Tliu fifteenth ordinary general meeting of the South AfricanInstitute of Electrical Engineers was held in the Lecture Theatreof the South African Schoul of Mines, Johannesburg, on Thursday,the 20th April, 1911, at 8 p.m., the President, Mr. J. H. Rider, inthe chair.

There were present:—29 members : Messrs. J. W. Kirkland,E. W. Bentley, W. Elsdon-Dew, A. G. E. Heather, E. H. Michell,W. H. Perrow, G. A. Webb, L. B. Woodworth, C. W. R. Campbell(Members of Council), J. R. Bradley, E. Crowther, E. Ehrenberg,E. le Fort, P. E. Gregson, R. C. Hickling, C. W. Inggs, L. H. Mar-thinusen, R. Mortimer, J. E. Maudlen, C. McCann, A. B. Nicholetts,G. Nowlan, E. H. Owtram, F. F. Parker, T. S. Roering, P. Sannders,W. Sutton, S. P. Sather.

29 Associate Members: Messrs. J. S. Ross (Associate Memberof Council), A. N. Aikman, S. Blythe, E. D. Brunner, H. Bough,W. F. M. Bowman, A. Cooper, R. B. Canning, T. S. Collins, F.Davidson, J. A. Dingwall, J. C. Ferguson, A- Hare, 0. J. Henthorn,B.Isaacs, W. H. Jameson, G. W. Lowe, J. R. Macdonald, D. McCall,C.A. Mader, J. A. Mills, S. F. May, B. T. Ohlseu, V. Pickles, D. M.Ross, A. E. Scott, T. F. Whimster, J. J. Ward, C. S. Wright.

(S Associates and Students: Messrs. W. 1ST. Arnold, M. M. Behr,J. S. Bell, P. F. Burnett, I. Glasser, H. Hodgson, F. L. McKowen,H. E. Zurich.

23 Visitors, and Fred Rowland, P.O.I.S., Secretary.

PROCEEDINGS

AT

FIFTEENTH ORDINARY GENERAL MEETING.

April 20th, 1911.

1 11s. fid.1 J. Why took/divided.

Minutes.

' The minutes of the fourteenth ordinary general meeting, asprinted in the March Transactions, were confirmed.

Membership.'I

Messrs. 0. McCann and D. McCall were appointed scrutineers,fand, after their scrutiny of the ballot papers, the President an-|nounced that the candidates for membership and associate mem-|hership had been elected as follows :—i

As a Member :1

Bhydkn, Chart.es Lumsdex, Victoria Palls and Transvaal Power Co.,)Ltd., P.O. Box 2(571, Johannesburg. Construction Engineer.j

As Associate Members :j

Anson, Joseph Walter, A.M.I.E.E., Messrs. H. Eckstein i^ Co.,jP.O. Box 149, Johannesburg. Assistant Electrical Engineer.\

Foley, John Fi.okrence, Transvaal Gold Mining Estates, Ltd., P.O.jBox 49, Pilgrims Rest. Electrician.j

Harks ess, James William, New Modderfontein Gold Mining Co.,fLtd., Benoni. Electrician. .|

^t'EEle. Harry William, Van Ryn Deep.Ltd., P.O. Box 22o, Beuoui.|.Electrician. ,4

Ward, Joseph Jekkkies, Victoria Falls and Transvaal Power Co.,\Ltd., Post Office, Rosherville. Electrical Engineer.\

WiiioiiT, Charles Samuel, Rosherville Power Station, Cleveland.jForeman Electrician.1

;jThe Secretary announced that since the last meeting, the

following Associates had been admitted :—Hudson, William Michael, 14, Jorrisen Street, Bniamfontein.J

Principal, Manual Training Centre, G-ermistoii.|Read, Ernest Percy, Robinson Gold Mining Co., Ltd., 1, Fifth;'

Street, Booysens Reserve.]Russell, Eorert, Victoria Falls and Transvaal Power Co., Ltd.. :i

P.O. Box 121, Fordsburg. Station Electrician.iWriuiit, Hiiiiii Walter, Victoria Falls and Transvaal Power Co.,i

Ltd., P.O. Box 121, Fordsburg. Record Clerk.

Presentation of Prizes.

The President then presented the book prizes which hadbeen awarded by the Institute to the successful students at the:School of Mines Evening Classes, as follows ;—;

Electrotechiiics—Stage I. 1 Is. Od.G. Newman.Stage II. 2 2s. Od.No award.Stage III. The Institute's) XT,

i>a^ i i rNo award.Bronze Medal)

Electricity and Magnetism ( G. Powis 1 Prize

fil)Proceedings at Fifteenth Ordinary, General Meeting. April, 1911.

DISCUSSION.

Mr. L. B. Woodworth (Member of Council) : In connection with Mr. Campbell's most interesting paper, I should like tomake a few remarks on one or two points which occur to me.

In line construction for high tension work the question ofjoining, in phase and overhead ground wires, is of great importance. In many cases shutdowns are due to broken joints inline or ground wires, such breaks occuring at joints, the jointsfailing through careless workmanship. I have seen severalfailures resulting from solder (at too high a temperature) beingpoured upon the joint. In some cases joining clamps or Crosbyclips have been screwed either too tight, or too slack.

The question of the type of insulator is also of great im-tance. Resistance to surface arcing or flash over depends uponthe material, texture of surface and shape of insulator. Usingporcelain having a smooth surface the question of shape has to bedecided. If a pin insulator is used then the question of multi-petticoat, or umbrella or bell with pin guard has to be decided.To properly guard a pin insulator and conductor from the effectsof a power arc following a flash over, I think that in addition tothe metallic ring around the lower petticoat of insulator, additionalprotection should be insured by having a protective bindingsheath round the conductor at each insulator, such sheath beingburnt by the arc (instead of the conductor). In many cases itwill be found that a conductor is seriously weakened by amomentary arc burning through one or more strands of the saidconductor, whereas if a metallic binding sheath had been usedthe conductor would not have been affected. To my mind thesuspension type insulator gives the system the greatest factor ofsafety as it is subjected to only compressive strains, and having ahigher factor of safety, both electrically and mechanically, thanpin insulators, and producing less torsional stress on the crossarmin event of a wire breaking. This type of insulator certainlyneeds higher and more expensive poles and frequent anchoring ofthe line wire. Where several insulators of this type are used inseries, they should be joined together by hard drawn copper cableheld fast by bolted clamps, the wires connecting the insulatorsbeing reinforced by suitable sleeves on wearing surfaces. Byusing this type of insulator we can make the factor of safety

Ai'Kll,, 1911.Troubles on Overhead Power Lines,51

TROUBLES ON OVERHEAD POWER LINES.By C. W. E. Campbe^l (Past President).

(Mead at March Meeting.)

52Trimbles mi Overhead Power Lines.Al'lill,, 11)11.

against flash-over much greater than by using the pin type insulator. This safety factor is helped by the shape, ease ofcleaning, and detecting flaws and less liability of spattering ofrain, which are all to the advantage of the suspension typeinsulator.

Having thus guarded as far as possible against trouble withinsulators, the next question' is that of protection from lightningand abnormal rises in voltage. The disposition of the arresters isalways an interesting problem. I remember a case where a 3,000volt two-phase power circuit was brought 3 or 4 miles and endedat a pole directly in front of the transformer house. This endpole had horn type arresters erected upon it The line wascontinued into the building by means of H.T. rubber coveredwire and went to isolating links, and thence to the main switch.Between the links and the swith, choke coils were cut in, andmulti-gap arresters connected. Great trouble was experienced byheavy discharges on these arresters. Even when thirteen 1,000volt gaps were left in each arrester, discharges continued to takeplace at frequent intervals. It was decided to carry the mainoutside line some distance beyond the transformer house andplace an extra set of arresters on the end pole. Since this changethe arresters inside the building have been free from discharges.In some cases I have known arresters and choke coils to be soarranged that when a mild rise in voltage occurred, it found thefinest combination of apparatus erected for producing highfrequency oscillations that it could possibly wish for.

