. 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 . the outlet. Considerable care was taken in laying the concrete to keepthe walls of the intake chamber and the draft tube as smooth as possible. Thesingle draft tube saves the excessive losses usually found in double-runnerunits with the draft tubes discharging toward each other. Moreover,there is no sudden enlargement of the draft tube at the discharge of therunner such as is frequently found and causes se
. 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 . the outlet. Considerable care was taken in laying the concrete to keepthe walls of the intake chamber and the draft tube as smooth as possible. Thesingle draft tube saves the excessive losses usually found in double-runnerunits with the draft tubes discharging toward each other. Moreover,there is no sudden enlargement of the draft tube at the discharge of therunner such as is frequently found and causes serious losses. Accordingto Camerers formulae for obtaining the increased efficiency of a large run- 58 HYDROELECTRIC PRACTICE ner over a small one of the same type, the efficiency of the main turbineshould be about per cent, more than that for a model runner. However,this does not take into account the smaller proportionate mechanical lossesin the large unit in place (the efficiency of the large wheel in place is from3 per cent, to 4 per cent, higher than that given by a model runner) as com-pared with the mechanical losses in a model runner at the works of manu- 85,000 Volt Liaea. Fig. 33.—Joint Transformer House for No. 2 and No. 4 Stations of Appalachian Power Company on New River facturer, amounting to about per cent., nor does it consider the betterdraft tube conditions in place. During the tests the flow over a special weir was calculated by Bazinsformula, as this was considered to suit the conditions better and becauseBazins experiments have been conducted with so much greater care thanexperiments on which other weir formulae are based. It also gave moreobservation results. As compared with the Cornell experiments, Bazinsformula gives a discharge about per cent, greater, and as compared with LOW, MEDIUM AND HIGH HEAD DEVELOPMENTS 59 the Frese formula from 1 per cent, greater for the higher heads observeddown to about per cent, for the lower heads obser
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