The thirteenth ordinary general meeting of the South AfricanInstitute of Electrical Engineers was held in the Lecture Theatreof the South African School of Mines, Johannesburg, on Thursday,the 9th February, 1911, at 8 p.m., the President, Mr. J. H. Rider,being introduced to the chair by Mr. W. Elsdon Dew.

There were present:—29 members: Messrs. J. W. Kirkland,P. W. Bentley, W. Elsdon-Dew, A. E. Gibbs, A. G. F. Heather,F. H. Michell, W. H. Perrow, G. A. Webb, L. B. Woodworth{Member^ of Council), J. Askew, H. Collens, R. Curtis, H. H.Dahl, E. Ehrenberg, F. le Fort, 0. T. Gibb, P. Herd, S. Hill, R. C.Hickling, C. W. Inggs, W. H. James, C. McCann, R. Mortimer,A. B. Nicholetts, G. Nowlau, F. H. Powell, S. P. Bather, F. B. Stiff.

19 Associate Members: Messrs. G. H. B. Bernard, E. Y.Perrow (Associate Members of Council), A. N. Aikman, P. J.Bailey, W. F. M. Bowman, R. B. Canning, T. S. Collins, E. Dalton,T. K. Eastland, J. H. Emms, J. 0. Ferguson, R. W. Fowler, B.Isaacs, G. W. Lowe, H. J. Lewis, A. S. Neilson, A. E. Spiers,A. E. Scott, D. Webster.

10 Associates and Students: Messrs. D. A. Bradley, H. Brown,P. F. Burnett, J. S. Bell, M. M. Behr, E. M. Dahl, I. Glasser, P. A.James, D. S. Kinsey, W. 0. Lindemann.

26 Yisitors, and Fred Rowland, F.O.I.S., Secretary.

PROCEEDINGS

AT

THIRTEENTH ORDINARY GENERAL MEETING.

February 9th, 1911.

Minutes.

The minutes of the second annual general meeting, as printedin the January Transactions, were confirmed.

Membership.

Messrs. W. H. James and C. W. Inggs were appointedscrutineers, and, after their scrutiny of the ballot papers, thePresident announced that the candidates for membership andassociate membership had been elected as follows :—

As Members :

Griffin, Joseph Darii:s, A.E.G-. Electrical Co. of S.A., Ltd., P.O.Box 1129, Johan-nesburg. General Mana^er and Chief Engineer.

Izon, Edwin Gji.iikkt, Messrs. H. Eckstein & Co., P.O. Box 149,Johannesburg. Engineer.

Maxwell, Hugh Bernard, M.I.E.E., Messrs. Reunert Si Lenz, P.O.Box 92, Johannesburg. Electrical Engineer.

As Associate Members :Bough, Henuy, Rand Mines Power Co., Ltd., P.O. Box 121, Fordsburg.

Assisting Constructional EngineerMills, John Alfred, Robinson Randfontein G.M. Co., Randfontein.

Electrician.

The Secretary .announced that since the last meeting, thefollowing had been admitted :—•

As Associates :

Bailey, Geokoe Ernest Augustus, Robinson Deep G.M. Co., Ltd.,P.O. Box 1488, Johannesburg. Electrician.

Dons, Delancey Valentine, Robinson Deep G.M". Co., Ltd., P.O.Box 1488, Johannesburg. Electrician.

Stanley, Thkopuilus Sciireiner, Robinson Deep G.M. Co.. Ltd.,P.O. Box 1488, Johannesburg. Electrician.

As Students :

Arnold, William Naylor, New Goch G.M., Ltd., P.O. Box 109(1,Johannesburg. Apprentice.

Perks, Harry, Robinson G.M. Co., Ltd., P.O. Box 1024, Johannesburg. Electrician.

General, Busin^^^.

Mr, C. W. Inggs (Member) ; I beg to propose that, in theabsence of technical papers relating to South Africa, this Instituteobtains from members, friends of members and other sources,information dealing with electrical work and its development inFrench, Portuguese, Belgian, German and British Africa, forincorporation in the journal. In making this proposal, I wish

Proceedings at Thirteenth Ordinary General Meeting. Fun., 1911.

to point out that this Institute exists for the development of electrical engineering in the whole of South Africa and must not helimited to the Rand, and that, being privileged as we are to havemade our debut with what is practically the commencement ofthe history of United South Africa, we ought to show our faithin the enormous future before our profession by enlarging thescope and thus strengthening the influence of our Institute.

Mr. F. H. Michell seconded the proposal, which was carriedunanimously.

The President: I desire to call the attention of memhers tothe appointment of the Honorary Treasurer for the year, and fivecommittees, as follows :—

Hon. Treasurer : Mr. F. H. Michell.Finance Committee : Messrs. G. H. B. Bernard, W. Elsdon

Dew. W. H. Perrow, (he Hon. Treasurer and the President (ex officio).

