Correspondence on Hydro-Electric

33s CORBESPONDENCE ON [Minutes of

Correspondence.

Mr.. duderson. Mr. A. C. ANDERSONthought that the Paper, descriptive of works of greatimportance, was alltoo short, and many would lament the lackof detail, especiallyas regarded troubles experienced. He wished to ask why the construction of the Talarn dam was notcarried on continuously. The figures for overall efficiency given on p. 300 presumably referred to the Canlarasa installation, and were stated tobe “ confirmed by individual plant and machine trials,’’ though it was not always clear to which power-house the Author referred. If thetrials were actuallycarried out on the site, it wouldbe valuable to know exactly how the quantity of water discharged fromthe turbines wasmeasured. The percolation mentioned on p. 304 was remarkable ; it would be of interest to know what the temperature of the percolation water was, and at the same time the temperature of water at the bottom of the reservoir. The turbines at Camarasa were shown fitted with relief valves. What was the size of the valves, and the time of opening and closing on one set, when full load was thrown off ; and had the guaranteed over-pressure of 18 Ibs. been complied with ? It would be interesting to know what the Author regarded as “ fairly close andinherent regulation” for the generators,because the figure did not appear to be given, and it was thus difficult to criticize the statement.Regulation should not betoo close for that class of work. Reactances appeared to have been used at Se&, and probably at Tremp ; were they also employed at Camarasa, and, if so, had they adequately protected the generators when shorts occurred on the line? Considerable usehad been made of phase-compensators on thesystem, whichrepresented very sound practice, resulting inremarkable economy. Thetransmission-line conductors were presumably of copper, butthe material actually used was not stated.The Author said the suspensioninsulators were six in series, while Figs. 13 would make it appear that they were seven in series. It was satisfying to note that two lightningguard-wires were used on theline from Serbs to Barcelona.The Author’s figures of costswere valuable, and would be still more so if hecould give an accurateidea of thefactor by whch to multiply them to arrive at present day values, and state whether interest during construction was included ?

Nr. P. BOLTONconsidered that the outstanding feature was the Yr. Bolton- completeness of the utilization of the energy available. It was the grasp of all essential points, and the interest excited, that led to a desire for more enlightenment on some of the details, to enable the designs to be properly appreciated. The average annual flow of the River Pallaresa was given as about 49,100 million cubic feet per annum, or 1,560 cusecs. The catchment-area, however, was not stated ; that was of equal interest, and the figure would be of considerable service for reference. The spillway was designed to deal with 70,600 cusecs,which was forty-fivetimes the meanannual flow. It wouldbe of interestto knowon whatthe Spanish Government’srequirements were based for that flood-discharge. The coffer-damsmust havebeen oneof the most interestingproblems to be dealt with, seeing that a discharge of over 70,000 cusecs had to be provided against in a confined river-channel. Any information the Author could supply on the designs and costs of such temporary worksshould add materially tothe Paper.The reasons for the ratherabnormal sections of theTalarn and Camarasadams had beenexplained. It was not clear, however,whether the Spanish Governmentwould have raised objections toalternative designs whereby the hydrostatic pressure was partially or wholly relieved by means of trenches within or under the dam, or for which the hydrostatic pressurewould not be of suchserious importancein the case of alternative designs, such as an arched or reinforced- concretestructure. The nature of thedam-site appeared to be favourableto such alternatives. Prom the quantities given in Table VI, Appendix A, it would appear that the plums were not confined to the middle third, but were distributed throughout the concrete, with a view to economy of material. It was remarkable that certain dams were built with the plums confined to the middle third, whereas others (notably in India) were built up of random masonry with lime-mortar joints, showing that a dam composed essentially and almost entirely of plumsgave satisfactory results in practice. It was stated that the power-tunnel was cut through rock, presumably of limestone, and lined with ce‘ment. Was that the Asland Portland cement or the sand mortar referred to ? Since a speed of 22 feet per second was allowed for, and limestone might have beenmixed with the cement, it appeared,without further explanation, to involve the risk of serious trouble in the future. The electrical details given were full of interest, but some figures of importance were omitted, whichwould add materially to the value of thePaper. Por instance : “ Fairly close andinherent regulation was specified for the generators.” An amplification of 22