In the circuit we may have singly, oscillations due tochanges in load, arcing grounds, etc., lightning effects^-directstroke or inductive, and static strains of a lesser degree due to airfriction, or if conditions be right a combination of two or more ofabove.

The first case is caused by varying load, and the intensity isgreater the greater or more abrupt the change of load ; the morepowerful and destructive surges being those due to effects ofshort circuit ; that is the change from short circuit to opencircuit, or the opposite. Arcing grounds and discharges to earthproduce under certain conditions severe oscillations in the powercircuit, and generally produce short circuit conditions. Protection from direct lightning stroke is. almost an impossibility^whilst for inductive lightning effects, several types of arrestersare available.

In considering the class of arrester to use one must notforget that in some cases the arrester will come into action byinductive effects of lightning, or static effects due to air frictionon line wires, and being so set, or arranged singly, or incombination on one or more phase wires, they produce on thesystem a series of oscillations which, under certain conditions,

build up to such an extent that a severe breakdown results on thesystem.

Taking the above into consideration it seems to me theproper protection needs the combination of two or more types ofarresters, or in other words, one arrester with its choke coil mustlook after lightning effects; another type which might bedesignated maximum surge alleviator will take care of abnormalrises in voltage, whilst the third type will be connected directlyto the line without intermediate spark gaps, and will continuallydrain the line of static effects due to wind friction, light surgesdue io switching operations, etc. Each piece of apparatus cominginto action according to the intensity and nature of the conditionsarising whether singly or in combination.

Mr. A. G. F. Heather {Member of Council) -. Mr. Campbell,in opening this discussion, made no mention of one very peculiarand, to my mind, very unusual trouble that we experienced abouteighteen months ago. It was during a very heavy wind stormthat the roof of a building about 150 feet in length, was blownover one of our 10,000-volt lines. Fortunately, the lines did notcome down, but a number of poles were bent, and the cast-ironbases broken. It took us just over four hours to resume serviceon that particular line. The day after that I may mention we hada snowstorm, and the lines in this country are not designed tomeet that contingency. Another frequent cause of trouble,especially on lines constructed on short poles, is due to the longwhips used by men driving oxen. They swing these whips aboutfreely, and frequently bring the guard netting into contact withthe lines. Mr. Price made some remarks with reference to therelative cost of underground and overhead distribution. In theearly days of the electrical distribution of power, the differencebetween overhead and underground distribution was very great,but I should like to ask Mr. Campbell whether he considers thatnowadays, when we are adopting high steel towers with longspans, the relative difference in cost is so great. It seems to methat when we take into account the cost of freight and railage onthese large steel towers, the labour of erection and cost of repairs,the difference is not nearly so great. It is quite an open questionin my mind whether the extra cost of cables is not more thancounterbalanced by the ease of repair of overhead lines. ThePresident made some mention of the comparative immunity oflines at higher voltages from trouble, and he also suggested thatthe possible explanation was the high quality of insulation onsuch high voltage lines, I have found that, taking insulators withthe same factor of safety, we experience more trouble on the10,000-volt lines than those which run at the higher voltages, andI thinh the whole question is largely one of design of the

Ai'KU., 1911.Troubles on Overhead Power Lines.53

insulators to meet the distribution of di-electrio stress on thevarious petticoats, and the factor of safety for which the insulatorsare tested. Mr. Price referred to the question of connecting theoverhead lines coming into the station by means of undergroundcables, and considers that that would diminish the trouble. Ithink it does, but my experience has been that it often onlytransfers the trouble to the cables. As regards arrester discharges,I think the chief trouble we experience is not due to the actualarrester discharge itself, but to the very heavy surges on thesystem which follow the arrester discharge, and I think it is quitepossible that some means might be found-—say a combination ofhorn arrester and water jet—to diminish the strength of thesesurges, which after all, apparently, cause all the trouble with thehigh tension distribution system.

Mr. J. Milne (Associate Member) : The following questionsdeal with matters not usually considered of much importance bythose engaged in power work.

I refer first to the disturbance caused to a telephone systemby any incident which throws an adjacent power installation outof balance. Considering only the three-phase system existingalong the Witwatersrand, we find that with everything in goodorder, the electrostatic and electromagnetic fields, outside a comparatively small radius of the power wires, are practically nil.This is due to the fact that the sum of the potentials of the threewires at any moment is equal to zero, and the sum of the currentsat any definite point is also equal to zero. When such conditionsexist there will be no interference on telephone lines but theslightest departure from the ideal immediately involves them.

Figures 1 and 3 are oscillograms taken on March 6th of thisyear. They clearly shew the effects of a faulty power system ontelephone lines.

No. 1 was taken on a junction line between Johannesburgand Krugersdorp, approximately twenty miles apart, and No. 2was taken on the same line, extended five miles further West to theRandfontein Fstates. The junction line was earthed at both endsin each case. Could Mr. Campbell explain the circumstancesunder which such a disturbance took place ? Further, what isthe normal condition of the three-phase system so far as theneutral points are Concerned.

In the event of a fault occurring, what steps would be takento keep the faulty system working (1) if the trouble is due to abreak ? (2) If the trouble is due to an earth ?

Mr. Gibbs mentioned that trouble was experienced with thepilot cables and his remarks would lead one to believe that all ofit was due to the sportsman. In an experience extending overmany years I have found that the sportsman is responsible for

54Troubles mi Overhead Pmver Linen.Avail., 1911.

Fio. 1.—Oscillograph record of power leakage. Johannesburg-KrugersdorpJunction Line. Length, 2,0 milts metallic ect. Line very noisy.Date, 6/3/11.

Fju. 2.—Oscillograph record of power leakage. Johannesburg-BandfonteinEstates Junction Line. Length, 211 miles metallic cct. Speechimpossible. Date, 6/3/11.

perhaps one per cent, of all the faults on aerial cables, whilelightning, power systems and faulty material are responsible for.10 per cent, faulty construction being responsible for the balance.

The pilot cables are erected in spans of approximately 500feet and of course have a huge sag. Apart from the danger ofdanger of using zinc slings on such long spans, the strain on thecable at the highest part of each span must be sufficient to breakthe lead sheath at that point in a very short time. I believe someform of catenary suspension is necessary under such circumstances.

The design of the pilot cables is interesting. In one, thepilot wires are screened with lead foil while the telephone wiresare twisteil in pail's in the usual manner, one wire of the pairbeing tinned to distinguish it from its mate. This arrangementof tinning one wire of a telephone pair would be liable to throwa long line out of balance, with the result that the line wouldalways be noisy. In another type the pilot wires are not screenedbut each pair of telephone wires is screened separately with lead

F.g 2.

55Trimbles on Overhead Poieer Lines.April, till 1.

foil. This would have the effect of seriously increasing thecapacity of the telephone pairs. However, each wire is wrappedwith a continuous spiral of iron wire, and I should like to be informed whether the increased inductance expected from the ironwire is specially meant to counteract the increased capacity due tothe lead foil screening, and also how the two types of cablementioned compare in the matter of speech and quietness. Theremarks on tinning one conductor of a pair of telephone wiresalsq applies to the second type of cable.

