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 ( Subject to Revision.) 
 
 DCCXXXIII.* 
 
 ON RATING ELECTRIC-POWER PLANTS UPON 
 HEAT-UNIT STANDARD. 
 
 THE 
 
 BY WM. S. ALDRICH, MORGANTOWN, W. VA. 
 
 (Member of the Society.) 
 
 The progress of power-plant engineering has reached such a 
 stage of development that electric-power plants should be con 
 tracted for on a somewhat similar basis of guaranteed perform- 
 ance as that now in vogue for pumping plants. There should 
 be guaranteed a definite output, in the case of the electric plant, 
 to be measured at the switchboard and expressed in kilowa^s, 
 per 1,000,000 B. T. U., supplied to the steam used in the whole 
 plant. 
 
 Following are some of the advantages of having such a stand- 
 ard for this purpose founded upon the heat -unit basis : 
 
 (1) It is a simple basis , involving quantities easily measured. 
 
 (B. T. U. Input.) The computation is based upon the quan- 
 tity of heat required to raise all of the feed water from its tem- 
 perature to that of the steam at the boiler pressure, with such 
 additional determinations and allowances as are now regularly 
 made in obtaining the similar quantity of heat supplied in the 
 duty trials of pumping engines. 
 
 (Kilowatts Output.) The work is obtained from corrected 
 voltmeter and ammeter readings, at the switchboard, for a defi- 
 nite interval of time at a given specified load, which is main- 
 tained uniform throughout. 
 
 „ * To 1)e Panted at tl.e Hartford meeting (May, 1897) of the American 
 Society of Mechanical Engineers, and forming part of Volume XVIII. of the 
 Transactions. 
 
 V 
 
 X\ 
 
 ^18 
 
 
 \y^' 
 
2 
 
 ON RATING ELECTRIC-POWER PLANTS. 
 
 (2) It applies to all plants operated by any hind of heat engine. 1 
 
 The present way of stating such performance is : (a) kilowatts 
 per pound of coal ; (b) kilowatts per cubic foot of gas ; (o') kilo- 
 watts per gallon of oil— according to the kind of heat engine 
 furnishing the motive power for the plant. The proposed stand- 
 ard is superior to such ratings as the latter, and furnishes a 
 common, practical and scientific one for all of them. They 
 involve the efficiency of the boiler, or of the gas producer, and 
 this last requires the determination of the thermal value of the 
 fuel. It is not alone the difficulty of such determinations but 
 the unsatisfactory nature of the fuel basis which has led to its 
 disuse in pumping plants. 
 
 (3) It forms the most satisfactory basis for comparison of plants. 
 
 Efforts are being continually made to obtain such ratings for 
 existing electric-power plants as will enable the probable per- 
 formance of similar projects to be predetermined when installed 
 and operated in like manner. Sufficient and reliable data may 
 be obtained at various proportional parts of the full load of the 
 plant as will enable one to determine what may be called the 
 characteristics of the particular type of electric-power plant 
 under consideration. The inherent advantages of each type of 
 plant will then appear in its characteristic curves, showing the 
 variations in its efficiency and economy at various proportional 
 parts of its full load or rated normal capacity. Then it will 
 be possible to compare, at different loads, system with system 
 and plant with plant. Such determinations and comparisons 
 will be all the more valuable if based upon commonly-accepted 
 standards and ratings, such as the heat unit proposed. 
 
 (4) It will facilitate the predeterminaticn of the performance of 
 
 electric-power plants. 
 
 The engineering precedent which will be established by such 
 a standard will promote the predetermination of the efficient 
 and economic performance of electric plants quite as much as 
 similar ratings have accomplished for pumping plants. While 
 both units are rarely built by the same concern, as in the case 
 of the latter, still this should not debar the installing engineer 
 from advocating the use of such guarantees based on the heat- 
 unit basis if his work is to hold its own in the light of the 
 
ON RATING ELECTRIC-TOWER I LA NTS. 
 
 8 
 
 o'uarantees and contracts made in other branches of engineer- 
 ing and notably so in the installation of pumping machinery. 
 
 (5) It will promote the most economical arrangement of plants. 
 
