Fundamentals of Electric Power Systems

Fundamentals of Electric Power Systems

(Parte 1 de 7)

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Fundamentals of Electric Power Systems

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X.-P. Zhang University of Birmingham

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Restructured Electric Power Systems: Analysis of Electricity Markets with Equilibrium Models, Edited by Xiao-Ping Zhang Copyright © 2010 Institute of Electrical and Electronics Engineers

1.1 INTRODUCTION OF ELECTRIC POWER SYSTEMS
because DC transmission was impractical due to higher power losses

Commercial use of electricity began in the late 1870s when the inventive genius of Edison (Fig. 1.1 ) brought forth the electric incandescent light bulb. The fi rst complete electric power system was the Pearl Street system in New York, which began operation in 1882 and was actually a DC system with a steam - driven DC generator. With the development of the transformer, polyphase systems, and AC transmission, the fi rst three - phase line in North America was put into operation in 1893. It was then found that AC transmission with the help of transformers was preferable

With the development of electric power systems, interconnection of neighboring electric power systems leads to improved system security and economy. However, with the advent of interconnection of large - scale power systems, operation, control and planning of such systems become challenging tasks. With the development of digital computers and modern control techniques, automatic generation control (AGC) and voltage and reactive power control techniques have been introduced to operate and control modern large - scale power systems. Load fl ow solution has become the most frequently performed routine method of power network calculation, and can be used in power system planning, operational planning, operation control, and security analysis. With the advent of interconnected large - scale electric power systems, new dynamic phenomena, including transient stability, voltage stability, and low - frequency oscillations, have emerged. With the development of an electricity market, electricity companies engage in as many transactions in one hour as they once conducted in an entire day. Such increased load demand along with uncertainty of transactions will further strain electric power systems. Moreover, large amounts of decentralized renewable generation, in particular wind generation, connected with the network will result in further uncertainty of load and power fl ow distribution and impose additional strain on electric power system operation and control. It is a real challenge to ensure that the transmission system is fl exible enough to meet new and less predictable supply and demand conditions in competitive

Xiao - Ping Zhang

POWER SYSTEMS CHAPTER 1

2 CHAPTER 1 FUNDAMENTALS OF ELECTRIC POWER SYSTEMS electricity markets. FACTS (fl exible AC transmission systems) devices are considered low - environmental - impact technologies and are a proven enabling solution for rapidly enhancing reliability and upgrading transmission capacity on a long - term cost - effective basis. FACTS can provide voltage regulation, congestion management, enhancement of transfer capability, fast control of power oscillations, voltage stability control, and fault ride - through. The ever - increasing frequency of blackouts seen in developed countries has increased the need for new power system control technologies such as FACTS devices. With the development of advanced technologies and operation concepts such as FACTS, high voltage DC (HVDC), wide area measurements, microgrid systems, smart metering, and demand - side management, the development of smart grids is underway. It has been recognized that SCADA/ EMS Supervisory Control and Data Acquisition/Energy Management System plays a key role in the operating electricity networks and that state estimation is the key function of an EMS.

1.2ELECTRIC POWER GENERATION
1.2.1Conventional Power Plants
1.2.1.1Fossil Fuel Power Plants Basically, fossil fuel power plants burn

fossil fuels such as coal, natural gas, or petroleum (oil) to produce electricity. Traditionally, fossil fuel power plants are designed for continuous operation and large - scale production, and they are considered one of the major electricity production sources. The basic production process of a fossil fuel power plant is that the heat energy of combustion is converted into mechanical energy via a prime mover, a steam or gas turbine, then the mechanical energy is further converted into electrical energy via an AC generator, a synchronous generator.

It should be mentioned that the by - products of power plant production such as carbon dioxide, water vapor, nitrogen, nitrous oxides, and sulfur oxides need to be considered in both the design and operation of the power plant. Some of these by - products are harmful to the environment. In dealing with this, clean coal technology can remove sulfur dioxide and reburn it, which can enhance both the

Figure 1.1 Pioneers of electric power systems

George WestinghouseNikola TeslaThomas Alva Edison effi ciency and the environmental acceptability of coal extraction, preparation, and use.