Papers Committee: Messrs. F. W. Rentier, W. C. Brown,C. W. R. Campbell, A. G. F. Heather," J. M^ Kirkland,B. Price, L. B. Woodworth and the President (ex officio).

Elections Committee : Messrs. A. G. Gibbs, A. G. F. Heather,B. Price, J. S. Ross, L. B. Woodworth and the President(ex officio).

Draft Regulations Committee : Messrs. W. C. Brown, C. W. R.Campbell, W. Elsdon Dew, J. W. Kirkland, W. H. Perrow,B. Price and the President (ex officio).

Prize Award Committee : The President and Vice-Presidents.

Students' Section.

The Secretary announced that it had been intended to hold .a meeting of the Students' Section on Saturday evening, but,through unforeseen circumstances, this had to he abandoned.Due notice of the meeting would be given to students.

The President's (Mr. John H. Rider, V.P.I.E.E.)Inaugural Remarks.

Gentlemen,'—The request with which you honoured me toaccept the office of President of your Institute was so recent thatI have not been able to prepare any presidential address of theordinary kind. Not only have I been too busy to give the timeto the matter to prepare an address which would be satisfactoryboth to yourself and to me, but my presence in this country is ofsuch recent date, that I am not familiar enough with local

Fkb., 1911. Proc^edings at Thirteenth Ordinary General Meeting.3

4'IVie President's Inaugural Remarks.Fkh., 1911.

conditions and circumstances to attempt the task. With your kindpermission, I will content myself this evening with a few briefremarks, and will give you a formal address at the end of my yearof office, when I shall be, I hope, in a much better position toundertake it.

I take it that this Institute was not founded in any way tobe antagonistic to any of the existing scientific bodies in SouthAfrica, but rather that it was intended to fill a gap, and to givegreater prominence to electrical work, and help to those engagedin the industry.

The Institute can and should be a great power for g'ood, andits influence can be felt in many ways. Not only is it a means ofbringing men together, with the result that personal interchangeof ideas which is so essential to one's progress can be obtained,but the various experiences of the members are placed before theInstitute. It is not merely in the matter of the reading of papersthat good can be done. What I am most anxious to See is thatlive discussions should follow the papers. Papers should be considered either (1) as permanent records of work done, or (2) assuggestions for new work and improvement in old. Thereseems to be an unexampled diffidence on the part of members ofthis Institute, speaking generally, to take part in discussions.Either it is due to an excessive modesty, which I can hardlyrealise when I look around, or to the fact that members generallyhave nothing to say. I cannot accept either of these alternatives,because, whatever position a man holds, whether it be humble orgreat, he is bound to have experiences which do not fall to thelot of the other man. In other words, every man, whoever he be,knows something which the other man does not, and it is thatsomething which he should tell the Institute in the discussions ofthe various papers which are read. Even if a man only speaks adozen words, those words may contain some idea or thoughtwhicli may lead to great good, and I can assure the members that,

' so far as I am concerned, the shortest contributions to discussionswill be most thankfully received.

One of the difficulties which results from the presentscarcity of papers, and the necessity to work from hand tomouth, as it were, is that members do not see, Copies of the papersbefore the actual meeting at which they are to be read. Theresult is that, immediately after the reading of any paper, themeeting starts to discuss other papers which were read perhapsseveral months before, and in which the interest has probablylargely declined. If members would only come, forward a littlemore promptly with offers of papers, It would be possible to havethem circulated before the meetings, so that they could be readand digested. The discussion could then take place while thesubject was hot, with the result, I am sure, that more interest

A SUGGESTED COMMUTATORLESS DIRECTCURRENT GENERATOR.

By E. GrOTK and E. Davidson (Associate Members).

(Mead at September Meeting).

FINAL DISCUSSION.

The President : I should like the authors to answer one ortwo questions in connection with this paper. Will they tell uswhat good they think will result commercially from the practicalapplication of a dynamo made in the way they suggest. Do theythink that the troubles which are experienced to-day withcommutators and brushes on high class D.O. machines,particularly those with inter poles, are so great that the extraexpense which their particular machine would no doubt entailin manufacture, would be warranted. In this country, at any

would be shown and more valuable contributions received to thediscussion.

