. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . radius. (c) Coefficient of roughness. (d) The conduit-form, etc. The grade will depend on several conditions. In the first place the char-acter of the ground will place certain limits on the velocity of flow, which GENERAL SURVEY OF WATER-POWER ENGINEERING 11 must not be so great as to injure the conduit-bed. The grade necessary tomaintain the velocity within the desired hmit will also depend on the char-a
. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . radius. (c) Coefficient of roughness. (d) The conduit-form, etc. The grade will depend on several conditions. In the first place the char-acter of the ground will place certain limits on the velocity of flow, which GENERAL SURVEY OF WATER-POWER ENGINEERING 11 must not be so great as to injure the conduit-bed. The grade necessary tomaintain the velocity within the desired hmit will also depend on the char-acter of the interior surface of the conduit, being less for a smoother sur-face. The form and area of cross-section also affects the grade, becausethey affect the velocity of flow—in other words, there will exist a loss inkilowatts due to the grade, and the conduit-form, coefficient of roughness,and mean hydraulic radius are but affected parts due to the grade. Should the character of the ground (conduit-bed) be of such a quahty,for the major part thereof, as to limit the velocity of water, the next near-est grade with the least effect on the kw. loss, should be adopted. In Fig. 6. •40 50 60 Size of Conduit in Square FeetNote:-It will be noted that these curves follow the principal of Kelvins Law shown in Fig. 153 Fig. 6.—Curves for Determining the Most Economical Size of Watei Conduit it is shown that, for a given capacity in cubic feet seconds (any other meas-ure can be employed if desired), with the sale price of energy per kw. yearfixed and the purchase price of materials for building the conduit fixed,the most economical section may readily be found by simply comparingthe difference in energy sales (kw. year loss) with the difference in yearlycosts (fixed charges). This reasoning applies to all kinds of water-conduits,whether closed or open. To illustrate these considerations, reference will be made to a practicalcase, the values of which are taken from actual practi
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