Turbines at Niagara Falls. A number of turbines installed at Niagara Falls, N. Y., are here briefly described; they are about 5,000 horse-power each; a canal leads water from the river to the wheel pit. The water is carried down the pit through steel penstocks to the turbines, which are placed 136 feet below the water level in the canal. After passing through the wheels the waste water is conveyed to the river below by a tunnel 7,000 feet long. The “plan” Fig. 126 shows a cross-section of the wheel pit, with an end view of a penstock, wheel case and shaft. Fig. 126 exhibits part of a vertical section of the wheel pit and a side view of this penstock, with the enclosing case and shaft of the turbine.
Top View or Plan of Fig. 126.
This turbine has a rock-surface wheel pit, but this surface is protected by a brick lining having a thickness of about 15 inches. The width of the wheel pit is 20 feet at the top and 16 feet at the bottom, and the cylindrical penstock is 71⁄2 feet in diameter. The shaft of the turbine is a steel tube 38 inches in diameter, built in three sections, and connected by short solid steel shafts 11 inches in diameter, which revolve in bearings. On the top of each shaft is a dynamo for generating the electric power.
In Fig. 126 is shown a vertical section of the lower part of the penstock, shaft, and twin wheels. The water fills the casing around the shaft, passes both upward and downward to the guide passages, through which it enters the two wheels, causes them to revolve, and then drops down to the tail race at the entrance to the tunnel, which carries it away to the river. The gate for regulating the supply is seen upon the outside of these wheels, both at the top and bottom, [Fig. 126].
[Fig. 128] gives a larger vertical section of the lower wheel with the guides, shaft, and connecting members. The guide passages, and the wheel passages, are triple as shown so that the latter may be filled not only at full gate, but also when it is one-third or two-thirds open, thus avoiding the loss of energy due to sudden enlargement of the flowing stream. The two horizontal partitions in the wheel are also advantageous in strengthening it. The inner radius of the wheel is 311⁄2 inches and the outer radius is 371⁄2 inches, while the depth is about 12 inches. In this figure the gate is represented closed and to open, it moves downward uncovering the guide passages as shown in Fig. 126, the position it occupies loaded.
In [Fig. 127] is shown a half-plan of one of the wheels, in a part of which are seen the guides and vanes, there being 36 of the former and 32 of the latter. Although the water on leaving the wheel is discharged into the air, the very small annular space between the guides and vanes, together with the decreasing area between the vanes from the entrance to the exit orifices, ensures that the wheels move like reaction turbines for the three positions of the gates correspond to the three horizontal stages or openings through the guides as shown in [Fig. 128], i.e., three stages of gate.
Note.—A test of one of these wheels, made in 1895, developed 5,498 electrical horse-power, generated by an expenditure of 447·2 cubic feet of water per second under a head of 135·1 feet. The efficiency of the dynamo being 97 per cent., the efficiency of the wheel and approaches was 821⁄2 per cent.