In addition to coal, natural gas is considered another major source of electricity generation, using gas and steam turbines. It is well known that high effi ciencies can be achieved by combining gas turbines with a steam turbine in the so - called combined cycle mode. Basically, natural gas generation is cleaner than other fossil fuel power plants using oil and coal, and hence produces less carbon dioxide per unit energy generated. It is worth mentioning that fuel cell technology may provide cleaner options for converting natural gas into electricity, though such a generation technology is still not competitive in terms of generation costs.

1.2.1.2CCGT Power Plants The combined cycle gas turbine (CCGT) process

utilizes rotational energy produced from gas turbines driving AC generators as well as the additional power made available from the waste heat contained in the gas turbine exhaust. The heat is passed through a heat recovery steam generator, one for each gas turbine, and the steam generated is then used to produce rotational energy in a steam turbine driving a second AC generator.

exceed 655° C, while the lower temperature of a steam plant is determined by the

For a thermal power station, high - pressure steam requires strong, bulky components and high temperatures require expensive alloys made from nickel or cobalt. Due to the physical limitation of the alloys, practical steam temperatures do not boiling point of water. Considering these constraints, the maximum effi ciency of a steam plant is between 35% and 42%.

a steam temperature between 420 and 580° C. This will in turn increase the CCGT

In contrast, for a combined cycle power plant, the heat of the gas turbine ’ s exhaust can be used to generate steam driving a heat recovery steam generator with plant thermal effi ciency to 54%.

1.2.1.3Nuclear Power Plants Nuclear power technology extracts usable

energy from atomic nuclei via controlled nuclear reactions and includes nuclear fi ssion, nuclear fusion, and radioactive decay methods. Nuclear fi ssion is the one most widely used for power generation today. The production process of a nuclear power plant is that nuclear reactors are used to heat water to produce steam, the steam is converted into mechanical energy via a turbine, and the mechanical energy can then be further converted into electrical energy via an AC generator, a synchronous generator. More than 15% of the world ’ s electricity comes from nuclear power, where nuclear electricity generation is nearly carbon - free. It is estimated that replacing a coal - fi red power plant with a 1 GW nuclear power plant can avoid emission of 6 – 7 million tons of CO 2 per year. According to data from the International Energy Agency, existing nuclear power plants in operation worldwide have a total capacity of 370 GW. Most of them are second - generation light - water reactors (LWR) that were built in the 1970s and 1980s. Around 85% of the nuclear generation capacity is in US, France, Japan, Russia, the UK, Korea, and India. Third - generation nuclear power plant technology was developed in the 1990s to improve the safety and economics of nuclear power. However, due to the Chernobyl nuclear power accident in 1986, demand for

4 CHAPTER 1 FUNDAMENTALS OF ELECTRIC POWER SYSTEMS constructing new nuclear power plants was much reduced and hence only a limited number of third - generation reactors have been built. The fourth generation of nuclear reactors has been developed within an international framework where safety and economic performance are improved, nuclear waste is minimized, and proliferation resistance is enhanced.

Nuclear power is a capital - intensive technology where the cost of electricity generated from new power plants depends on investment cost, discount rate, construction time (typically 5 – 7 years or even longer), and economic lifetime (say 25 – 40 years). It was estimated by the International Energy Agency in 2006 that, with an assumed carbon price of $25/tCO 2 , the contribution of nuclear power generation to global electricity supply would increase to some 19 – 2% by 2050, where global nuclear power plant capacity would be at least doubled. Nuclear power could reduce global CO 2 emissions by 6% to 10%. With increasing oil prices and concerns about CO 2 emissions, there is growing interest in nuclear power generation. It has been recognized that nuclear power is one of the options to secure the supply of energy.

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1.2.2Renewable Power Generation Technologies
1.2.2.1Wind Energy Generation Wind energy is a clean, renewable, and

