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OTHER TESTS The test results obtained in Chicago have been amply verified by tests that have been made in Boston and Schenectady upon 5000-kw machines of similar design. One of these machines was tested in the new plant of the Boston Edison Company on January 29, 1907, and gave the following result, which when reduced to similar conditions is as good as those obtained at Chicago. TEST OF 5000-KW Turbine geNERATING UNIT AT BOSTON, JANUARY 29, 1907 Load Gauge Pressure Vacuum Superheat
142° F. 13.52 lbs. per kw-br. This test in Boston was verified by three separate runs with different sets of instruments; some of which were specially calibrated for the purpose. Another of these 5000-kw machines
Fig. 25000-Kw, 5-STAGE Curtis TURBINE, 750 R.P.M. LOAD-WATER RATE
CURVE-175 POUNDS GAUGE PRESSURE, 150 DEGREES SUPERHEAT,
28-INCH VACUUM This curve shows results of a test made in Schenectady on a machine for the New York
Central Railway Company's Yonkers station. The condenser used was too small to carry load higher than the curve extends
was tested in Schenectady, and its results are shown by curve in Figure 2. The condenser used in this test was very small, and it is only possible to run a limited degree of load with a low vacuum. This test indicates an agreement under similar conditions with the results shown by the Boston machine.
The other test curves here shown are obtained from smaller four-stage machines under conditions noted in connection with the curves. These results, while not so striking as those of the large five-stage machines, are very good as compared with other steam units, and are particularly good for such relatively low speeds.
Fig. 3-2250-KW, 4-STAGE CURTIS TURBINE, 900 R.P.M. LOAD-WATER RATE
CURVE-160 POUNDS GAUGE PRESSURE, 150 DEGREES SUPERHEAT, 28-INCH VACUUM
The work division between stages of this machine is arranged with a view to good over
Fig. 4-1000-Kw, 4-STAGE Curtis TURBINE, 1500 R P.M. LOAD-WATEK
RATE CURVE-170 PouNDS GAUGE PRESSURE, 170 DEGREES SUPER
HEAT, 28-INCH VACUUM The machine from which this test was taken is designed for use with both 25-cycle and
60-cycle generators, With the latter it runs at 1890 r.p.m., and its steam economy is considerably better
Turbine and Reciprocating Engine
In order to judge the results accomplished by this recent turbine development, it is interesting to make a comparison with a large reciprocating engine of the type which large turbines are superseding. The following curve, Figure 5, shows the results obtained by test from one of the 5000-kw engines in one of the Interborough Metropolitan Company's plants. These curves were published by Mr. H. G. Stott in a paper presented to the American Institute of Electrical Engineers about a year ago. The turbine load curve shown on the same sheet is derived from tests of 5000-kw machines above mentioned. The difference of steam economy at all loads would be the equivalent of a very iarge fuel saving under similar conditions, and the great superiority at overload shows that such a turbine if installed in
FIG. 5–COMPARISON OF 5000-Kw, 4 CYLINDER COMPOUND ENGINE WITH
5000-Kw, 5-STAGE CURTIS TURBINE OPERATING UNDER THE SAME
CONDITIONS. Bowl PressURE 175 POUNDS SATURATED STEAM The engine curves here given are taken from a paper presented to the American Institute
of Electrical Engineers by Mr. H. G. Stott. The turbine curve is derived from curve No. 2 and from test of machine in Boston, quoted above
the same station would give a very much greater peak capacity. From this comparison it can easily be calculated that the cheapest way to enlarge a reciprocating engine station is to install turbines in place of the engines.
In addition to these advantages in the matter of capacity and fuel consumption, the turbine has many practical merits which need not be enumerated. There is, however, one point, brought up by recent experience, which is interesting in this connection. The large turbines here described operate with very large clearances, and consequently are in no way subject to deterioration by wear or increase of leakage. The economy of reciprocating engines is greatly affected by leakage and by correct adjustment. We recently made a test of three reciprocating engines operating a large plant, each having a rating of about 2000 horse-power. It was found that they all gave a steam consumption of about 34 pounds per kilowatt-hour condensing, while the same engines if in adjustment would consume not more than 20 pounds per kilowatt-hour. The superiority of Curtis turbines in this respect is not confined to a comparison with reciprocating engines, since steam turbines of other types are generally dependent upon adjustment and are so arranged that high economy can exist only with a condition of very small clearance. Small clearance naturally involves care and danger of mechanical difficulty.
The vertical-shaft steam turbine has been rapidly introduced, and machines of this type have been installed in great numbers in all parts of the world. Many different designs have been made to meet different conditions, and, as is natural in such a process, mistakes have been made which in some cases have caused serious inconvenience. I will not attempt to give any complete explanation of these difficulties, but it may be useful to explain that the most serious troubles have arisen from unexpected tendencies to vibration in certain particular designs. The balanced condition of a vertical machine is peculiar, and certain conditions must be conformed to in order that steady running may be obtained Certain machines that have given trouble in this respect have been sent out in considerable numbers, and in many cases it has been impossible to afford immediate relief for the trouble. Generally speaking, however, the vertical type has shown itself to be wonderfully dependable and free from many of the diffculties which endanger the operation of other kinds of machinery.
Our more recent experiences have enabled us to greatly improve all the mechanical conditions governing the action of our turbines. Bearings and steam packings are much improved. The valve mechanisms have been brought to a simple and reliable condition. Means for providing freedom from vibration have been discovered, and all parts have been designed and proportioned in the light of experience.
In connection with steam units that are capable of affording such high degrees of overload economy, it is particularly desirable that generators be used that are capable of operating continuously with very heavy overloads, and efforts are being made to accomplish this result, both in connection with machines already installed, and with new designs that are being produced. On account of the necessary compactness of high-speed electrical apparatus, the losses are concentrated into a very small space, and the dissipation of heat produced presents an interesting problem. If air is used for cooling electrical apparatus, about 90 cubic feet rising 20 degrees centigrade in temperature will carry away the heat equivalent of about one kilowatt. From this it appears that to dissipate the heat from one of the large units above described when operating at 15,000 kilowatts, it will be necessary to circulate 35,000 cubic feet of air a minute, notwithstanding the fact that the efficiency of the generator under that condition is considerably over 97 per cent.
Where such units are installed in stations and allowed to take their ventilating air from the roon, they are liable to get an insufficient supply, or to draw in air which has already been heated by contact with other heated surfaces. It is therefore desirable to make arrangements in such station by which an ample supply of air for ventilating generators is obtained from outside of the building. In many existing plants it would be economical and desirable to install blowing apparatus, in order to provide for increased capacity, and in other cases where apparatus is designed to move large quantities of air, it would be desirable to make connection to sources of cool air, without the necessity of blowers. In every case coolness of the apparatus should be sought as a measure of safety and reserve capacity.
DISCUSSION MR. MASON: I should like to ask what the proportion of cost of auxiliaries would be where a higher vacuum is necessary; that is, there must necessarily be some increased cost for an auxiliary required to be able to produce a better vacuum than 27 inches. I should also like to know what the proportional charge is that goes against the auxiliaries in the steam consumption on these tests.