MT. Bolton. thisrather indefinite statement wodd be welcome. In Pip. 13 themasts wereshown carryingtwo three-phase circuits, but in explanation it was only stated that theswitchboard had all the most modern appliances. Typical diagrams of connections at a generating- station and at a sub-station would help towards the proper under- standing of the electrical lay-out, and would show whether “ split ” conductors were adopted or not. A description of any unforeseen difficulties that had appeared in the operation of the electrical side of the installation, and the steps that hadhad to be takento put them right, would be a valuable addition. The cost of the synchronous- condenser installation was given as g30,000, which sum of money providedfor 19,000 kva. of movingmachinery, switchgear, etc. That worked out at about ;El 8s. per kva., which seems an incon- ceivably low figure. Moreover, the revenuewas increased by E80,OOO yearly, showing a return for interest of about 250 per cent. on the capitalspent on that item, after providing for all othercapital charges and working-costs.The insulators were of thepin type, with four petticoats, which did not prove satisfactory in working. If they were used onthe 110,000-volt circuit,that was not surprising. In that connection any reference to insulators of American design and manufacture in comparison with British wouldbe welcome, as it was generallyrecognized that those of British manufacturewere more reliable. Recent improvements in the attachment of the insulators to the pins were almost of sufficient importance to open up the question again of the suitability of pin-type insulators for voltages over a declared pressure of 60,000 volts, which was usually taken as the limitingpressure at present. In Appendix A, Tables I1 and V, the costs of the Serbs and Tremp installations were clearly set out, but the itemof “ Administration and General Charges,” amounting to about 25 per cent. of the total cost of the works, appeared to be extraordinarily high. Thecost of the Camarasa installationwas given as 227. 4 perkilowatt. It would appear that the cost at Tremp was 265.0 per kilowatt, andat Serbs about S4600per kilowatt, giving an average figure of about €43.0 per kilowatt for the three installations more particularly described. 3Lr. Caldwell. Mr. J. CALDWELLwas speciallyinterested in the design of the standards employed to support the overheadline from Serbs to Barcelona. It would be interesting to know if they were of riveted construction,fabricated indistant workshops. Themanufacture of such transmission-line standards bymeans of electric-arc welding was now standard practice on the Continent,where users had found thatthat method ensured a strongerstructure at reducedcost, combined with the advantage of erection in situ. In view of .the

present demand for such lattiee poles and masts for transmission-xr. cddwc~. lines and wireless aerials, he wished to direct attention to a par- ticularform of standard now being supplied in Belgium. They were 72 feetlong overall, of which 5 feet was embedded.They carriedtwo three-phase lines and a guard-wire,altogether seven wires, on spans of 525 feet, and the stress due to the pull of the wires with a maximum wind blowing across the line was calculated to amount to about 1,350 lb. horizontal pull at the topof the post. They were of square section, 40 inches by 40 inches at the ground level, tapering to19 inches by19 inches at the top.The longitudinals and the corners were of T-bar 3% inches by 3& inches by f inch in the lower section and 2 inches by 2 inches by 4 inch in the upper. The lattice bars were also T-bars 12 inch by 18 inch by f inch and 18 inchby l# inchby inch respectively. Thattype of post could be readily constructed on thc site from steel members delivered bundled or loose as might he convenient, or sent in two sections, arranged with a bolted joint between them. At the pre- scribed working-load a deflection of 6$ inches was measured 3 feet on the butt sideof the load, and,at double that load, the deflection was 9f inches on a sample post placed horizontally with the butt end embedded in niasonry and loaded to the point corresponding with thecentrc of pull when erected. No pmnanentset was noticcahleon completion of the t,est. !rho welded ports weighod 10 per cent. less than those rimt,ed in t,he usual way, and as tmo welders could comldetc one in 9 hours, using about 45 nnitu and 425 feet of No. 10 A.W.P. electrodes, the costof erection should not exceed 3% per post, Whera transport was difficult such posts could be built up with portable welding plant at convcnitmt pods on theline, Another application of eloctric-arc welding in hydraulic power installations mas the construction of pipcs of large dianletor. The method had not yet bern adopted in England, hut was under considerationfor some specificcases. He had mentionod those details of construction to direct attention to ilnprovelnents, which provided greater efficiency and lowcr installation-costs. Mr. A. S. C~IWNSPAN would have appreciated, from thecivil MP. engineer's point of view, a few more details appertaining to the actual construction of the dams and canals, pointing outhow the difficulties met with had been overcome. Although he realized that the Paper, in itspresent form, contained much information, be hoped that the Author would find an opportunity to describe the most important features of construction. In view of theresults of tests given in Table VII, it mould he useful to in\-estigate the question of nsing adulterated cement. The figures New, llowercr, uot, very conviucing

1x7. Gnnapan. asto the economy effected by using sand-cement.Thr figures showed that at theages of 28 days and 3 months, l : 3 mortar, made of Asland Portland cement, was 32 per cent. stronger than thesimilar mortar made of sand-cement containing 55 per cent. of Portland cement and 45 per cent. of sandstone. If to that were added the additional cost of sandstone, it was questionable whether the saving effected was worth considering, particularly if the working-stresses were increased pro rata tothe ultimatestrength. It would be important to make a series of percolation tests inaddition tothe compressive and tensile tests, whenever the question of adulterated cement was considered. Percolation tests would certainly be of paramount importance when the concrete was reinforced, and if the Author had any figures relat,ive to such tests, Mr. Grunspan would be indebted to him if he would furnish them, together with the specificat,ion of the sand cement,namely, how the sand and cement wero mixed, what degree of fineness was stipulated for the sand, and also the degree of dryness. Mr.Steven~. Mr. THEODORESTEVENS wished toask t,he Authorfor some addit,ional information, and whether he correct,ly understood some of his figures. Did the Camarasa units give rated full load at three- quarter gate-opening ? Taken over the year 1917 (Appendix A, Table I, column G), the cubic feet per kilowatt averaged 257-was t,hat based on measurements by a meir ? Could the Author state how that compared withthe water rate under test conditions ? The consumption for a mhole year aas a valuable figure to have in comparison wit,htest results. With roferencc to phase-compensation, this was the first time he had seen definite figurm given to show the actual cost,, and net profit obtained from so considerable an installation of synchronous condensers. Could the Author state what the total energy loss was in the phase-compensators alone, cmluding the addit,ional loss in t,ransmission-linesincident to thegreater pomr which the synchronous condensers enabled the lines to carry ? He n,ould like to know l~ow thedifferent platk~were utilized during differenthours of the day, and the outputs of t,he different sub- stations. Had t,he Author found that thc precautions taken with roferencc t,o protection against lightning were sufficient '6 What had been the general nature of the troubles experienced in operating these transmission-lines and was the construction sufficiently atrong to meet the general conditions of the service ? Had any troubleof a mechanical nature been experienced in connection with theoperation of t,ho plant or of the transmission-line3 '? As full infonnat,ion as practicable concerning the control of the wat,m at the top of the penst,ocb nwkl be of interest. The heighb of the dam wero 269

