Electric Power

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Posted by sonny 04/24/2009 @ 02:07

Tags : electric power, energy and water, business

News headlines
PG&E opposes two solar-power bills - San Jose Mercury News
"We are certainly a strong supporter of solar by our customers, and have been for quite some time," said David Rubin, PG&E's director of service analysis and chairman of the board of the Solar Electric Power Association, which represents 500 US...
Ethiopia to distribute 4.5 million power saving bulbs for free - Ethiopian Review
Addis Ababa, Ethiopia – The Ethiopian Electric Power Corporation (EEPCo) announced that it has finalized preparations to distributed 4.5 million power saving bulbs imported with more than 40 million birr. EEPCo public relations head, Misikr Negash told...
Solar shines - Arizona Daily Star
Backpacks, even clothing, could generate power to recharge cell phones or cameras. Prototypes are done and research to optimize them is underway. • June — Tucson Electric Power and the Arizona Research Institute for Solar Energy have formed a...
Pittsburg car thief hits pole, knocks out power - San Jose Mercury News
By Robert Jordan PITTSBURG — About 7600 Pacific Gas & Electric Co. customers lost power for an hour and half Saturday night after a man who stole a car crashed into a power pole. Pittsburg police Lt. Jim Calia said the vehicle was stolen from in front...
Thousands remain without power following storms - The Associated Press
Consumers Energy in Michigan says about 22400 of its customers statewide had no power as of 6 pm Saturday. Iowa and Wisconsin also had scattered outages. The storms produced torrential rain. The National Weather Service said parts of northern Illinois...
Honda counts on power of engines in a hybrid world - Reuters
"Today's competitive hybrid car is 'integral', which requires a delicate balance of engine, electric motor, batteries, power splitter, and the rest of the vehicle." said Takahiro Fujimoto, a manufacturing expert at the University of Tokyo....
Behind the Wheel | 2010 Ford Fusion Hybrid A Detroit Hybrid That Hums - New York Times
between electric and gas modes. While most hybrids can operate on electric power alone only up to about 25 miles an hour, the Fusion Hybrid can be coaxed up to 47 mph before the gas engine kicks in. But all-electric mode will take you only a mile or so...
The buzz is building for 'smart grid' power system - Richmond Times Dispatch
More than a century after Edison invented a reliable light bulb, the nation's electricity distribution system, an aging spider web of power lines, is poised to move into the digital age. The "smart grid" has become the buzz of the electric power...
Japan's Utility, Property Stocks Rise; Resource Shares Decline - Bloomberg
By Masaki Kondo Tokyo Electric Power Co., Asia's biggest utility, gained 1.8 percent. Mitsui Fudosan Co. added 2.1 percent. Mitsubishi Corp., a trading company that gets more than half its profit from commodities, lost 1 percent....

Electric power

Electrical power is distributed via cables and electricity pylons like these in Brisbane, Australia.

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.

When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work. Devices convert electrical energy into many useful forms, such as heat (electric heaters), light (light bulbs), motion (electric motors), sound (loudspeaker) or chemical changes. Electricity can be produced mechanically by generation, or chemically, or by direct conversion from light in photovoltaic cells, also it can be stored chemically in batteries.

In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power (also referred to as active power). That portion of power flow due to stored energy, that returns to the source in each cycle, is known as reactive power.

The ratio of real power to apparent power is called power factor and is a number always between 0 and 1.

The result is a scalar since it is the surface integral of the Poynting vector.

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Electric power transmission

Transmission lines

Electric power transmission is the bulk transfer of electrical power (or more correctly energy), a process in the delivery of electricity to consumers. A power transmission network typically connects power plants to multiple substations near a populated area. The wiring from substations to customers is referred to as Electricity distribution, following the historic business model separating the wholesale electricity transmission business from distributors who deliver the electricity to the homes. Electric power transmission allows distant energy sources (such as hydroelectric power plants) to be connected to consumers in population centers, and may allow exploitation of low-grade fuel resources such as coal that would otherwise be too costly to transport to generating facilities.

Usually transmission lines use three phase alternating current (AC). Single phase AC current is sometimes used in a railway electrification system. High-voltage direct current systems are used for long distance transmission, or some undersea cables, or for connecting two different ac networks.

Electricity is transmitted at high voltages (110 kV or above) to reduce the energy lost in transmission. Power is usually transmitted as alternating current through overhead power lines. Underground power transmission is used only in densely populated areas because of its higher cost of installation and maintenance when compared with overhead wires,and the difficulty of voltage control on long cables.

