1240 THE COLLIERY GUARDIAN. December 13, 1918. top and bottom covers, and baffle plates inside the radiator, which cause the air to impinge in a thin stream against a large radiating surface. Part of the heat is radiated by the machine itself in the usual way for a totally enclosed motor of the orthodox type. It is claimed that with this system it is possible to approach within quite reasonable limits of the capacity of a ventilated motor of given frame size without th? use of anything excessive in the size of the radiator. The only objection to this system is the bulky super- structure. The reasons for wishing to instal a totally enclosed motor often lie in the fact that the motor is situated in an - inaccessible or congested position, and it will be found that the superstructure is a deter- rent to its use. It is obvious that the structure can be mounted sideways, and this may help in many cases, although it might influence adversely the efficiency of the radiator. An improvement which suggests itself almost to any- one would be to extend the shaft of the motor and mount a fan with a suitable guard to deflect a stream of fresh air on to the radiator. This suggestion has, in fact, been covered by a recently published .patent, and a direct current motor is built on that principle by Electromotors Limited. The foregoing methods of cooling entail the use of a radiator as a super or sub- structure ; the following are self-contained with th? machine : — In the earliest type of artificially cooled totally enclosed motor a fan was mounted at the end of the machine; this sucked air through holes in the outer cover and forced it through a narrow gap around the motor casing. This device was used by the British Thomson-Houston Company many years ago. It im- ^4— . Fig. 2.—Cross-section through Totally- enclosed Thrfe-phase Siemens Motor. * I Th ■' A77 § 3 3 Fig. 3.—Cross-section through Totally- enclosed Direct-current Mavor & Coulson Motor. proves the cooling of the machine, but is not really a “ totally-enclosed ” motor according to the defini- tion of the term, because the fan plate leaves a gap through which the outside air can penetrate partially in the interior. The same objection applies to the system shown in fig. 1, which has been proposed by Schroder and pro- duced by the British Westinghouse Company. In fig. 2 the machine is enclosed in a shell made of thin heat conducting material inside the frame. The fan at the end of the armature shaft forces the air between the motor casing and this inner shell. This method is an improvement on the previous one, as the internal heated air is closer to the external cooling air, being only separated from the latter by thin sheet metal. Furthermore, a portion of the heat is carried by conduction to the inside part of the frame, which is also in contact with the cooling air. This method has been proposed by Messrs. Siemens Brothers Limited. A variation of this method has been proposed by Messrs. Mavor and Coulson Limited. The cas:ng is corrugated; a fan circulates the cold air inside the machine, whilst another fan circulates the cold air between this corrugated casing and a sheet metal cover surrounding the machine. The improvement of this method on the other two consists in the fact that the surface dividing the cold and hot air is made much larger. • Fig. 3 shows an entirely new conception. The cold air is taken right through the machine by a series cf pipeBs connecting the two end covers or flanges in the frame. The hot air, which is circulated in the machine by means of a fan, impinges on these pipes, to which it communicates the heat carried away from the armature. In all these methods, however, the internal air plays the main role by conveying the heat to the cold circulating air, and this latter- hardly comes into contact with the heated part of the machine, so that a very small portion of the heat is taken away by conduction. Tn fact, the hot air jackets the machine. The author has endeavoured to improve upon these methods, and the results of his research in this matter seems to constitute a great advance in totally enclosed machines. Fig. -I shows a cross-section through an alternating current three-phase motor. The chief characteristic of the invention is the circulation of the air through a cooling system cast integrally with the frame in such a manner that the external dimen- sions are not increased appreciably. The cooling chambers are channels cast in the webs supporting the laminae, so that the actual weight of a housing built according to this method is not greater than that of the ordinary standard motor. The cooling channels are cooled by drawing cold air from outside through another series of channels so arranged that the cooling air entirely surrounds the hot air channels. The crux of the invention consists in crossing over the two currents of air so that the cooling air is also in con- tact with the outside of the stator laminae or magnet ring. By this means a very large area of cooling surface is obtained. The cooling air does not enter the motor in any way, but merely blows through the Fig. 4.—Cross-section through totally- enclosed Three-phase Emcol Motor. JIBIMIWH Fig. 5.—Cross-section through Totally- enclosed Direct-current Emcol Motor. Fig. 6.—Temperature-rise of a 10-h.p. Three-phase Emcol Motor. /OQ oo/mg System opera Hon _____&£ / i 5 & 4- Ik S k v Hours, space between the outside periphery of the laminae and removable cover and around the tubes. The outer detachable cover allows of the cleaning of the tubes and the removal of any fluff or dirt which may accumulate in the corrugation and may impair the efficiency of the fan. Mr. H. C. E. Jacoby has proposed to build direct current motors on the same principle by surrounding the magnet frame by two or more rings of sheet metal. These rings are spaced apart to form annular chambers, which are- connected respectively to the interior of the machine and to a supply of cold fluid, so as to permit of the hot air in the interior of the machine being sandwiched between layers or annuli of cold fluids, one of the cold fluid layers being in contact with the magnet ring. Thus the frame of the machine is in contact with the cool air supply, and the internal air is both cooled by the same air and by natural radia- tion through the thin sheet metal cover in contact with the atmosphere (fig. 5). This construction necessi- tates