In offering their remarks, members need not be afraid thatwhat they say would not read well in the Transactions. Editingcan always be done and the art of public speaking is so valuableto the present day man, that every endeavour should be made byeach member to cultivate it. Meetings like these are a mostvaluable help, and, by making a beginning in a small way,members would soon find that speaking at discussions wouldbecome for them a very easy matter, particularly if they took thetrouble to look up the subject for a few minutes before comingto the meeting. Long speeches are never required, and I havedealt with this matter somewhat at length because lam convincedthat to become what I indicated at the beginning, namely, a grealpower for good in the electrical engineering world, we must havegood live discussions, and the Engineers who constitute themembership of this Institute have experiences every day whichshould be made known by them to their fellows.

I thank you for the honour you have done me in placing mein this Chair, and I can promise you that nothing shall be wantingon my part, not only to further the interests of the Institute, butto do good to the large and increasing number of ElectricalEngineers who earn their livelihood on the Rand.

Feb., 1911. A Suggested Comiti'ittitorless Direct Current Generator.

DISCUSSION.

The President : Those of you who have read Mr. McCann'spaper will notice that he confines his remarks to two-stage compressors, either large compressors direct coupled to steam engines,large compressors belt driven by motors, or small compressorsbelt or gear driven. Apparently he is considering only thosetypes of compressors which up till recently have been general onthe Rand. As you know, there are now some very large compressors here of the turbine type being put in both at Roshervilleand at the Robinson Mine, and if any gentleman present has anything he can tell us about that type of compressor, as compared

ELECTRICALLY-DRIVEN AIR COMPRESSORS.By OHAS. MoOann (Member).

(Rend at October Meeting).

rate, what ^ould be the practical use of a machine such as theyhave described. As you all know, we are using here nothing bntthree-phase machines, and D.C. motors and dynamos can bebought at scrap prices.

Mr. J. W. Kirkland {Vice-President) •, In spite of whatI said at a previous meeting I fear that the machine proposedand described in the paper under discussion is inoperative. If,however, anyone were to produce a D.C. machine which wouldcominutate without excessive wear of the commutator andbrushes, the demand for that machine would be considerable, notonly in Africa, but everywhere else in the world. Among thechief reasons why the transmission of power electrically is nowlimited to 100 or 150 miles is the fact that with A.C. there arethe phenomena of induction and capacity. These cannot beavoided except by adopting very low frequency which involvesextreme cost of transforming apparatus. If only we couldproduce power by D.C. of very high voltage, we would avoid, notonly the cost of transformation, but the inconvenient fact that thepeak of the E.M.F. of an A.C. is some 40 per cent, higher thanthe square root of the mean square or effective value. I thinkMessrs. Grote and Davidson have endeavoured to meet a real andexisting demand all over the world for power transmission,

Electrically-Driven Air Compressors.Feu. 1911.

with reciprocating compressors, I am sure it would be a valuablecontribution.

Mr. J. W. Kirkland (Vice-President) : I am glad to havebeen associated with our President in connection with someturbo-compressors which have been put in on these fields. Thepurpose of these machines is to supplement the capacity ofexisting steam-driven compressors by means of electrical power.It was first suggested by Mr. Behr, and later taken up byMr. Robeson, to compress air slightly in a turbo-compressor andso deliver it under moderate pressure to existing reciprocatingcompressors. By taking air at the normal atmospheric pressurewhich exists here-—slightly over 12 lbs. per square inch—andcompressing it up to, say, absolute 18 lbs., we increase the capacityof the steam-driven compressors by 50 per cent. The ideainvolved in this scheme of compound compression is somewhatlike that of using reciprocating engines in connection with lowpressure steam turbines. We employ two kinds of machines, eachin its most efficient pressure range.

Mr. W. Elsdon Dew {Member) : The author of this paperhas seemingly made out a good case for himself, but I fear thatthe engineers of the Rand are not convinced that he is correct.I regret that he has not touched on the question of the possibilityof boosting of air, by using boosting compressors driven byelectric motors. Even in the present long air mains undergroundfeeding distant slopes there is considerable loss. If small boosterswere utilise'!, say where 10 or 12 drills were at work, there is thepossibility of great improvement in the efficiency of these drills-,as it is well known that air drills are very much more efficientat the higher pressures. I felt when I heard that the author wasgoing to read this paper, that he would touch on this part of thesubject, and if he bad given us a few figures it would, I think,impress Engineers who have dealt with air problems and thesubject of an efficient supply of air underground.

Mr. Chas. M. McCann (Member) : I should like to remarkthat in my paper, I advocated the use of turbo-compressorsunderground, not reciprocating compressors.

The President : I think it would be very interesting tohave figures, of the relative costs of driving ordinary reciprocatingcompressors by motors and steam engines.

1911.Electrically-Driven Air Compressors,

DISCUSSION.

