The essentials of a modern hydraulic turbine as illustrated by Fig. $. include: (a) The run ner; (b) the guide vanes, which are usually pivoted, so the openings between them can be opened or shut, thus forming gates; (c) the case, which supports the guides and gates, and has bearings which support the runner.
In Fig. 4 the case includes a spiral channel surrounding the gates and runner, for the pur pose of conducting water to all parts of the cir cumference of the wheel at -uniform velocity. The spiral chute is often omitted from the case, especially where the turbines operate under relatively low heads. In such cases, it is fre quently replaced by a spirally formed compart ment of concrete, forming a wheel pit, in which the turbine is set. The pivoted, or as they are called, •Fincke gates, are an adaptation of a similar contrivance which was used on some of the earlier American stock pattern turbines. The spiral chute is an adaptation of a similar form of case, used on primitive wooden or iron central discharge turbines. The principal de siderata of an hydraulic turbine are: (1) High efficiency; (2) good efficiency when operating at part gate or partial capacity; (3) compactness; (4) high speed; (5) adaptability to speed regu lation. These results are all attained in a re markable degree in the type of turbine illus trated in Fig. 4.
Power developments are generally classified as low medium and high head installations. The type of the turbine and the mode in which it is set in the flume depend largely upon the head, and this governs in a general way the entire layout of the power development.
The essential features of a modern water power development comprise: (1) A dam to impound the Water. The dam may be of logs, sawn timbers, stone or concrete, and sometimes of steel or a combination of one or more of these with earth embankments It is usually provided with a spillway or gates. (2) Head gates to control the water to be diverted, and trash racks, the latter to exclude ice and de bris. (3) A conduit which• may be either an open canal, an open timber or metal flume or head race, or a closed pipe of wood or steel.
A long closed flume is usually connected to a surge tank near its downstream end. (4) A wheel pit (if open) or a penstock (if closed) containing the turbine or turbines. (5) The tur bine itself with its runner, guides, gates and casing. (6) A draft tube to convey the water from the wheel to the tail race. (7) A tail race, which is usually an open channel, to convey the water back to the natural stream. (8) A speed governor.
Power developments may be classified ac cording—to the manner in which a sufficiently concentrated fall or head is obtained, as (1) developments, and (2) de velopments.
Fig. 5 illustrates various modes of setting hydraulic turbines in power plants. Fig. 5-a shows a vertical turbine in an open concrete flume. This mode of setting is most generally used for relatively low head developments. The wheel compartment is often spiral in form. Fig. 5-6 shows horizontal turbines in an open rec tangular flume. In Fig. 5-6 there are two tur bines or runners combined in a single unit. dis charging into a common compartment between them, called the draft chest. The size of a tur the stream instead of wasting its energy in eddies and swirls and friction on the rough stream bed, flows smoothly and slowly through the pond to the dam with very little loss of power by fric tion. In a cascade development, the power plant is located immediately downstream from the dam or natural fall. Where a canal is used to concentrate the fall it is usually made tni bine of a given capacity generally varies some what inversely as the speed of the turbine. By the use of two runners forming a single unit, as in Fig. 5-b, the capacity of the power unit is doubled without decreasing the speed, or in other words, a given power is obtained at a much higher speed than would result from the use of the single turbine runner of equal capacity. Fig. 5-c shows a vertical turbine with a closed spiral concrete penstock. This type is often used for medium heads. Fig. 5-d shows a horizontal tur bine, with a spiral supply chute combined with the turbine case. This type is most commonly used for high head power developments.