the use of an end shield for the distribution of the cold and hot air to their respective chambers. In conjunction with Mr. H. C. E. Jacoby, the author recently proposed to cast the magnetic ring of direct current machines with a multiplicity of longi- tudinal channels in such a way that the channels do not interfere with the proper distribution of the magnetic flux. These channels are connected alter- nately with the interior of the machine and with the outside cooling medium. An internal fan circulates the hot air in one series of channels, and a protected outside fan circulates the cooling fluid in the other series of channels. A 10 horse-power three-phase motor manufactured by the New British Electric Supply Company, of London, is a standard design for a 10 horse-power four-pole open type 50-period machine, which on a six hour full load test showed a temperature rise of only 54 degs. Fahr, on the wind- ing, the temperature rise of the air inside the motor being 46 degs. Fahr. When loaded to 14 horse-power, the final temperature rise was 65 degs. Fahr, on the winding, and of the air inside 59 degs. Fahr. For purposes of comparison, tests were taken on the same motor with the cooling system rendered in- operative, so as to bring the motor under the con- dition of an ordinary totally enclosed motor. The results of these tests are shown by the curves in fig. 6. It should be noted that the motor in every case was run at the current and voltage that gave the best efficiency for that particular load. As an orthodox totally enclosed machine, it could barely be rated at 5 horse-power for continuous rating. At that load the losses are roughly half the losses at the 10 horse-power rating, which is shown on the diagram, and this enables me to formulate the following con- tention : The output of an enclosed motor of this type with a given temperature rise is the same as the output of a standard open type motor of the same bulk and the same weight of active electric material. The output of an enclosed motor of this type is times larger than the output of a standard totally enclosed motor of the same dimensions and weight of active material for the same temperature rise. Since these tests were carried out, larger motors built under the author’s patent have fully confirmed these con- tentions. Further improvements are being brought out in the design of these machines, and doubtless they will assist materially the application of elec- tricity to such industries as coal mining, steel and iron manufacture, chemical works and, last but not least, traction. In this latter field the standard practice has consecrated the almost exclusive use of totally enclosed motors, because in most cases the service con- ditions are such that the motors have a tendency to pick up the dust, dirt and mud of the highways. The strenuous conditions of starting, stopping, and in many cases the high voltages, render the intro- duction of dust and dirt in the motor extremely dangerous to the reliability of the operation. It is true that many very ingenious semi-enclosed motors have been devised to obtain ventilation and guard against the introduction of moisture and dirt, but in my opinion they are only half-way solutions. In coal mining, especially in connection with the driving of face tools, such as coal cutters, it is neces- sary to have the highest possible power in the smallest compass if the working of small seams is to be rendered economical. The author is convinced that, proceed- ing on the lines already indicated, much smaller totally enclosed motors than hitherto can be made. DEVELOPMENT WORK IN COLLIERIES. The following is a copy of a circular letter, dated December 5, issued to collieries by Mr. W. A. Lee on behalf of the Controller of Coal Mines :— Defence of the Realm Regulation No. 9 (Gr).— Development Work. I am directed by the Controller of Coal Mines to refer to paragraphs A (a) (1), (2) and (3) of the directions of March 16, 1918, given under the above Regulation. Although the need for coal is as great as it has been at any time during the war, the fact that miners are now being released from the Forces in large numbers, and that, upon general demobilisation, all the miners who have been recruited during the war, and are still in the Forces, will be free to return to the coal mines should they be willing and able to do so, makes it desirable for the Controller to consider the piactica- bility of some relaxation in regard to the regulation of development work under the directions of March 16, 1918.* At the same time it must be recognised that the release of miners from the Army which is now in progress is for the express purpose of producing more coal, and that it is still only possible to permit develop- ment work of the kind specified in paragraph A (a) (1), (2) and (3), where it can be done without diverting the labour of men already at the mines and of men returning from the Forces from work immediately productive of coal. lam therefore to inform you that, without cancelling the directions of March 16, 1918,f the Controller is prepared to give the most favourable consideration to applications under the portion of these directions above quoted, where it is clear that the work intended to be done is necessary to provide full employment in view of the coming demobilisation. Paragraph (A) (a) (1) (2) and (3) reads as follows :— A.—No owner of a coal mine shall, without previous written notice to the Controller of Coal Mines :— (a) Incur any expenditure on the following objects :— (1) The sinking, widening, or deepening of shafts (including underground shafts) or the continu- ance thereof. (2) The making or driving of slants or adits for the purpose of hauling coal, and of cross measure or stone drifts. (3) The opening or reopening of seams. * And the explanatory letter from the Controller to Sir Thomas Bat cliff e-Ellis of April 12, 1918. f Or the explanatory letter of April 12, 1918. We are informed by Fastnut Limited, 49, Queen .Vic- toria-street, London, E.C., that Fastfit wrenches can now be delivered from stock. The company was not able to deliver them during the past two or three years. Messrs. John Mills and Sons, engineers, Walker Gate Brass Works, Newcastle, announce that they will show specimens of their lamps at the British Science Products Exhibition to be held in the Manchester College of Tech- nology, December 27 to January 9.