Mr. W. Elsdon-Dew (Member of Council) : This Instituteis fortunate in having this paper amongst its records. I am notaware that this subject has been treated previously in such amanner, and for reference purposes it is particularly useful, andI am sure the members of this Institute will find it most helpful,and in this respect I would particularly refer to what the authorhas called attention to on page 320, viz., the balancing of phasevoltage. I shall quote his words :—-

" The unbalancing of phase voltage may be due to a relatively large load on one phase (say, a number of arclamps). If ^^ transformers supplying energy to thecircuit have both their primary and secondary winding"Y" connected and ungrounded, no suitable neutralpoint can be maintained, consequently serious unbalancing may result."

This is perhaps not so fully recognised as it should be, andthere are cases of motors that ^re showing signs of overheating,which fault may be traced to this cause. From the facts quotedof particular experiments, it is apparent that this unbalancing ofvoltage has a greater effect in small motors than in large ones,and this is what we might expect. As the author points outvery graphically in Fig. 2, curves D and E (page 321 j there arerelatively greater effects at light loads than at full loads withunbalanced voltages.

The unstable condition of transformers having both theirprimaries and secondaries "Y" connected, is often the cause ofoverheating of many motors, and upon investigation and correction of this fault, motors now running with high temperatureswould be greatly improved.

The author has pointed out a certain condition which, froma manufacturer's point of view, may be economy, but from auser's point of view, is a very doubtful advantage. I refer tothe practice of using the same stampings of laminations for manydifferent ratings and speeds of motors. Now while the advisabilityof using the same frame or shell does not offer the same objections,I must say that when one finds that motors of the same size madeby one maker give worse efficiencies and power factors than

NOTES ON THREE-PHASE INDUCTION MOTORS.By Philip Heed (Member).

(Bead at November Meeting).

Notes o.t Three-pknse Induction Motors.Fi-:r,., 11)11,

Feb., 1911.Notes on Three-phase Induction Motors.9

motors of the same size by other makers, one is inclined to lookfor faults, and one will not have to go very far to find someif one has the opportunity of examinin^ the winding.

This practice of using the same stampings, having slots toodeep or too large for the wires of the particular motor required,has allowed a most reprehensible practice to come into vogue.I refer to the practice of filling these slots with more orless unstable packing. This packing is not doing any usefulwork, either electrically or mechanically. The user has, to acertain extent, paid for material that he has no wish to have inhis motor.

What are the principal causes of faults in electrical machinery ?It is not faulty insulation so much as windings that have graduallybeen shaken out of position ; insulation that has lost its properties ;and wires, subject to vibration, chafing through their covering.

In three-phase motors, those who have had repairs to do onthem can endorse what I say in this respect, for faults develop incoils or between adjacent wires, because the wires are not properlyfixed or solidly laid. The packing, with its coatings of varnish,may be quite satisfactory for a year or so after leaving the factory,but what is the result after years of working, when heat has takenaway most of the mechanical strength of the packing ?

I remember well when Mr. Ferranti was building his firstlarge alternators, at Deptford, about 1890, that the vibration ofwires in the slots was the cause of some of his troubles. Themeans he adopted to get a solid job was not by half filling the slotwith packing, but having the slot the right size, and coils wedgedin, and the conductors solidly fixed with a minimum of insulationthat was lasting in its properties. Perhaps I have spoken ratherat length on this matter, but I deprecate any diversion from thebest practice even for the sake of cheap motors, made to sell, andultimately a source of annoyance and a disgrace to engineering.

The author refers to the possibility of an attendant arrivingat a false impression by observing the readings of the amperemeters. The alternating current ammeter is not a reliable instrument if other observations are not taken at the same time, but, asa general guide, its usefulness to the unskilled attendant must notbe deprecated, though I feel quite confident that a daily log keptof the temperature of motors as they are running, will be foundto be a most useful guide for watching the condition of motors.As you are aware, the usual statement about motors running hotis most misleading, and a thermometer, with maximum indicator,left on a motor in a suitable position would give more reliableinformation than anything else.

As pointed out by the author, the effect of low voltage andlow periodicity is detrimental, and extra heating results. At thesame time, as briefly referred to, motors of low periodicity have a

higher overload capacity than motors of the same power andhigher periodicity.

This brings ns to the final summary of the author's paper,and, in speaking of the choice of capacity and speed of motors,he advocates what no doubt is fully recognised as the bestpractice, assuming a condition of a 50 cycle proposition, but it isnot at all obvious that a 25 cycle proposition would not alter someof these arguments. The elimination of the belts, with theirattendant losses and troubles, might save a great deal more in ayear than a slight difference in the efficiency of the motor, andthere are many other important factors which must appeal tothose engaged in power work in this matter of periodicity, but itis not necessary^ to go into them now. I fully appreciate and endorse the author's reference to the saving that results by obtainingthe best motors, best not only in efficiency and power factor, butalso in mechanical design and strength. This fact will be muchmore appreciated when proper records are kept of the operation ofmotors, and the power bill is closely scrutinised. Maintenancecosts will be closely watched, and this will be the guide inmatters of comparison in this respect.

