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Unit 51: Electrical Technology

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. At the end of this course the learner will be able to… Know the methods used to produce electrical energy

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Unit 51: Electrical Technology

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  1. Unit 51: Electrical Technology The Characteristics and Principles of AC and DC Generators and the features of a Range of difference Power Station

  2. Course Aims • At the end of this course the learner will be able to… • Know the methods used to produce electrical energy • Know the properties and applications of conductors, insulators and magnetic materials • Know the physical arrangements of supply, transmission and distribution equipment • Know how electrical energy is used to support applications of electrical technology

  3. Agenda • At the end of the session the learner will be able to… • Describe the characteristics of an electrical power generating system

  4. Electrical Power • Electrical power can be produced in many ways… • 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

  5. Electrical Power • 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.

  6. Electrical PowerGeneration • 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.

  7. Electrical Power:Supply & Demand • 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.

  8. Electrical Power:Supply & Demand • 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?

  9. Electrical Power:Supply & Demand • 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?

  10. Fossil Systems • 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

  11. Fossil Systems • 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

  12. Fossil Fuels • 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

  13. Coal PoweredPower system • 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

  14. The Future ofCoal Powered Power systems • 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

  15. Hydroelectric Power systems • 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

  16. Hydroelectric Power systems • 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.

  17. The Future of Hydroelectric Power systems • 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.

  18. Nuclear Fission Systems • 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.

  19. Nuclear Fission Systems • 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.

  20. Nuclear Fission Systems • 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… • BWR – Boiling water reactor • PWR – Pressurised water reactor • HTGR – High temperature Gas-cooled reactor • LMFBR – Liquid metal fast breeder reactor

  21. Nuclear Fission Systems • 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

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