and 318 feet respectively, and the particularsof the class of material Nr. Stevens. used were of great interest ; he would like the Author to give his views concerningthe relation between loading weightsat thebase of the dam, and maximum stresses in the dam itself. On the question of building cost, if he was correct in adding the sixth and seventh items in Table VIII, the cost worked out at S1 17s. 6d. per cubic metre of gross volume of building, or 1s. Id. per cubic foot of that volume. It seemed that the administrative charges in the three casesrequired some explanation. Onp. 312 it was shown that 26 per cent. of the total cost was thus allocated for the Serbs plant ; on p. 313, 23 per cent. for Talarn and Tremp installation ; whilst on p.316, only 10.4 per cent. of the total cost of the Camarasa installation was allocated to administration and general expenses. Was there a particular reason for the very high percentage in two cases and the low percentage in the third ? Comparing the distance of transmission, which the Author stated was 120 miles, with the distance,115 miles, from theRiver Shannon, wherewater-power wasavailable inIreland, to Dublin, the Barcelonawork showed that it would be equally advantageous to develop the Shannon’s water-power. Of course in Ireland the available headswere considerably less than in theBarcelona installation, but in the Reportof the Water-PowerResources of Ireland Sub-Committee, the available power on the Shannon was stated toaverage 52,000 E.HP. ; and considering that Irelandhad at presentinstalled electrical plant no greater than that total,it would appear well worth while to develop that power. It was evident thatthere was sufficient to enable it to be utilized partly for industrialpurposes and partlyfor lighting and general supply to the cities and towns. The flow of the River Shannon, averaged over 25 years, was five times as much as the flowat Pobla, stated as 49,000 million cubic feet per annum, with, asalready mentioned, lowerheads in the case of the Shannon? Thestorage in the Shannon loughs was given inthe Report referred to as 10,000 millioncubic feet, which was 30 percent. greater than the storage in the Talarnreservoir. Mr. W. L. STRANGEnoted that the section of the Talarn dam Mr. Strange. had been increased because of the leaky nature of the foundations. When such foundationswere thus defective, three methodsof treat- ment were practicable. The first was that described in the Paper, in which the section of the whole of the superstructure was widened from the consideration that it was buoyed up by the waterleaking below the base, whereby,virtually, thespecific gravityof the masonry

1 Transactions of the Inst. C.E. of Ireland, vol. xlv., p. 41.

~r.~trungo.was reduccd by that of the water. That was the conditionmost prejudicial tostability, and the t,reatment wa? conscquently the most expemive.The second method was applicable tothe case where the fissures were less numerolw but extended toa great depth. The foundationswould then be deepened,as required by thepressure- head and nature of tho strata, and excavated to thc full width of the deepened base. The masonry would be constructcd to fill thc excavation completely, so as to make it continuous with the natural rock on each side of the trench ; thus itcould neither slide nor over- turn. The third and cheapest method could be adopted where the fissures, although numerous, were smalland shallow. A deep cut-off trench would be excavated on the up-stream side and filled with cement concrete to reduce leakage, and another deep trench dug on the down-stream side and filled vith insoluble rocky debris to induce drainage, thus preventing the sub-foundation water from exerting upward pressure on the dam. The Author stated that the borings made did not disclosc t,he many defects in thc rock foundations subsequently found. This would usually be the case, and it would thu be advisable to examine such foundations by trial pits instead, and, after a seemingly reliable base had been obtained, to test it by further trial pits sunk therein, so as to gain an idea of sub-foundation condit,ions and design the n.ork accordingly. All cracks and fissures in the bed should bc made as impermeable as possible, the larger ones being opencd out and filled with cement mamnry or concreto, and thesmaller ones bcing grouted with cement. Tho mriat,ion of mat,erial in thc constructionof the hase of the dam (Pig. 3, Plato 2) seemed open to the objection that, it mightlead to differences of settlemcnt whicl~uight subject the whole lnass to strain. Such strain would ba lcsscned wem ille concroto msdo, not with rigid, rapidly-setting cement, but with elastic, slow-setting hydraulic lime, andcarried up slowly, so thatpracticability and timo might be secured for theinitial sett,lements to adjust themselves gradually. NI.. Twlo~. Mr. )\l. T. TAYLORc,onsi(lered that great praise wns doe to t,lle promoters of the ~ty,~ro-e~ectric~chcmos <~iscuised in theI’aper and the results achioved by them, and that the engineering staff should stand out as an object-lesson to British engincera. On looking over Fig. 7, thc magnit,ude ol the developments and thererourcefulness and Yiflion of both pronlotcr3 and cngiuecrs alikv could not he rrlistal