Mr. C. W. R. Campbell (Past President) : I regret that u^original remarks were prepared in a very hurried way, as I was onthe point of going away on account of ill-health. I notice that agood manyof the speakers have referred to arresters. I did not touchon the arrester question because I more or less considered that wewere dealing solely with line troubles,and I do not think that, generally speaking, arresters save the line troubles very much, and arechiefly put in to save the sub-stations, sub-station apparatus, andgenerating station apparatus. Mr. Wood worth mentions protectingsheathing. I believe that in some instances this may be useful,but in the great majority of cases of trouble on our 10,000 and40,000-volt systems we have found that where a flash over hasoccurred, or a bird or anything else has caused trouble, if thetrouble is really serious, the insulator is utterly smashed, and theline comes down on the cross-arm, and then, if nothing trips intime, no protecting sheaths or anything would save the line,because a 120 mm. line just fuses right off at once. With regardto jointing, perhaps it is a little old-fashioned, but I am comingstrongly to the conclusion, after a certain amount of experience,that there is absolutely nothing better for jointing on a high-tension line, if you have large conductors, than the old Crosbyclamp, as long as you have at least two in opposite directions. Iremember a test which we made a little time ago on somesuspension insulators, and we used galvanised stranded steel wirebetween the two suspensions. We went up to seven tons withoutslipping with two Crosby clamps put on by an inexperienced man,who, I do not think, had ever used a spanner before in his life.There is a prejudice on the part of most people against the Crosbyclamp, but I am a believer in it when properly put on, especiallyin high tension work and on large conductors.

Mr. Gibbs says that I have omitted all mention of one causeof trouble, and that is, the accompanying pilot wires which existon all the lines of the Victoria Falls and Transvaal Power Company.I have here a few samples of this sort of trouble which I willshow the members. In some cases where a pilot cable has beenput up under lines in commission, and before it has beenconnected at either end, a heavy single-phase fault on the line

5fiTroubles on O^erhedd Power Lines.Ai'Kin, Mil.

above has caused the pilot cable to burn out all over the place. Itis very difficult to understand at the present moment, becausethese pilot cables are earthed to the pole in every instance. Theyare earthed to the suspension wire by zinc suspensions, and yetwe have a tremendous hole burnt in the middle of a span, andthe zinc suspensions burnt off, when there is no connection ateither end. One of the great troubles is, as Mr. Gibbs hasmentioned, bullet holes. I have one or two specimens here. Thegreat time of trouble with pilot cables in this country is at theend of the dry season. We have with all pilot cables an air spaceand paper insulation, and the consequence is that all cables putup during the dry season run smoothly. They may have anyamount of small holes in the lead but work satisfactorily. Duringthe first rain storm, however, we find the trouble, and every cablefalls down at once, and it is troublesome to locate the faults.There is another point of interest which was referred to by Mr.Gibbs in connection with long lines being dead and free at eitherend, and yet giving a considerable shock while the building ofthe line is in progress. That was followed up in the discussionby Mr. Price, who asked the question as to whether the fact ofthe lines being charged when not under current was due tolightning only, or was produced by wind or dust. It is a matterof common experience to all of us that the linesman, the manwho has to do the work and is liable to be called out at anymoment, generally fears a very heavy dust storm more than theordinary lightning storm. The average lightning storm does notworry one so much, bnt a really decent dust storm—especially ifit is travelling in any way parallel, or nearly parallel to the line—•is extremely troublesome.

Mr. Webb's remark on the same subject of heavy dischargeswhen the sun is intense is very marked, and you notice it morein the dry season than in the wet season. There were severalremarks about raising the voltage and lessening the troubles. Iam not quite certain what is the real explanation of the fact, butin our small experience it certainly has been a fact. It is verydifficult, though, in some cases, to say whether it has been thehigher voltage, but one thing has been particularly noticeable.In one case where the lines are running alongside one another forthree or four miles, one at 10,000 and the other at 40,000 volts,the 10,000-volt line causes the more trouble. That may bepartly accidental, but it is difficult to say.

M'1. Heather asks about the question of cost. I feel that ona long transmission line, with a moderately high voltage, therewould be found to be very little difference. There would be acertain difference in the first cost, but when you consider thereliability of the modern cable, I do not think there is much init, for a few years a1- any rate.

ArKll,, 1911.Trouble^ on Overhead Power Lines.57

I must especially thank Mr. Milne for his contribution to thediscussion, this being the first contribution from a memberconnected with the G.P.O., and I hope that at an early date weshall have the pleasure of a paper from him enlarging on thisspecial subject of telephone cable work. The subject with whichhe deals is one of the most interesting to anyone handling longtransmission systems. He asks for the circumstances underwhich the disturbance shewn by the oscillograms took place.At the time, the neutral point of a large transformer was earthedat Bantjes, a certain amount of current flowing through the earthconnection due to the system being out of balance. On removingthe earth this trouble, of course, at once disappeared.

In answer to Mr. Milne's enquiries as to what steps wouldbe taken to keep the faulty system working, I may point outthat it is not possible for us to run at all on a fault, and in allcases the line affected is cleared at once. In the majority ofcases we now have a duplicate supply. I may also mention thata break is almost invariably an earth.

In my experience, with cables carrying telephone pairs hungdirectly under power transmission lines, a rather • differentproposition from carrying them at some distance from such lines,I can certainly put faults on the transmission lines as the cause ofthe majority of troubles. This subject is at present under carefulinvestigation.

On the "Victoria Falls Power system a number of differentdesigns are in use. I cannot say that any difference is perceptiblein speech and quietness between the two types mentioned, but itis really difficult to really make a close comparison owing to thedifferent lengths of the circuits, and the combinations in whichthe various types are used. I am of the opinion that the continuousiron wire spiral has the effect of counteracting the capacity dueto lead foil screening, but, from a practical point of view, I ratherprefer the unscreened type, owing to possible troubles frombreaks in the iron spiral, several of which have already occurred.

Mr. Campbell then exhibited a collection of insulators andpilot cables which had been damaged ^iming line troubles, andalso explained a series of photographs thrown on the screenillustrating various breakdowns ami their causes.

Mr. J. W. Kirkland (Vice-President): I should like tomake a few remarks in connection with this matter, although Ihave had very little practical experience. It has never been myprivilege to get nearer tne operation of a high tension line than toassist in the acquisition of a right-of-way for a 70,000-volt line inAmerica. This line runs on its own right-of-way, 100 feet wide,all the way from the Susquehanna River, where the power Stationis, to the city of Baltimore. The mechanical design of the

58Jroubles mi Overhead P^iver Lines.Armi., 1911.

transmission line is quite different to what is usual in this country.It might be described as the entire^^ flexible system of support.Suspension insulators, 5 in series, are used for each conductor atevery pole, supplemented by tie poles with insulators in thedirection of the strain. The intermediate poles carry the weightof the wires, and the tie poles, at intervals I think of about half amile, hold the line in case of breakage. There is a 2,000 feet spanacross the river, close to the power station, running from poles120 feet high on each side. The question of lightning arrestershas been spoken of a good deal in this discussion, and also thevalue of horn gaps and water jets. It seems to me that theproper place for horn arresters is in the midst of a line, and Iwould rather have too few than too many. The other suggestionfor the protection of a line, which certainly is beneficial as regardshigh potential work, is the water jet. It appears to protect theline from high potential static discharges better than do staticdischarges which are simply multiple gap arresters. The jetprevents the line from soaring away from the earth potential, as acompletely insulated line will do. Of course, a 3,000-volt linewith an earthed neutral will not rise away from the earth potentialmore than the Y voltage of the line, but a completely insulatedline without an earthed neutral can rise, all wires together, to avery much higher potential, so that we may get a strain from allthe phases to earth, which is near the limit of the insulators. Now,these static charges on the lines can come from dust storms, or byinduction from clouds abo^e. The static charge carried by cloudsmay raise the total potential of a line very much higher than thenormal with respect to earth. The water spray arrester willrelieve that, but it has not great capacity as regards energy. Theenergy- to be dissipated in the case of a surge is very great, or,rather, the power is very great. You get a large amount of energyin a very short space of time. The capacity of the jet arresterdepends upon the rate at which the water is flowing, and uponother features of design, but it seems obvious that the quantity ofwater discharging from the jet and impinging on the cones haslittle capacity as compared with the energy which flows throughthe line which it is necessary to dissipate. The aluminium cellarrester has been found successful in many cases because it hasthe property of dissipating a very large amount of energy, andbeing of metal and cooled by liquid, it has considerable heatcapacity, and, of course, practically all the electrical energydissipated turns into heat.