 The power plant is an aggregation of units and of an ever- 
 increasing complexity. It is therefore quite as essential to have 
 the whole system economically arranged as to have the most 
 economical units. It is this economy of arrangement or of 
 installation, so to speak, which, in a measure, the duty of a 
 pumping plant so clearly expresses when based upon the heat- 
 unit standard. It is such a method of stating the final outcome 
 of the arrangement of all of the details of a power plant of 
 which designers, builders, managers, and owners wish to know 
 the value. 
 
 (6) Heat-unit specifications will form proper basis of agreements. 
 
 Builders of both engines and dynamos are equally interested 
 in the adoption of some such common standard. Unfortunately, 
 however, in many cases, this interest extends only so far as the 
 economic performance is concerned of the individual machines 
 which they manufacture. 
 
 (7) Contract trials of electric plants should be based on heat units. 
 
 Contract trials of the completed plant are necessary to estab- 
 lish the guarantees of satisfactory fulfilment of contract as to 
 both efficiency of installation and economy of operation. The 
 present method of basing the performance of such upon the 
 final plant efficiency is misleading. In electric installations, 
 particularly, there is a set ot conditions insuring a maximum 
 value for such an efficiency, usually at some fractional load. 
 There is also in such plants another set of conditions, at some 
 other load, insuring maximum economy of operation of the 
 engine. Only contract trials for definite periods of time, at 
 specified and uniform loads (at various proportional parts of the 
 full load), will enable all claims to be adjusted regarding guar- 
 anteed efficiency or economy, when such is based upon the quan- 
 tity of heat supplied to the system in thermal units. 
 
 (8) It will advance this industry along engineering lines. 
 
 The business of power-plant design, construction, installation, 
 and management is not altogether in a formative period. Nev- 
 
4 
 
 ON RATING ELECTEIC-POWER PLANTS. 
 
 ertheless, when an electric-power plant can be contracted for on 
 the basis of so many kilowatts output per 1,000,000 B. T. U. in 
 the steam supplied to the plant, and that at a certain specified 
 load, or proportional part of the full load, then we may expect 
 somewhat the efficiencies, economies, guarantees and contracts 
 now being regularly realized in some of the other lines of power 
 generation. 
 
 The subject is developed in this paper as follows : 
 
 (1) The Heat-Unit as a Basis for Rating S 'earn Power Plants. 
 
 (2) The Heat-Unit Required for such a Standard. 
 
 (3) Present Use of the Heat-Unit in Steam-Pumping Plants. 
 
 (4) Present Way of Stating Performance of Electric Plants. 
 
 (5) The Load Factor in Power-Plant Ratings. 
 
 (6) Proposed Use of Heat-Units in Electric Plants. 
 
 (7j Determination of the Heat Supplied to the Steam. 
 
 (8) Performance of the Boiler not in Evidence. 
 
 (9) Determination of Work Done by Electric Generators. 
 
 (1) THE HEAT-UNIT AS A BASIS FOR RATING STEAM-POWER 
 
 PLANTS. 
 
 It is not the purpose of this paper to review the line of argu- 
 ment for such a use of the heat unit as a standard basis for 
 rating and comparing the performance of steam-power plants in 
 general. Nor is it proposed to advocate anew the great value 
 of heat-unit specifications as the proper basis of agreement 
 between contractor and builder, on the one hand, and the sub- 
 sequent contract trials on this basis as the most satisfactory 
 means of adjusting all claims in power-plant installations, on 
 the other hand. 
 
 The heat unit is the most scientific basis for the engineer to 
 use in stating the final performance of any power plant driven 
 by a heat-engine. It is, in consequence, the most satisfactory 
 standard upon which to base an agreement between the con- 
 tracting parties for the installation. 
 
 The merits of the heat-unit standard in these particulars * 
 cannot be longer open to discussion. It has been so completely 
 defined for pumping plants, for instance, and is in such constant 
 and satisfactory use in this branch as to prove its engineering <?• 
 value. 
 
 Heat unit ratings are also coming into more general use as the 
 most suitable standard upon which to base the performance of 
 
ON EATING ELECTRIC-POWER PLANTS. 
 
