5 ' 37 . g 
 
 M 2 REMOTE STORAGE 
 
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 ( Subject to Revision.) 
 
 DCCLXVU 
 
 
 NOTES ON RATING ELECTRIC POWER PLANTS UPON 
 THE HEAT-UNIT STANDARD. 
 
 (SECOND PAPER.) 
 
 BY WM. S. ALDRICH, MORGANTOWN, W. VA. 
 
 (Member of the Society.) 
 
 These notes refer to a paper t on this subject read by the 
 author before the Hartford meeting (May, 1897) of this Society. 
 No comparative data were given in the original paper. It was 
 known that the Committee on Data of the National Electric 
 Light Association had a report in preparation for the Niagara 
 Falls convention, June 8, 1897. This was the fourth and 
 probably the last of such valuable reports. It was deemed ex- 
 pedient, rather than refer to the previous reports, to await the 
 publication of the 1897 report for the data needed in discussion 
 of the author’s paper. 
 
 The earlier reports of the above Committee on Data have 
 been full of instructive information relating to many types of 
 steam-power electric plants. In all of the cases finally reported, 
 their rating has been based on watt-hours per pound of coal. 
 Over three years ago Mr. F. M. Eites, at the Montreal meeting 
 of our Society, discussed the data of the Washington conven- 
 tion of the association (1894). His remarks X at that time were 
 
 b * To be presented at tbe New York meeting (December, J897) of the American 
 | Society of Mechanical Engineers, and forming part of Volume XIX. of the 
 | Transactions. 
 
 f Transactions of the American Society of Mechanical Engineers, vol. xviii., 
 | No. 738, “On Rating Electric Power Plants upon the Heat-Unit Standard,” fry 
 William S. Aldrich. 
 
 X Transactions of the American Society of Mechanical Engineers, vol. xv., No. 
 I 509, “ A New Method of Compound Steam Distribution,” by F. M. Rites. 
 
2 RATING ELECTRIC POWER PLANTS I HEAT-UNIT STANDARD. 
 
 so pertinent to tlie whole question of the economy of electric 
 power plants that it will not be amiss to quote them here. 
 
 “ It is impossible that competent engineering ability should 
 be confined exclusively to the manufacturing industries. 
 
 “ It cannot be assumed that the average intelligence of the 
 designers and operators of electric light stations is inferior to 
 that displayed in establishments of different character, and yet 
 the enormous discrepancy between the actual results and those 
 which should be realized surely deserves some attempt at 
 explanation. 
 
 “It is but proper to note that the Committee has chosen the 
 record of a very high duty as a basis of comparison, and that the 
 nature of the exacting service of electric light and street railway 
 plants precludes the possibility of a close approximation to the 
 highest economy under more favorable conditions ; but these 
 figures are entirely unexpected and incidentally somewhat ridic- 
 ulous, considering the energy with which the last per cent, of 
 efficiency of the electric apparatus is insisted on by its users. 
 
 “ Possibly some reason for such a remarkable state of things 
 may be found in the miscellaneous engineering errors which 
 usually follow an ignorantly wasteful policy, but these are as 
 frequently met in other power plants. Perhaps, also, stations 
 improperly proportioned and generally unfitted for economic 
 competition may be found in the list, but these are far from 
 sufficient to account for such universal failure to realize even a 
 moderate degree of efficiency. 
 
 “ There seems'to be but one general explanation applicable to 
 electric light or railway stations which can account with any 
 degree of probability for such extravagant fuel consumption, 
 and that is the excessive wastefulness of the steam-engine under 
 varying conditions of load.” 
 
 Tt is proposed in the present paper (I.) to discuss briefly the 
 progress shown during the past four years in the economic per- 
 formance of steam-power electric plants as summarized by the 
 Committee on Data of the National Electric Light Association ; 
 (II.) to show that the very low economy of such electric-light 
 and railway stations is not entirely due to uneconomical engines 
 and variable loads ; (III.) to present a few notes upon a further 
 consideration of the heat-unit rating for such plants. This 
 treatment will have specially in view the necessity for some 
 standard rating by means of which the design, installation, test- 
 
RATING ELECTRIC POWER PLANTS I HEAT-UNIT STANDARD. 3 
 
 ing, and management, as well as specifications and contracts for 
 these plants, may be reduced to a satisfactory basis for advanc- 
 ing this industry along engineering lines. 
 