Mr. W. Elsdon-Dew, M.I.E.E. (Member of Council): Thecauses of trouble on overhead power lines can be divided underthree headings :—

Mechanical Faults, Electrical Faults, Wilful Damage,

Al'ML, 1911.Troubles nn Overhead Power Lines.59

The first cause can be considered to be possibly eliminated, asexperience is gained, and time proves the better practice in suchwork.

The second is, perhaps, shrouded in greater mystery, and inthis respect one finds the greatest diversity of opinion expressedby engineers. In this respect the conditions of service, and ofthe load carried by the power lines, will afford perhaps strikingdifferences.

With regard to the last cause, this is, perhaps, impossible toeliminate altogether, and will affect a power line at times, notconsistent with reason and sense. The caution to be taken toprevent this is, perhaps, a State affair; in any case it is a Stateaffair when the culprit is brought to book.

A few remarks on mechanical troubles may be interesting.Binding of wires to insulators.—Personally, I believe in the

copper wire binder, if put on with a preliminary lapping of thebinding wire on to the power wire to prevent chafing. Clamps Ihave found too severe, both to the insulator and wire. While onthis subject, I may remark that I feel somewhat uncertain of thereliability of the suspension type of insulator, unless a suitableflexible clamp or ear is used for carrying wires.

It will be found that with lines laid off in long distances,precautions can be taken to prevent a break away of the powerlines from travelling any great distance, and for this reasonregular distances must be decided upon for shackling off all wiresin this respect. I have adopted 1,200 yards as a convenientdistance for sections ; any fault in a section of this lengihcan be repaired by one gang, and other Sections will not beaffected.

As pointed out by Mr. Campbell, the better practice withregard to passing from one shackle to the next, is to bring thewires under the cross arm, but the wires must be continuous, orif jointed, must be of equal mechanical strength to the wires, incase of a break away from the shackle on any one side.

With regard to the overhead earth wires, which are nowrecognised as protective devices, and which more or less screen thepower wires from direct lightning flashes, it must not be lostsight of that mechanical strength in these are highly essential,and it is also necessary to have these wires connected to goodearth plates as often as it is possible.

The lay-off of a long length of power line through countrywhere the exact position of the lines are not of great importancefrom the question of power supply, requires much thought andforesight. In this respect, the decision of a route may involvemuch greater expenditure for transport than another route.Further, it is of importance to obtain particulars of the conditionswhich affect, lightning storms. I have found that, in highly

GOTroubles on Overhead Power IJnes.Ai'KiL, 1911.

mineralised areas, this has a marked influence on the powerlines while lightning storms are in the vicinity.

Regarding electrical faults, it appears from the discussionthat line, troubles become less as the voltage gets higher, and inthis respect I think one can trace the reason to higher safetyfactors^ It is evident that one takes more precautions to haveinsulation and clearances abnormally high for the higher voltagesthan for the lower voltages, and with faulty material causingflash overs and shorts, lines have had troubles from surges anddisturbances which have really been started in a small way. Ithink it is really necessary to have a much higher safety factorthan has been the rule in the past, if one wishes to insureimmunity from insulator faults and flash overs.

I should like to refer to one or two points which have comeout in this discussion, and also to give a few experiences. Grassfires very often cause a flash over on overhead power lines. Inthis respect I have had, perhaps, rather serious experiences inconnection with a 3,000-volt line on which the flashes over mostlyoccurred in the dry season, when the burning of grass in countrydistricts is done quite indiscriminately, and I had to takeprecautions to have the grass under the' lines burnt off on theday when we had to shut down for a general clean up. I foundthat this saved a great deal of trouble, "as we were then free fromshuts down at night.

The subject of water jets has been touched on. As I claimto have had a little experience in this direction, and knowledge ofthe actual work which these arresters do, I will give a shortoutline of what my experience has been. The power lines I speakof were equipped with. Siemens horn arresters in their old (1896)

Trnuhles on Overhead Power Linen.Ath.il, 1911.

In connection with the 3,000 volt line with which I was experimenting, the distance of the gap and the thickness of the jetwas a difficult matter to find out, and it took me some time tocome to a decision about it, as such experiments bad to be carriedout only when lightning storms were actually about. I eventuallydecided on a gap of about 1^-in. with a jet of 3/lfiths in thickness.The pressure of water was about 40 lbs. After using that jetarrester, I was able to bring the original form of arrester(Siemens 1896 type) to a much closer distance than ever before,and I have had no trouble whatever in surging or damage toapparatus. In fact, originally I had to keep these horns at a distance of 3 mm. to protect the plant from excessive surging, and Iam now able to reduce that distance to 2^ mm., and since these,water jets have been in use, we have had no trouble from burnouts through direct flashes or inductive effects. When we havehad what might seem direct flashes to earth from lightning, these

form. That form of arrester has now been modified, and thereason for this modification is that in the old form, when a sparkflashed across the arrester gap, the surge of current following onthe flash is so great that it generally does a great deal of damageto the generating plant and other protective devices.

The latter form of arrester has been adopted simply to availoneself of the opportunity of getting the discharge dissipatedquickly.

When I first started experimenting with the water-jetarresters, I had to find out what actually was the action ofthis permanent leak on the whole system, and the following is asketch of a simple form of apparatus which I adopted :—

mil.Troubles on Overhead Power Lines(12

To explain what I think is the reason for this : The waterjets do not allow the line to pile up electrostatic charges. Theywill not allow high frequency surging currents to accumulatewhen this effect of an arc on the horn arresters is going on. Iam fully convinced that this stopping of discharges on the hornarresters under ordinary conditions point to the line being protected by that water jet to a much greater extent than theoriginal horn was able to do. Further, by so materially reducingthe snrge and breaking it up quickly as it does when there is adirect flash to earth, is indeed a very strong argument in thisrespect.

With regard to water jets affecting the insulation of thewhole system, I may mention that I am able to test the lineinsulation with an electrostatic instrument periodically on eachshift. This is done, and if any deterioration on the line is detectedit is not lost sight of. The water jets can be cut off, the insulationtaken and the water jet again put on and insulation checked.

The figures for this test are under normal conditions :—-

97 x 20 the original line insulation without water jets.With water jets, that is reduced to 92 x 20.

This shows a reduction of line insulation by five points asworked out by these figures, but this is not all that may be taken asthe changed condition of the whole system. The conditions arealtered in many ways. The lines are gradually dischargedthrough the jets and their static condition is brought near earthpotential. It is not a 5 per cent, loss of current; in fact in anytests I made I was not able to find out any leak of more that onequarter ampere to earth through the water.

The water jet arrester continually drains the line of anycharges accumulating, and. though without capacity to let off heavycharges in conjunction with the horn, works most satisfactorily.

water jets not having tiie capacity to carry oft'the heavy currents,the horn arresters come into action and this they have done severaltimes. Instead of the heavy discharge and surge following over,and perhaps hanging for a long time before breaking, such as maybe seen from many illustrations, these water jet arresters willprevent any surge, and the arc on the horn arrester will break atabout this position

AlMtli., 1911.Trimbles on Overhaul Power Lines.03

In regard to shackles, I see that an attempt has been made toput in a copper strip to take up the irregularity of the porcelain.The copper strip has hardly had enough attention given to it andis not soft enough, but I have adopted a rather strong piece ofleather under the bolt and I hope it may be effective in taking upany irregularity of strain on the porcelain.

