The penstocks are made up of steel or concrete and arranged in the form of conduits,
supported by the anchor blocks. The penstocks are used to carry water to the turbine. For the low
head (less than 30 m) power stations, the concrete penstocks are used. The steel penstocks are
suitable for any head.
There are certain protective devices attached to the penstocks.
The automatic butterfly valve completely shuts off the water flow if the penstock bursts.
The air valve maintains the air pressure inside the penstock equal to the outside atmospheric
The anchor block supports the penstock and holds it in the proper position.
The surge tank also protects the penstock from sudden pressure changes.
The main two types of water turbines are,
- i) Impulse and ii) Reaction
In an impulse turbine, the entire pressure of water is converted into a kinetic energy in a
nozzle. Then the water jet is forced on the turbine which a large velocity which drives the wheel.
It contains elliptical buckets mounted on the periphery of a wheel. The force of water jet on
the buckets drives the wheel and the turbine. There is a needle or spare at the tip of the nozzle.
The governor controls the needle which controls the force of the jet, according to the load
demand. The impulse turbines are used for the high head power stations.
In the reaction turbines, the water enters the runner, partly with pressure and partly with
velocity head. There are two types of reaction turbines.
- i) Francis and ii) Kalpan
The reaction turbine consists of an
outer ring of stationary guided blades and an inner ring of rotating blades. The guided blades
control the flow of water to the turbine. Water flows radially inwards and changes to a
downward direction when it passes through the rotating blades. While pass ing over the rotating
blades, the pressure and velocity of water are decreased. This causes reaction force to exist
which drives the turbine. For large variation of head, Kalpan is used as its efficiency does not
vary with change in load. For fairly constant head, a Francis or propeller turbine is used.
The reaction turbines are used for the low head power stations.
- If the proper site is selected, the continuous water supply is available.
- Requires no fuel as water is used.
- No burning of fuel hence neat and clean site as no smoke or ash is produced.
- It does not pollute the atmosphere.
- The operating cost is very low as free water supply is available.
- The turbines in this plants can be switched on and off in a very short period of time.
- It is relatively simple in construction, self-contained in operation and requires less
- It is robust and has very long life.
- It gives high efficiency over a considerable range of load. This improves the overall system
- It provides the additional benefits like irrigation, food control, afforestation etc.
- Being simple in design and operation, highly skilled workers are not necessary for the daily
operation. Thus a man power requirement is low.
- Due to the construction of dam, very high capital cost.
- The low rate of return.
- Uncertainty of availability of water due to unpredictable rainfall.
- As its location is in hilly areas and mountains, the long transmission lines are necessary for the
transmission of generated electrical energy. This requires high cost.
- The large power stations disturb the ecology of the area by the way of disforestation,
destroying vegetation and uprooting people.
- Highly skilled and experienced persons are necessary at the time of construction.