Mr. C. W. Inggs (Member) : I would like Mr. Dew to tellus whether this breaking down of the insulation, due to vibrationof the conductors, to which he refers, occurred in slip ring orsquirrel cage motors ? I have always considered that, owing tothe very large starting currents, the windings in squirrel cagemotors must be subject to very great vibration ; now one cancalculate what the attractive or repulsive forces between adjacentwires will be, but, unfortunately, one cannot calculate what thelimit of mechanical resistance of an insulating material is to theseforces, and, therefore, not having personal experience of a breakdown in this connection, I have been waiting till some incidentoccurred which would either ratify or disprove my idea. I takeit that, in any case, Mr. Dew refers to stator windings.

Mr. W. Elsdon Dew (Member) : In reply to Mr. Inggs, Iwould say that in both cases I have found vibration mostdetrimental to the insulation of the machine. The squirrelcage motor, to which I can particularly refer, I had to re-wind,and the square bars of rotor were originally driven into the slotsand were all more or less earthed : the die to which the laminations were punched evidently was a poor one, as the laminationswere irregular and made the slots rough, and although the motorran for twelve months without the least sign of trouble, the vibration ultimately got through the coverings of the bar windings, andthe result was a breakdown. I have had the same vibration inordinary slip ring motors, and in this respect, I can say when I

10Notes ou Three-phase Induction Motors.Feb., 1911.

Feb., 1911.Notes o'n Three-phase Induction Motors.11

found it within the slots, it was gene^^lly at a place where thewindings were loose, while externally, it was found where thewires were crossing one another or lying more or less loosely onthe outside of the stampings ; the actual fact that it happenedat these places shew that there is vibration going on and if thereis the least chance of any looseness, and where there are no solidfixings of the windings in the slots, a breakdown is sure tofollow.

The President: I think a very important point mentionedin this paper was the fact that, in order to cheapen production,,makers are in the habit of using stampings of one uniform sizefor several ratings. Now, probably that state of things has beencaused by competition in selling the motors, but I quite agreewith Mr. Dew that, from the user's point of view, it is a practicenot to be recommended. To get a good motor, it must be designedin all its parts for the work it has to do, and I think manufacturer'sare rather apt to misunderstand the meaning of the word efficiency.You get high figures quoted for a motor, and you get a low price,and efficiency and improved power factor are frequently obtainedby reducing the clearances, particularly in indnction motor's, withthe result that a smaller machine can be got to do the work. Thisis all very well from the manufacture^'s point of view, but theuser has to consider it, not entirely from the point of view ofprice, but whether that motor is going to give him any trouble inrunning, and that brings in the great consideration of consequentialdamage. It is the little attention to details that frequently makesor mars the success of a scheme. If you get a motor made to giveyou high power factor and high efficiency, with a small machineand small cost, and that motor is put down merely to drive anisolated machine—I used the illustration once before—say a chaff-cutter, it does not matter if it breaks down ; but a motor hasfrequently to oe used as a link in a chain, witn a good manymore important things than the motor itself dependent upon it.When you have tronble with a motor, it is not the failure of themotor which affecis you, but the failure of other apparatus onwhich the motor depends. If makers and users would only learnthat, hi buying motors which will give high efficiency in the truesense, it is not the machine made with superlatively highefficiencies on the test bed that will fully meet their 1'eqnirements,but machines which will run with ample mechanical clearancebetween rotors and stators, with bearings amply designed for thework and a carcase which is large enough to dissipate the heatgenerated, then the commercial result, which is what determines,our success, will be very much better.

The meeting then adjourned to the Electrotechnics Laboratory,when Mr. F. H. Michell demonstrated the working of the KelvinBalance, the Oscillograph and other electrical apparatus. Themeeting terminated at 10-30 p.m.

DISCUSSION.

Mr. F. H. Michell (Hon. Treasurer) : In a country likethis, with propositions so widely distributed and so isolated, Ithink this subject, which Mr. Woodworth has brought up so ably,is one deserving of discussion by every member. I hope beforethe discussion closes to have something more to say about itmyself, but in the meantime, I should like to ask the authorif he would kindly give us in his reply some information relatingto the class 5 machines—separators using static electricity. Herefers to the fact that in the United States and Mexico particularly,such machines are very largely used, and are very successful. Manyof you know that Professor Dobson, some time ago, carried out anumber of experiments with a static separator in the laboratoryof this College, but I do not know that any practical result camefrom them. At any rate, many points were brought forwardwhich were of great interest. Personally, I know very littleabout these static separators and how far they have been successfulin other parts of the world, but 1 am sure that if Mr. Woodworthwould give us some figures in connection with them, they wouldbe much appreciated. The static machine, which was used inconnection with the experiments I have mentioned, is in thelaboratory now, and members will have an opportunity of seeingit working at the close of this meeting.