 5 
 
 prime movers in power plants deriving their energy from fuel, 
 whether by steam-engines or other heat-engines. The value of 
 such a standard has been ably advanced by Prof. C. H. Pea- 
 body in a paper* before this Society, from which we quote as 
 follows : 
 
 “ It is customary to state the performance of a steam engine 
 in pounds of steam used per horse-power per hour, a method 
 which is open to objection, since the value of a pound of steam 
 depends on the pressure and quality of the steam. It has fre- 
 quently been urged upon the attention of engineers that the 
 British thermal unit (B. T. U.) should be used in stating the 
 performance of engines. ... In order to obtain convenient 
 numerical quantities it is advisable to state engine performance 
 in British thermal units per horse-power per minute. Incident- 
 ally, this method has the advantage that it may be used for any 
 heat engine, such as a hot-air engine or a gas engine.” 
 
 (2) THE HEAT UNIT REQUIRED FOR SUCH A STANDARD. 
 
 The acknowledged scientific standard of temperature, of 
 0 degree Cent., is evidently impracticable for a heat unit stand- 
 ard. Prof. H. A. Howland has shown that such a temperature 
 is out of the question, because the mechanical equivalent of 
 heat is not definitely determined and probably cannot be at this 
 critical point. Nevertheless, such is the basis of the scientific 
 heat-unit, the calorie — the quantity of heat required to raise the 
 temperature of one kilogram of pure water one degree from 
 0 degree Cent. 
 
 The temperature of 39.1 degrees Fahr., at which water attains 
 its maximum density, is equally undesirable, notwithstanding 
 that it is the old British standard temperature of the days of 
 Rankine. The determination of the mechanical equivalent of 
 heat at this critical temperature offers similar difficulties to those 
 of the freezing point. At neither of these points can the specific 
 heat of water be satisfactorily determined. 
 
 “ There is practical convenience in choosing 62 degrees Fahr. 
 for the standard, because it is near the mean temperature of the 
 air during experimental work,” as Prof. C. H. Peabody lias 
 pointed out. Besides, the specific heat of water may be defi- 
 
 * Transactions of the Armrican Society of Mechanical Engineers, Vol. XIII., 
 No. 484, on the “Economy and Efficiency of the Steam Engine,’' by C. H. 
 Peabody. 
 
6 
 
 ON EATING ELECTRIC-POWER PLANTS. 
 
 nitely known at this temperature ; therefore “ it is more scien- 
 tific to take an easily verified quantity for the standard.” 
 
 The British thermal unit now used, or the mechanical equiv- 
 alent of the heat required to raise the temperature of one 
 pound of water one degree from 62 degrees to 63 degrees Fahr , 
 is that of Professor Rowland’s determination, of 778 foot-pounds. 
 This temperature is also that of the new British standard of 
 weights and measures, and more clearly approaches the 15 
 degrees Cent, of the French standard — a temperature frequently 
 used and readily maintained in electrical and other testing 
 
 O 
 
 work. 
 
 The only objection to the British thermal unit used in connec- 
 tion with the watt is that this heat-unit is not, like the watt, one 
 of the units based on the scientific standards of the C. G. S. 
 system. Of course, such a heat-unit is to be found in the 
 calorie. But its mechanical equivalent requires that the most 
 accurate scientific measurements be made at the critical tem- 
 peratures for water, which have been found to be quite impos- 
 sible of determination. 
 
 (3) PRESENT USE OF THE HEAT-UNIT IN STEAM PUMPING PLANTS. 
 
 The use of the lieat-unit in this connection was first sug- 
 gested* by Dr. Chas. E. Emery, member of this Society. He 
 proposed that the duty of pumping engines should be based 
 upon the foot-pounds of work done by the steam-pump on an 
 expenditure of 1,000,000 B. T. U. in the steam supplied to the 
 plant. 
 