experts in legal matters and of suitable nationality had been most MI.T~YIOI. desirable, and specialist3 in such important matters as appraisals and economical acquisition of similar undertakings and the general administration of the varied electric power undertakings involved, had beenfound necessary. Unfortunately, the Paper appeared to be lacking-mainly dueto its brevity-in its purpose,namely, to provideinteresting points for discussion ; in fact it was scarcely full enough to cover properly any one of the hydro-electric iustalla- tions (Serhs, Tremp,and Camarasa) mentioned;and because of the brevity of thePaper judgment could be basedonly on the summary of resultsgivcn throughout. Quite a number of very interesting features were involved, although nothing special or novel in character was introduced. More thananything else, perhaps, the Paper leant towards more detailed description of the dams. But looking at it from adifferent aspect, and keeping inmind the title, and the natural andphysical features of the differentdevelop- ments, such ever-present and lasting problems were presented &S,for instance, a series of hydro-electric developments, each installation differing in its hydraulic properties and power-capacity, their in- dependentyet iutcrdependent regulation and parallel operation, and the control and operating features of tbo extra-high voltage apparatueand long-distancct,ransmission-system, the receiving- station conditions and their varicd operating functions, etc. There rertainly exist,ed manyfeatures of thesehydro-elect,ric developments-both hydraulic and electrical-contrasting widely and quite as important as the dcsign and coustruction and summary of costs mentioned in the Paper, upon which an interesting and profitable discmsion ahonlrl result. The omission of detail frustrated intelli- gent discussion on many points well worthy of further mention, and left the observer to ask questions. The total costs for concessions and watcr-rightswere about : 2 Set& installation...... 50,670 T~larnand Tremp installation ...... 24,860 Cnmnmas instdlation ...... , 14,165 . -98,636 Approximately 2 per cent. uf the total capital cost. Perhaps expropriation laws had rendered Some help in keeping down the cost, and it might be that,, aswas nsual in most Latin-American countries,the concessions andwater-rights were originally held by local residents to be marketed at their price. Where Mr. Taylor was engaged (British East Africa) water-rights could neither be bought uor sold. He was heldresponsible [or thewater-right

Mr.Taylor. permits, and for their complete investigation and final preparation for issue to applicants. As they wereissued by the Government free of charge to desirable applicants,who were compelled to follow out the requirements laid down in the rules governing the issue of water-permits, an end was made of profiteering in them. Riparian proprietors were fully safeguarded, and,if lands changed ownership, the water-rightsreverted automatically to the Governmentuntil the new riparian owner applied for andreceived a new water-permit. Due, no doubt,to thegeneral brevity throughout the Paper, a proper explanation was lacking as to why the highestpossible efficiency of the turbines and penstocks of the Tremp installation was put aside, seeing that something like 37,000 HP. in turbine capacity was involved. Neglecting the great importance, and the future and ultimate requirements of the plant, it was evident that the installation drew every moment of its operation directly and exclusively fromstorage (and, perhaps, appreciable draughthead), that long- period storage was questionable or uncertain, and that the amount which was available above the penstocks had been dearly bought. There must have existed somegood reason or reasons for permitting such water-powerwaste. Several different views might be taken; but looking at the position simply from the unnecessary costs of buildings and foundations, etc., there was reason to believe that, if theeight turbines installed had beenreplaced by four single- runnerturbines, much saving in the width of the power-station building and its expensive foundations and in the length and cost of travelling crane, etc., would have been made. With such large installations and with large units it was not only efficiency alone which counted, it was also reliability in service. It was somewhat doubtfulwhether gooddesign, construction, characteristics, and durability of materials, etc., had any special bearing in the matter. True, high-class design and construction would cost more money ; but it would also, in general,afford longer life, the cost of its upkeep mould be a minimum, the interruptions would be fewer, and the efficiency would be higher and would remain relatively higher for a longer period of time than with a cheaper and obviously inferior unit. In fact the fixed charges of the lower priced unit-taking the fixed charges as (a)loss in revenue due to loss in efficiency ; (b)cost of upkeep ; (C) the sumof revenue loss due to interruptions of service -might if added to the purchaseprice of the higher-priced unit, pay for thedifference in a short period of operation-perhaps during the first year's service. Before leaving this point, Mr. Taylor would like to repeat his views recently expressed,l that, a turbine installation _____ ' Proc. Institution of Mechmical Engineers, Jan. 1920, p. 190.