A power transmission network is referred to as a "grid". Multiple redundant lines between points on the network are provided so that power can be routed from any power plant to any load center, through a variety of routes, based on the economics of the transmission path and the cost of power. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line, which, due to system stability considerations, may be less than the physical or thermal limit of the line. Deregulation of electricity companies in many countries has led to renewed interest in reliable economic design of transmission networks. However, in some places the gaming of a deregulated energy system has led to disaster, such as that which occurred during the California electricity crisis of 2000 and 2001.

Overhead conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Copper was sometimes used for overhead transmission but aluminum is lower in weight for equivalent performance, and much lower in cost. Overhead conductors are a commodity supplied by several companies worldwide. Improved conductor material and shapes are regularly used to allow increased capacity and modernize transmission circuits. Conductor sizes range from #6 American wire gauge (about 12 square millimeters) to 1,590,000 circular mils area (about 750 square millimeters), with varying resistance and current-carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to the skin effect, that causes most of the current to flow close to the surface of the wire.

Today, transmission-level voltages are usually considered to be 110 kV and above. Lower voltages such as 66 kV and 33 kV are usually considered sub-transmission voltages but are occasionally used on long lines with light loads. Voltages less than 33 kV are usually used for distribution. Voltages above 230 kV are considered extra high voltage and require different designs compared to equipment used at lower voltages.

Since overhead transmission lines are uninsulated wire, design of these lines requires minimum clearances to be observed to maintain safety. During adverse weather conditions of high wind and low temperatures, overhead conductors can exhibit wind-induced oscillations which can encroach on their designed clearances. Depending on the frequency and amplitude of oscillation, the motion can be termed gallop or flutter.

The advantages can in some cases outweigh the disadvantages of the higher investment cost, and more expensive maintenance and management.

Most high-voltage underground cables for power transmission that are currently sold on the market are insulated by a sheath of cross-linked polyethylene (XLPE). Some cable may have a lead or aluminum jacket in conjunction with XLPE insulation to allow for fiber optics to be seamlessly integrated within the cable. Before 1960, underground power cables were insulated with oil and paper and ran in a rigid steel pipe, or a semi-rigid aluminum or lead jacket or sheath. The oil was kept under pressure to prevent formation of voids that would allow partial discharges within the cable insulation. There are still many of these oil-and-paper insulated cables in use worldwide. Between 1960 and 1990, polymers became more widely used at distribution voltages, mostly EPDM (ethylene propylene diene M-class); however, their relative unreliability - particularly early XLPE - resulted in a slow uptake at transmission voltages. While cables of 330kV are commonly constructed using XLPE, this has occurred only in recent decades.

In the early days of commercial use of electric power, transmission of electric power at the same voltage as used by lighting and mechanical loads restricted the distance between generating plant and consumers. In 1882 generation was with direct current, which could not easily be increased in voltage for long-distance transmission. Different classes of loads – for example, lighting, fixed motors, and traction (railway) systems – required different voltages, and so used different generators and circuits.

Due to this specialization of lines and because transmission was so inefficient that generators needed to be close by their loads, it seemed at the time that the industry would develop into what is now known as a distributed generation system with large numbers of small generators located nearby their loads.

In 1886 in Great Barrington, Massachusetts, a 1kV AC distribution system was installed. That same year, AC power at 2kV, transmitted 30km, was installed at Cerchi, Italy. At an AIEE meeting on May 16, 1888, Nikola Tesla delivered a lecture entitled A New System of Alternating Current Motors and Transformers, describing the equipment which allowed efficient generation and use of polyphase alternating currents. The transformer, and Tesla's polyphase and single-phase induction motors, were essential for a combined AC distribution system for both lighting and machinery. Ownership of the rights to the Tesla patents was a key commercial advantage to the Westinghouse Company in offering a complete alternating current power system for both lighting and power.

Regarded as one of the most influential innovations for the use of electricity, the "universal system" used transformers to step-up voltage from generators to high-voltage transmission lines, and then to step-down voltage to local distribution circuits or industrial customers. By a suitable choice of utility frequency, both lighting and motor loads could be served. Rotary converters and later mercury-arc valves and other rectifier equipment allowed DC load to be served by local conversion where needed. Even generating stations and loads using different frequencies could be interconnected using rotary converters. By using common generating plants for every type of load, important economies of scale were achieved, lower overall capital investment was required, load factor on each plant was increased allowing for higher efficiency, allowing for a lower cost of energy to the consumer and increased overall use of electric power.