 The adoption of this standard was the logical outcome of the 
 old one, by which the “ duty ” was rated in foot-pounds per hun- 
 dred pounds of coal burned under the boiler. The ordinary 
 specification of an evaporation of 10 pounds of water, from and 
 at 212 degrees Fahr., under atmospheric pressure, would result 
 in 965,700 B. T. U. supplied to the whole plant per hundred 
 pounds coal burned under the boiler. Another advance was 
 made when it was proposed to state this “ duty ” on the basis of 
 the 1,000 pounds of feed water supplied to the system, rating 
 the heat units per pound of water evaporated as before, from 
 and at 212 degrees Fahr. But it was clear that the efficiency of 
 the boiler should have nothing to do with the “ duty ” of the 
 
 * United States Centennial Commission, International Exhibition, Group XX. ; 
 Vol. VI., pages 21 and 115 of the Report of the Judges. 
 
ON EATING ELECTRIC-POWER PLANTS. 
 
 pumping engine. It was therefore hut a slight step, and one in 
 the right direction, to change the standard to that of 1,000,000 
 B. T. U. in the steam supplied to the plant. 
 
 Such use of the heat-unit was further considered before this 
 Society in the “Report of Committee on a Standard Method 
 of Conducting Duty Trials of Pumping Engines.” * The adop- 
 tion of this method has since resulted in most remarkable 
 developments in this branch of industry. Unprecedented econ- 
 omies of pumping engines have been brought about. Installa- 
 tions and contract trials upon such a basis have furnished 
 valuable engineering precedent. The “duty” of pumping en- 
 gines can be so closely approximated that binding contracts are 
 willingly entered into by the builders. Bids are advertised for 
 with the understanding that “ No bids will be considered offer- 
 ing less duty than 130,000,000 foot-pounds.” 
 
 The question was opened afresh and the cause further pro- 
 moted by Mr. A. F. Hall in a recent paper f before the Society, 
 in which he writes thus : 
 
 “But why use variable quantities as coal and steam for units 
 when the heat-unit is just as simple to obtain and use, and one 
 which requires but little study to understand ? ... It has in 
 it the elements of simplicity, and places all engines upon an equal 
 footing for comparison, which no other proposed method does.” 
 
 (4) PEESENT WAY OF STATING THE PERFORMANCE OF ELECTEIC- 
 
 POWEE PLANTS. 
 
 It has been previously noted, in the abstract of advantages of 
 the heat-unit basis over the present ratings, that the latter are : 
 (a) kilowatts per pound of coal ; (b) kilowatts per cubic feet of 
 gas ; (c) kilowatts per gallon of oil. This is merely to inaugu- 
 rate a method of stating such performance for electric plants 
 as that which has been tried and found wanting for pumping 
 plants. Neither do builders of engines and dynamos care to 
 be held responsible for the performance of the heat-generating 
 plant, whether it be a steam boiler or a gas producer. 
 
 The watt, the kilowatt, or the watt-hour basis is perfectly 
 
 * 1 ransactions of the American Society of Mechanical Engineers, Vol. XI., No. 
 331 — “ Report of Committee on a Standard Method of Conducting Duty Trials 
 of Primping Engines.” 
 
 f Transactions of the American Society of Mechanical Engineers, Vol. XV., 
 No. 584 — “ Heat-Units and Specifications for Pumping Engines,” by A. F. Hall. 
 
8 
 
 ON EATING ELECTRIC- POWER' PLANTS. 
 
 intelligible. The fuel record is on the most unsatisfactory and 
 unreliable basis that could have been selected for such ratings. 
 The kind of coal or other fuel is rarely stated. It is always a 
 variable quantity. Even if noted, it enables one to form only a 
 vague notion of what the economic rating should be with any 
 other kind of fuel. Such records and ratings are not of perma- 
 nent value. They are not given on a rational and scientific 
 basis in conformity with the standards in electrical and other 
 engineering work. It is proposed to substitute- the lieat-unit as 
 the standard, about which there can be no dispute, unless it be 
 as to the kind of lieat-unit' which should be chosen. This objec- 
 tion has been considered in a preceding section with regard to 
 the merits of the British thermal unit and the calorie of the 
 French standard. 
 
 (5) THE LOAD FACTOR IN POWER-PLANT RATINGS. 
 
