Power System
• Electric power systems are real-time energy delivery
systems. Real time means that power is generated,
transported, and supplied the moment you turn on
the light switch.
• The power plants transform other sources of energy
in the process of producing electrical energy. For
example, heat, mechanical, hydraulic, solar, wind,
geothermal, nuclear, and other energy sources are
used in the production of electrical energy.
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Power System
• High-voltage (HV) power lines in the transmission
portion of the electric power system efficiently
transport electrical energy over long distances to
the consumption locations.
• Finally, substations transform this HV electrical
energy into lower-voltage energy that is transmitted
over distribution power lines that are more suitable
for the distribution of electrical energy to its
destination, where it is again transformed for
residential, commercial, and industrial consumption.
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Faraday’s Law an Electricity
Generation
• Faraday`s Law: A voltage is produced on any
conductor in a changing magnetic field.
• If one takes a coil of wire and puts it next to a
moving or rotating magnet, a measurable voltage
will be produced in that coil.
• Generators use a spinning magnet (i.e. rotor) next
to a coil of wire to produce voltage. This voltage is
then distributed throughout the electric power
system
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how a generator works?
• coils of wire mounted on stationary housings, called
stators, where voltage is produced due to the
magnetic field provided on the spinning rotor.
• The rotor is sometimes called the field because it is
responsible for the magnetic field portion of the
generator.
• The rotor’s strong magnetic field passes the stator
windings (coils), thus producing or generating an
alternating voltage (ac).
• The amplitude of the generator’s output voltage
can be changed by changing the strength of
rotor’s magnetic field.
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how a generator works?
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Three Phase Generator
• Three coils are placed in the presence of a
changing magnetic field, three voltages are
produced.
• When the coils are spaced 120 degrees apart in a
360 degree circle, three-phase ac voltage is
produced.
• Three-phase generation can be viewed as three
separate single-phase generators, each of which
are displaced by 120 degrees.
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Three Phase Generator
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Three Phase Generator
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Lenz’s Law
• A current flowing in a wire produces a magnetic field
around the wire.
• This law describes the relationship between the
production of magnetic fields and electric current
flowing in a wire.
• Increasing the voltage or the number of turns in the
winding increases the strength of magnetic field
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Three Phase Generator
Components
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Rotor Poles
• Increasing the number of magnetic poles on the
rotor enables rotor speeds to be slower and still
maintain the same electrical output frequency.
• Generators that require slower rotor speeds to
operate properly use multiple-pole rotors.
• For example, hydropower plants use generators
with multiple-pole rotors because the prime mover
(i.e., water) is very dense and harder to control
than light-weight steam.
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Rotor Poles
• 𝑅𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑠 𝑝𝑒𝑟 𝑚𝑖𝑛𝑢𝑡𝑒 =
120×𝑓
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑜𝑙𝑒𝑠
=
7200
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑜𝑙𝑒𝑠
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Generator Connections
• There are two ways to connect three windings that
have a total of six leads (the ends of the winding
wires) symmetrically
1) Delta
2) Wye
• The generator nameplate specifies which winding
configuration is used on the stator.
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Generator Connections
• Delta: Delta configurations have all three windings
connected in series. The phase leads are connected
to the three common points where windings are
joined.
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Generator Connections
Delta connected generator
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Generator Connections
Wye connected generator
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Types of Generating Stations/Power
Plants
• Depending on the form of energy converted in
electrical energy, the generating stations are
classified as:
1) Steam power stations
2) Hydroelectric power stations
3) Diesel power stations
4) Nuclear power stations
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Steam Power Station
• A generating station which converts heat energy of
the coal combustion into electrical energy is known
as steam power station.
- Steam is produced in the boiler by utilizing the
heat of coal combustion.
- The steam is then expanded into the prime
mover(i.e., Steam turbine) and is condensed into
condenser to be fed back to the boiler again.
- The steam turbine drives the alternator/generator
which converts mechanical energy of the turbine into
electrical energy.
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Schematic arrangement of Steam Power Plant
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Steam Power Station
• The arrangement of the steam power station can
be divided into six stages:
1) Coal and ash handling arrangement
2) Steam generating plant
3) Steam turbine
4) Alternator/AC Generator
5) Feed water
6) Cooling arrangement
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Stem Power Station
• Coal and ash handling plant: Coal is crushed into
small pieces in order to increase its surface
exposure, which helps the rapid combustion of coal
without using large quantity of excess air.
• The pulverized/crushed coal is fed to the boiler by
belt conveyers.
• Coal is burnt in the boiler and the ash produced
after the complete combustion of the coal is
removed to the ash handling plant and then
delivered to the ash storage plant for disposal.
• The removal of the ash from the boiler furnace is
necessary for the proper combustion of the coal.
