Hydro Electric Power Plant

In hydro Electric plants energy of water is utilized to move the turbines which in turn run the electric generators. The energy of water utilized for power generation may be kinetic or potential. The Kinetic energy of water is its energy in motion and is a function of mass and velocity, while the potential energy is a function of the difference in level/head of water between two points. In either case continuous availability of water is a basic necessity. To ensure this water collected in natural lakes and reservoirs at high altitudes may be utilized or water may be artificially stored by constructing dams across flowing streams. The ideal site is one in which a good system of natural lakes with substantial catchment area, exists at a high altitude. Rainfall is the primary source of water and depends upon such factors as temperature, humidity, cloudiness, wind etc. the usefulness of the rainfall for power purposes further depends upon several complex factors which include its intensity, time distribution, topography of land etc. however it has been observed that only a small part of the rainfall can actually be utilized for power generation a significant part accounted for by direct evaporation, while another similar quantity seeps into the soil and forms the underground storage, some water is also absorbed by vegetation. Thus, only a part of water falling as rain actually flows over the ground surface as direct run off and forms the streams which can be utilized for hydro-schemes.

History of Hydro Electric Power Plant.

First hydro-electric station was probably started in America in 1882 and thereafter development took place very rapidly.

Application of Hydro-electric Plant.

Earlier hydro-electric plants have been used as exclusive source of power, but the trend is towards use of hydropower in an inter-connected system with thermal stations. As a self- contained and independent power source, a hydro-plant is most effective with adequate storage capacity otherwise the maximum load capacity of the station has to be based on minimum flow of stream and there is a great wastage of water over the dam for greater part of the year. This increases per unit cost of installation. By interconnecting hydropower with steam, a great deal of saving in cost can be affected due to:

1) Reduction in necessary reserve capacity.

2) Diversity in construction program.

3) Higher utilization factors on hydro-plants, and

4) Higher capacity factors on efficient steam plants.

In inter-connected system the base load is supplied by hydropower when the maximum flow demand is less than the stream flow while steam supplies the peak. When stream flow is lower than the maximum demand the hydro plant supplies the peak load and steam plant the base load Hydro means water, Power is a conventional renewable source of energy which is clean free from pollution and generally has a good environmental effect. However, the following factors are major obstacles in the utilization of hydro-power resources.

a) Large investments

b) Long gestation periods

c Increased cost of power transmission.

Essential Features of Hydro-electric power plant

The following are the essential elements of hydro-electric power plant.

1. Catchment area:

The whole area behind the dam draining into stream or river across which the dam has been built at a suitable place, is called catchment area.

2. Reservoir:

This is where water is stored for use as and when needed. The type and arrangement depend on topography of the site. A reservoir is employed to store water which is further utilized to generate power by running the hydraulic turbines.

a. Natural Reservoir. b. Artificial Reservoir. A natural reservoir is a lake in high mountains.

An artificial reservoir is built by erecting a dam across the river.

Water held in upstream reservoir is called storage whereas water behind the dam at the plant is called pondage.

3. Dam:

A Dam is a barrier to confine or raise water for storage or diversion to create a hydraulic head. A hydro-electric dam diverts the flow from the river to the turbines and usually increases the head. A reservoir dam stores water by raising its level. Dams are built of concrete or stone masonry, earth or rock fill, or timber. Masonry dams may be solid-gravity, buttress or arch type. A barrage is a diversion dam, especially at a tidal power project. A weir is a low overflow dam across a stream for measuring flow or maintain water level, as at a lake outlet. A dike is an embankment to confine water; a levee is a kike near the bank of a river to keep low land from being overflowed.

 

4. Penstock:

This is a conduit (conduits) that carry water to the turbines. They are made of reinforced concrete or steel. A surge tank is installed next to each penstock for overflow control and protection of penstock from bursting.

5. Water turbine:

Water turbines are used to convert hydraulic energy of flowing water into rotational mechanical energy.

