Hydro Electric Power Plants what are they? How do they work?

HYDROLOGIC CYCLE.

WHAT IS A HYDRO ELECTRIC POWER ?

• Hydro-electric power is electricity produced by moment of fresh water from rivers and lakes.
• In hydro stations downward flow of water (due to gravity)contains kinetic energy, which is converted to the mechanical energy.
• Centuries ago water wheels were used to produced this power.

HOW DOES IT OPERATE ?

The electricity that is generated depends on two things :

•   The distance water has to fall.
•   The quantity of water flowing.

The water is collected and stored above the dam for use when it is required.Other dams simply arrest the water and divert down to the power station through pipe line.Turbines are more sophisticated than water wheels.The blades are attached to the shaft and when flowing water presses against blades the shaft rotates.After the water is given up is energy to the  turbine it discharge through pipelines or channels called trail race.

MAIN COMPONENT OF HYDROELECTRIC PLANT.

• Dam or barrage
• Reservoir and forebay
• Water conduit system
• Trail race
• Surge tank
• Prime mover
• Power house
• Spillway

Dam :  This is constructed to provide head of water to be utilized in the turbine

Reservoir  : The main purpose of the reservoir is to store the water

Forebay: This is regulating reservoir storing water temporarily . It can be considered as surge reservoir near to the intake.

Water conduit system : This carries water from the reservoir to the turbine through the pressure tunnels or turbine called penstocks.

Tailrace : Water is discharged in to the tailrace after passing through the turbine which carries into the river. This is open channels or tunnel depending on the power house location.

Surge tank : It is provide to act as pressure release valve of the water conduit system from the effect of water hammer

Spillway : It discharges the excess water of reservoir beyond the full permission level and act as a safety valve of the reservoir.

Prime mover : The head of the water is converted to the kinetic energy in the prime mover. This is turbine.

CLASSIFICATION OF HYDRO PLANTS.

Based on constructional features

Run-off river plants : These plants generate power on the rivers with continuous flow through the year with small seasonal variations. They do not have large reservoir  or diversion of water away from the main channel

Valley dam plants: Dam is constructed for storing water. Power house is stored at the toe of the dam. No diversion from main river is involved

Diversion canal plant : A diversion canal with flat slope in which the flow from the river is diverted through the canal to power house.  A weir is constructed at the end of canal to create pool of water (forebay)

Classification based on plant capacity

Micro hydro plants    < 100 kW

Mini Hydro plants  100 kW to 1 MW

Small Hydro plant  1 MW to few MW

Hydro plant   More than few to 1000 MW

Super Hydro plant   more than 1000 MW

Base on Head

High head plants  71 m-250 m

Due to high head , small water can produce large amount of power. Therefore this type is economical.

Medium Head Plants 15 -70 m

Larger volume of water in needed.  Therefore  a reservoir  of a large capacity with large catchment  area is required.

Water is generally taken from the main reservoir to forebay  then through penstock to power house. Surgetank is not required.

Low head plant s (<15 m)

Water required is much larger than the high head plants.  Run off river plants and tidal plants come in to this category.

TURBINES

As water sources vary the  water turbine is designed to suit for different locations. The design is largely depends on the head and water available.

There are there types of turbines:

• Pelton wheels
• Fancis turbine
• Kalpan or Propller type.

Pelton wheels

This is used where a small flow of water is available with a ‘large head’. It resembles the waterwheels used at water mills in the past. The Pelton wheel has small ‘buckets’ all around its rim. Water from the dam is fed through nozzles at very high speed hitting the buckets, pushing the wheel around.

Francis Turbine

The Francis turbine is used where a large flow and a high or medium head of water is involved. The Francis turbine is also similar to a waterwheel in that it looks like a spinning wheel with fixed blades in between two rims. This wheel is called a ‘runner’. A circle of guide vanes surround the runner and control the amount of water driving it. Water is fed to the runner from all sides by these vanes causing it to spin.

Propeller type turbines

Propeller type turbines are designed to operate where a small head of water is involved. These turbines resemble ship’s propellers. However, with some of these the angle (pitch) of the blades can be altered to suit the water flow.