Hydroelectric power generation, schematic, ELEMENTS OF HYDRO-ELECTRIC POWER STATION, Advantages, Factors influencing the selection of site for hydro electric power stations, CLASSIFICATION OF HYDRO-ELECTRIC POWER STATIONS

1. HYDROELECTRIC POWER PLANT
 BY:- GURKIRAT SINGH

2. A power station in which potential or kinetic
energy of water is converted into into electrical
energy are called hydro-electric power stations.

4. 1.Catchment area: The surrounding area of a hydro-electric power plant from where
water is collected into its reservoir is called catchment area.
2. Reservoir : A large storage rank is called a reservoir. A reservoir may be a natural lake
or an artificial one. Artificial reservoirs are made by constructing one, two or more dams
across flowing streams.
3. Dam : A strong wall with large base, behind which water s stored is called a dam.
A dam, according to its structural material, may be masonry dam, rock filled dam or
earthen dam. It Performs two functions :-
(a) It creates the necessary water head and
(b) Stores water in the reservoir.
4. Spillway: The ways or passages for water to be released from the dam, when water
increases beyond its safe level are called spillways.
5. Valve House: The cabin in which controls are kept to operate the valves of the sluice
gales of the penstock is called value house.

5. 6. Surge Tank : An open tank connected to the penstock which regulates water
supply through the penstock or suppresses the water hammerage is called surge tank.
7. Rack: At the entrance of the tunnel racks are provided to prevent the ingress of
floating and other materials to the turbine. Racks arc built up from long flat bars
placed vertically. The space between the bars varies from 40 mm to 200 mm in
accordance with the minimum width of water passage through the turbine.
8. Penstocks : Huge steel or reinforced steel pipes that carry large quantity of water
from valve house go the scroll case of the turbines are called penstocks.
9. Water Turbines (Prime Movers) : A device or machine that converts the
hydraulic energy of water,(potential and kinetic energy) into mechanical energy
(rotatory motion) is called a water turbine or water wheel.
10. Draft tube: It is an air tight pipe of suitable diameter. It is connected at the
bottom of the scroll case of the turbine and provides outlet for the water coming from
the rotor (wheel). Draft tube discharges water in the tail race. It is provided in the
power plants to increase the head acting on the water turbine.

6. 11. Tail race: Draft tube discharges water in the tail race, which may lead it to the
same stream or to another.
12. Alternator: An alternator is coupled to the turbine, which converts mechanical
energy into electrical energy. The alternators employed in these power plants are of
salient pole type, operating at slow speeds.
13. Control room : In the control room all the controlling equipment, protective
devices, indicating instruments etc. Are placed on the panels.
14. Switch yard : The Open place where various electrical equipment like
transformers (step up) circuit breakers, CTs, PTs etc. are installed is known as switch
yard.

7. As no fuel is used in this case, so there are no charges of fuel and transportation.
Operating cost is low, as fewer highly skilled engineers and operators are required at
the time of operation.
 Low maintenance cost, as the auxiliary plant is considerably smaller in size.
 As these stations are situated away from the developed areas, therefore, cost of land is
negligibly small.
 High efficiency (80 to 90%), as the stand by losses are very low.
 It is very near and clean plant, as no smoke, dust or ash is produced.
 It can be put into service instantly.
 These plants have long life.
 Very acute governing is possible with turbines, therefore, these plants have constant
speed or frequency.
 These plants, in addition to generation of electrical energy also serve other purposes
such as Irrigation, flood control etc.

8. These plants should be installed where adequate quantity of water is available.
The wide variation of rainfall during the year makes it necessary to store water for
continuous power generation throughout the year therefore the reserve work should
have huge capacity and large catchment area.
Water collected behind the dam must have sufficient head to deliver adequate
potential energy.
The land should be very strong to withstand the weight of dam, building and heavy
machinery.
Adequate transportation facilities must be available or there should be possibility of
providing the same to transport heavy machinery and building materials.
The site selected should be such that at the time of construction there must be
possibility of stream diversion.

9. On the basis of operating head, hydro-electric power stations may be
classified as;
(i) Low head p4wcr stations.
(ii) Medium head power stations.
(iii) High head power stations.

10. Low head hydro-electric
power stations: The simple
layout of a low head power
station is shown in fig. Mostly
in this case a dam is constructed
across the river or stream and a
fall is created. Since the head is
quite low, large quantity of
water is required for a specific
power output. Therefore, the
penstocks of larger diameter and
shorter lengths are used. As said
earlier, in low head power
stations kaplan turbines
(reaction turbines) are
employed. The generators
employed are of salient pole
type, low speed and larger
diameter.

11. Medium head hydro-electric power stations: A medium-head power station is
shown in fig. Depending upon the head, the characteristics of medium head power
station may be either of high head or of low head power stations. Mostly in medium
head power stations horizontal shaft francis turbines (reaction turbines) are employed.
However, if the head is quite low kaplan turbines may be employed and if the head is
quite high pelton wheels may be employed.

12. High head hydro-electric power
stations: The layout of high head power
station is shown in fig 20. In this case, dam
is constructed to close down the valley
which forms a reservoir for storage of
water. Since the head is quite high, small
quantity of water is required for a specific
power output, therefore, the penstocks of
small diameter and longer lengths are
required. A surge tank is constructed to
reduce the effect of water hammerage on
the penstocks in case of sudden closing or
opening of sluice gates of the water
turbines. As said earlier, in these power
stations pelton wheels (impulse turbines)
are employed. The generators employed are
of comparatively high speed and small
diameter having non-salient pole type rotor.

13. BY:- GURKIRAT SINGH