Penstock

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Figure 1. A penstock at a hydroelectric facility.

Penstocks are pipes or long channels that carry water down from the hydroelectric reservoir to the turbines inside the actual power station. They are made of steel and allow water to flow through under high pressure. They are a vital component of a hydroelectric facility that allows water to move to the turbine. Grates or filters can be attached to the ends of penstocks to trap large debris such as branches. This ensures that debris cannot enter the channel and block the flow of water.

The amount of water that is allowed to flow through the penstock can be controlled with a gate called a sluice, which can be raised and lowered to increase or decrease the flow rate. When the sluice is fully open, water flows freely down through the penstock. However, when it is closed slightly the flow rate is reduced, and thus less water enters the penstock and reaches the turbines.

It is important to be able to control the amount of water that can enter the penstock for a number of reasons, primarily to allow people to regulate the amount of water that exits the penstocks at the other end. During dry seasons, penstocks may be wide open to allow water through, while during wet seasons they are closed partially to prevent flooding. Containment ponds are generally built before the entrance to the penstock to hold water in storage before being let through the penstock. These ponds act to reduce additional pressure on the sluice from the accumulation of stored water. The ability to close off the penstocks ensures that they can be regularly inspected, serviced, and repaired. Penstocks require regular cleanings to remove debris and during these cleanings, holes, cracks, and other issues can be discovered and fixed. This helps prevent catastrophic dam failures.

Size of Penstocks

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  Figure 2. The Tretheway Creek hydroelectric facility has more than 4 km of penstock buried underground.
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  Figure 3. The Itaipu hydroelectric facility has 20 large penstocks. Each penstock is 142.2m long and 10.5m in diameter.

Depending on the type of hydropower facility, the size of the penstock will vary. Some facilities have long penstocks, and others have short and wide penstocks. Long penstocks, like the Tretheway Creek hydroelectric facility in Figure 2, are chosen to transport water to a generating station further down the river. Long penstocks are usually used for run-of-river hydropower. Short and wide penstocks, like in the Itaipu hydroelectric facility in Figure 3, are used to carry a large quantity of water to the turbines. Therefore, the diameter of the penstock also varies dramatically depending on how much water needs to be delivered. The penstocks at the Itaipu hydroelectric facility are 10.5 meters in diameter, approximately the length of a passenger bus (seen in Figure 3).

For Further Reading

• Spillway
• Hydroelectric facility
• Hydroelectric dam
• Primary energy
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