Transcript Unit 51: Electrical Technology - News

Unit 51: Electrical Technology
The Characteristics and Principles of
AC and DC Generators and the
features of a Range of difference
Power Station
Course Aims
•
NDGTA
At the end of this course the learner will be
able to…
1. Know the methods used to produce electrical
energy
2. Know the properties and applications of conductors,
insulators and magnetic materials
3. Know the physical arrangements of supply,
transmission and distribution equipment
4. Know how electrical energy is used to support
applications of electrical technology
Agenda
NDGTA
• At the end of the session the learner will
be able to…
– Describe the characteristics of an electrical
power generating system
Electrical Power
NDGTA
• Electrical power can be produced in many
ways…
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Chemical reactions
Heat
Light
Mechanical energy
• The majority of our electrical energy is
generated in power plants. These convert the
energy produced by burning coal, oil, or natural
gas, by falling water, or by nuclear reactions into
electrical energy
Electrical Power
NDGTA
• Electrical generators at these power plants are
driven by steam or gas turbines, or by hydraulic
turbines (in the case of hydro-electrical plants).
• There are other alternative methods of electrical
power generation such as solar cells,
geothermal systems, wind-powered systems,
magnetohydrodynamic (MHD) systems, nuclear
fusion systems and fuel cells. These may very
well become more prominent in the future as the
earth’s natural resources become depleted and
we search for more sustainable forms of
electrical power.
Electrical Power
Generation
NDGTA
• Most power plants use are either fossil fuel
steam plants, nuclear fission steam plants or
hydro-electrical plants.
• Fossil fuel and nuclear plants utilise steam
turbines to deliver mechanical energy needed to
rotate the large 3-phase generators (alternators)
• Hydro-electric plants ordinarily use vertically
mounted hydraulic turbines where the force of
flowing water is utilised as the source of
mechanical energy.
Electrical Power:
Supply & Demand
NDGTA
• Power plants are sited near cities, large
industries – generally places where large
amount of electrical energy is consumed.
• Supply and demand is different to other
consumer products in as much as it must
be supplied at the same time it is
demanded – there is no simple storage
system for electrical energy.
Electrical Power:
Supply & Demand
NDGTA
• Plant load (demand) and Capacity Factors
are two measures that are used to
measure the significant variation in the
load requirements at different times.
• Demand Factor = Average load for a time period
Peak load for a time period
• A power plant has an average load of 220 MW and a
peak load of 295 MW over a 24-hour period. What is the
load factor?
Electrical Power:
Supply & Demand
NDGTA
• Capacity Factor = Average load for a time period
Output capacity for a time period
• A power plant has an average load of 112 MW and an
output capacity of 166 MW. What is the capacity factor?
Fossil Systems
NDGTA
• Fossil fuels are the result of large organic
materials whose structure has been changed
over millions of years as a consequence of
being subjected to high pressures and
temperatures under the earth’s surface.
• These deposits are known to us as coal, oil and
natural gas.
• A basic fossil fuel system is shown in handout 1
Fossil Systems
NDGTA
• A fossil fuel (coal, oil, natural gas) is burned to
produce heat energy.
• The heat from the combustion process is
concentrated within the boiler where circulating
water is converted into steam.
• High-pressure steam is used to rotate a turbine.
• The turbine shaft is connected directly to the
electrical generator and provides the necessary
mechanical energy to rotate the generator.
• The generator converts mechanical energy into
electrical energy
Fossil Fuels
NDGTA
• Fossil fuels are used to supply heat by
means of chemical reactions: carbon
based materials being burned as a result
of their reaction with oxygen.
• Fossil fuels vary according to…
– Their natural state (solid, liquid, gas)
– Their ability to produce heat
– The type of flame or heat they produce
Coal Powered
Power system
NDGTA
• Coal is in a solid state. It is normally pulverised
into fine particles which are then fed into the
furnace by air pressure produced by force-draft
fans.
• The coal is held in a suspension until it is ignited.
The suspended particles enables sustained
combustion to take place.
• The maximum efficiency of a coal fired electrical
power plant is around 40%
• Efficiency = power output / power input
The Future of
Coal Powered Power systems
NDGTA
• Pulverised-coal systems have been used for many
years, these days however there are an increasing
number of environmental restrictions on these systems.
• Major problems include
– Sulphur dioxide and nitrogen oxide emissions
– Coal is the dirtiest of the fossil fuels – with respect to
environmental factors
• With reserves of oil and gas becoming more scarce coal
may very well play an increasingly bigger role in the
future generation of electrical power
• Environmental impact of mining and the transportation of
the coal to the power station
Hydroelectric
Power systems
NDGTA
• The use of water as a power system goes
back to ancient times. The use of water to
generate electrical power however saw its
development early in the last century.
• The energy of flowing water is used to
pass blade of a hydraulic turbine which
produces rotation of a shaft. See Handout
2
Hydroelectric
Power systems
NDGTA
• One of the difficulties of the hydro-electrical generating
system is controlling the flow of water to ensure the
constant rotational speed of 50 Hz. This is achieved by
blade-angle adjustment and the amount of water being
channelled onto the blades of the turbine. These must
be continuously controlled to match demand.
• The efficiency of hydro-electric turbines can be > 85%
• Pumped-storage hydro-electric systems can the use of
the turbine from to act as a pump to pump water back
into the reservoir at times of low demand.
The Future of
Hydroelectric Power systems
NDGTA
• At present only a small amount of electricity is
generated by hydroelectric power <10%.
• Discounting construction costs the cost of
electrical generation is relatively in-expensive.
• Creating a source of water that can be used for
hydro-electric power generation can bring other
benefits: recreational benefits, irrigation, flood
control – but at what cost to the environment
itself: flooded valleys; lost communities living in
the valleys; the amount of water needed to
satisfy our needs.
Nuclear Fission Systems
NDGTA
• Nuclear fission is a complex reaction that results
in the division of the nucleus of an atom into two
or more nuclei.
• The splitting of the atom is brought about by the
bombardment of the nucleus with neutrons,
gamma rays or other charged particles and it is
referred to as induced fission.
• When an atom splits it releases an enormous
amount of energy in the form of heat.
Nuclear Fission Systems
NDGTA
• Nuclear reactions ‘burns’ nuclear fuel
whose atoms split causing the release of
heat. – see Handout 3. This occurs in the
reactor.
• The heat from the fission process is used
to change circulating water into steam.
• The high pressure steam rotates a turbine
which is connected to an electrical
generator.
Nuclear Fission Systems
NDGTA
• The splitting of the nuclei needs to be controlled
(moderated) – if left uncontrolled then there
could be a multiplying of reactions i.e. a chain
reaction which could potentially be very
dangerous.
• A nuclear power station is classified by the type
of moderation it uses…
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BWR – Boiling water reactor
PWR – Pressurised water reactor
HTGR – High temperature Gas-cooled reactor
LMFBR – Liquid metal fast breeder reactor
Nuclear Fission Systems
NDGTA
• Considerations relating to the generation of
electrical energy by means of a nuclear fission
systems.
– Location – normally sited near a source of plentiful
water
– Mining of the ore - environmental impact
– The long half-life and the problems with dealing with
hazardous waste – much research being done to
transmute the ‘daughter’ nuclei to reduce the impact
of half-life
– Dealing with people’s fears - Fukishima