Things to Know About Power Generation Station Part 3 – Round UP

Penstocks

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

pressure.

The anchor block supports the penstock and holds it in the proper position.

The surge tank also protects the penstock from sudden pressure changes.

Water Turbines

The main two types of water turbines are,

1. 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.

1. 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.

Advantages

1. If the proper site is selected, the continuous water supply is available.
2. Requires no fuel as water is used.
3. No burning of fuel hence neat and clean site as no smoke or ash is produced.
4. It does not pollute the atmosphere.
5. The operating cost is very low as free water supply is available.
6. The turbines in this plants can be switched on and off in a very short period of time.
7. It is relatively simple in construction, self-contained in operation and requires less

maintenance.

8. It is robust and has very long life.
9. It gives high efficiency over a considerable range of load. This improves the overall system

efficiency.

10. It provides the additional benefits like irrigation, food control, afforestation etc.
11. Being simple in design and operation, highly skilled workers are not necessary for the daily

operation. Thus a man power requirement is  low.

Disadvantages

1. Due to the construction of dam, very high capital cost.
2. The low rate of return.
3. Uncertainty of availability of water due to unpredictable rainfall.
4. 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.

5. The large power stations disturb the ecology of the area by the way of disforestation,

destroying vegetation and uprooting people.

6. Highly skilled and experienced persons are necessary at the time of construction.