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Steam Power Station
• Steam generating plant: It consists of the boiler for the
production of steam and other auxiliary equipment for the
utilization of flue gases.
a) Boiler: The heat of the combustion of coal in the boiler is
utilized to convert water into steam at high temperature and
pressure. The flue gases from the boiler make their journey
through super heater, economiser, air pre-heater and are
finally exhausted to atmosphere through the chimney.
b) Super heater: The steam produced in the boiler is wet and is
passed through a super heater where it is dried and
superheated by the flue gases on their way to chimney.
c) Economiser: An economiser is a feed water heater (the water
being fed to the boiler) which derives heat from the flue
gases to increase the feed water temperature.
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Steam Power Station
d) Air Preheater: It increases the temperature of the air
supplied for coal burning by deriving heat from the flue
gases. The advantages of the air preheater are the
increased thermal efficiency and the increased steam
capacity of the boiler.
• Steam Turbine: The dry and superheated steam from the
super heater is fed to the steam turbine through the
main valve. The heat energy of the steam when passing
over the blades of the steam turbine is converted into
the mechanical energy. After giving heat energy to the
turbine, the steam is exhausted to the condenser which
condenses the exhausted steam with the help of cold
water circulation.
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Steam Power Station
• Alternator/Generator: The turbine is coupled with the
alternator which converts the mechanical energy of the
turbine into electrical energy.
• Feed water: The condensate from the condenser is used
as feed water to the boiler. Some water is lost in the
cycle which is made up from the external source. The
feed water on its way to the boiler is heated by water
heater and economizer. This will help in raising the
overall efficiency of the plant.
• Cooling arrangement: Water is drawn from the natural
source of supply such as river, canal or lake and is
circulated through the condenser. In case the
availability of the water from the source of supply is not
assured, cooling towers are used. When hot water from
the condenser is passed on to the cooling tower it is
cooled.
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Steam Power Station
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Advantages:
The fuel (coal) used is cheap.
Less initial cost as compared to other generating stations.
It requires less space as compared to the hydroelectric
power station.
The cost of generation lesser than that of diesel station.
Disadvantages:
It pollutes the atmosphere due to the production of large
amount of smoke and fumes
The cost of generation is higher than hydroelectric station.
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Efficiency of Steam Power Station
• The efficiency of the steam power station is quite low
(25%-35%) mainly due to two reasons. One, a huge
amount of heat energy is lost in the condenser secondly
heat losses occurs at various stages of the plant.
(i) Thermal Efficiency: The ratio of the heat equivalent of the
mechanical energy transmitted to the turbine shaft to
the heat of combustion of coal is known as thermal
efficiency of the steam power station.
𝐻𝑒𝑎𝑡 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙
𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑑 𝑡𝑜 𝑡𝑢𝑟𝑏𝑖𝑛𝑒
𝑇ℎ𝑒𝑟𝑚𝑎𝑙 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
𝐻𝑒𝑎𝑡 𝑜𝑓 𝑐𝑜𝑎𝑙 𝑐𝑜𝑚𝑏𝑢𝑠𝑡𝑖𝑜𝑛
More than 50% of the total heat of combustion is lost in the
condenser. The other heat losses are lost in the flue gases,
radiation, ash etc.
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Efficiency of Steam Power Station
• Overall Efficiency: The ratio of heat equivalent of
electrical output to the heat of combustion of coal
is known as overall efficiency of the steam power
station.
𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = η𝑂𝑣𝑒𝑟𝑎𝑙𝑙
𝐻𝑒𝑎𝑡 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑜𝑢𝑡𝑝𝑢𝑡
=
𝐻𝑒𝑎𝑡 𝑜𝑓 𝑐𝑜𝑚𝑏𝑢𝑠𝑡𝑖𝑜𝑛 𝑜𝑓 𝑐𝑜𝑎𝑙
The overall efficiency of the steam power station is less
than the thermal efficiency. This is because some
losses occurs in the alternator.
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Hydro-electric Power Station
• A power station which utilizes which utilizes the
potential energy of water at high level for the
generation of electrical energy is known as
hydroelectric power station.
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Schematic Arrangement of
Hydroelectric Power Station
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Hydro-electric Power Station
• The dam is constructed across a river or lake and water
is stored at the back of the dam to form a reservoir.
• A pressure tunnel is taken off from the reservoir and the
water is brought to the valve house at the start of the
penstock.
• The water is taken from the valve house to the turbine
through a huge steel pipe known as penstock.
• The water turbine converts hydraulic energy of water
into mechanical energy. The turbine derives the
alternator which converts mechanical energy of turbine
into electrical energy.
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Hydro-electric Power Station
• A surge tank (open from the top) is built just before the
valve house and protects the penstock from bursting in
case the turbine gates are suddenly close due to
electrical load being thrown off.