 I. — PERFORMANCE OF ELECTRIC POWER PLANTS ON A COAL BASIS. 
 
 From the several reports of the Committee on Data of the 
 National Electric Light Association, Tables I. and II. have been 
 compiled. An inspection of these will show what little progress 
 has been made during the last four years in such installations. 
 In fact, the expectations of the (1894) committee seem not to 
 have been realized in that they looked for much better values 
 in the reports of subsequent years. It is a matter with which 
 the mechanical engineer is most directly concerned. His work 
 in the design and installation of even the most recent central 
 station is open to criticism that cannot be applied to the elec- 
 trical features of the same. Electrical engineers themselves 
 acknowledge that the efficiency of the modern dynamo has prac- 
 tically reached the limit set by structural and economic consid- 
 erations. Mr. Kites’ remarks, quoted above, are singularly ap- 
 plicable to the conditions existing at the present day. In the 
 light of what he has said, the following comparative data should 
 be carefully studied by the mechanical engineer. 
 
 TABLE I. 
 
 Showing Results of Four Years’ Progress in the Economic Per- 
 formance of Steam-power Electric Plants. 
 
 Year. 
 
 Convention of the Nat. 
 Electric Light Assoc., 
 at— 
 
 No. of Stations 
 
 Watt-hours per Pound of Coau. 
 
 Reported. 
 
 Maximum. 
 
 Minimum. 
 
 Average. 
 
 1894. . 
 
 Washington 
 
 65 
 
 208 
 
 25 
 
 91.7 
 
 1895. .1 
 
 Cleveland 
 
 24 
 
 262 
 
 36 
 
 128 
 
 1896. . 
 
 New York 
 
 81 
 
 237 
 
 33 
 
 108 
 
 1897.. 
 
 Buffalo 
 
 14 
 
 269.5 
 
 98.7 
 
 156 
 
 
4 
 
 EATING ELEGTEIC TOWEE PLANTS I HEAT-UNIT STANDAED. 
 
 TABLE II. 
 
 Equipment of the Stations Given in Table I., Showing the Maximum 
 and Minimum Economy. 
 
 Year. 
 
 Economy. 
 
 Boilers. 
 
 Engines. 
 
 Dynamos. 
 
 Daily Out- 
 put, Watt- 
 hours. 
 
 Fuel. 
 
 r 
 
 1894 \ 
 
 l 
 
 Maximum 
 
 
 1 
 
 Arc, Power, and 
 Incandescent. 
 Arc and Incan- 
 
 7,971,600 
 
 80,670 
 
 Coal, Hard 
 
 (208) 
 
 Minimum 
 
 
 ! | 
 
 Screenings. 
 
 Coal. 
 
 (25) 
 
 
 ! 
 
 descent. 
 
 f 
 
 1895 \ 
 
 l 
 
 Maximum 
 
 (262) 
 
 Minimum 
 
 (36) 
 
 Horizontal Water 
 Tube. 
 
 Horizontal Tubu- 
 lar. 
 
 Trip. Exp. Con- D i rect Con- 
 densing. 1 nected. 
 
 High S p e e d Belted Direct. 
 Non-cond’g. I 
 
 22,967,952 
 
 2,790,565 
 
 i Soft Coal, i 
 Hd. Scn en’gs. 
 Bitumin. Pea. 
 
 r 
 
 1896 -j 
 
 l 
 
 Maximum 
 (23 7) 
 
 Minimum 
 
 (33) 
 
 Horizontal Tubu- 
 lar. 
 
 Horizontal Tubu- 
 
 High Speed Belted Direct. 
 Comp. Cond’g 
 
 High S peed Belted Direct. 
 Condensing. 1 
 
 3,270,392 
 
 203,555 
 
 Bitumin. Lump. 
 
 Anthracite 
 
 Buckwheat. 
 
 f 
 
 Maximum 
 
 Water Tube. 
 
 Vertical Couid. Dir. Connected. 
 
 
 
 1837 1 
 
 (2:19.5) 
 
 Minimum 
 
 Horiz. Tubular. . . 
 
 Cond’g 4-Valve 
 Comp. Cond’g. 
 Comp. Cond’g. 
 
 Incandescent. 
 Belted to Dyn., 
 Belted to C.-Sh. 
 
 
 Screenings. 
 
 l 
 
 (98. 7 ) 
 
 and Water Tube. 
 