ELECTRICAL SEPARATORS.By L. B. Woodwoeth, A.M.I E.E., A.Am.I.E.E.

(Member of Council).

(Read at January Meeting.)

12Eleetiiail Separators.Fkh.. 1911.

Control ok Electric: Winders.—In a paper read before the Manchester Section of the Institution of Electrical Engineers on December tith,Dr. E. Rosenberg (British Westinghouse Electric & Manufacturing Co.)dealt with the control of electrically driven main winders. The authorpointed out that, besides starting and stopping ordinary loads, it is oftennecessary to lower unbalanced loads, in which case the motor, if it be used atall, must work as a generator. If no tail rope is used, and the load on theup-going cage is just balanced by the load on the down-going cage, then therope weight will, in the first half-trip, exercise a positive, and in the secondhalf a negative torque, and the winding machine has at first to act as a motorand then as a brake.

In the case of Ward-Leonard control, as long as the speed of the motor-generator is kept constant, the shunt regulator of the generator determinesits E.M.F., and the speed of the constantly excited winding motor will attaina value which gives an E.M.F. of the winding motor only slightly higher,because a slight difference will give rise to a circulating current of sufficientmagnitude to balance the torque impressed by the load. Assuming that theexciting voltage is kept constant, that there is no flywheel and no artificialslip in the motor-generator, that the slip of the induction motor at full loadis 2 per cent., that the controlling machine has a drop in voltage from no loadto full load of 5 per cent., and that the winding motor has a drop in speed of5 per cent from no load to full load, then the difference of the motor speedbetween no-load torque and full-load torque will be approximately 12 percent. If the winding motor has to exercise a negative torque of half thevalue of the normal working torque, the difference in speed will grow to 18per cent. This difference of 18 per cent, grows in proportion if the controllerlever is put into a position for a low speed. For half excitation the liftingspeed for normal load will be about Hi) per cent, of the full (no-load) speedand the lowering speed for a load which would require half braking torquewill be about 56 per cent, of the full speed. If an Ilgner set with increasedslip is used, or if the excitation is not constant, the differences will be greater.It is therefore necessary to use a speed indicator, and not to depend upon apositive relation between the position of the control lever and the speed ofthe winding engine. With Ward-Leonard control, the movements of thelever in order to come to rest are nearly the same whether the motor is drivingor driven, and a very great braking torque can be obtained.

With a D.C. shunt motor fed direct from the 'bus-bars, and providedwith combined series and shunt regulation, breaking is done most effectivelywithin the range of shunt regulation without any additional apparatus, as themotor will work as a generator if driven from outside and return power tothe line. For a given position of the shunt regulator (with the series resistances cut out) the motor when exercising half full-load brake torque willdevelop a speed approximately 7 per cent, higher than the motoringspeed forthe same position. When resistance is inserted in the armature circuit, theE.M.F. of the motor working as a generator will have to be considerablygreater than the 'bus-bar voltage in order to return power through theresistance to the line. Thus 80 per cent, motor speed at full load wouldcorrespond to 110 per cent, generator speed for 50 per cent, brake torque, anda position for creeping speed of the motor, say 5 per cent., would allow agenerator speed for 50 per cent, brake torque of 148 per cent. Consequently,such controller positions are not suitable for lowering loads, and regenerativecontrol should only be used with the controller in ''full-on" position.Regenerative control cannot be used to slow down the motor at the end of

ABSTRACTS AND NOTICES

Fkh., 1911.Abstracts and Notices.19

the trip. The controller has to be moved into the " off " position and themechanical brake applied, or it may be moved beyond the " off " position andthe first steps for the lifting; movement used. In case the speed throughout^he lowering trip has to be kept lower than the speed which the motordevelopes with all the armature resistance cutout, for instance, for loweringof men, counter-current must be use.I during the whole trip. Regularbraking with counter-current is a very safe, but naturally wasteful, method.

With a polyphase induction motor, the conditions are analogous to thoseof a D.C. shunt motor (without shunt regulator) fed direct from the 'bus-bar.If the rotor is short-circuited, the machine will, for a slight increase in speed,act as a generator and return power to the line. The generating speed onhalf-load would be only 3 per cent, above the full-load motor speed. Liquidcontrollers, however, are seldom completely short-circuited and, therefore,the speed difference might be nearer to (1 or 8 per cent. To brake the motordown to lower speeds, counter-current is required. Driving the motor at over-synchronous speeds with resistance insetted (controller in lowering position)would here also cause too high a speed to he reached.