6. Generator:

This machine is used to convert rotational mechanical energy transferred from the turbine through the shaft, into electrical energy. the produced electrical energy is transmitted to the transformer for long distance transmission.

Advantages and Disadvantages of Hydro-electric plant.

Advantages of hydro-electric plant.

1. No fuel charges.

2. A hydro-electric plant is highly reliable.

3. Maintenance and operation charges are very low.

4. Running cost of plant is low.

5. The plant has no standby losses.

6. The plant efficiency does not change with age

7. It takes a few minutes to run and synchronizes with the plant

8. Less supervising staff is required.

9. No, ash problem and atmosphere is not polluted since no smoke is produced in the plant.

10. No fuel transportation problem.

11. In addition to power generation these plants are also used for flood control and irrigation purposes.

12. Such a plant has comparatively a long life 100-125 years as against 20-45 years of a thermal plant.

13. The number of operations required is considerably small compared with thermal power plants.

14. The machines used in hydro-electric plants are more robust and generally run at low speeds at 300-400 rpm. where the machines used in thermal plants run at speed of 3000- 4000 rpm. therefore, there are no specialized mechanical problems or special alloys required for construction.

15. The cost of land is not a major problem since the hydro-electric stations are situated away from the developed areas.

Disadvantages of Hydro-electric Plants.

1. The initial cost of the plant is very high.    

              It takes considerably long time for the erection of such plants.

2. Such plants are usually located in hilly areas far away from the load center and as such they require long transmission lines to deliver power, subsequently the cost of transmission lines and losses in them will be more.

3. Power generation by the hydro-electric plant is only dependent on the quantity of water available which in turn depends on the natural phenomenon of rain. So, if the rainfall is in time and proper and the required amount of can be collected, the plant will function satisfactorily otherwise not.

Types of Dams.

1) Fill Dams.

a. Earth dams

b. Rock-fill dams.

2) Masonry Dams.

a. Solid Gravity dams.

b. Buttress dams

c. Arch dams.

3) Timber Dams.

Classification of Hydro-electric Power plant.

A. According to the availability of head

i) High head power plants. (100 meters and above)

ii) Medium head power plants. (30 to 500 meters)

iii) Low Head power plants. (25 to 80 meters)

B. According to the nature of Load

i) Base load plants.

ii) Peak load Plants.

C. According to the quantity of water available

i) Run-of River Plant without Poundage.

ii) Run-of river plant with Poundage.

iii) Storage type Plants.

iv) Pump Storage plants.

v) Mini and Micro-hydel plants.

Hydraulic Turbines

A hydraulic turbine converts the potential energy of water into mechanical energy which in turn is utilized to run an electric generator to get electric energy.

Classification of Hydraulic Turbines.

• According to the head and quantity of water available.

i) Impulse Turbine Requires high head and small quantity of flow.

ii) Reaction Turbine Requires low head and high rate of flow.

• According to the name of originator.

i) Pelton turbine---named after Lester Allen Pelton of California USA. It is an impulse type of turbine and is used for high k=head and low discharge.

ii) Francis turbine---named after James Bichens Francis. It is a reaction type of turbine for medium high to medium low heads and medium small to medium large quantities of water.

iii) Kaplan turbine---named after Dr. Victor Kaplan. It is a reaction type of turbine for low heads and large quantities of flow.

• According to the action of water on the moving blades.

i) Impulse turbine

ii) Reaction turbine

(1) Impulse Turbine

(a) Pelton Turbine

(2) Reaction Turbine

(a) Francis Turbine

(b) Kaplan Turbine

• According to the direction of flow of water in the runner.

i) Tangential flow Turbine (Pelton Turbine)

ii) Radial flow turbine (no more used)

iii) Axial flow turbine (Kaplan Turbine)

iv) Mixed (Radial and Axial) flow turbine (Francis Turbine)

• According to the disposition of the turbine shaft

i) Vertical Shaft Turbine

ii) Horizontal Shaft Turbine.

Hydo power plant



Published by science tube 14 September 2020