Surge Shaft And Drop Shaft- A surge shaft is a vertical tunnel that is frequently used with the pressure conduit of considerable duration. The main purpose of presenting a surge tank is to lessen the gap between the free water surface and turbine thereby decreasing the water hammer impact on the penstock and also protect the upstream tunnel from high strain rises. The concrete lining is done in the Surge shaft of the M30 design.
Grouting is done after the concrete lining in order to ensure the stability of the liner and to decrease the water hammering effect.
Water Hammering effect in Hydroelectricity Plant:
The water hammering is described because of the change in the pressure rapidly above or under ordinary pressure because of sudden adjustments in the rate of water flowing in accordance. The water hammer occurs at all the points in the penstock among the surge tank and the turbine because of the unexpected changes in the demand of the water during the load fluctuations.
Thus surge tank helps in stabilizing the velocity and pressure in the penstock and protects penstock from water hammering and negative pressure or vacuum,
Important Functions of Surge Shaft:
- It should protect the conduit system from high internal pressures.
- It should help the hydraulic turbine regarding its regulation characteristics.
- It should store the water to raise the pressure in pressure drop conditions.
SALIENT FEATURES OF SURGE SHAFT
|TOP ELEVATION OF SURGE SHAFT||1065.00m|
|DEPTH OF SURGE SHAFT||165m|
Drop shaft Depending upon the terrain, the tunnel had to be designed accordingly so as to provide optimal cover below the earth’s crust. When the terrain is mountainous, cover usually varies along the lengths. Drop shaft is mainly used in that place where the cover is not of optimum thickness.
Drop shaft is a vertical fall given to the main tunnel so as to provide it the required pressure. The machine served its purpose of drilling and then blasting was done. This cycle had to be repeated until the depth of 42m was reached. To cope up with the flow and its impacts on its walls, the reinforced concrete lining was also provided in the drop shaft. The drop shaft had an excavated and finished diameter of 6.2m and 5m respectively. The lining should be done with reinforced concrete; the thickness of the lining should be from 500mm to 700mm.