Mr. Woodworth has referred to the advantage of carryingoverhead lines past the power house and putting horn arrestersthere. I may say that I went further than this, by takingthe line past the "power house, bringing it back in a loop andthen connecting on to my switchboards, etc. Originally I Imd aset of horn arresters on the line in the building just at rightangles to the line, and added this set of horn arresters outside thebuilding at the extreme end. These horn arresters were set atfin. outside and 3 mm. or ^in. inside. In every case the hornarresters outside would go off while the others would show nomark or indication of lightning having passed through. In thisrespect I found that the line could be aptly compared to a waterpipe, the surge of water in the pipe going past the branch andaccumulating its pressure at the extreme end.

The question of birds has cropped up, and the hawk seemsto have got into trouble. To prevent a hawk alighting on theinsulators and coming into contact with the wires, I have used apiece of ordinary wire, attached to the cross arms as shewn in theaccompanying sketch, and I hope to find that this has the effectof keeping the birds off. The guard wire is of an equal distancefrom all power lines as these are from other parts of the pole.

A toil, 1911.Troubles on Overhead Power Lines.

Arm I., 1911.Troubles on Overhead Power Lines.65

I find that in Mr. Price's discussion, reported on page i55 ofthe Transactions, he refers to the water jet arresters and givesreasons for its success under certain circumstances. He says thatthe water jet arresters would no doubt be successful (in a systemwhere all the lines are insulated and there is no earthed neutral.Mr. Kirkland has also referred to this in his remarks this evening,and says that the water jet arrester with an earthed neutral wouldnot be found of great service. I hardly agree with this. I thinkit has been lost sight of that on the whole of the appliances andapparatus, either generators or transformers, between the lines andthe neutral points there is a highly inductive circuit, and in thisrespect the static charges and the high frequency currents will nottravel all through these windings to earth—at least it is not theeasiest path to earth, and if they have to get through these inductive circuits are liable to cause damage. If the water jet isconnected to the three-phase wires of any system, although having a neutral, I think it could still act as an intermediate path toearth and protect, or assist to protect, the transformers and otherappliances.

Mr. A. E. Scott (Associate Member) : 1 should like to ask,in this connection, if the use of knohs, made of special metal, hasever been tried, taking a series through resistance to earth. Onthe London Electric ^ailway, which is supplied at 10,(100 voltsthree-phase, we certainly had .underground cables, some of themtwenty miles long, hut these knohs were used, and with a very lowload or sometimes with no load at all, we could get a very nearapproach to resonance. We had these knobs connected across eachof the phases in series through a. resistance to earth, and theneutral points of the generators were also earthed. I have manytimes heard these knobs spark across when there was a surge orany bad switching, and there was practically no occasion of abreakdown. Seeing that the effect of resonance is a very nearapproach to lightning, I thought that for the relieving of theinductive effects which bring about an extra rise of potential onthe lines, this might be of some use,

Mr. J. W. Kirkland (Vice-President) : These knobs are verylargely used for the protection of cables nowadays, in mountedseries on porcelain, and known as " static dischargers." TheCinderella Deep Gold Mining Company has put in some of themfor protecting their cables going underground. It is an alternativemeans to the water jet for preventing the accumulation of static.

Mr. C. W. R. Campbell: I tried these knobs on a 10,000volt line some little time ago, and had a whole set of them throughresistance'-; in series. It was most interesting. The whole timethey were discharging. They were continuously taking staticcharges of the lines, but during a ing surge one day the whole

arrangement was literally blown to pieces, and I did not try themagain.

Mr. F. H. Michell {Member of Council,} : With referenceto Mr. Campbell's remarks, reported on page 24 of the MarchTransactions, in connection with lines running north and southbeing the most troublesome, it has been suggested to me by Mr.A. H. Renner, one of our members who is not present this evening,that the troubles occurring on lines running east and west on theRand are rather less, because of the fact that there are distributedthroughout the distance in that direction headgears, funnels andvarious other points which tend to maintain the potential betweenthe ground in the vicinity of the lines and the charged cloudswithin a safe limit.

Mr. C. W. R. Campbell: In this respect, I think thatthere is a great deal in the suggestion which has been just made.I always notice that we have considerably less trouble duringlightning storms on lines which are protected by tall trees, andthe lines running through the ordinary surface works. But thatdoes not hold everywhere, because one of the most troublesomeparts of one line which is in my mind is the best protected in thatrespect. I think, however, that it holds as a general rule. I thinkI can say tiiat unprotected lines running east and west are far lessliable to trouble than the same type of line running north andsouth.

Mr. C. W. Inggs (Member) : I notice that several membersgive prominence to their experience that lines running north bysouth are much more strongly acted on by lightning than othersrunning east by west. Such is also my experience, and I thinkit is due to the impedance of the earth's magnetism on the rapidlyoscillating lightning discharge waves choking them before theyreach any east by west lines. I do not think sufiicient noticehas been taken of the effect of lightning on a line of lowresistance, such as is the overhead earthed protecting wires. Mr.Nowlan mentioned an instance when cutting this line intosections and putting a small resistance between each, caused animprovement, and I think this agrees with the theory of the ease.The value of an earthed overhead wire, is as Mr. Price hasalready stated, to ward off the electrostatic effect, though experience is not entirely in favour of its use ; the electromagneticeffect, on the contrary, I am inclined to think it increases.

Taking first the electrostatic effect, repeated discharges dueto this effect may he seen by watching lightning arresters on afine sunny and windy day, if one end of the line happens to hedisconnected, hut I have not seen an arrester carry over powercurrent due to it, the reason being that unless there should be anextremely large condenser in parallel with the line there is not

66Troubles im <)verhea,d Power Lima.Apart, 1911.

sufficient quantity in the spark to cause appreciable heatingeffect. In fact, an electrostatic spark of twenty feet long may betaken with impunity on the person, only giving a sharp prickingsensation as I know by experience. Moreover, machines whosebelts yield sparks three or four feet long, do not, to my knowledge,go to earth although the shortest path for the spark would bethrough windings to earth. The point I wish to make is thatthese electrostatic pressures are almost harmless. When weconsider the electromagnetic effect, however, we find that anydisturbance on a system creates a surge, and that the quantity ofcurrent is nearly always sufficiently great to prepare the path forthe power discharge. In operating a Wirnshurst machine withcondenser in place giving about a i to 6 inch spark, any conductors that may be round the room and nearly but not quitetouching may be observed to spark to one another, this isgenerally called the Hertzian effect. Now we must also considerthat did these conductors touch one another a current dischargewould take place through them without visible result. In thecase of lightning we have the same effect on a grander scale ; thedischarge between clouds inducing enormously high frequencylow voltage currents in any conductor in the active zone, andthese currents depend almost entirely upon the resistance of thecircuit for their magnitude. These currents are dangerous, notso much from their voltage which is comparatively low, butbecause of their disruptive power, and because of their electromagnetic effect on conductors nearby.

This is so wel^, recognised a fact that the latest rules forerecting lightning conductors advise the use of iron wire of No. 8gauge for individual conductors as having sufficient dischargingpower and yet acting as a resistance in the circuit. Theattractive or repulsive effect on neighbouring conductors waswell indicated in the English church steeple, where, whena flash occnred, one of the bell bearings, a block of ironweighing nearly 1 cwt., and which was adjacent to withouttouching the copper lightning conductor, was torn out of itsplace and thrown to the opposite side of the belfry. This,I think, also accounts for the effect mentioned by Mr. Priceof a side flash taking place from a straight piece of line, to, as Iread his remark, an earth wire running parallel. Also, since forequal capacity in K.W. the power line for 100,000 volts is, say,twice the resistance per foot of the line for 50,000 volts, we mayconclude that less trouble due to these induced surges will beexperienced on 100,000 volts. Some colour is lent to this theorywhen we consider that the large power transmission plantsrunning at 100,000 volts in America and having no trouble fromlightning, use no cable larger than 3,000 B. & S. about 0^ iuch indiameter.