Dr. Rosenberg then described the use of a D.C. motor as a dynamicbrake by disconnecting the armature from the line, and connecting it to aresistance. If the machine is constantly excited, the braking torque will be ina direct proportion to the speed of the motor, and in inverse proportion tothe resistance. It would be necessary at first to increase, then to reduce theresistance, or a constant resistance could be used which would only limit thespeed of the lowering load, and other means could be used to bring theload to rest at the end of the trip. To use an induction motor as adymamicbrake, the stator is connected to a low-voltage D.C. supply and the three slip-rings to a three-phase resistance. The machine then represents an A.C.generator with stationary field, the exciting winding of which is distributedin the slots, and with a rotating polyphase armature connected to resistances.As the air-gap is small, the armature reaction is exceedingly high, and thishas a very important influence, because it is only for small armature reactionthat (at constant speed) the torque will be in inverse proportion to theresistance. As soon as the armature current exceeds a certain limit areduction of the resistance will even reduce the braking torque.

The author then dealt with the different ways of connecting a three-phase winding to a D.C. supply, and necessary value of current to producethe same magnetic conditions as at full-load with a A.C. supply. A methodof determining the relations between torque, speed, and resistance underthese conditions was given, and tests on a 30 H.P. motor were described. Itwas shown that the torque always increases with increased D.C. excitation,whereas for a decrease of resistance the torque might be increased ordecreased, dependent upon the momentary speed. Consequently, it is notsafe to use the variable resistance of the controller for braking, as the drivermay easily overshoot the mark in trying to make the brake more effective,and then he would not be able to stop the load. It would, however, bepossible to change the resistance automatically in proportion to the frequencyof the rotor currents. For a constant excitation and a constant resistance inthe armature there exists a critical speed up to which the torque increases andafter which the torque goes down with increased speed. If the excitingcurrent and the resistance are high enough, however, it is possible to insurethat the brake torque wanted is well below the obtainable maximum torque,and that the speed wanted is well below the critical speed. For stoppingmechanical brakes would be supplied.

Turning to eddy-current brakes, the author pointed out that there is anessential difference between those with copper discs and those with cast-ironarmatures. The latter had the important advantage that there was a steadyincrease in torque with increasing speed, and no critical speed after which thetorque diminished as with copper disc brakes. His explanation was that thevirtual resistance of the cast-iron armature cannot be considered as a constant

14Abstracts and Notice"-Feb., 1911.

Jamieson Andrew. A Text-book of Steam and Steam Engines, includingTurbines and Boilers. Yol. I, 17th ed. Bevised. Crown 8vo. pp. 852.C. Griffin. 10s. fid.

Electro-plating and Electro refining of Metals, The. Being a new edition ofAlexander Watt's Electro-Deposition. Bevised and largely re-writtenby Arnold Philip. 8vo. pp. 704. C. Loclcoood. Net, 12s. fid.

Sheldon, Samuel, and Houstnann, Erick. Dynamo Electric Machinery ; theConstruction, Design and Operation of Direct-current Machines. 8th ed.Completely re-written. Cr. 8vo. pp. 338. C. Lockwoud. Net, 12s.

..Cruickshank, B., and McKay, B. F. Machine Sketches and Designs forEngineering Students. 4to. E. Arnold. Is. fid.

Harrison, H. H. Engineering Mathematics Simply Explained. 3rd ed. Cr8vo. pp. 172. P. Marshall. Net, Is. fid.

Jamieson, Andrew. A Text-book of Applied Mechanics and MechanicalEngineering. Vol. f, Applied Mechanics. 8th ed. Bevised. Cr. 8vo.pp. 418. V. Griffin, fis.

Crocker, Francis B., and Arendt Morton. Electric Motors ; their Action,Control and Application. 8vo. pp. 298. C. Lockwood. Net, 10s. GJ.

Tembie, W. H. Elements of Electricity for Technical Students. Cr. 8vo.Chapman <5 Hall. Net, 8s. fid.

Ennis, W. D. Applied Thermodynamics for Engineers. Illustrated. Boy.8vo. Constable. Net, 21s.

NEW BOOKS.

Feb., 1911.Abstracts and Notices.—New Books.15

value, but that it increases with increased periodicity. He considers that forlow speeds the flux penetrates the whole depth of the cast-iron armature,and that with increased speed, and therefore increased voltage, the currentdensity near the surface increases, and shields the deeper parts, so that thecurrents crowd on the skin of the armature. Therefore, with increasingperiodicity the resistance of the eddy-current path increases, and this also hasthe ef^ect that the resultant flux does not tend to fall off, since in order tomaintain the current with the increased resistance, a higher E.M.F. is required.The eddy-current brakes as used in connection with large hoistingengines are able to deal with continuous trips of unbalanced loads, and it ispossible to regulate the speed without use of the mechanical brake down toa very low value. The field is excited from D.C. 'bus bars which are fed bymotor-generator and on which a storage battery is floating ; therefore thebrake is also available in case of failure of the main supply current, and insuch cases the excitation is switched in automatically.

