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Principle and Selection of a Hydro-Electric Power Plant

  •  Hydro energy hydro energy is the energy generated by the force of water. This is a powerful way of generating electricity the hydro energy is converted into electric energy by hydro electric power plant and this energy is called as hydro electricity. History of hydro electric power plants world's first hydroelectric power plant was built across the Fox River in Appleton Wisconsin in u.s. in the year 1882. India's first hydroelectric power plant

    hydroelectric power plant requires a water reservoir so these plants are constructed near big dams water stored in dams has potential  energy the water under pressure is carried by penstock and supply to the turbine through the inlet valve penstock is a pipe made up of steel or concrete a surge tank reduces the excessive water force on the penstock here trash rack prevents the debris from getting entry into the powerhouse due to the force of water the turbine starts rotating due to which mechanical energy is produced. The turbine is connected to the generator therefore the generator produces the electricity the voltage of this electricity is raised by using a transformer and is transferred by the distribution lines.

    In a hydraulic power plant, several structures such as dam, conduits, intakes, surge tank and power house are involved. To select a site several alternative layouts are to be studied and the most economical one is adopted. The scope for the site investigation depends partly on the availability of existing published data, partly on the nature and size of the proposed plants and partly on the difficulties preset by the existing topographical and geological features, which in turn affects the number of alternatives that have to be studied. Site investigations are carried out is two main stages.

    1. 1. Preliminary investigation –to provide sufficient information to find out the practicability of the proposed scheme and to choose between alternatives.
    2. 2. Final investigation –detailed exploration of recommended site to establish the suitability and to enable the final design.

    Investigations include the following:

    1. Hydrological
    2. Topographical
    3. Geological

    (i) Hydrological investigations

    (a) Water availability

    Run-off data at the proposed site must be available beforehand. If not available calculation are based on the rainfall data.

    (b) Water storage

    Necessity to store the water for continuous power generation as there is a wide variation in rainfall during the year. Storage capacity and minimum quantity of water available are calculated with the help of mass curve. Two types of storage in use are as follows:

    1. Storage for one year only with no carryover for the next season full at the beginning empty at the end of the year.
    2. (2) Enough storage sufficient even during worst dry periods.

    (c) Water head

    It depends on topography. Increase in head reduces water to be stored and therefore the capital cost.

    (d) Ground water data

    Stability of ground slopes, amount and type of grounding required to prevent leakage.

    (ii) Topographical Investigation

    Topographical features of the whole catchment area should be mapped either by ground surveying or aerial surveying methods (for larger area and difficult terrain).

    (iii) Geological Investigation

    To provide most accurate picture of the ground character of the site. Selection depends in the following factors:

    1. Light basin of ample size
    2. Narrow outlet requiring a dam of less volume
    3. Strong foundation to support dam structure
    4. Safe and ample spill way to dispose surplus water
    5. Water should not submerge valuable mineral and agricultural land
    6. Availability of material for constructing a dam
    7. Distance from load centre to reduce the cost of creation of transmission lines and their maintenance
    8. (h) Access to site by rail and road

    (iv) Consideration of water pollution effects

    Poor-quality water results in foul-smelling gases, corrosion of metallic structure and electrical equipment, overheating of machine parts. Water gets polluted by submerged vegetation mineral deposits, presence of algae. Leaves, twigs, logs under water decay and generate bad smelling gases. Thermal stratification and depletion of oxygen in lower strata generate harmful gases, such as CO2, H2S, CH4, pollute the water.

    (v) Effects of water pollution

    (a) Damage to dam structure and fitting

    Water containing H2S, CO2 and CH2 is highly corrosive to dam structure. H2SO4 formed by oxidation of H2S attack the cement and disintegrate the concrete. These gases increase the solubility of soil and rocks. Structures, metallic piping and penstock are also affected by the gases.

    (b) Damage of electrical machinery

    Presence of corrosive gases such as H2S and SO2 affect the voltage drop at brush contacts in generator leading to poor commutation. Silver contacts of relays get blackened and lead to high contact resistance and failure of relay occurs. Copper bus bars corrode.

    (c) Health hazard to operating personnel

    Headache, dizziness, dryness, nose, throat, chest pain are the effects of H2S. High concentration of H2S may even cause paralysis.

    (vi) Sedimentation effect

    It reduces the capacity of reservoir and causes rapid erosion of turbine blades.

    (vii) Environment aspects of site selection



    • Power Plant Engineering

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