power station

A power station (also referred to as a generating station, power plant, or powerhouse) is an industrial facility for the generation of electric energy.
At the center of nearly all power stations is a generator, a rotating machine that converts mechanical energy into electrical energy by creating relative motion between a magnetic field and a conductor. The energy source harnessed to turn the generator varies widely. It depends chiefly on which fuels are easily available and on the types of technology that the power company has access to.

1 History 2 Thermal power stations 2.1 Classification 2.1.1 By fuel 2.1.2 By prime mover 2.2 Cooling towers 3 Other sources of energy 3.1 Hydroelectricity 3.1.1 Pumped storage 3.2 Solar 3.3 Wind 4 Typical power output 5 Operations 6 See also 7 References 8 External links

History

The world's first power station was built by Sigmund Schuckert in the Bavaria town of Ettal and went into operation in 1878  The station consisted of 24 dynamo electric generators which were driven by a steam engine. It was used to illuminate a grotto in the gardens of Linderhof Palace.
The first public power station was the Edison Electric Light Station, built in London at 57, Holborn Viaduct, which started operation in January 1882. This was an initiative of Thomas Edison that was organized and managed by his partner, Edward Johnson. A Babcock and Wilcox boiler powered a 125 horsepower steam engine that drove a 27 ton generator called Jumbo, after the celebrated elephant. This supplied electricity to premises in the area that could be reached through the culverts of the viaduct without digging up the road, which was the monopoly of the gas companies. The customers included the City Temple and the Old Bailey. Another important customer was the Telegraph Office of the General Post Office but this could not be reached though the culverts. Johnson arranged for the supply cable to be run overhead, via Holborn Tavern and Newgate.

 Thermal power stations

Rotor of a modern steam turbine, used in power station.

Main article: Thermal power station

In thermal power stations, mechanical power is produced by a heat engine that transforms thermal energy, often from combustion of a fuel, into rotational energy. Most thermal power stations produce steam, and these are sometimes called steam power stations. Not all thermal energy can be transformed into mechanical power, according to the second law of thermodynamics. Therefore, there is always heat lost to the environment. If this loss is employed as useful heat, for industrial processes or district heating, the power plant is referred to as a cogeneration power plant or CHP (combined heat-and-power) plant. In countries where district heating is common, there are dedicated heat plants called heat-only boiler stations. An important class of power stations in the Middle East uses by-product heat for the desalination of water.
The efficiency of a steam turbine is limited by the maximum temperature of the steam produced and is not directly a function of the fuel used. For the same steam conditions, coal, nuclear and gas power plants all have the same theoretical efficiency. Overall, if a system is on constantly (base load) it will be more efficient than one that is used intermittently (peak load).
Besides use of reject heat for process or district heating, one way to improve overall efficiency of a power plant is to combine two different thermodynamic cycles. Most commonly, exhaust gases from a gas turbine are used to generate steam for a boiler and steam turbine. The combination of a "top" cycle and a "bottom" cycle produces higher overall efficiency than either cycle can attain alone.

Classification

CHP plant in Warsaw, Poland.

Geothermal power station in Iceland.

Coal Power Station in Tampa, United States.

Thermal power plants are classified by the type of fuel and the type of prime mover installed.

By fuel

• Fossil fuelled power plants may also use a steam turbine generator or in the case of natural gas fired plants may use a combustion turbine. A coal-fired power station produces electricity by burning coal to generate steam, and has the side-effect of producing a large amount of carbon dioxide, which is released from burning coal and contributes to global warming. About 50% of electric generation in the USA is produced by coal fired power plants
• Nuclear power plants^[6] use a nuclear reactor's heat to operate a steam turbine generator. About 20% of electric generation in the USA is produced by nuclear power plants.
• Geothermal power plants use steam extracted from hot underground rocks.
• Biomass-fuelled power plants may be fuelled by waste from sugar cane, municipal solid waste, landfill methane, or other forms of biomass.
• In integrated steel mills, blast furnace exhaust gas is a low-cost, although low-energy-density, fuel.
• Waste heat from industrial processes is occasionally concentrated enough to use for power generation, usually in a steam boiler and turbine.
• Solar thermal electric plants use sunlight to boil water, which turns the generator.

HydroelectricityDams built to produce hydroelectricity impound a reservoir of water and release it through one or more water turbines, connected to generators, and generate electricity, from the energy provided by difference in water level upstream and downstream.

