Working of surge tank
A surge tank
is a small reservoir of tank in which the water level rises or falls to reduce
the water pressure swings in side the conduct (penstock).
The main
function of surge tank is to provide space for holding water during load
rejection by the turbine and also supplies an additional water when the load on
the turbine increases. It also relieves water hammer pressures within penstock
under sudden changes in water flow.
Location of surge Tank :
If the power
house is located with in a short distance of the works, surge tanks are not
necessary. Hence run of river plants and medium head plants does not requires
surge tank.
Generally
the surge tanks are used in high head schemes. These are usually located as
close as possible to the power house, to reduce the length of the penstock and
also it is placed on high ground to reduce the height of the tower.
The best
location will be the point where the flat sloping conducts and the steep
sloping penstock meet and is show in
Function of surge Tank
The main functions of surge tank can be summarized as follows, namely.
1. It stores water at load rejection, until the conduct velocity is decelerated to the new steady state value.
2. It supplies additional water required at load demand, until the conduit velocity is accelerated to the new steady state value.
3. It provides a free reservoir surface as closed to the turbine as possible to absorb and compensate water hammering effect.
Types of surge tank:
Depending on
the shape the surge tanks are mainly classified in to following types,
Namely.
1. Simple cylindrical surge tank
2. Restricted orifice (or) throttle surge tank
3. Simple surge tank with special design
4. Bell mouth spillway surge tank.
5. Differential type surge tank.
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