable addi- tion. The typography and general appearance of the book are, of course, beyond criticism. Mr. John Bigland, of Henknowle, Bishop Auckland, formerly agent for Messrs. Pease and Partners Limited, left estate valued at £8,022 4s. 10d., with net personalty, £5,618 18s. 7d. The Coal Exports Committee again call attention to the necessity for the utmost precision practicable in the informa- tion given in application for licences for the export of coal. This precision is more especially desirable in :—(a) Descrip- tion of the nature or quality of the coal; in addition to its allocation to one of the groups, anthracite, steam, gas, household, manufacturing, coking, etc., it should be specified whether it is large or small, screened or unscreened, treble, double, peas, duff, etc.; (b) indication of the collieries from which the coal is intended to be drawn; unless they belong to some well-defined group, the names of all the collieries should be given; (c) description of the ultimate use or destination of the coal; (d) information as to the general character of the inward cargo of the vessel named, which is of considerable importance in certain cases. Any vague- ness or omission in the foregoing respects may prejudice the application.