Fig. 29.—Section of Power-house No. 2 at Niagara Falls.

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The eleven pairs of wheels at the second Niagara power-house have their centre line 128.25 feet below the canal level and a draft tube for each pair of wheels extends to a point below the tail-water level. It is entirely practicable to use more than a single pair of turbines on the same vertical shaft, as is shown at the Hagneck station on the Jura, in Switzerland, where the head of water is about twenty-one feet and four turbines are mounted on each vertical shaft. The combined capacity of these four wheels on each shaft is 1,500 horse-power and its speed is 100 revolutions per minute. At the top of each shaft an 8,000-volt generator, with external, revolving magnet frame, is mounted. The use of four wheels per vertical shaft presents no great difficulty and should be resorted to more frequently in the future.

Fig. 30.—Interior of Power-house, Buchanan, Mich.

For horizontal, direct-connected turbine wheels and generators the nearly uniform practice is to locate the generators in a single row from one end of a station to the other, and this brings the turbines into a parallel row. On this plan the shaft of each connected generator and its group of turbines sets at right angles to the longer sides of a station and approximately parallel with the direction in which water flows to the wheels. The typical water-power station with direct-connected units is thus a rather long, narrow building into which water enters on one side through penstocks and leaves on the other through tail-races. Such stations usually set with one of the longer sides parallel to the river into which the tail-water passes and between this river and the canal or pipe line. At Massena the electric station occupies the position of a dam between the end of the power canal and the Grass River, being about 150 feet wide and 550 feet long. Canal water entering this station passes through its wheels to the river under a head of about 50 feet. A similar construction was followed at Sault Ste. Marie, where the power-station separates the end of the canal from the St. Mary’s River. This station is 100 feet wide, 1,368 feet long, and is to contain 80 sets of horizontal wheels, each set being connected to its own generator, and through these wheels the canal water passes under a head of approximately 20 feet. Ten generators are placed in line at the Cañon Ferry station which is 225 by 50 feet inside, and each generator is driven by a pair of horizontal wheels under a head of 30 feet. This station sets between a short canal and the Missouri River, near one end of the dam. Passing from water-heads of less than 50 to those of several hundred or even more than 1,000 feet, the general type of station building remains about the same, but there is an important change in the arrangement of direct-connected wheels and generators. With these high heads of water, wheels of the impulse type, to which the water is supplied in the form of jets from nozzles, are employed. These jets pass to the wheels in planes at right angles to their shafts, instead of flowing in lines parallel to these shafts like water to pressure turbines. The shafts of impulse wheels and their direct-connected generators are consequently arranged parallel with the longer instead of the shorter sides of their stations. This plan results in long, narrow stations with water entering at one and leaving at the other of the longer sides, just as in the case of direct-connected turbines under moderate heads. Stations with direct-connected impulse wheels are even longer for a given number and capacity of units than are stations with pressure turbines. Colgate power-house, on the North Yuba River, contains seven generators, each direct-connected to an impulse wheel and shafts all parallel to its longer sides. This station is 275 feet long by 40 feet wide, and the water which enters one side by five iron pipes, 30 inches each in diameter, under a head of about 700 feet, is discharged from the other side into the river.

Fig. 31.—Plan of Generating Station near Cedar Lake for City of Seattle, Wash.

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