By allowing multiple generating plants to be interconnected over a wide area, electricity production cost was reduced. The most efficient available plants could be used to supply the varying loads during the day. Reliability was improved and capital investment cost was reduced, since stand-by generating capacity could be shared over many more customers and a wider geographic area. Remote and low-cost sources of energy, such as hydroelectric power or mine-mouth coal, could be exploited to lower energy production cost.

The first transmission of three-phase alternating current using high voltage took place in 1891 during the international electricity exhibition in Frankfurt. A 25 kV transmission line, approximately 175 kilometers long, connected Lauffen on the Neckar and Frankfurt.

Voltages used for electric power transmission increased throughout the 20th century. By 1914 fifty-five transmission systems each operating at more than 70 kV were in service. The highest voltage then used was 150 kV.

The rapid industrialization in the 20th century made electrical transmission lines and grids a critical part of the economic infrastructure in most industrialized nations. Interconnection of local generation plants and small distribution networks was greatly spurred by the requirements of World War I, where large electrical generating plants were built by governments to provide power to munitions factories; later these plants were connected to supply civil load through long-distance transmission.

Engineers design transmission networks to transport the energy as efficiently as feasible, while at the same time taking into account economic factors, network safety and redundancy. These networks use components such as power lines, cables, circuit breakers, switches and transformers.

Transmission efficiency is improved by increasing the voltage using a step-up transformer, which reduces the current in the conductors, while keeping the power transmitted nearly equal to the power input. The reduced current flowing through the conductor reduces the losses in the conductor and since, according to Joule's Law, the losses are proportional to the square of the current. Halving the current makes the transmission loss one quarter the original value.

A transmission grid is a network of power stations, transmission circuits, and substations. Energy is usually transmitted within the grid with three-phase AC. DC systems require relatively costly conversion equipment which may be economically justified for particular projects. Single phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors. In the 19th century two-phase transmission was used, but required either three wires with unequal currents or four wires. Higher order phase systems require more than three wires, but deliver marginal benefits.

The capital cost of electric power stations is so high, and electric demand is so variable, that it is often cheaper to import some portion of the needed power than to generate it locally. Because nearby loads are often correlated (hot weather in the Southwest portion of the United States might cause many people there to turn on their air conditioners), electricity must often come from distant sources. Because of the economics of load balancing, wide area transmission grids now span across countries and even large portions of continents. The web of interconnections between power producers and consumers ensures that power can flow, even if a few links are inoperative.

The unvarying (or slowly varying over many hours) portion of the electric demand is known as the "base load", and is generally served best by large facilities (and therefore efficient due to economies of scale) with low variable costs for fuel and operations, i.e. nuclear, coal, hydro. Renewables such as solar, wind, ocean/tidal, etc. are not considered "base load" but can still add power to the grid. Smaller and higher cost sources, such as combined cycle or combustion turbine plants fueled by natural gas are then added as needed.

Long-distance transmission of electricity (thousands of kilometers) is cheap and efficient, with costs of US$ 0.005 to 0.02 per kilowatt-hour (compared to annual averaged large producer costs of US$ 0.01 to US$ 0.025 per kilowatt-hour, retail rates upwards of US$ 0.10 per kilowatt-hour, and multiples of retail for instantaneous suppliers at unpredicted highest demand moments). Thus distant suppliers can be cheaper than local sources (e.g. New York City buys a lot of electricity from Canada). Multiple local sources (even if more expensive and infrequently used) can make the transmission grid more fault tolerant to weather and other disasters that can disconnect distant suppliers.

Long distance transmission allows remote renewable energy resources to be used to displace fossil fuel consumption. Hydro and wind sources can't be moved closer to populous cities, and solar costs are lowest in remote areas where local power needs are minimal. Connection costs alone can determine whether any particular renewable alternative is economically sensible. Costs can be prohibitive for transmission lines, but various proposals for massive infrastructure investment in high capacity, very long distance super grid transmission networks could be recovered with modest usage fees.

At the generating plants the energy is produced at a relatively low voltage between about 2300 volts and 30,000 volts, depending on the size of the unit. The generator terminal voltage is then stepped up by the power station transformer to a higher voltage (115 kV to 765 kV AC, varying by country) for transmission over long distances.

Transmitting electricity at high voltage reduces the fraction of energy lost to Joule heating. For a given amount of power, a higher voltage reduces the current and thus the resistive losses in the conductor. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the losses by a factor of 100, provided the same sized conductors are used in both cases. Even if the conductor size (cross-sectional area) is reduced x10 to match the lower current the losses are still reduced x10. Long distance transmission is typically done with overhead lines at voltages of 115 to 1,200 kV. At extremely high voltages, more than 2,000 kV between conductor and ground, corona discharge losses are so large that they can offset the lower resistance loss in the line conductors.