 When the output of the plant is referred to, it is usually in 
 terms of its load factor. Thus, for any one day’s record of the 
 performance of a good electric plant it would be at present ex- 
 pressed as, say, 200 watt-hours per pound of coal, with load 
 factor of 40. From the very definition of this term “ load 
 factor ” and the limitations placed upon it, it is apparent that 
 the same factor may be obtained in quite a number of different 
 ways. It is needless to point out that there will be a different 
 coal bill for each and every set of conditions giving one and the 
 same load factor. 
 
 This load factor expresses the rate of working. Professor 
 Unwin* states the case very clearly thus : “ There may be vari- 
 ous load factors according to the precise fluctuation considered. 
 But for the object at present in view, the consideration of the 
 influence of variation of load on the efficiency of steam plant, 
 the load factor may be taken to be the ratio of the area of a 
 day’s load curve to the area of a rectangle enclosing it. It is 
 equally the ratio of the average load during the day to the 
 maximum load at any time during the day.” 
 
 Such a load factor, therefore, takes no consideration of the 
 performance under a steady load, but mainly represents the 
 result of the general average of all of the various fluctuations 
 during any given time interval, as one day. For the purpose of 
 
 * “ On the Development and Transmission of Power fiom Central Stations,” 
 hy W. C. Unwin, London, 1894. 
 
ON EATING ELECTRIC-POWER PLANTS. 
 
 9 
 
 fchis paper it cannot be considered as being at all equivalent to 
 wliat is herein termed “ the proportional part of the full load,” 
 under which condition all parts of the system may be consid- 
 ered as running under a constant load. It is the performance 
 under the latter uniform conditions which forms. the basis for 
 comparison of ratings by the British thermal unit standard. 
 
 (6) PROPOSED USE OF HEAT-UNITS IN ELECTRIC PLANTS. 
 
 It is proposed to state the performance of steam-power elec- 
 tric plants in kilowatts per 1,000,000 B. T. U. supplied to the 
 steam used in the complete plant. 
 
 It is apparent that the same line of arguments, pro and cow, 
 is quits likely to arise as in the case of similar ratings for 
 pumping plants. However, such a basis is equally adapted to 
 meet the growing requirements for some standard in these latter 
 types of steam-power plants. 
 
 In this case, moreover, it is possible to start upon a right 
 basis from the beginning. The practice of rating the perform- 
 ance upon the watt-hours per pound of coal has not become so 
 rooted that it cannot be changed to that now proposed. The 
 necessity for such a standard in this case is none the less real, 
 nor is its final adoption less probable on account of the radi- 
 cally different conditions under which these two types of power 
 plants are regularly operated ; namely, uniform loads in pump- 
 ing plants and extreme and often rapidly-varying loads in the 
 electric plants. 
 
 As long as electricity continues to be generated by machinery 
 driven by heat-engines, as well as when it comes to be generated 
 from coal direct, it is believed that there is no better standard 
 than that already adopted in steam engineering. The unit of 
 measure for the total heat put into the system — namely, the 
 British thermal unit —is that upon which the output in kilowatts 
 may be most satisfactorily based. 
 
 (7) DETERMINATION OF THE HEAT SUPPLIED TO THE STEAM. 
 
 The method of procedure, by which the quantity of heat sup- 
 plied to the system is determined from the feed-water measure- 
 ments, has been ably set forth in the report * of the Committee 
 
 * Transactions of the American Society of Mechanical Engineers, Vol. XL, 
 No. 381 — “ Report of Committee on a Standard Method of Conducting Duty Trials 
 of Pumping Engines.” 
 
10 
 
 ON RATING ELECT niC-POWER PLANTS. 
 
 on Duty Trials of Pumping Engines. It is equally applicable to 
 the case of the electric plant, and is as follows : 
 
 “ Starting with a heat-unit basis of computing duty, it is pro- 
 posed to make the computation from the quantity of heat sup- 
 plied to the complete plant ; using not only that supplied to the 
 engine cylinders, but that supplied to all the necessary parts of 
 the engine, such as the steam-jackets, the donkey feed-pump, the 
 independent air-pump, if this be driven with steam, and any 
 other apparatus using steam which is necessary to the opera- 
 tion of the engine. 
 
