What is Forebay in Hydroelectric Power Plant ?
It is a structure located at the beginning of penstock pressure shaft that satisfy the function of head regulation and elimination of water hammer effect. It is a large water body that fulfills similar functions as the surge tank. A forebay is sometimes also referred as head pond. A forebay may consists of trash rack at the beginning of penstock pipe. The functions of a forebay can be pointed as below:
- It allows transition of watercourse from open channel flow to pressurize flow maintaining the necessary submergence.
- It protects the penstock pipe form water hammer effect caused due to sudden acceptance and rejection of load in turbines.
- Temporary storage of water when load on turbine is suddenly decreased.
- Temporary supply of water when load on turbine is suddenly increase.
- It serves the function of head regulation.
- Spilling of excess water through side spillway if any.
What is Difference Between a Surge Tank & Forebay ?
A surge tank or a fore bay is constructed in a hydroelectric power plant with the same purpose of eliminating the effect of water hammer. But a surge tank is constructed when there is a pressurized flow in headrace that feeds to surge tank where as if the headrace flow is of open channel type, then construction of forebay is necessary.