1911.Troubles mi Overhead Power Lines.(17

Mr. F. Davidson {Associate Member^ : At the last meetingthe subject of long transmission lines being charged before anyapplications of current being applied was discussed. One speakertold us his experience of this phenomenon took place during awind. Another experienced the same thing after a brightsunshiny day.

Since then I have gone to the trouble of ascertaining otherengineers' experiences, and without any exception they havenoticed this state of affairs occurs either during wind or onbright days. As far as I can see there is only one factor common

) both states of the weather—and that is—in both instances wehave what may be termed, a "drying" day.

This suggested to me that the solution of the matter mightpossibly be as follows :-—

The molecules of moisture are drawn up from the earth'ssurface, and the fact of the rupture from their former positionmayr impart a static charge to each molecule. The molecules ontheir way upwards come in contact with the lines, and in doinggive off their charge to them. Prompted by this idea I carriedout certain experiments with an artificial line, made of barecopper, stretched on bobbins on a wooden frame. I regret to saythat I obtained absolutely no results byr drawing moisturethrough them. On the other hand, I found that by heating thewhole line by means of a blow lamp and. then suddenly coolinghalf the line by means of an electrical blower, a minute currentwas set up between the two halves of the line. In my opinion,the fact of overhead lines becoming either statically charged, orgenerating a current before being connected to any source ofelectrical supply, presents a very facinating subject, and I intendto continue my experiments in this direction with betterapparatus than that which I have so far used. Mr. Campbell'sreference to a dust storm opens up yet anothers views of thissubject. Mr. Campbell told us of a curious incident of a smallbird being found badly burnt after a great amount of pitting ofthe lines had occurred, and directly under the spot where thispitting had taken place. This is certainly very curious, and Ican only account for it byr thinking the bird was carrying something—probably a long straw, or some such thing for nestbuilding.

In reference to Mr. Campbell's remarks as to the building inof conductors to insulators, I notice he is inclined to favour theordinary binding wire rather than clamps. It is true that in theevent of a line breaking these binders allow the line to slipthrouph and so save the bending of the insulator pins, but thefact of allowing the line to sag to such an extent causes it to shortcircuit with those belovv it, and this might very effectually causedamage to plant at the supply end, which damage would

68Troubles on Overhead Power Lines.April, 1911.

DISCUSSION.

Mr. J. Askew (Member) : I should like to add my thanksto Mr. Philip Herd for his very useful paper on three-phaseinduction motors. Mr. Herd has given us some useful figuresand curves demonstrating what should influence us in theselection of three-phase motors.

I should like to make a few remarks from the point of viewof a resident electrician on the mines.

NOTES ON THREE-PHASE INDUCTION MOTORS.By Philip Hbbh {Member).

(Read at November Meeting).

April, 1911.Trmiblm vh Overhead Power Lines.fi9

probably be of much greater magnitude than a few bent insulatorpins.

I should like to ask Mr. Heather how an ox whip canpossibly bring the wire guards in contact with the lines, as fromwhat I have seen of the V.F.P, lines there appears to be a bigclearance between lines and guards.

The President: This discussion is now closed, and beforegoing on to the other items on our agenda, I would like to express,on behalf of the members, our sympathy with Mr. Bernard Pricein his indisposition, and I am sure we trust to see him with usagain at the next meeting. I also desire to move a hearty vote ofthanks to Mr. Campbell for having opened this discussion, andfor having enabled us to see actual examples of breakdowns, andthe photographs thrown on the screen by means of the lantern.

Mr. C. W. R. Campbell: When I started this discussionin an informal way, I had no idea that it would develop into sucha discussion on lightning arresters. I am sorry that I did notbring forward tire lightning aspect a good deal more, but I do notthink that our main troubles on the actual lines are due tolightning. I could have brought a great many more examples oftroubles if I had continued the effects of the line troubles intothe snh-stations, I must say that I did not give much a^tentionto the lightning side of the question, because I absolutely confinedmyself to the lines, and in the case of the lines I have dealt with,all arresters are inside the sub-stations. I hope that on somefuture occasion we may be able to have a discussion solely onlightning arresters and lightning phenomena.

The object of the mines in using electricity in the place ofair and steam driven machinery is to economise and bring abouta reduction in mining operations, it is, therefore, reasonable toassume that motors for the mines should be of a type suitable forinstalling, even to the face of the rock in the mine, if necessary,which will not require any greater preparation in installing, or,any more attention or skill in running than is usually given toair or steam driven machinery.

In selecting motors for the mines very careful attentionshould be given to the particular work which the motor isdesigned for, as well as the conditions and attendance the motorwill be subjected to in doing this work, and not only should themaker's efficiencies be considered but also the mechanicalstrength and durability of the motor as well as simplicity inoperation.

This will be better understood by the following instance :—A 30 H.P. 200 volt 968 K.P. three-phase slip-ring motor of

a very good make was installed to drive a conveyor belt, normalload 22i to 25 H.P. At a recent meeting this motor was very welldescribed as being a link in the chain whereby any stoppage ofthis motor effected the whole of the reduction plant, unless thestoppage was made good during the day, or, by working overtimeat night. The short circuiting and brush lifting device of thismotor was weak for the handling it was subjected to, namely,unskilled white labour and natives (part of crusher staff'), andhad been running about six months when it was taken to theshop for general repairs and renewals of brush lifting and shortcircuiting gear.

During the six months this motor was running two sets ofshort circuiting contacts were burnt out, and the short circuitingdevice repaired at least two or three times per month at anaverage cost per month of 6 l()s.: this not including the inconvenience caused by the stoppage of the belts, or the extramoney paid to crusher staff in the case of working overtime.Having no spare motor of that size, a 40 H.P. 200 volt 750R.P.M. three-phase slip ring motor was temporarily installed inits place, with a more reliable and simple short circuiting andbrush lifting device. This motor has now been running a littleover 3 months, and though electrically it is not so efficient as the30 H.P. motor, the running efficiency of this part of the plant isvery much greater, and though handled under exactly the sameconditions as the 30 H.P. motor not one single repair has beenneeded, or stoppage, has been reported of this motor since it wasinstalled. I mention this particular case which is, more or less,one among many in which good motors may prove very inefficientthrough weak design of operating gear, and rough handling themotor may be subjected to when put to practical use on themines.

70Notes on Ihree-phuse Tnduetirm Motors.April, 1911,

DISCUSSION.

Mr. F. Davidson {Associate Member) : I would like to takethis opportunity of adding my thanks to the author for an exceeding interesting paper, the more so as he has chosen a subjectwhich is outside the practical experiences of the majority of themembers of this Institute, but there is one portion of his paperwhich, I think, requires a little explanation. On page 873 of theTransactions, and in paragraph 2 he says—•" For example, a twozone machine having two cross belts will have an output ofapproximately 25 cwt. per shift of 10 hours, working on onegrade of ore."

Now I should like to ask the author how he arrives at thisapproximate figure of 25 cwt,, and will a two zone machinehaving two cross-belts and a magnet, the winding of which take17 amps, at 05 volts, deal with 25 cwt. of ore irrespective of thewidth of the belts and the distance they are from the, main

ELECTRICAL SEPARATORS.By B. B. Woodworth, A.M.I K.R, A.Am.I.F.K.

(Member of Council).

{Read at January Meeting.)

To obtain an all round efficient motor plant on the mines Ishould suggest some system of record keeping, which would notonly record the actual work and efficiencies of the motor, but thenumber of hours run, say, during twelve months, the cost ofrepairs and the value of those repairs. Such records placed inproper hands must soon lead to the adoption of motors, not onlyfor high efficiencies, but high running efficiencies over the wholeof the plant.