of, say,78 per cent. efficiency, paying a dividend, mightnot beable to NI. Taylor. pay if the maximum efficipcyremained at 72 percent., even though the total cost of such a turbine installation was but 6 per cent. of the hydro-electricdevelopment. In money the output loss would mean a decrease in value of the samepercentage for theentire development,including thesater-rights, reservoir, dam, conduit- line, turbines,including auxiliaries,generators, transformers, transmisfiion-lines, etc., and in fact everything which was covered by the total amount invested. Every 1 per cent. of efficiency of the 28,000-kilowatt turbo-generatorinstallation represented (on the basis of Table IV for 5,240-hours yearlyoperation) almost 1,500,000 kilowatt-hours. If the installation had been designed to give the same efficiency as the Camarasa installation, 80.5 per cent.,the increased annualenergy-output for the new condition nonld be nearly 5.25 million kilomatt-hours, which, when sold at 1.0d. per kilowatt-hour, would represent an additional income of f21,870 a year; at a 10 per cent. interestthat nonld represent a capital investment of fZ18,700. The question broughtout by that argumentwas : Why had itbeen allolred ? Looking at the fore- going in another nay, it might be said that the company could afford to pay a premium of f72,900 for every 3.5 percent. of added efficiency, and t,hereby obtain a 30 per cent. return on the additional investment. It NUS unfortunatethat so littleinformation was given as to the Serhs canal, the average cost of which figured out at f9 per lincar foot. It would be interesting to know if, for the total length of l2 miles, the two cross sectious givendiffered much. KO gradient was given, and it mouldbe of interest to know the average. Whatmaterials Imd bcm used inlining the canal ? What he-board was allowed ? He would liketo know also the maximum, minimum, and average value of the ronglums factors. A section of the forebay seemed desirable, as Pig. 7, Platr, 2,sllowed the penstock entrance open to inflow of sand, debris, ctc. In the Sork plantthe operat,ing head was about 160 feet,the power capacity of mch tnrbinr was 11,000 IIP., and a Iargc qusntity of water was involved, requiring a large mctionnl area at &e end of the draught-tube ; this was mentioned Ijecause thcre appeared to be something amiss with therelative dimensions shown in Fig. 7. Also, distinct from theTrenlp power-station layout,the Serin power- stationarrangement providedexcellently for t,he necessary con- venienthandling of the pon,er-trausforllleru. In tho economical lucatiun,dr~ign,andnrrangcment of the Camarasa power-ntation,etc., to wit t,he bwt o,"'.&tingcunditions and accosribility, much diffirolty must have been cncountcred. It uwseen that practically the whole

Mlr.Ta~lor.of thegravity and pressure waterways were throughnatural rock. With reference to theacknowledged high speed of the turbine the conditions being : unit horse-power, 17,500 ; head, 246 feet; revolutions per minute, 375, Mr. Taylor would like to know which of the following the Author thought best : (1) the lower speed, with higher cost of building and generators and a higher and a longer- period efficiency guarantee, or (2) the higher speed with lower cost of building and generators and, at thebest, equal efficiencybut without a long-period efficiency guarantee. Of unusual interestat thepresent time of high prices waa the capital cost of hydro-eleotrio developments at home and abroad. From the figures given, the cost per horse-power for the three installations discussed was :-

Total :-S5,049,736 capital cost ; li7,250 HI'. plant oaphcitg ; S30 per ITP.

As regarded the extra-high-voltage lines and terminal apparatus, it nould be of special interest to know the connections (star or delta, earthcdneutral or otherwise) of generators and transformers wed. Was itto be undcrsbood that the pin-typeinsulator was used onthe 110,000-volt lines ? For sonleyears now that type has bccn foundunsatisfactory for voltsgesabove F0,000 or thereabouts. Jlr.17ererbur~. Mr. H. E. YERBURYobserved that,this intmosting and instructive P.zper emphasized the advantages that accrued by the adopion of phase-compensating arrangements.The inst,allation of over-excitd syuchronoua plant for railway and uthcr supply vas essential for cHicient working. Thc all-round saving that could bc cffected by consunmrs drawing current at unity power-factor should be taken into account in the charges for elect,ricity. Inthe under- t,aking under review, did such a consumer get a concession compared with a consumer taking current at, sap, 0'8 power-factor ? If so, were the units measured by kilowatt-hour meters and also n.nttlasu- component meters ? $power-factor of O'8called for a 25per cent. increaze in the tot,al kilo-volt-amperes, so that the capacity of the generatingplant and cables was ipcreased by thatpercentape;

hence the total capital would he increased, making the total costs Mr. Ysrbnfy. of generation higher ; there was, also, the loss of efficiency in generation and distribution due ato lagging powcr-factor. Hence it seemed practical to grant a concession, up to6 per cent., to a consnnler who, by installing synchronous machinery, raised the power-factor, and bronght commercial advantageto the supply undertaking. The Author gave figures for the kilowatt-hours generated. It would add tothe value of thePaper if he woul$ give comparative figures for the units sold, and pcrhapshe would feel disposed to add a few particulars regarding the extra-high-tension switchgear, stating thecapacity of the oil-tanh and length of switch-break on the 110,000-volt system. The AUTHOR,in reply, explained that the fact that the work on the Talarn dam had not been carried on continuously was due to financial andnottoenginceringconditions. As to trouble experienced, no serious troubles had arisen in any department. The small leaks madc mention of, both at Tremp andat Camarasa, were incident to the class of installation, and were geological rather than engineering in character. All the hydraulic and electrical machinery had worked smoothly, and no serious trouble had been experienced since the final adjustments were made. The figures for overall efficiency given on p. 300were the resultof testscarriedout on the Tremp installation for the purpose defined, namely, to furnish data necessary for the design of the hydro-electric installation at Camarasa. The figures, as regards the Trempperformance, were given in detail inAppendix A, and acomparison between the proved results at Tremp and the anticipated results at Camarasa was given in Table IV. The results were plant efficiencies and not efficiencies of individual machines. The plant e5ciencywas determined first by measuring the flow into the Talarn reservoir, and secondly, by keeping record of the waste water, so that the total quantityof water utilized at the power-house was determined and checked. Records of the kilowatt-hours corresponding therewithwerealso kept. As a result thewater-consumption per kilowatt-hour was determined. In theTable referredto, however, the results each month were given.Where individualteste were made on machines, in addition to a complete set of gauges, Pitot tubes were used inthe draught-tubes.The resultsvariously obtained were in satisfactory agreement. The pressure-regulators, for automatically limiting the rise of pressure in the pipe-lines on the load being suddenly thrownoff the turbine,were connected with the automatic governor ; the system was a special design of Messrs. Escher, Wyss, andmet thespecified conditions. The diameter of the relief-valve was 43i inches.