 
 A comparison of tlie above with some of the best results ob- 
 tained in modern mill engines has been noted by the commit- 
 tee, as follows : 
 
 In the 1894 report compared to the performance of the engine 
 of the Chelsea Jute Mills, Brooklyn, N. Y., showing a coal con- 
 sumption of 1.482 pounds per indicated horse-power per hour ? 
 with the load varying from 495.21 to 764.96 horse-power. If 
 such a performance were possible in the central station, it should 
 result in over 409 watt-hours per pound of coal, on the basis of 
 the committee’s assumption of 90 per cent, for the mechanical 
 efficiency of the engine and for the same efficiency in the dynamo. 
 
 In the 1896 report the committee called attention to the 
 then world’s record for steam economy as shown by the Chest- 
 nut Hill pumping station engine at Boston — a steam con- 
 sumption of 11.22 pounds per horse-power per hour, or an effec- 
 tive pump liorse-power per hour on 1.34 pounds of coal. If the 
 efficiency of the direct-connected electric generators should 
 compare favorably with that of the pumps of this engine, with 
 no allowance for variation in load, anthracite coal used in the 
 plant with the same economy of installation should produce 557 
 watt-hours per pound of coal. 
 
 In the 1897 report of the committee, Mr. F. R. Low, member 
 of our Society, very fully discussed the several sources of loss 
 
EATIN’G ELECTRIC POWER PLANTS : HEAT-UNIT STANDARD. 5 
 
 in tlie electric power plant, stating the discrepancies would be 
 made up mainly from the following items : (1) Decreased boiler 
 efficiency ; (2) lesser normal efficiency of engine ; (3) impaired 
 conditions of engines ; (4) unfavorable engine load ; (5) leak- 
 age ; (6) condensation; (7) auxiliaries; (8) heating. It is not 
 our purpose to discuss this admirable report ; but there is no 
 reason why every feature of installation of an electric power 
 plant should not be as fully considered in design and construc- 
 tion as in the case of the modern high-duty pumping station. 
 In fact, it has been repeatedly pointed out that the chief dif- 
 ferences are those due to the running conditions of electric 
 plants, and not entirely due to sudden and wide variations of 
 load. Messrs. A. G. Pierce and R S. Hale report * of the per- 
 formance of the Boston stations of the Edison companies : “ In 
 our test we have finally found the variation due to causes which 
 we first thought negligible, to be more than the variation due 
 to the change of load.” 
 
 In this connection it is important to notice the results of 
 Mr. H. A. Foster’s analysis of the tests of twenty-two different 
 power plants, f These included manufacturing establishments 3 
 electric-light stations, pumping engines, etc. Plants above 200 
 horse-power show a remarkable uniformity in fixed charges ; 
 namely, interest on first cost, depreciation, taxes, and insurance. 
 The operating expenses gradually decrease in plants from 200 
 to 1,000 horse-power, above which capacity the operating ex- 
 penses seem to remain remarkably uniform and quite irrespec- 
 tive of load variations. The large electric stations supplying 
 many smaller industries are scarcely affected by the instan- 
 taneous load changes in one or more of these particulars. 
 
 The conclusions to be drawn from all of the preceding 
 clearly indie ate that the economy of the modern high-duty 
 pumping-engine plant is due to a refinement of design and 
 economic arrangement of the installation that has not yet been 
 reached in the electric power plant. Anything which tends to 
 advance the latter industry along the lines which have been so 
 clearly marked out in the development of the former, merit the 
 
 * Quoted by Mr. F. R. Low, rcpo*t of Committee on Data, National Electric 
 Light Association, Buffalo meeting, June 8, 1897. 
 
 •f Transactions of the American Institute of Electrical Engineers, vol. xiv., 
 “ V ariations in the Cost of Steam Power,” by Mr. H. A. Foster. Paper pre- 
 sented at the annual convention, July 28, 1897. 
 
6 
 
 EATING ELECTRIC POWER PLANTS : HEAT-UNIT STANDARD. 
 
 attention of those having such work in hand. It is believed 
 that the standard heat-unit specifications aud the subsequent 
 contract trials of pumping plants upon this basis have combined 
 to develop this industry to an unprecedented degree. 
 
 It is not therefore too much to expect that similar standard 
 heat-unit specifications and contract trials of electric power 
 plants will advance this industry also along the same engineer- 
 ing lines. At least the efficiencies, economies, guarantees, and 
 contracts now being realized in pumping stations should be 
 much more nearly approached by the modern electric power 
 plant. 
 