Transmission and distribution losses in the USA were estimated at 7.2% in 1995 , and in the UK at 7.4% in 1998.

As of 1980, the longest cost-effective distance for electricity was 4,000 miles (7,000 km), although all present transmission lines are considerably shorter.

In an alternating current circuit, the inductance and capacitance of the phase conductors can be significant. The currents that flow in these components of the circuit impedance constitute reactive power, which transmits no energy to the load. Reactive current flow causes extra losses in the transmission circuit. The ratio of real power (transmitted to the load) to apparent power is the power factor. As reactive current increases, the reactive power increases and the power factor decreases. For systems with low power factors, losses are higher than for systems with high power factors. Utilities add capacitor banks and other components throughout the system — such as phase-shifting transformers, static VAR compensators, physical transposition of the phase conductors, and flexible AC transmission systems (FACTS) — to control reactive power flow for reduction of losses and stabilization of system voltage.

At the substations, transformers reduce the voltage to a lower level for distribution to commercial and residential users. This distribution is accomplished with a combination of sub-transmission (33 kV to 115 kV, varying by country and customer requirements) and distribution (3.3 to 25 kV). Finally, at the point of use, the energy is transformed to low voltage (100 to 600 V, varying by country and customer requirements - see Mains power systems).

High voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is required to be transmitted over very long distances, it is more economical to transmit using direct current instead of alternating current. For a long transmission line, the lower losses and reduced construction cost of a DC line can offset the additional cost of converter stations at each end. Also, at high AC voltages, significant (although economically acceptable) amounts of energy are lost due to corona discharge, the capacitance between phases or, in the case of buried cables, between phases and the soil or water in which the cable is buried.

HVDC links are sometimes used to stabilize against control problems with the AC electricity flow. In other words, to transmit AC power as AC when needed in either direction between Seattle and Boston would require the (highly challenging) continuous real-time adjustment of the relative phase of the two electrical grids. With HVDC instead the interconnection would: (1) Convert AC in Seattle into HVDC. (2) Use HVDC for the three thousand miles of cross country transmission. Then (3) convert the HVDC to locally synchronized AC in Boston, and optionally in other cooperating cities along the transmission route. One prominent example of such a transmission line is the Pacific DC Intertie located in the Western United States.

The amount of power that can be sent over a transmission line is limited. The origins of the limits vary depending on the length of the line. For a short line, the heating of conductors due to line losses sets a "thermal" limit. If too much current is drawn, conductors may sag too close to the ground, or conductors and equipment may be damaged by overheating. For intermediate-length lines on the order of 100 km (60 miles), the limit is set by the voltage drop in the line. For longer AC lines, system stability sets the limit to the power that can be transferred. Approximately, the power flowing over an AC line is proportional to the sine of the phase angle of the voltage at the receiving and transmitting ends. Since this angle varies depending on system loading and generation, it is undesirable for the angle to approach 90 degrees. Very approximately, the allowable product of line length and maximum load is proportional to the square of the system voltage. Series capacitors or phase-shifting transformers are used on long lines to improve stability. High-voltage direct current lines are restricted only by thermal and voltage drop limits, since the phase angle is not material to their operation.

Up to now, it has been almost impossible to foresee the temperature distribution along the cable route, so that the maximum applicable current load was usually set as a compromise between understanding of operation conditions and risk minimization. The availability of industrial Distributed Temperature Sensing (DTS) systems that measure in real time temperatures all along the cable is a first step in monitoring the transmission system capacity. This monitoring solution is based on using passive optical fibers as temperature sensors, either integrated directly inside a high voltage cable or mounted externally on the cable insulation. A solution for overhead lines is also available. In this case the optical fiber is integrated into the core of a phase wire of overhead transmission lines (OPPC). The integrated Dynamic Cable Rating (DCR) or also called Real Time Thermal Rating (RTTR) solution enables not only to continuously monitor the temperature of a high voltage cable circuit in real time, but to safely utilize the existing network capacity to its maximum. Furthermore it provides the ability to the operator to predict the behavior of the transmission system upon major changes made to its initial operating conditions.

To ensure safe and predictable operation the components of the transmission system are controlled with generators, switches, circuit breakers and loads. The voltage, power, frequency, load factor, and reliability capabilities of the transmission system are designed to provide cost effective performance for the customers.