 “In contract tests, if a steam-pump be used for the boiler 
 feed-pump, the quantity of heat supplied for operating this ap- 
 paratus is to be included in the total quantity, not only in cases 
 where both boiler and engine are supplied by one party, but 
 also where the boiler is furnished by a separate contractor. In 
 this connection it should be added that if the engine contractor 
 does not furnish the boiler feed-pump, he should be permitted 
 to specify, if he desires, the kind of feeding apparatus which 
 shall be used during the test. 
 
 “ The heat-unit method requires that the actual total heat of 
 the steam shall be known, and for this purpose allowance will 
 necessarily be made for any moisture or superheat contained by 
 the steam furnished to the engine.” 
 
 The method is further thus specified in Mr. A. F. Hall’s 
 paper, previously referred to : 
 
 “ Each pound of water fed to the boiler is to be debited with 
 the heat required to raise all of the water from the temperature 
 it has at its entrance to the boiler to that corresponding to the 
 boiler pressure, and the amount of heat required to convert 97 
 per cent, of the water into steam of boiler pressure from the 
 temperature corresponding to this pressure.” 
 
 This is allowing for 3 per cent, moisture. The amount of 
 moisture in any case would be determined by calorimetric 
 measurements of the quality of the steam supplied by the boiler 
 to the engine, and similarly allowed for. 
 
 (8) PERFORMANCE OF THE BOILER NOT IN EVIDENCE. 
 
 This is ’the case for similar reasons to those which have ruled 
 out the boiler p erformance in determining the duty of pumping 
 plants. The steam-generating plant and the steam motive- 
 
ON EATING ELECTBIC-PwWER PLANTS. 
 
 11 
 
 power installation form two elements wholly distinct from each 
 other. They may be, in some cases are, quite independent of 
 each other. 
 
 The thermal value of the fuel used must be brought into the 
 case if the performance of the plant is to be based upon the 
 heat supplied to the boiler furnace. Such a coal basis is too 
 uncertain, and is the least desirable one at present from which 
 to determine the heat supplied. 
 
 The boiler plant is the only portion of the installation in 
 which the imman element has a hand in the economic per- 
 formance. 
 
 It is most desirable to eliminate this as far as possible. 
 Upon the skill of the fireman, or upon what may be called his 
 personal equation, very much of the economy and efficiency of 
 the boiler will depend. If mechanical stokers are used, even 
 then the skill of the attendant is quite an important item. 
 
 However, at this stage of development, builders of engines 
 and dynamos do not care to be responsible for the performance 
 of the boiler plant, which is often furnished and installed by 
 entirely different parties. They wish to know the *• duty,” as 
 in the case of pumping engines, regardless of the boilers, or 
 irrespective of how the steam is supplied, provided it is com- 
 mercially dry. 
 
 ( 9 ) DETERMINATION OF THE WORK DONE BY THE ELECTRIC 
 GENERATORS. 
 
 This reduces simply to voltmeter and ammeter readings at 
 the switchboard. These are to be further corrected for any 
 instrumental errors. The load during trial should be main- 
 tained as nearly constant as practicable. Latest forms of re- 
 cording instruments make it quite possible to obtain accurate 
 records throughout any specified period. The extreme simplic- 
 ity and the high degree of accuracy attainable, in the case of 
 the electric plant, should be strong points in favor of adopting 
 such a standard rating as here proposed. 
 
 Direct-connected units in electric plants make this method 
 as feasible and as practicable as in direct-acting pumping 
 engines. It is of course possible, but quite improbable, that 
 steam-power electric plants of any magnitude will be belt- 
 driven in the future. The standard performance of such instal- 
 
12 
 
 ON HATING ELECTBIC-POWER PLANTS. 
 
 lath n involves taking into account the small percentage of loss 
 aue to the slipping of the belt or rope drive. This must be 
 stipulated in the specifications and allowed for in like manner 
 ro the percentage of slip in steam-pumping engine trials. The 
 cases are not exactly analogous, but they may be similarly con- 
 sidered in the specifications and determined in the contract 
 trial.