Some terms associated with hydro-electric power plants are given below:
(a) Spillways , Hydro Spillways of hydroelectric power plant :
A spill way provides discharge of surplus water from storage reservoir into the river down stream side of the dam. It is a sort of safety valve for the dam.
(b) Run off of hydroelectric power plant :
A run off is that portion of precipitation which makes its way towards stream, lakes or oceans. Run off is possible only when the rate of precipitation is more than the rate of water infiltration into the sub-oil.
(c) Hydrograph of hydroelectric power plant :
Hydrograph is a graphical representation between discharge and time. It shows the variation of flow with time.
(d) Unit hydrograph of hydroelectric power plant :
Unit hydrograph is a hydrograph with a volume of 1 cm (or meter) of run-off resulting from a rainfall of specified duration and a real pattern.
(e) Flow duration curve of hydroelectric power plant :
It is a plot of flow available during a period against percentage of time.
(f) Mass curve of hydroelectric power plant :
Mass curve is a plot of cumulative volume of water that can be stored from stream flow versus time in days, weeks or months.
(g) Run of the river plant without pondage :
These plants do not have facilities for storage of water. Flowing water of the stream is used for generating power.
(h) Run of the river plant with pondage :
The utility of a run off the river plant is enhanced by providing storage facilities for water. Such plants can be operated even during off season when the flow of water in the river declines.
Trash rack of hydroelectric power plant :
Trash rack is provided at the inlet end of penstock on the dam to prevent entry of debris which might damage the wicket gates and turbine runners. These are made of steel bars.
Forebay of hydroelectric power plant:
This is a regulating reservoir used to store water temporarily when the load on the plant is reduced. The water from forebay can be used when the load on the turbine increases.
Surge tank of hydroelectric power plant :
Surge tank is provided usually on medium and high head plants. As the load on the turbine decreases the surge tanks acts as a reservoir for holding water. Also pressure variations due to rapid changes of flow of water are taken care of by the surge tanks.
Penstock of hydroelectric power plant :
Penstock is a conduit for conveying water from storage to the turbines. Generally steel pipes are used for this purpose.
Runway speed of hydroelectric power plant :
It is the maximum speed at which a turbine wheel would run under the worst conditions of operation (with all gates open allowing maximum flow of water under maximum head).
Governor of hydroelectric power plant:
Governor is a device used on turbines to regulate the flow of water in proportion to the load on the plant so that constant turbine speed may be maintained.
Draft tube of hydroelectric power plant:
Draft tube a pipe work installed at the turbine discharge to permit a negative or suction head to be established at the runner exit so that turbine can be installed above the tail race. It also converts a large proportion of the velocity energy rejected from the runner into useful pressure head i.e., it acts as recuperator of pressure energy.
Cavitation of hydroelectric power plant:
Cavitation is the formation of bubbles or cavities when the pressure in any part of the turbine drops below the vapour pressure cavitation causes pitting of metal surfaces.
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