With the development of hydrogen technology, it will be important to fi nd ways to produce hydrogen more effi ciently. Hydrogen does not occur freely in nature in large quantities. Nuclear power could be used to generate hydrogen when load demand and electricity prices are low. The generated hydrogen could be stored to generate electricity and be fed back to the power grid when load demand and electricity prices are high. Alternatively, the stored hydrogen could be used to power hydrogen vehicles. Such a scenario would have a great impact on the operations of nuclear power plants, power grids, and electricity markets. The economics of a mixed portfolio of nuclear power and hydrogen energy need further relatively inexpensive source of renewable energy. It is considered one of the most developed and cost - effective renewable energy technologies. Electricity from wind generation is generally competitive with electricity produced by conventional power plants. Wind turbines can be situated either onshore or offshore. According to the Global Wind Energy Council, global wind power capacity has continued to grow at an average cumulative rate of over 30%, and in 2008 there was more than 27 GW of new installations. By the end of 2008, the total installed global wind power capacity was over 120 GW. It has been recognized that the United States overtook Germany to become the number one market in wind power while China ’ s total capacity doubled for the fourth year in a row. The ten countries with the highest installed wind power capacity are the US (25 GW), Germany (24 GW), Spain (16.8 GW), China (12 GW), India (9.6 GW), Italy (3.7 GW), France (3.4 GW), UK (3.2 GW), Denmark (3.2 GW), and Portugal (2.9 GW).

With implementation of European Commission targets on the promotion of electricity produced from renewable sources in the internal electricity market, wind power in Europe increased from 48 GW in 2006 to 65 GW in 2008 . According to [9] , by the end of 2008, there was 65 GW of wind power capacity (63.5 GW onshore and 1.5 GW offshore) installed in the EU - 27, of which 63.9 GW was in the EU - 15. Among the EU countries, Germany and Spain continue to be Europe ’ s leaders with total installed wind energy capacities of 24 GW and 17 GW, respectively where 63% of the EU ’ s installed wind energy capacity is located in these two countries.

With the development of wind power generation, there is growing penetration of wind energy into power grids. A wind power generation system normally consists of a wind turbine, a generator, and grid interface converters, if applicable, among which the generator is one of the core components. In the development of wind power generation techniques, synchronous generators, induction generators, and doubly fed induction generators have been employed to convert wind power to electrical power. Wind turbines usually rotate at a speed of 30 – 50 rev/min, and generators should rotate at the speed of 1000 – 1500 rev/min, so as to interface with power systems. Hence, a gearbox must connected between a wind turbine and a generator and requires regular maintenance; it also causes unpleasant noise and increases the loss of wind power generation. In order to overcome these problems, wind power generation with a direct - drive permanent magnet generator without a gearbox was developed. The permanent magnet generator driven directly by the wind turbine is a multi - pole and low - speed generator. Different types of direct - drive permanent magnet generators were developed for wind power generation, such as axial - fl ux and radial - fl ux machines.

Rapid technology development has enabled these prices and market growth.

There are technical and economic challenges for large - scale deployment of wind power generation due to the intermittent nature of wind power and unpredictability in comparison to traditional generation technologies. Hence, increasing levels of wind power generation on the system will increase the costs of balancing the system and managing system frequency within statuary limits. With the increase of wind power penetration on the system, the impact on system operations as well as market operations should be examined. With the development of advanced energy storage technologies, it is expected that the intermittency of wind power generation can be handled in more effective ways.

1.2.2.2Ocean Energy Generation The oceans cover more than 70% of the

earth ’ s surface and are the earth ’ s largest collector and retainer of the sun ’ s vast energy. Ocean energy includes tidal and wave energy.

Tidal power generation is nonpolluting, reliable, and predictable, and most modern tidal concepts use a dam approach with hydraulic turbines where tidal energy exploits the natural ebb and fl ow of coastal tidal waters due to the interaction of the gravitational fi elds of the earth, moon, and sun. Coastal water levels change twice daily, fi lling and emptying natural basins along the shoreline. In order to be practical for energy production, the height difference needs to be at least 5 meters. The tidal currents fl owing in and out of these basins can be used to drive mechanical devices to generate electricity. The fi rst large - scale tidal power plant in the world

6 CHAPTER 1 FUNDAMENTALS OF ELECTRIC POWER SYSTEMS was built in 1966 at La Rance, France, and can generate 240 MW. There is another related tidal energy technology called tidal stream technology. Tidal streams are fast sea currents caused by the tides, often magnifi ed by topographical features such as headlands, inlets, and straits that force water through narrow channels due to the shape of the sea bed. According to the World Offshore Renewable Energy Report 2002 – 2007 generated in the UK, worldwide, the potential capacity of tidal energy is around 3000 GW. It is estimated, however, that less than 3% is located in areas suitable for power generation.

(Parte 1 de 7)

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