The-hllmr. Wit,h reference tu the regulation of the generaturn, the following wfre thc rcsult,s of the tests made :- A.1.E.E:. hle~aoo.

Thc dut,hor's cxpericnce was dcarly to t,he effect that regulation of generators for tlis class of work should bc fairly close, sincc trouble was vastly more likclyto occur with machines of bad regulation, in that thcvoltage increase was much greater under that condition. Thc damage done to trsnslornlcrs, ctc., from excessive voltage was likcly to be more t,han that horn cxocssivo current from short circuits in thc externallincs. Tbc transnlissionconduct,urs were of copper. Seven insulators were shown on t,he part,icular standard illustrated. Such were used on the lines from Serbs to Reus and Barcelona, being the newer lines constructed under his direction ; the Hewlett type of insulator was notthen available. In tbc linesreconstructcd theinsulators were six inseries, and were of the Hewlett type. It would be impossible, withany degree of accuracy, to give figures comparing the costs of those installations with present-day costs. The cost of material roSe very considerably in Spain during the war, and at the end of the war the cost of labour also increased very cousiderably. On going over the figures of the Camarasa costs in a gcneral way some time ago, the conclusion was reached that the works, comprising thedam, canals,spillways, and power-house, independent of the electrical and hydraulic machinery, would cost about double undcr conditions obtaining at that part,icular time in Spain. With reference to thequestions ralsed by Mr. Bolton, a few years ago there was a flood on the River Ebro, to which the Segre and Pallaresa were tributariw, which might havejustified the Government engineers in asking fora spillway of the ratio of forty-five times the meanannual flow. Withinthe Author's knowledge, however, the conditions xadd be met witha spillway devigned to deal with thirty times the mean annual flow. The principal source 01 water was the

melting snow and ice in the Pyrenees. Thedrainage-area of the The*uthor. Pallaresa from the confluence to Talarn was 2,900 square kilometres. Above the Talarn damit was 2,070 square kilometres. On the Segre the drainage-area above the confluence was 4,210 square kilometres. The drainage-area of the Ribagorzana was 3,500 square kilometres. In extra dry years the areas might be contributed to substantially by autumn rains, but the amount was variable and occasionally of great value. Connection diagrams, to be of use, would have to be on a larger scale than could be reproduced in the “Proceedings.” In considering the comparatively high cost of Tremp, it must be remembered it was a reservoir installation and contributed to the output of both Camarasa and Serba, and would also contribute to other installations that might be constructed in the future. As to the cost of temporary works, the work in the base of the dam had been carried out largely in low-water months. The cost of coffer- dams,diversion-tunnel, and care of water,had approximated to 240,000. Having regard to the way such items were mixed up in general construction costs, the figure was only approximate. So far as he knew, the Spanish engineers would not be satisfied with a dam of smaller base, whether or not the hydrostaticpressure was partly or wholly relieved by means of trenches within or under the dam. His opinion wasthat theywere perfectly justifiedin asking for a dam of this thickness, and he would not consider putting in a dam with a smaller base under similar conditions, the leakage at the sides of the dam as well as the base-pressure being considered. Plums had been used throughout the dam, the only limit to theiruse being the economic limit. With a greater percentage of plums than that shown, the cost of construction would have been increased, owing to thedifficulty in quarrying and placing the plums. He did not see that there was any limit, other than the economic limit, in the percentage of plumsused, inthat stone was strongerthan concrete. Asland Portland cement hadbeen used in the liningof the tunnels.The administration costs of the Camarasainstallation were low, the installation being simple in character. With reference to Mr. Grunspan’s questions, it would not be possible to go into the matters he raised without greatly increasing the scope of the Paper. Owing to the particular conditions, the use of sand cement had been an imposed condition, time considered ; but nevertheless a very substantial saving was effected. Replying specifically to the questions raised by Mr. Stevens, the Camarasa units weredesigned to work at best efficiency, and to givefull output of the generators at three-quarter gate-opening. The tests made in 1917were on the Tremp plant; the Camarasa