 II. — PLANT ECONOMY AS RELATED TO ENGINE ECONOMY AND VARI- 
 ABLE LOADS. 
 
 This seems to be the chief feature of Mr. Rites’ explanation 
 of the very low economy of the electric power plants reported 
 upon up to the time of his paper previously referred to. We 
 certainly do not wish to be misunderstood as taking issue with 
 this explanation ; but it is apparent, from a careful study of the 
 last four years’ record of the Committee on Data, that some 
 very uneconomical engines have produced remarkable results in 
 point of economy of operation and efficiency of installation. 
 The best of engines may be poorly operated on the one hand, 
 and the whole plant badly arranged on the other hand. 
 
 We enter as strong a plea as any one for the most economical 
 engine in electric power plants ; but we wish to add a further 
 requirement, that there should be economic installation and 
 efficient operation to produce the best all-round results in the 
 course of a day, a month, or a year. We think these two feat- 
 ures may possibly have produced the lowest cost of steam 
 power yet recorded ; namely, $11.55 per year of 3,070 working 
 hours, reported by Dr. R. H. Thurston,* member of our Society. 
 The plant is at the Warren Steam Cotton Mill, Providence, R. I. 
 The 1,950 horse-power “ Allis ” cross-compound condensing 
 engine (cylinders : 32 and 68 inches by 5 feet stroke, 74 revolu- 
 tions per minute), with Heine water-tube boilers, at 155 pounds 
 steam pressure, show an economic performance of 1.35 pounds 
 coal per horse-power per hour. 
 
 The question will continue to be asked : Why are not such 
 
 Reported by Dr. R. H. Thurston, in Science , October 1, 1897. 
 
FATING ELECTRIC POWER PLANTS : HEAT-UNIT STANDARD. 7 
 
 results obtainable in electric power plants with similar units ? 
 Low cost of steam power or of electric power is not due entirely 
 to multiple-expansion engines of the greatest individual econ- 
 omy ; for in the last noted instance, as reported by Dr. Thurs- 
 ton, the cross-compound condensing engine replaced a quadru- 
 ple-expansion engine. 
 
 Concerning the effect of variation of load upon modern elec- 
 tric power plant engines, it is further interesting to note that 
 Messrs. A. G-. Pierce and It. S. Hale state of the Boston Edison 
 stations in the report previously noted : “As a matter of fact, 
 the steam per indicated liorse-power in our two 200 units holds 
 within 12 per cent, over a range from | up to full out-put.” 
 
 Along the same line it is to be noted that throughout quite a 
 wide range of load variation the compound engines reported 
 by Mr. A. K. Mansfield,* at the recent Hartford meeting, show 
 a remarkably uniform rate of steam consumption. The ques- 
 tion naturally arises whether such uniformity under wide varia- 
 tions of load is not more of a characteristic of compound engines 
 than formerly considered by those who lay all the blame upon 
 the steam engine for the poor showing in the economy of elec- 
 tric power stations. 
 
 With dynamos which electrical engineers now design and 
 build, maintaining an efficiency over 93 per cent, from about J 
 load to 20 per cent, over load, directly coupled to cross-com- 
 pound condensing engines (let us say) which mechanical engi- 
 neers are designing and building, having a characteristic low 
 range of steam consumption between similar limits of light load 
 and over load, the question will naturally arise : Why cannot 
 the two units be more economically put together, installed, and 
 operated ? 
 
 III.— NOTES ON HEAT-UNIT RATING. 
 
 In the discussion which followed the presentation of the 
 author’s paper on this subject before the Hartford meeting, as 
 well as in conference with members and other electrical and 
 mechanical engineers since, it will appear that the following 
 points have been brought out : 
 
 That the heat-unit, as a basis for such ratings, is both rational 
 
 * Transactions of tlie American Society of Mechanical Engineers, vol. xviii., 
 No. 727, “The Best Load for the Compound Steam Engine/’ by Mr. A. K. 
 Mansfield. 
 
8 RATING ELECTRIC TOWER PLANTS : HEAT-UNIT STANDARD. 
 
 and scientific. It is, however, not in consequence the most 
 satisfactory standard for use by builders, contractors, and prac- 
 tical engineers dealing with this class of motive-power machin- 
 ery ; namely, steam engines and dynamos. 
 
 That great differences of opinion exist as to the proper defini- 
 tion of the heat-unit required for such a standard. There are at 
 least four different heat-units commonly employed. 
 
 That the present extensive and satisfactory use of the lieat- 
 unit for steam-pumping installations is as it should be and is 
 all right in that place ; but this is no argument for its introduc- 
 tion and use in a similar manner in the rating of steam electric 
 plants. 
 
 That the present way of stating the performance of electric 
 power plants, however unsatisfactory, is easily understood by 
 all parties interested. Chief of these, of course, is the capitalist ; 
 he can readily comprehend rating based on the coal bill. 
 