The transmission system provides for base load and peak load capability, with safety and fault tolerance margins. The peak load times vary by region largely due to the industry mix. In very hot and very cold climates home air conditioning and heating loads have an effect on the overall load. They are typically highest in the late afternoon in the hottest part of the year and in mid-mornings and mid-evenings in the coldest part of the year. This makes the power requirements vary by the season and the time of day. Distribution system designs always take the base load and the peak load into consideration.

The transmission system usually does not have a large buffering capability to match the loads with the generation. Thus generation has to be kept matched to the load, to prevent overloading failures of the generation equipment.

Multiple sources and loads can be connected to the transmission system and they must be controlled to provide orderly transfer of power. In centralized power generation, only local control of generation is necessary, and it involves synchronization of the generation units, to prevent large transients and overload conditions.

In distributed power generation the generators are geographically distributed and the process to bring them online and offline must be carefully controlled. The load control signals can either be sent on separate lines or on the power lines themselves. To load balance the voltage and frequency can be used as a signaling mechanism.

In voltage signaling the variation of voltage is used to increase generation. The power added by any system increases as the line voltage decreases. This arrangement is stable in principle. Voltage based regulation is complex to use in mesh networks, since the individual components and setpoints would need to be reconfigured every time a new generator is added to the mesh.

Wind turbines, v2g and other distributed storage and generation systems can be connected to the power grid, and interact with it to improve system operation.

Under excess load conditions, the system can be designed to fail gracefully rather than all at once. Brownouts occur when the supply power drops below the demand. Blackouts occur when the supply fails completely.

Rolling blackouts, or load shedding, are intentionally-engineered electrical power outages, used to distribute insufficient power when the demand for electricity exceeds the supply.

Rarely, and for short distances, a utility will use pilot-wires strung along the transmission line path. Leased circuits from common carriers are not preferred since availability is not under control of the electric power transmission organization.

Transmission lines can also be used to carry data: this is called power-line carrier, or PLC. PLC signals can be easily received with a radio for the long wave range.

Optical fibers can be included in the stranded conductors of a transmission line, in the overhead shield wires. These cables are known as OPGW or Optical Ground Wire. Sometimes a standalone cable is used, ADSS or All Dielectric Self Supporting cable, attached to the transmission line cross arms.

Some jurisdictions, such as Minnesota, prohibit energy transmission companies from selling surplus communication bandwidth or acting as a telecommunications common carrier. Where the regulatory structure permits, the utility can sell capacity in extra dark fibers to a common carrier, providing another revenue stream.

Some regulators regard electric transmission to be a natural monopoly and there are moves in many countries to separately regulate transmission (see Electricity market).

Spain was the first country to establish a Regional Transmission Organization. In that country transmission operations and market operations are controlled by separate companies. The transmission system operator is Red Eléctrica de España (REE) and the wholesale electricity market operator is Operador del Mercado Ibérico de Energía - Polo Español, S.A. (OMEL) . Spain's transmission system is interconnected with those of France, Portugal, and Morocco.

In the United States and parts of Canada, electrical transmission companies operate independently of generation and distribution companies.

Merchant transmission is an arrangement where a third party constructs and operates electric transmission lines through the franchise area of an unrelated utility. Advocates of merchant transmission claim that this will create competition to construct the most efficient and lowest cost additions to the transmission grid. Merchant transmission projects typically involve DC lines because it is easier to limit flows to paying customers.

The only operating merchant transmission project in the United States is the Cross Sound Cable from Long Island, New York to New Haven, Connecticut, although additional projects have been proposed.

A major barrier to wider adoption of merchant transmission is the difficulty in identifying who benefits from the facility so that the beneficiaries will pay the toll. Also, it is difficult for a merchant transmission line to compete when the alternative transmission lines are subsidized by other utility businesses.

Some research has found that exposure to elevated levels of EMF (electromagnetic fields), including ELF (extremely low frequency) fields, such as those originating from electric power transmission lines, may be implicated in a number of adverse health effects. These include, but are not limited to, childhood leukemia , Alzheimer's, adult leukemia, breast cancer, neurodegenerative diseases (such as amyotrophic lateral sclerosis), Miscarriage, and clinical depression. Although there seems to be a small statistical correlation between various diseases and living near power lines, any physical mechanism is not clear. One proposed mechanism is that the electric fields around power lines attract aerosol pollutants.

One response to the potential dangers of overhead power lines is to place them underground. The earth and enclosures surrounding underground cables prevent the electric field from radiating significantly beyond the power lines, and greatly reduce the magnetic field strength radiating from the power lines, into the surrounding area. However, the cost of burying and maintaining cables at transmission voltages is several times greater than overhead power lines (see section above, "Underground transmission").

