GENERATING STATIONSINTRODUCTION

The special plant which is producing bulk electric power is known as power plant or generating station.Depending upon the form of energy converted into electrical energy generating stations are classified as:1.thermal power stations2.Hydro electric power stations3.Neuclear power stations

What is HEPHEP (Hydroelectric Power) is an

environmentally friendly way to generate electricity.

A dam is built to trap water, usually in a valley where there is an existing lake.Water is allowed to flow through tunnels into the dam,to turn turbines and thus drive generators.Notice that the dam is much thicker at the bottom than at the top,because the pressure of the water increases with depth.

Hydroelectric Power Plant

Water in dam (P.E.)

Turbine (M.E.)

Generator (Electrical)

Nozzle (K.E.)

Energy conversion in hydroelectric power plant

Anatomy of A Hydroelectric Power Plant

DAM

Dams are structures built over rivers to stop the water flow and form a

reservoir

The reservoir stores the water flowing down the river. This

water is diverted to turbines in power stations.

SPILLWAY

A spillway as the name suggests could be called as a way for

spilling of water from dams. It is  used to provide for the

release of flood water from a dam.

It is used to prevent over toping of the dams which could

result in damage or failure of  dams

PENSTOCK AND TUNNEL

Penstocks are pipes which carry water from the reservoir to the turbines

inside power station. They are usually made of  steel and are equipped with

gate systems. Water under high pressure flows through the penstock.

A tunnel serves the same purpose as a penstock. It is used when an

obstruction is present between the dam and power station such as a

mountain.

SURGE TANK

Surge tanks are tanks connected to the water conductor system. It serves the

purpose of reducing water hammering in pipes which can cause damage to pipes.

The sudden surges of water in penstock is taken by the surge tank, and when the

water requirements increase, it supplies the collected water thereby regulating

water flow and pressure inside the penstock.

POWER STATION

Power station contains a turbine coupled to a generator. The

water brought to the power station rotates the vanes of the

turbine producing  torque and rotation of turbine shaft. This

rotational torque is transferred to the generator and is

converted into electricity.

POWER STATION CONTD

The used water is released through the tail race. The

difference between head race and tail race is called gross head

and by subtracting the frictional losses we get the net head

Advantages

Once the dam is built,the energy is virtually free

Water can be stored above the dam ready to cope with peaks in demand

much more reliable than wind,solar or wave power

No waste or pollution produced

Electricity can be generated constantly

Hydro-electric power stations can increase to full power very quickly unlike other power stations

disadvantages

The dams are very expensive to build,however many dams are also used for flood control or irrigation,so building costs can be shared

Building a large dam will flood a very large area upstream,causing problems for animals that used to live there

Finding a suitable site can be difficult - the impact on residents and the environment may be unacceptable.

Water quality and quantity downstream can be affected, which can have an impact on plant life.

Hydrological Cycle

Steam power plants The generating station which convertes

heat energy of coal combustion into electrical energy is known as thermal power station .

Steam is produed in the boiler by utilising the heat of coal combustion.steam is then expanded in the prime mover and is then condensed in the condenser to be fed into the boiler again. The steam turbine drives the alternator which converts mechanical energy of the turbine into electrical energy.

Steam power station

Major components of steam power plants are 1.Coal and ash handling plant2.Steam generating

plants(boiler,economiser,super heater,air preheater)

3.Steam turbine4.Alternater5.Feed water6.Cooling arrangement

Coal handling system it consists of a coal storage unit ,where coal is

stored in bulk. Clean and dry coal is then transported through conveyor system for further processing in the crusher .crushing and pulverization of coal is important to reduce the size of particles for effective combustion.

BoilerThe heat of combustion of coal is utilised to convert

water into steam at high temperature and pressure.Super heaterThe steam produed in the boiler is wet and is passed

through the superheater where it is dried and superheated

by the flue gases by their way to chimney.

EconomiserIt extracts a part of heat from the flue gases to

increase the temperature of feed water before supplying to the economiser.

Air preheaterIt extracts a part of heat from the flue gases to

increase the temperature of air used for coal combustion before supplying to the boiler.

steam turbineThe dry and superheted steam is fed to the

steam turbine .the heat energy of steam is when passing over the blades of the turbine is converted into mechanical enegy(kinetic). After giving heat energy ,the steam is fed to the condenser .

AlternatorThe steam turbine is coupled to an alternator.

It converts mechanical energy of the turbine into electrical energy .

Feed waterThe condensate from the condenser is used

as feed water in the boiler.Cooling towerThe hot water from the condenser is passed

through the cooling tower where it is cooled

Neuclear power plant

The schematic diagram of neuclear power plant is shown in fig.the whole arrangement can be divided into four main sections

1.neuclear reactor2.heat exchanger3.steam turbine4.Alternator neuclear reactor it is an apparatus in which neuclear fuel like

u235 subjected to neuclear fission.it houses the the fuel rod of uranium ,moderator (graphite rod)and control rod(cadmium)

.

Heat exchangerThe coolant gives up heat to the heat

exchanger which is utilised in raising the steam.

Steam turbineThe steam produced in the heat exchanger is

fed to the steam turbine .the heat energy of steam is when passing over the blades of the turbine is converted into mechanical enegy(kinetic). After giving heat energy ,the steam is fed to the condenser .

AlternatorThe steam turbine is coupled to an alternator.

It converts mechanical energy of the turbine into electrical energy .

Feed waterThe condensate from the condenser is used

as feed water in the boiler.Cooling towerThe hot water from the condenser is passed

through the cooling tower where it is cooled

Block diagram of typical supply system

There are two systems of tapping from the mains

1.tree system2.distributed system In tree system sub circuits are tapped from the

main circuits at some convenient place .now a days this system is out of practice.

AdvantagesThe length of the cable required for the installation

of wiring is less. So the initial cost is less .DisadvantagesFuses in the installation are scattered and location

of the fault is not easy.Voltage available at different points of load will

vary.Appearance of the system isnot so good.

Distribution system this system is most commonly used.in this system

the main distribution circuit is brought to one or more distribution boxes from where it is further distributed to different branch circuits.

Advantages1.Fault finding is easy2.The voltage available at different points of the

circuit will be the same3.Extension of the circuit is easyDisadvantagesThe length of the cable required for the installation

of wiring is more. So the initial cost is more .

Arrangement of tree system

Distribution system

Grounding/earthing

Enclosure connected to neutral wire

Ground wire connected to enclosure

System grounding