• The governor opens or close the turbine gates in
accordance with the changes in the electrical load. If
the electrical load increases the governor opens the
turbine gates to allow more water and vice versa.
• When the turbine gates close, there is a sudden
stoppage of water at the lower end of penstock and as
a result the penstock may burst.
• The surge tank absorb this pressure by increase in its
water level.
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Constituent of Hydroelectric
Power Plant
 Hydraulic structure
 Water turbines
 Electrical equipment
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Hydraulic Structure
• Hydraulic structure includes dam, spillways,
headworks, surge tank and penstock.
Dam: A dam is a barrier which stores water and
creates water head.
Spillways: There are times when the river flow exceeds
the capacity of the reservoir. Such a situation arise
during heavy rain fall. In order to discharge the surplus
water into the river on the down stream side of the
dam, spillways are used.
Headworks: The headworks consists of diverting
structure at the head of an intake. They are used to
divert debris and sediments for controlling the flow of
water into the turbine.
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Hydraulic Structure
• Surge tank: It is a small reservoir or tank (open at the top)
in which water level rises or falls to to reduce the pressure
swing in the conduit.
 When the load on the turbine decreases, the governor
closes the gates of the turbine, reducing water supply to
the turbine. The excess water at the lower end of the
conduit rushes back to the surge tank and increases its
water level and the conduit is protected from bursting.
 On the other hand, when load on the turbine increases,
additional water is drawn from the surge tank to meet
the increases load requirement. Hence it overcomes the
abnormal pressures in the conduit.
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Hydraulic Structure
• Penstock: Penstocks are open or closed conduit
which carry water to the turbine. They are generally
made of reinforced concrete or steel.
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Hydraulic Structure
 Automatic butterfly valve shuts off water flow into
the penstock if it ruptures.
 Air valve maintains the air pressure inside the
penstock equals to the out side atmospheric
pressure. When the water runs out of penstock
faster than it enters, a vacuum is created which
may cause the penstock to collapse. Under such
situations, air valve opens and admits air in the
penstock to maintain the inside air pressure equals
the outside air pressure.
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Water Turbine
• Water turbines are used to convert the energy of
falling water into mechanical energy. The principle
types of the turbine are:
1) Impulse turbines
2) Reaction turbines
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Electrical Equipment
• The electrical equipment od hydr0-electric power
station includes alternators, transformers, circuit
breakers and other switching and protective
devices.
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Diesel Power Station
A generating station in which diesel engine is used as prime
mover for the generation of electrical energy is known as
diesel power station.
Advantages:
(1) The design and layout of the plan is quite simple.
(2) It occupies less space.
(3) It can be located at any place.
(4) It can be started quickly and can pick up load in a short time
(5) There are no standby losses
(6) It requires less quantity of water for cooling
(7) The overall initial cost is much less than that of steam power
station of the same size.
(8) The thermal efficiency of the plant is higher than that of steam
plant
(9) It requires less operating staff.
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Diesel Power Station
• Disadvantages:
(1) The plant has high running cost as the fuel (diesel)
used is costly.
(2) The plant does not works satisfactory under
overload conditions for a longer period.
(3) The plant can only generate small power
(4) The cost of lubrication is generally high
(5) The maintenance charges are generally high
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Schematic Arrangement of Diesel Power Station
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Diesel Power Station
• Fuel Supply System: It consists of storage tank, strainer,
fuel transfer pump and all day fuel tank. The oil is stored
in the storage tank. From storage tank, oil is pumped to
smaller all day tank at daily or short intervals. From this
tank, fuel oil is passed through strainers to remove
suspended impurities. The clean oil is injected into the
engine by fuel injection pump.
• Air Intake System: This system supplies necessary air to
the engine for fuel combustion. Filters are provided to
remove dust particles from air.
• Exhaust System: This system leads the engine exhaust gas
outside the building. A silencer is usually incorporated in
the system to reduce the noise level.
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Diesel Power Station
• Cooling System: The cooling system consists of a
water source, pump and cooling towers. The pump
circulates water cylinder and head jacket. The
water takes away heat from the engine and itself
becomes hot. The hot water is cooled by cooling
towers and is recirculated for cooling.
• Lubricating System: This system consists of
lubricating oil tank, pump, filter and oil cooler. The
lubricating oil is drawn from the lubricating oil tank
by the pump and is passed through the filters to
remove impurities. The oil coolers keep the
temperature of the oil low.
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Diesel Power Station
• Engine Starting System: This is an arrangement to
rotate the engine initially. For large units,
compressed air is used for starting. Air at high
pressure is admitted to few of the cylinders, making
them act as reciprocating air motors to turn over
the engine shaft. The fuel is admitted to the
remaining cylinders which makes the engine starts
under its own power.
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