Historically, local governments have exercised authority over the grid and have significant disincentives to take action that would benefit states other than their own. Localities with cheap electricity have a disincentive to making interstate commerce in electricity trading easier, since other regions will be able to compete for local energy and drive up rates. Some regulators in Maine for example do not wish to address congestion problems because the congestion serves to keep Maine rates low. Further, vocal local constituencies can block or slow permitting by pointing to visual impact, environmental, and perceived health concerns. In the US, generation is growing 4 times faster than transmission, but big transmission upgrades require the coordination of multiple states, a multitude of interlocking permits, and cooperation between a significant portion of the 500 companies that own the grid. From a policy perspective, the control of the grid is balkanized, and even former Energy secretary Bill Richardson refers to it as a "third world grid". There have been efforts in the EU and US to confront the problem. The US national security interest in significantly growing transmission capacity drove passage of the 2005 energy act giving the Department of Energy the authority to approve transmission if states refuse to act. However, soon after using its power to designate two National Interest Electric Transmission Corridors, 14 senators signed a letter stating the DOE was being too aggressive.

In some countries where electric trains run on low frequency AC (e.g. 16.7 Hz and 25 Hz) power, there are separate single phase traction power networks operated by the railways. These grids are fed by separate generators in some traction powerstations or by traction current converter plants from the public three phase AC network.

Radio and television broadcasters use specialized transmission lines to carry the output of high-power transmitters to the antenna.

High-temperature superconductors promise to revolutionize power distribution by providing lossless transmission of electrical power. The development of superconductors with transition temperatures higher than the boiling point of liquid nitrogen has made the concept of superconducting power lines commercially feasible, at least for high-load applications. It has been estimated that the waste would be halved using this method, since the necessary refrigeration equipment would consume about half the power saved by the elimination of the majority of resistive losses. In one hypothetical future system called a SuperGrid, the cost of cooling would be eliminated by coupling the transmission line with a liquid hydrogen pipeline.

Superconducting cables are particularly suited to high load density areas such as the business district of large cities, where purchase of an easement for cables would be very costly.

Single wire earth return (SWER) or single wire ground return is a single-wire transmission line for supplying single-phase electrical power for an electrical grid to remote areas at low cost. It is principally used for rural electrification, but also finds use for larger isolated loads such as water pumps, and light rail. Single wire earth return is also used for HVDC over submarine power cables.

Every radio transmitter emits power wirelessly. Both Nikola Tesla and Hidetsugu Yagi attempted to devise systems for large scale wireless power transmission. Tesla claimed to have succeeded. Yagi also proposed a similar concept, but the engineering problems proved to be more onerous than conventional systems. His work, however, led to the invention of the Yagi antenna.

Another form of wireless power transmission has been studied for transmission of power from solar power satellites to the earth. A high power array of microwave transmitters would beam power to a rectenna. Major engineering and economic challenges face any solar power satellite project.

Another form is the operation of a crystal radio powered by the radio station it is tuned to; however, the energetic efficiency is extremely low. Small scale wireless power was demonstrated as early as 1831 by Michael Faraday. By 1888, Heinrich Rudolf Hertz had proven that natural radio waves exist and can be captured.

The Federal government of the United States admits that the power grid is susceptible to cyber-warfare. Cyber spies are currently mapping the electrical grid. The United States Department of Homeland Security works with industry to identify vulnerabilities and to help industry enhance the security of control system networks, the federal government is also working to ensure that security is built in as we develop the next generation of 'smart grid' networks. On April 8, 2009, it is believed that China or Russia have infiltrated the U.S. electrical grid and left behind software programs that could be used to disrupt the system, according to current and former national-security officials. China denies intruding into the U.S. electrical grid. The North American Electric Reliability Corporation (NERC) has issued a public notice that warns that the electrical grid is not adequately protected from cyber attack. One counter measure the U.S. should consider is disconnecting the power grid from the Internet to decrease the likelihood of attack. Massive power outages caused by a cyber attack, would cause a crisis making it difficult for the government and emergency workers to respond to critical concerns leading to national trauma.

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Potomac Electric Power Company

The Potomac Electric Power Company (known as Pepco) is a public utility supplying electric power to the city of Washington, D.C., and to surrounding communities in Maryland. It has operated there since the 1920s.

Pepco was founded in the late 19th Century as a subsidiary of the Washington Traction and Electric Company, one of the private streetcar companies in Washington. Surplus power was then sold to other electric streetcar companies and to cable car companies so that they could convert to electricity. Later, the power was also sold to business and residential customers. The Public Utility Holding Company Act of 1935 forced the North American Company, the holding company, to sell the streetcar business and operate just the public utility.