Concluding, the author states that it is impossible to say which is the bestsystem of control. For lowest power consumption, if the starting and braking periods and the periods of trips with reduced speed are of long duration,the Ward-Leonard system might prove the most efficient. With differentstarting and running conditions the simrle A.C. motor system might be themost efficient, and in other cases might be preferred on account of its lowerinitial cost. If current is charged on a flat-rate basis, an equaliser wouldbe out of place, because ic not only increases the initial costs, but also thetotal current consumption. A charge on the maximum demand system, onthe other hand, will turn the balance in favour of equaliser systems. Thequestion also whether any inducement is offered to the power consumer fora good power factor might turn the balance in a given case from the direct-coupled slow-speed A.C. winding motor to the War.I-Leonard system withhigh-speed motor-generator.—Electrical Engineering^ January 5, 1911, p. V.

SELECTED PATENT APPLICATIONS.(TRANSVAAL.)

Provisional applications for Letters Patent will be inserted in this list ascomplete Specifications. Complete Specifications have to be submittedwithin nine months after the provisional application has been supplied, andon the acceptance of the complete Specifica^ion, the applicant must advertiseit in three issues of the Gazette. The application and Specification, togetherwith drawings, etc., shall thereupon be open to public inspection. Anyperson may within two months from the date of the latest advertisement, orabout eleven weeks from the date of acceptance, give notice in writing to theRegistrar of Patents of any objection to the granting of such patent.

In the list (P) means Provisional Application ; (C) means CompleteSpecification. The date signifies when filed.

(P.) 467/10. Wiliam Henry Hutchinson (11, Malcolm Canmore Inglis(2). Improvements in gripping and handling appliances. '21/9/10.

(C.) 469/10. Frederick Arthur Maxmillian Schiechel. Apparatus forseparating minerals and like minerals. 22.9.10.

(0.) 473/10. Ernest Holroyd Martin. Improvents in discharge meansfor stamp mills and other crushing machinery. 26.9.10.

(C.) 475/10. Norman Frederick White (1), Thomas Robert Dibden(2), Percy James Drain (3). An improved safety catch gear for mineskips, or cages lifts, elevators and like vehicles. 27.9.10.

(P.) 47^/10. Frank William Girdler Brown. Improvements in guiding skips, cages and the like, in mine shafts and otherwise. 29.9.10.

(C.) 479/10. Robert J. McNitt. Improvements in the electrolyticmanufacture of alkali metals and alU>3rs of alkali metals. 30.9.10.

(P.) 482/10. James A. Lamberton. An improvement in safety catchesfor use on any form of conv^yance used in mine shafts. 4.10.10.

(P.) 484/10. James Ceggie. Improvements in dust collectors forrock drilling machines and the like. 5.10.10.

(P.) 485/10. Richard Barrat Brown. Automatic self-coupling buffer.6.10.10.

(P.) 487/10. Samuel Raybould. Improvements in guides for thestems of the stamps of stamp mills. 7.10.10.

(P.) 488/10. John Fraser Price (1), Robert Oraib (2). Improvementsin means for separating liquids from crushed ore products. 7.10.10.

(C.) 489/10. Maurice de Redon de Colombier (1), Jules Clement (2).Improvements in separating metallic particles from their admixtures,7.10.10.

(C.) 490/10. (fustaf Henrik Fabrau Berglund. Improvements inautomatic couplings for railway and other vehicles. 7.10.10.

P.) 493/10. Hans Charles Behr. Improvements in hoist apparatusemploying cyliudro-conical drums. 7.10 10.

(C.) 496/10. Thomas Edwards. Improvements in ore roastingfurnaces. 1.10.10.

(0.) 497/10. Hans Peter Rasmussen. Composition for the use ofelectric insulating and other commercial purposes. 8.10.10.

(C.) 499/10. Foaker Kohler. The " Kohler " automatic brake for usein skips, cages, lifts, etc. 10.10.10.

(C.) 509/09. Francis Joseph Watts (1), Fraser Joseph Alexandra (2).Improvements in electrically actuated apparatus for cleaning and scouringamalgamating plates or surfaces. 10.11.09.

This patent application covers an electric motor with gearing attachedfor rotating a suitable brush for cleaning amalgam plates.

16Selected Patent Application!!.Ft:n., 1911.