The Author. plant at that time was not in operation. The general result of the measurements at Tremp for that year, to which he presumed Mr. Stevens referred, were that the average water-consumption during the year was about 13q per cent. higher than that corresponding withthree-quarter gate-opening, which was the point of highest efficiency. Withreference to phase-compensation, the measured results indicatedthat the totalenergy loss in thephase-compensators by themselves did not exceed 3,000,000 kilowatt-hours-this was exclusive of theadditional loss in transmission-lines,which loss wouldbe incident totransmitting the greater amount of power saved and delivered into Barcelona. He was of the opinion that the running of a grounded conductor in the plane and above the three conductors in each circuit gave the best known form of protection from lightning. The effectiveness of such guard-wires depended largely on the system of earths. With thesteel towers the earths were fairly effective. Thelines were occasionally struck, but he did notsee how that was to be prevented, and thegeneral experience was that ina great many cases overhead ground-wireswere effective. Themethod adopted of spark-gaps and electrolytic cells has been found entirely effective in the protection of the power-houses and transforming stations. No trouble of a mechanicalnature had beenexperienced withthe operation of theplant in general, andthe transmission-lines,since converted to the suspension.type, had been free from trouble. Two important failures occurred to his mind, but they did not indicate any general structural weakness. One was in the case of practically a hurricane coming up a valley, over which there was an extra long span ; apparently the guard-wirescame loose and short-circuited the lines, so that they all burnt off. In that instance the tops of the towers opened over backwards ; the base sections, which were set incement, as-was the universal practice, stoodfirm. In theother case transmission-lines coming down the side of a mountain became heavily coated with sleet, described as being in places 15 inches in depth, and the top towers gave way under the weight : they had beenreinforced. In connectionwith such transmission-lines little trouble was to be anticipated provided all the fasteningswere kept properly tightened. He had given the constants of the Camarasa dam, but as the relation between loading weights nearthe base and the maximum stresses in the damwas not a linear functionof the height, and as aconsider- able explanationwould be required, he had not includedin theTable values of the maximum stresses. Calculations as to the maximum stressesin dams had been thesubject of widediscussion and

differences of opinion. His own calculations, based on the general The Author. supposition that with a dam of the proportions given, in which the ratio of maximum to minimum pressure as between the two ends of the base did not exceed 1.45, led to the conclusion that there would not be any considerable variation from the trapezian law, and that the maximumstresses in the damwould be in the vicinity of the down-stream toe, and would not be greaterthan thecalculated, since, as the pointof maximum stressreceded from the down-stream toe, the cosine of the angle of application increased. The angle R was determined from the formula given in the Paper and cot U = H G - 1 = -. The maximum stress in the dam was calculated as B the vertical pressure divided by cos2 a. In other words, the vertical pressures multiplied by 1.7would give the corresponding maximum compressions in the dam. Near the base of the dam the maximum compressive stress on thetrapezian lawbasis would not exceed 300 lbs. per square inch, giving a safety factor of approximately eight with sand-cement concrete after the dam was a year old, and a safety factor of approximately eleven with the stronger mixture used in the base. With a curved pressure-line the maximum compressive stress would be less, and the factors of safety greater. In the case of the higher levels he believed the ratio held very approximately at the point for which the weight was taken. At elevation 310 the maximum compressive stress in the dam would be 230 lbs. per square inch, at elevation 330, 160 lbs. per square inch, and at elevation 350, 88 lbs. per square inch. In order that the constantsgiven for the Camarasa dam might not be misunderstood, it would appear that some further explanation of Pig. 8 was required. Figs. 14 showedtwo series of curves,which might be taken as representing the extreme limits of what might occur at thedown-stream half of the base of the dam. One assumed the trapezian law of pressure-distribution and corresponding values were given in the Table referred to ; the other assumed such deviation from the trapezian law as might be expected as a maximum. Themaximum compressivestress would lie between the values C and D shown on the curves. Departure from the trapezian law, however,lessened the maximumpressure inthe base. It was of interest tonote how smalla deviation from the trapezian law produced a very considerable difference in the characteristic of the equal-pressure lines at thebase of the dam. Mr. Stevens was correct on the question of building cost as given in Table VIII. A certain amount of extra work that had to be done had been carried forward in the accounts as transforming-station [THE INST. C.E. VOL. CCXIII.] 2A

The Author. building. To get the total cost of the building the two items had now been added toget,her as Nr. Sterens suggested. He was unable fairly to account for the difference in administrative charges. To begin with, Dr. Pearson had 3r very largc and exprnsivo staff

Figs. 14.

X b&-*'C,,] '"....""r*nr *,Wr uvrsl, p"~.~,,uFI R ., , .. .. ,Wiulh, ., .. 1' rm,lF"i.llln .*,i*lS /,. b.,,. ,,&',,.r,d ,;.a.n ., .. D. E&Y E,,"Y1 ii'*.," ,,,,., ,""..*" ,.,,., ''".8,''"II *?%D.

making surveys, not only in connection with the inst,allations that he constructed, but over a vcry large area, so as to make sure that hisconcessions would include as much of theavailable power as possible. and t,hat the particularproject,s he selected would compete