In 2001, the company was reorganized and became a unit of Pepco Holdings, Inc.

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Electric power industry in China

China's electric power industry has changed dramatically since the early 1990s to become the world's second-largest electricity consumer, after the United States. In April 1996, an Electric Power Law was implemented, a major event in China's electric power industry. This law set out to promote the development of the electric power industry, to protect legal rights of investors, managers and consumers, and to regulate generation, distribution and consumption.

China has abundant energy. The country has the world's third-largest coal reserves and massive hydroelectric resources. But there is a mismatch between the location of the coal fields in the north-east (Heilongjiang, Jilin and Liaoning) and north (Shanxi, Shaanxi and Henan); hydro power in the south-west (Sichuan, Yunnan and Tibet); and the fast-growing industrial load centers of the east (Shanghai-Zhejiang) and south (Guangdong, Guangxi and Guizhou).

China's power industry has become increasingly competitive over the past three years as a result of government-initiated structural reforms and China's entry into the World Trade Organization (WTO). Power companies, faced with the pressure of competition, are looking to transform their communications infrastructure to boost efficiency and productivity.

In 2007, China’s energy supply and demand both surged ahead at an amazing pace in the shadow of its 11.4% GDP growth. Total energy consumption increased by 7.8% equivalent to 2.65 billion tons of standard coal while the amount of electric power generated grew by 14.1% in 2007, to 326.32 million kWh. Thermal power still accounts for the bulk of the energy generated, 83%, followed by 14% from hydro, 2% from nuclear and less than 0.1% from wind power.

By the end of 2007, China's total installed capacity amounted to 713 million kilowatts. China's power demand continued a steady growth momentum in 2008, up 13% year on year. With the shutdown of small thermal power generating units and the slowdown of investment in power generation, the high growth rate of China's newly increased installation capacity in 2008 will decelerate, and the rate is expected to reach 11.8% year on year.

In the long term China's power industry, boosted by accelerated process of industrialization and urbanization, will have an average annual growth rate of 6.6% to 7.0% in the next ten years. This indicates that the power industry will require a great deal of investment.

Currently, investment in hydropower, wind power and nuclear power is increasing. However, investment in coal-fired power generation still ranks first.

The structure of China's power industry is expected to remain unchanged for a long time. At present, China's hydropower output amounts to 13.88 percent of the national total, nuclear power output accounts for 1.94 percent and wind power output amounts to 0.26 percent, while coal-fired power output amounts to at least 78% of the national total. China's coal-fired power generation will be in a stage of stable development until at least 2020, and China's installed capacity of coal-fired power generating units will remain at more than 70 percent.

Before 1994 electricity supply was managed by electric power bureaus of the provincial governments. Now utilities have seen been managed by corporations outside of the government administration structure.

To end the State Power Corporation's (SPC) monopoly of the power industry, China's State Council dismantled the corporation in December 2002 and set up 11 smaller companies. SPC had owned 46% of the country's electrical generation assets and 90% of the electrical supply assets. The smaller companies include two electric power grid operators, five electric power generation companies and four relevant business companies. Each of the five electric power generation companies owns less than 20% (32 GW of electricity generation capacity) of China's market share for electric power generation. Ongoing reforms aim to separate power plants from power-supply networks, privatize a significant amount of state-owned property, encourage competition, and revamp pricing mechanisms.

It is expected that the municipal electric power companies will be divided into electric power generating and electric power supply companies. A policy of competition between the different generators will be implemented in the next years .

China's electric power industry continuously maintains a high growth rate. By the end of 2000, the total installed power was 315 GW, that means an increase of 16,5 GW or 5.5% compared to 1999. Hydropower amounted to 77 GW, accounting for 15 %; thermal power amounted to 235 GW, accounting for 83 %.and nuclear power amounted to 2GW, accounting for 1 % of installed capacity. Electricity generation reached 1400 TWh, 13.5 % more than in the previous year. In 1999, the construction investment of the electric power industry reached 14 billion US dollars, of which 49.3 % were dedicated to thermal power, 12.5 % to hydropower 6.4 % to nuclear 26.1 %, to transmission lines and transformers and 5.7 %.to other investments.

By the end of 2010, it is expected that the total installed capacity will reach 500 GW. Annual generation of electricity will exceed 2040 TWh. BY the end of 2007, the total installed capacity was 713.29 GW,annual generation of electricity was 3255.9 TWh.

