Electric power transmission; a practical treatise for practical men by Bell Louis 1864-1923

Author:Bell, Louis, 1864-1923
Language: eng
Format: epub
Tags: Electric power production
Publisher: New York, McGraw publishing co.
Published: 1907-03-25T05:00:00+00:00

tion it is desirable to state in the way of warning, that there was obtained at the Holyoke flume some years ago a series of tests of turbines of more than one make, which showed enormously high efficiency, afterward traced to a constant error in the experiments. As the fact of the error was not so generally known as the result of the tests, occasionally reports are heard of phenomenal turbine efficiencies which are given in entire good faith, but based on .errors of experiment. It is only fair to say that the tests now made at the Holyoke flume are worthy of entire confidence.

As regards impulse turbines, data are hard to obtain. Those which are available indicate, however, that with an efficiency probably a little less at full load than that of pressure turbines under moderate heads, the half-load efficiency is generally considerably higher. This is owing to the fact that the buckets of the runner work entirely independently of each other, and the water acts in precisely the same way on each bucket whether it is received from all the nozzles formed by the guide blades, or from a part of them. The impulse turbines are generally regulated by cutting off more or less of the nozzles. The shaping of the surfaces in the runner and guide blades, and the smoothness of the finish, are of more importance in these wheels than in the ordinary pressure turbines. The impulse turbines are, as has already been stated, peculiarly adapted in point of speed and general characteristics for use on moderately high heads, arid in this work they give a better average efficiency and more economical use of water than any of the pressure turbines. For low heads their advantages are far less marked, and the pressure turbines are generally preferred.

The tangential impulse wheels are, at full admission of water, of an efficiency quite equal to that of the best turbines. At partial admission they cannot be expected to give the same results as do the best impulse turbines, inasmuch as they regulate generally by deflecting the nozzle away from the buckets, and hence wasting water. The variation of the stream by a needle valve considerably relieves this difficulty in cases where it can be successfully applied. For very high heads, however, the tangential wheels are preferable to any turbines, as they

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