favourablywith any otherscapable of a supplyto Barcelona, TheAuthor Surveys in connection with both Serbs and Tremp had been very expensive, since there bad been a considerable amount of expropriation,etc. In the case of Camarasa thesurveys had been of very small cost as there had been no necessity for the elaborate arrange- menta deemed necessary in the case of the first two installations. So far as he could see, there was no reason why the power of the RiverShannor could not be transmittedto Dublin, provided of course, the remaining conditions led to proper commercial results. The results given in Fig. 12 showed that, including losses in transformers and lines, t.he efficiency was approximately 92 per cent. for 115-mile transmission, with a line the total cost of which did not exceed f 10 per kilowatt. In reply to Mr. Strange, the section of the Talarn dam bad not been increased because of the leaky nature of the foundation, since that foundation was deemed to he very sound when the work was begun. It would be noted from Fig. 2 that a cut-off wall was employrd in the Talarn dam, as was the case in t,he Tremp dam also. The variation of material in the construction of the base had not caused any unequal settlement. Though the whole of the upper part of the amarasa dam was of uniform density, he would not hesitat,e to employ graded mixtures at different levels if the con ditions showed an economy in costs. The cost oi concessions and water-rights, at Tremp, Camarasa, and Scrhs, had depended almost entirely on local conditions. Scrbs wm situated much fart,her down the river, where agricultural conditions were more flourishing, and where the value of land was greater. At the Tremp reservoir, land was of less value, but, more land had had to be bought in order toget a suitable area for thereservoir. In the case of Camarasa, land was of comparatively small value, and the total arable area occupied was comparatively small. The differences arosepurely from local conditions, ratherthan from any policy influencing the cost of the land. Further information regarding the Serbs canal was given in the following Table (p. 356), which supplied information necessary to determine the frictional and other constants. Thelength of the upper canal was 19kilometres, t,he overall length of the lower canal, including reservoirs, was 5.5 kilometres. With the usual frictionalcoefficients applying to work of this class, it would be seen that the slopes were taken generally on the basis of obtaining velocities of it least doublo the normal velocities when required. The csnaln were lined throughout with cement, 10 centi- metres thick.There were regulating-gates at Lerida, theintake 2A2 Downloaded by [ University College London] on [21/09/16]. Copyright © ICE Publishing, all rights reserved. 356 CORRESPONDENCE ON [Minutes of

The Author. GENERALSECTIONS OF SERbSCANAL.

Earth. Rock.

N) Cubic Metres ,120I Cubic Jletre i0 Cubic Metre: 20 Cubic Metres per Second. 1 per Second. per Second. per Second. Upper Lower Upper Lower Bottom ' W idth metres,Width 6.40 5.70 8.50 8.82 18.3 Variable 13.6 1TOP 3, Variable Depth of water ,, 4.0 5.0 4.0 5.0

Area. .sq. metres 42.8 63.25 41.6 56.6

Perimeter.metres 18.50 22-40 17-32 20.00

Hydraulic radius ,, 2-82 2-31 2.40 2.83 Slope . . . . 0.00015 0.00026 0.00015 0.00026 Normal velocity metres per second) 1-40 2.06 1-44 2.061 Quantity cubic: metres per second; 60.0 120.0 59.8 117.0

of the canal, and also at Utchesa, the junctionof the upper andlower canals. The high level for all the canals and reservoirs, including the forebay at Serbs, was 145, which was the sill-level of the gates at Lerida. In Fig. 6, Plate 2, it would be seen that the crest of the diversion dam at Lerida was 148.30. Thecapacity of 120 cubic metres per second allowed for the lower canal was on the basis of 40,000-kilowattplant at Serbs. Throughout thecanal the banks were taken 1 metrehigher than the high-water level. Thedams alongside the reservoirs were 2 metres higher. Whenconsidering the efficiency of the Tremp power-house, it should be remembered that the general design was worked out to meet the requirements of the other installations down the river, and it was assumed that a certain amount of water would have to go down-stream,independent of theTremp output. The Tremp levels were taken to suit aproposed installation at Barcedana which was farther down the river. Further, Tremp was supposed to work at varying heads, and turbines of a design which permitted of the quick exchange of runners to suit the varying heads were adopted. The principal avoidable waste was in connection with the design of thepenstoch. Thesemight have been larger in diameter,, andarranged so thatthere was not a right-angle turn from a penstock to eachpair of turbines.The figures givenshowed that, evenunder existing conditions, the general results of the

Tremp power-house compared favourably with most power-houses ~he~uthor. of t,hcsame capacityand head. Except for the reason thatthe quantity of water taken from the Talarn dam nould have to meet the general needs of down-stream installations, undoubtedly Dr. Pearson would have made arrangements to securc a higher efficiency, and a more elaborate syst,em of pemtockq and discharge-tubes would probably have been installed. It should aho beborne in mind in connection with Tremp that theflow of t,he Pallaresa during the years Tremp had been in operat,ion has been Sound vastly more uniform than was to bo anticipated from the earlierresults. The earlier records indicatcd that, in ordcr to get t,he maximum ouput from the system as a whole, the average output of Tremp would be less than had been proved to be the casc. The topography at Tremp was such that efficiencies as high as t,hose at Canmrasa could hardly have bcon reachcd, since thepomr-canal at Camarasa hadan extremclysmall frictional loss, and sucha power-tunnel as not possible at Tremp. With the exception of the penstocksit, would beimpossible to designa plant of higher efficiency to nmt the conditions for which Trcmp %-as designed. Withthe Camarasa installation now xorking below Tremp, it was doubtful whether the total result would juntify the changing of the existing pipe-lines to secure a higher efficiency.There was nothing amiss withthe drawings shom on Fig. 7, Plato 2; the draught-tubes widened laterally, otherwise, to getproper outlet area, there u-ould be loss of hoad. Cnder bhe particular conditions dealt aith inSpain the type of infitallationput down wouldbe found more economical in the long run than installations designed with lower-speed turbines. Any gain in efficiency or saving in the wear of runners would be more than offset by the lower cost of the highapeed turbo-electrical installation. He was of the opinion that consumers with power-factors below the average should pay a higher price for energy, and he advised that the volt-ampere should be taken as a basis, and correction be made on the basis of the saving in capital in the distributionsyst,em. It was very difficult in practicc to determine the exact pou.er-factor, but recognition of this principle was being put into effect in deter- mining the selling-price to consumers with abnormally low power- factor.