troduction of hydro-electric power and
hydraulicturbines
Power may be developed from water by three fundamental processes : by action of its weight, of its pressure, or of its velocity, or by a combination of any or all three. In modern practice the Pelton or impulse wheel is the only type which obtains power by a single process the action of one or more high-velocity jets. This type of wheel is usually found in high-head developments. Faraday had shown that when a coil is rotat ed in a magnetic field electricity is generated. Thus, in order to produce electrical ener gy, it is necessary that we should produce mechanical energy, which can be used to rot ate the coil. The mechanical energy is produced by running a prime mover by the ene rgy of fuels or flowing water. This mechanical power is converted into electrical powe r by electric generator which is directly coupled to the shaft of turbine and is thus run by turbine. The electrical power, which is consequently obtaind at the terminals of the generator, is then transited to the area where it is to be used for
doing work.he plant or machinery which is required to produce electricity is collectiv ely known as power plant. The building, in the entire machinery along with other aux iliary units is installed, is known as power house.
Keywords hydraulic turbines hydro-electric power classification of hydel plants head scheme
There has been practically no increase in the efficiency of hydraulic turbines sinc e about 1925, when maximum efficiencies reached 93% or more. As far as maximum efficiency is concerned, the hydraulic turbine has about reached the practicable limit o f development. Nevertheless, in recent years, there has been a rapid and marked increa se in the physical size and horsepower capacity of individual units.
In addition, there has been considerable research into the cause and prevention of cavitation, which allows the advantages of higher specific speeds to be obtained at hig her heads than formerly were considered advisable. The net effect of this progress wit h larger units, higher specific speed, and simplification and improvements in design h as been to retain for the hydraulic turbine the important place which it has
long held at one of the most important prime movers.
1. types of hydraulic turbines
Hydraulic turbines may be grouped in two general classes: the impulse type which utilizes the kinetic energy of a high-velocity jet which acts upon only a small part of t he circumference at any instant, and the reaction type which develops power from the combined action of pressure and velocity of the water that completely fills the runner and water passages. The reaction group is divided into two general types: the Francis, sometimes called the reaction type, and the propeller type. The propeller class is also f urther subdivided into the fixed-blade propeller type, and the adjustable-blade type of which the Kaplan is representative.
1.1 impulse wheels
With the impulse wheel the potential energy of the water in the penstock is transf ormed into kinetic energy in a jet issuing from the orifice of a nozzle. This jet dischar ge freely into the atmosphere inside the wheel housing and strikes against the bowl-sh aped buckets of the runner. At each revolution the bucket enters, passes through, and p asses out of the jet, during which time it receives the full impact force of the jet. This produces a rapid hammer blow upon the bucket. At the same time the bucket is subjec ted to the centrifugal force tending to separate the bucket from its disk. On account of the stresses so produced and also the scouring effects of the water flowing over the w orking surface of the bowl, material of high quality of resistance against hydraulic we ar and fatigue is required. Only for very low heads can cast iron be employed. Bronze and annealed cast steel are normally used.
1.2 propeller runners
nherently suitable for low-head developments, the propeller-type unit has effecte d marked economics within the range of head to which it is adapted. The higher speed of this type of turbine results in a lower-cost generator and somewhat smaller powerh ouse substructure and superstructure. Propeller-type runners for low heads and small outputs are sometimes constructed of cast iron. For heads above 20 ft, they are made of cast steel, a much more reliable material. Large-diameter propellers may hav e individual blades fastened to the hub.