It seems likely the cost of power will need to rise substantially over the medium term (2-5 years) to curb wasteful energy consumption and slow the rate of growth in electricity demand. In theory, the government could raise power costs by a similar amount across the whole of China in the interests of inter-regional equity.

The central government has made creation of a unified national grid system a top economic priority to improve the efficiency of the whole power system and reduce the risk of localised energy shortages. It will also enable the country to tap the enormous hydro potential from western China to meet booming demand from the eastern coastal provinces.

The main problem in China is the voltage drop when power is sent over very long distances from one region of the country to another.

Long distance inter-regional transmission have been implemented by using ultra-high voltages (UHV) of 800kV, based on an extension of technology already in use in other parts of the world.

Following research and testing, SGCC has announced construction of the first long-distance UHV line from Sichuan, which is rich in hydro-electric potential, to the eastern load center of Shanghai.

Shanghai already receives hydro-electric power from the massive Three Gorges Dam on the Changjiang (Yangtze) at Sandouping in Hubei province. But the new DC 800kV UHV line would enable it to receive power from twice as far west from the Xiangjiaba dam on the Jinsha river (a tributary of the Changjiang much further upstream).

Xiangjiaba will have total generating capacity of 6,400 MW. When completed, the nearby Xilodu Dam will add a further 12,600 MW (about 55 percent of the size of the planned Three Gorges output), making it the world's third-largest hydro-electric dam, ranking after the Three Gorges and Brazil's Itaipu.

Xilodu and Xiangjiaba are two of a series of massive new hydro projects that the government plans in south-western and western China to take advantage of the massive run off from the Himalayas and the Tibet plateau.

SGCC plans to bring a single pole of the Xiangjiaba-Shanghai line into commercial operation within two years (2010) and the second pole a year later (2011). SGCC plans to complete a total of 10 UHV projects by 2015 and 15 by 2020. In most cases, these will bring power from massive new hydro facilities in south-western China to the industrial and residential centers of the east.

China is speeding up its hydropower development and its hydropower installed capacity will reach 250 GW by the year 2020. This means that 46-47% of China's water resource will be exploited and utilized by then.

China has massive untapped potential for generating hydro-electric power. The government's official survey data show the country could theoretically generate 694 GW from hydro sources, of which about 541 GW is technically feasible and 401 GW is economically feasible.

By end-2005, the country had installed 130 GW of hydro capacity. But there was still another 270 GW of capacity which would be both technically and economically feasible to develop. Untapped economically feasible hydro potential is equivalent to 4.5 times the peak summer power demand of Guangdong province - the site of China'a massive export-oriented and often foreign-invested manufacturing hub.

Two-thirds of the untapped hydro potential is located in the two neighbouring provinces of Yunnan and Sichuan in the south-west, which could each generate an additional 87 GW of power from hydro sources. The key point is both provinces could be linked by UHV transmission lines to the major load centres at Guangdong on the south coast and Shanghai-Zhejiang on the east coast.

Dams and power lines are already under construction. Provided both technologies can be mastered, south China's power problems could be solved within the next 4-7 years.

South China from the Changjiang valley down to the South China Sea was the first part of the economy to liberalize in the 1980s and 1990s and is home to much of the country's most modern and often foreign-invested manufacturing industries. Northern and north-eastern China's older industrial base has fallen behind, remains focused on the domestic economy and has suffered relative decline.

Northern and north-eastern China relies heavily on thermal generation from the local coalfields. Northern China will remain reliant on increasingly expensive and polluting thermal generation.

In terms of nuclear power generation, China will advance from the moderate development strategy to accelerating development strategy. Nuclear power will play an even more important role in China's future power development. Especially in the developed coastal areas with heavy power load, nuclear power will become the backbone of the power structure there. China has planned to build up another 30 sets of nuclear power generator within 15 years with total installed capacity of 36 to 40 million kWh, accounting for about 4% of China's total installed capacity of the electric power industry.

In terms of the investment amount of China's listed power companies, the top three regions are Guangdong province, Inner Mongolia Autonomous Region and Shanghai, whose investment ratios are 15.33%, 13.84% and 10.53% respectively, followed by Sichuan and Beijing.

China's listed power companies invest mostly in thermal power, hydropower and thermoelectricity, with their investments reaching CNY216.38 billion, CNY97.73 billion and CNY48.58 billion respectively in 2007. Investment in gas exploitation and coal mining follow as the next prevalent investment occurrences.

E-commerce in China is developing at full speed with its many advantages including low cost, high efficiency etc. With the advancement of electric power system reform, the electric utility industry of China has already possessed the basic condition of e-commerce development.

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Source : Wikipedia