 That the load factor, after all, has not so much to do with the 
 fuel economy of the plant, as such, however much the varying 
 loads may individually affect any of the units of the installation, 
 such as the steam-engine. Therefore, in the large city and 
 suburban steam-power and electric plants now being installed, 
 there is not the necessity for such strict adherence to eco- 
 nomic load factors as in the case of plants with smaller units. 
 
 That the watt expresses the activity or rate of the electrical 
 output, in joules per second. In this respect it is analogous 
 to the horse-power rating of mechanical output. Hence, the 
 standard rating should be in kilowatt-hours per 1,000,000 B.T.U. 
 supplied to the steam used in the whole plant. 
 
 That if the heat-unit basis is considered as the proper stand- 
 ard for the steam electric plant, the whole heat supplied to the 
 plant should be as carefully determined, and in the same man- 
 ner, as now in vogue for similar standard ratings and contract 
 trials for steam -pumping plants. 
 
 That the boiler should be in evidence in all cases in which 
 plant performance is mentioned. In the electric plant it is 
 economy of installation that is desired quite as much as in 
 the case of pumping plants. Why should the boiler perfor- 
 mance be urged into consideration in the former case and not 
 in the latter ? If it is a good thing to introduce it in either case 
 it would seem proper to do so in both cases. 
 
 That the common rating of performance of pumping plants in 
 
RATING ELECTRIC POWER PLANTS : HEAT-GNIT STANDARD. 
 
 9 
 
 foot-pounds per 1,000 pounds steam would be amply sufficient 
 for all purposes of rating electric plants for which the heat-unit 
 basis is advocated. This seems particularly plausible on ac- 
 count of the small variation in the total heat of one pound of 
 steam for quite a wide range of pressures now used in modern 
 electric plants. Taking the standard temperature of feed water 
 at 212 degrees Fahr. exactly 1,000 B.T.U. are required to raise 
 the temperature and evaporate one pound of feed water into 
 steam at 77.3 pounds per gauge (92 pounds abs.). Taking this 
 as suitable for a simple non-condensing engine, we may compare 
 it with that of 150.3 pounds gauge (165 pounds abs.), in which 
 1 013.5 B.T.U. are required to raise the temperature from 
 feed water (212 degrees Fahr.) and evaporate it into steam at 
 the given pressure.. In this case, therefore, if we adopt 1,000 
 pounds steam instead of the 1,000,000 B.T.U., we make an error 
 of only 1.3 per cent. It is claimed that this is within the usual 
 allowable errors of observation and measurements in power- 
 plant tests, and that there is not enough difference to warrant 
 the trouble required to obtain the performance reduced to a 
 B.T.U. standard. 
 
 In this connection it is interesting to note the progress shown 
 by the committee reports on data made to the National Electric 
 Light Association. In eleven out of the fourteen cases noted 
 in the report presented at the Buffalo meeting of that associa- 
 tion, the water per kilowatt-hour at best efficiency of the en- 
 gine is noted. As t the average temperature of the feed water in 
 the best stations reported is from 208 to 212 degrees Fahr., and 
 the best results are shown by the compound condensing en- 
 gines, we may conclude that the comparative water ratings are 
 within about 1 per cent, of what such comparative ratings would 
 be if based on the B.T.U. standard. 
 
 It is a question whether mechanical engineers will remain 
 satisfied with results even within this close degree of approx- 
 imation. The fact has been repeatedly pointed out by elec- 
 trical engineers that their system of units is altogether unique, 
 is thoroughly scientific (being based upon the C. G. S. system 
 and is the only system of engineering units universally adopted. 
 Mistakes are said to be occasionally avoided in the sister pro- 
 fession of mechanical engineering by the insistence on the ac- 
 curate use of terms and of units in electrical engineering. 
 Dealers in electrical stocks and capitalists exploiting electrical 
 
10 EATING ELECTRIC POWER PLANTS : HEAT-UNIT STANDARD. 
 
 enterprises generally have an appreciative insight into the 
 meaning of volts, amperes, and kilowatts. Why should the 
 time-honored heat-unit be so difficult of comprehension by the 
 same class of interested citizens ? 
 
 A quarter of a century ago Maxwell wrote : “ The conse- 
 quences of this demand for electrical knowledge and of these 
 experimental opportunities for acquiring it have been already 
 very great both in stimulating the energies of the advanced 
 electrician and in diffusing among practical men a degree of 
 accurate knowledge which is likely to conduce to the general 
 scientific progress of the whole engineering profession.”