To get the maximum efficiency results from a motor planton a mine the motors should be as nearly as it is possible of onetype, then all parts of motors of the same size would be interchangeable and the minimum of spares would be needed.Unskilled operators of motors would only have to learn how tooperate and look after the motor to be able to run the majority ofmotors on the mine, and the possibility of faulty operation of themotors would be minimised. A good many stoppages of the whole,or a part of the plant, breakdowns and repairs would thus beobviated, and the running efficiency of the plant increased inproportion.

Apku. 11)11..Electrical Separators.71

Electric; Powe^ in Collieries.—A paper with the above title wasread before the Ruby Engineering Society by Mr. J. Miller on January 19th.In the author's opinion, it is generally more profitable to instal generatingplant at the colliery, but if the load consists mainly of haulage, with littlepumping and ventilation, the load factor may be very low indeed, and theplant be running at low efficiency, so that it may be cheaper to take powerfrom a supply company. The author gives figures for a 250-kw. colliery set.which gave a total output of some 25,000 units per month. The capitalcharges amounted to 0'725d. per unit, and the running costs to 0'438d. perunit, giving a total of 0725d. per unit. These figures refer to a period whenthe set was only about a quarter loaded. Power was originally taken froma local supply company at the price of one penny per unit.

The author thinks that only the alternating-current system will be usedextensively in collieries in the future, giving as his reasons the greaterattention required by D.-C, motors, the advantage of being able to use oil-switches with A.-C. apparatus, and the ease and economy of A.-C. transmission at high pressure. He favours generation of three-phase current ata pressure of 3.300 volts, at which pressure pump and haulage motors couldbe supplied, while motors near the coal-face would be worked at 500 volts.For the prime mover, he advocates high-speed reciprocating engines, exceptwhere a large quantity of exhaust steam is available, in which case theinstallation of an exhaust steam turbine is advisable.

For distribution in the workings, the author favours armoured cablesdown the shaft, supplying a switchboard of the ironclad cellular pattern ator near the pit-bottom. The cables along the roads should also be armoured,and should be hung from wood props by pieces of cord, which will break ifthere is a fall of roof and allow the cable to fall. The armouring must beefficiently earthed and bonded throughout. Earthing at each individualmachine by burying a copper plate in puddled clay has been found satisfactory, but earthing on the surface is probably the safest method. Inconnection with the question of earthed or insulated neutral, the authorpoints out that the neutral must be earthed if the supply is from a company'smains without an intermediate transformer, as an earth on one phase in onecolliery following on an earth on another phase elsewhere may have seriousconsequences. The possibility of an increase of pressure across theremaining two phases, if one goes to earth in an insulated system, is a seriouselement of danger, but many colliery engineers still prefer the insulated

ABSTRACTS AND NOTICES.

72Abstracts and Notices-Arkil, 1911.

conveyor belt, the size of the pole-pieces of the magnet, and thedistance the pieces are from the cross-belts ? If these items haveto be taken into consideration we should require to know thefigures connected with them before being able to design amachine capable of handling 25 cwt. of ore, from the author'sdescription.

The meeting then closed.

system. A. leakage indicator should be used in all installations, and theleagage current should not exceed one milli-ampere per ampere of the supply.The author then briefly described the B.T.-H. Co.'s system of protectiondevised by Mr. E. B. Wedmore, and described in Electrical Engineering, June•2nd, 191 o; p. ^56.

Pumping methods, continued the author, have undergone a radicalchange by the introduction of electric power. For underground work,reciprocating pumps of the three or four ram type are employed, as they canbe constructed to pump against any head. Squirrel-cage motors can be used,as these pumps can be started light. Turbine pumps require less space andcost less, and are used where the head is constant and not too great. At theCowie Colliery, Stirlingshire, turbine pumps aggregating 400 h.p. andarranged in three stages have recently been installed by Mather & Platt at acost, including pipes, of about 1,000, to replace old reciprocating pumpsoperated with beams by a steam engine. The top lift pump discharges 900gallons per min. against a head of 144 yards. Electrically-driven turbinepumps of the self-contained vertical spindle pattern are invaluable forsinking operations, one great gain being the elimination of steam losses dueto leaky pipe-joints.

Turning to coal-cutters, the author referred to the possibility of workingsmall seams with them without producing an excessive percentage of smallcoal. The disc machine, used chiefly in long-wall working, where the coal isstrong, must be able to start up with more than full load torque, and therefore a wound rotor was essential for A.-C. machines. The bar machine isprobably the best type for general use. It is less liable to be held up bycoal falling on it, and has the great advantage that a squirrel-cage motor canbe employed to drive it, thus obviating the sparking difficulty. It can alsobe more easily adjusted than the disc machine to follow irregularities in thecoal seam. The chain type is extensively used with very solf and friablecoal, but does not appear to possess any advantages over the bar type forthis class of cutting. After referring to the necessity for interlockingarrangements for the plug connections of the trailing cable, the authoremphasises the importance of effectively earthing the motor casing. Themotors for coal-cutters vary between 20 and 40 h.p., and are of the totallyenclosed flame-proof type. In the case of a certain 2(i-in. seam of hardsteam coal, the underground cost of production per ton was reduced from5s. IJd. to 4s. 6^d. by the use of a coal-cutter, including capital charges andrepairs. Thus a saving of 7d. per ton was effected, besides the increase invalue due to the greater percentage of round coal.

With regard to haulage, Mr. Miller mentions that with main ropehaulage (used where a single road is to be worked with gravity return) it isessential that the motor should be capable of starting up slowly, to avoidexcessive strains on the tub couplings. For large gears, the maximum speedwould be from 8 to 12 miles per hour. Main and tail haulage, used for levelroads, also necessitates slow starting up of the motor with considerabletorque. Liquid starters are frequently used with these. Endless-ropehaulage, adopted extensively on long double roads, is arranged to run at I^to 2| miles per hour, and provides practically a steady load all day, so that asquirrel-cage motor, driving through a friction clutch, may be used. As anexample of the economy of electric haulage, the author mentions the case ofa 500-yard road with an endless-rope haulage running at 1| miles per hour,and absorbing 33 h.p. The total output of coal is 300 tons per day, and thecost of working 0'39d. per ton. When worked by steam gear situated at thesurface, the working cost was 1.77d. per ton, so that a saving of 500 perannum has been effected.

Electric locomotives, continued the author, require at least 6 ft. headway,and can only be used in intake roads near the down-cast shaft on account ofthe sparking at the trolley wire, and are not used much in this country.With regard to electric winding, the author thinks it probable that the heavy

Al'RIL, 1911.Abstracts and Xoticex.7,3

74Abstracts and Notices.Apkil, 1911.

c^pital charges of main electric winding gear will neutralise any saving inefficiency over steam winding, except where a cheap supply of power isalready available. Small winding gears of from 40 to 100 h.p. are employedin a number of cases to raise coal from one seam to another in order that themain winder may be run from one level only at the maximum speed. In amine of average size, the power used for ventilation would probably amountto several hundred horse-power, and would tend to ensure a good loadfactor. Finally, the author referred to the use of the Tirrill regulator andthe Holmes-Anderson fire-damp safety cut-out, described in ElectricalEngineering, Vol. VI., Mining Supplement, p. cxxvi.—Electrical Engineering,February 2, 1911, p. 57.

El.ECTKICITY IN MrNES AND THE P^EVENT^ON OF Aof'IDENTS.—At ajoint meeting of the Scottish branches of the Association of Mining Electrical Engineers and the National Association of Colliery Managers, whichwas held in the Glasgow Technical College, under the chairmanship of Mr.George Gibb, president of the latter Association, Mr. Kobert Nelson, H.M.Electrical Inspector of Mines, read a paper on the avoidance of accidents inthe use of electricity in mines. Electrical accidents in mines, he said, fellunder three heads—ignitions of firedamp, underground fires, and electricshock. Discussing those three heads, he said that between January 1, 1905,and December 31, 1910, electric shock below ground was responsible for 53recorded accidents and 55 deaths. During that same period ignitions offiredamp and underground fires caused by electricity had together beenresponsible for six accidents, causing 12 deaths.

Mr. Nelson submitted the following analysis of the 53 accidentsreferred to :—

Accidents. Deaths.Faults as regards the earthing of outer coverings of

apparatus :(a)Total absence of any connection to earth...13 ... 13(b)Break in continuity of earth connection...2 ... 2(c)Outer covering earthed, but connection with

earth inefficient ............7 ... 9Contact, direct or indirect, with live parts of cables :

(a)Direct contact with live cable exposed throughabrasion of the insulator .........ti ... fi

(b)Contact with a conductor (e.g., a signal wire)made live by its contact with a live cable exposed through abrasion of the insulation ...9 ... 9

(c)Contact with a joint inefficiently insulated ...5 ... 5Accidental contact with unprotected and unin

sulated Jive parts of apparatus :(a)Accidental contact with live parts inten

tionally exposed ......... ...H ... 8(b)Contact with a live part normally unex-

posed but improperly exposed for inspection whilst alive ......... ...1 ... 1

Inexperience in handling plant, or misadventure ...2 ... 2

Accidents. Deaths.Absence of or inefficient earthing ...... ... 22 ... 24Defective insulation of cable system ...... ...20 ... 20Contact with uninsulated live parts ...... ...9 ... 9Miscellaneous causes ............ ...2 ... 2

Carrying the analysis still further, Mr. Nelson showed that there wereon armoured cables 2 accidents, on concentric cables 2 accidents, and on un-armoured cables 20 accidents, while from the point of view of the relativesafety of low, medium, and high-pressure current, and of the three-phase

and direct-current systems there were on low pressure systems (250 volts andbelow) 4 accidents, on medium pressure systems (250 to 650 volts) 45 accidents, and on high pressure systems (above 650 volts) 4 accidents. Onthree-phase systems 83 accidents, and on direct-current systems 20 accidents.

He added that the mere provision of an efficient connection to earthwould have avoided two-fifths of the total number of electric shock accidents in mines ; but it was perhaps more remarkable still that such a provision, together with proppr attention to the insulation of those cablesystems upon which accidents occurred, would have avoided not less thanfour-fifths of the total number of accidents, Discussing the safeguards tobe observed as regarded the construction and workin^ of apparatus, headvocated careful and constant attention to two main items—(a) a soundconnection to earth for all outer coverings of apparatus ; (b) the coveringof all live parts which would otherwise be exposed to contact, with insulating material of such quality and thickness as to obviate danger, coupledwith the efficient protection of the insulating material against mechanicaldamage.

Difficulties were said to arise in connection with the making of a soundconnection to earth, but Mr. Nelson said he had not known any case in whichthey had proved to be insuperable. With a single earth plate it is notalways easy to make quite certain that the connection with earth is efficient.This difficulty can, however, be got over if it exists by sinking a secondearth plate about 20 yards or thereabouts from the first. It is also advisablefrom time to time to test the continuity of cable armouring, and to test theefficiency of individual joints in earth conductors for which purpose a pocketapparatus consisting of a 2 to 4-volt battery, with a lamp or an electric bellor a galvanometer was recommended. Earth conductors should always beof ample cross-section, if only to provide mechanical strength. If ofsufficient size in the first instance, and well-jointed, they could only failthrough mechanical damage so severe as to cause discontinuity. Theeffective protection of all live parts was also a matter which might beregarded from a mechanical siandpoint, since if suitable apparatus is obtainedits proper protection and maintenance in working require mechanical ratherthan electrical knowledge. Cables, motors and other apparatus should betested from time to time by an ohmmeter, and one ol these instrumentsshould be available at every mine in which electricity is in use, and such aninstrument should give double the working pressure. The complete enclosureof all live parts within a substantial earthed metallic outer covering was,said Mr. Nelson, in conclusion, the best safeguard, and a colliery managermight feel assured that in making this provision for security against anignition of firedamp he was also providing the best security against the riskof an outbreak of fire, and against the risk of electric shock.

In the course of the discussion which followed, Professor Jamiesonfully endorsed the conclusions stated by Mr. Nelson, but Mr. A. Anderson,urging that it was not necessary to use armoured cable under all circumstances, gave figures showing that the proportion of armoured to unarmouredcable was about 1 to 12) rather than 1 to 10. He disagreed, too, with theincreased use of high pressures underground, and urged that about 100volts was the safest line to go upon. Mr. Nelson said he could not quitefollow Mr. Anderson's line of argument, and that gentleman in reply saidhe would not earth a rotary transformer or converter, nor use armouredcable in a pit where there was saline water. In the case of a pit near theseashore where armoured cable had been installed, it began to give trouble inless than a week, and in six months it had to be replaced. Mr. Nelson hadadvocated the use of armoured cable in which the armouring itself requiredan additional external insulation or protection to protect it from the actionof such water, but Mr. Anderson urged the use of unarmoured cable rightaway, coated with a suitable preservative compound.— Electrical Engineer,April 14, 1911. pp. 404-5.

Apkii.. l!)ii.Abstract* and ^^ntices.75

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 Specification, 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) mean^ Provisional Application ; (C) means CompleteSpecification. The date signifies when filed.

(P.) 528/10. John Lidell. Improvements in apparatus for recoveringdiamonds and metalliferous matter from their admixtures. 24.10.10.

(P.) 529/10. Charles Edward Bennington. Ambulance dividing sheet.25.10.10.

(P.) 531/10. Samuel William Taylor. A pneumatic dust collector.26.10.10.

(P.) 535/10. George Mitchell. Improvements in and relating toprocess and apparatds for the treatment of ores. 29.10.10.

(C.) 536/10. Earnest James Hume (1). Walter Reginal Hume (2).Improvements in concrete pipes, columns, girders, blocks, and otherstructural material, and method of and means for manufacturing the same.29.10.10.

(P.) 537/10. Anthony Maurice Robeson. Improvements in orefeeders. 31.10.10.

(C.) 538/10. Hans Charles Behr (1), Charles Friedrich Eduard ^scarSchmitt (2). Improvements relating to the sub-division of streams of pulpand other liquid. 1.11.10.

(P.) 539/10. Godfrey Samuel Kope. A new or improved compositionfor igniting the fuses of blasting charges. 2.11.10.

(C.) 541/10. Eberhard Brauer. An improvement in the process ofcatalytic oxidation of ammonia. 4/11/10.

(P.) 544/10. Francis Neville Harris. Improvements in the method ofand apcaratus for sharpening rock and other steel drills. 7.11.10.

(O.) 546/10. Charles Cuthbert Freeman. A grinding pan dischargeand classifier. 8.11.10.

(C.) 551/10. Herbert Nosworth Roche. Improvements in electric waterheaters. 11.11.10.

(C.) 552/10. Niels Christian Nielsen. Improvements in the method ofavoiding formation of rust in tinned iron tanks or vessels. 11.11.10.

(C.) 553/10. Christian Eliza Liebenberg. Improvements applicableto headgear crushing plants for collecting the rock-dust produced therein.12.11.10.

(C.) 554/10. Robert Irving. Improvements in percussion drills. 12.11.10.(C.) 555/10. William M. Metzler. Improvements in and relating to

conveyor belts. 12.11.10.(P.) 558/10. Ludwig Walmer (1), George Wilbur Gqff (2). Improve

ments applicable to rock drilling machines for introducing water into theholes formed thei-ewith. 16.11.10.

(C.) 561/10. Reinhold Steinback. Improvements in grinding millsand the like. 17.11.10.

SELECTED PATENT APPLICATIONS;(TRANSVAAL.)

76Selected Patent Applicdtiuns.Aphn,, 19li.