 Pumped storage

A pumped-storage hydroelectric power plant is a net consumer of energy but can be used to smooth peaks and troughs in overall electricity demand. Pumped storage plants typically use "spare" electricity during off peak periods to pump water from a lower reservoir or dam to an upper reservoir. Because the electricity is consumed "off peak" it is typically cheaper than power at peak times. This is because the "base load" power stations, which are typically coal fired, cannot be switched on and off quickly so remain in service even when demand is low. During hours of peak demand, when the electricity price is high, the water pumped to the high reservoir is allowed to flow back to the lower reservoir through a water turbine connected to an electricity generator. Unlike coal power stations, which can take more than 12 hours to to start up from cold, the hydroelectric plant can be brought into service in a few minutes, ideal to meet a peak load demand. Two substantial pumped storage schemes are in South Africa, one to the East of Cape Town (Palmiet) and one in the Drakensberg, Natal.

solar

Electricity from:
Solar Energy

The ultimate source of much of the world's energy is the sun, which provides the earth with light, heat and radiation. While many technologies derive fuel from one form of solar energy or another, there are also technologies that directly transform the sun's energy into electricity.

The sun bathes the earth in a steady, enormous flow of radiant energy that far exceeds what the world requires for electricity fuel.

Since generating electricity directly from sunlight does not deplete any of the earth's natural resources and supplies the earth with energy continuously, solar energy is a renewable source of electricity generation. Solar energy is our earth's primary source of renewable energy.
There are two different approaches to generate electricity from the sun: photovoltaic (PV) and solar-thermal technologies.

• Initially developed for the space program over 30 years ago, PV, like a fuel cell, relies upon chemical reactions to generate electricity. PV cells are small, square shaped semiconductors manufactured in thin film layers from silicon and other conductive materials. When sunlight strikes the PV cell, chemical reactions release electrons, generating electric current. The small current from individual PV cells, which are installed in modules, can power individual homes and businesses or can be plugged into the bulk electricity grid.
  
  
• Solar-thermal technologies are, more or less, a traditional electricity generating technology. They use the sun's heat to create steam to drive an electric generator. Parabolic trough systems, like those operating in southern California, use reflectors to concentrate sunlight to heat oil which in turn creates steam to drive a standard turbine.
  
  Two other solar-thermal technologies are nearing commercial status. Parabolic dish systems concentrate sunlight to heat gaseous hydrogen or helium or liquid sodium to create pressurized gas or steam to drive a turbine to generate electricity. Central receiver systems feature mirrors that reflect sunlight on to a large tower filled with fluid that when heated creates steam to drive a turbine.

Solar Electricity Basics

The three most common types of solar-electric systems are grid-intertied, grid-intertied with battery backup, and off-grid (stand-alone). Each has distinct applications and component needs.

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Grid Intertied Solar-Electric Systems
Also known as on-grid, grid-tied, or utilityinteractive (UI), grid-intertied solar-electric systems generate solar electricity and route it to the electric utility grid, offsetting a home’s or business’ electrical consumption and, in some instances, even turning the electric meter backwards. Living with a grid-connected solar-electric system is no different than living with grid power, except that some or all of the electricity you use comes from the sun. In many states, the utility credits a homeowner’s account for excess solar electricity produced. This amount can then be applied to other months when the system produces less or in months when electrical consumption is greater. This arrangement is called net metering or net billing. The specific terms of net metering laws and regulations vary from state to state and utility to utility. Consult your local electricity provider or state regulatory agency for their guidelines.
The following illustration includes the primary components of any grid interie solar electric system. See our Solar Electric System Components section for an introduction to the function(s) of each component.

See also the following Home Power feature articles:
Energy Smarts-Efficiency Gains + Solar Electricity
Creating A Brighter Future
Getting Off the Lifetime Utility Payment Plan: Grid-Connected PV

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Grid-Intertied Solar-Electric Systems with Battery Backup
Without a battery bank or generator backup for your gridintertied system, when a blackout occurs, your household will be in the dark, too. To keep some or all of your electric needs (or “loads”) like lights, a refrigerator, a well pump, or computer running even when utility power outages occur, many homeowners choose to install a grid-intertied system with battery backup. Incorporating batteries into the system requires more components, is more expensive, and lowers the system’s overall efficiency. But for many homeowners who regularly experience utility outages or have critical electrical loads, having a backup energy source is priceless.
The following illustration includes the primary components of any grid intertied solar electric system with battery backup. See our Solar Electric System Components section for an introduction to the function(s) of each component.

See also the following Home Power feature articles:

Eight Years of Solar Electricity: and Counting...
Walking the Talk: Energy Group Gets Solarized

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Off-Grid Solar-Electric Systems
Although they are most common in remote locations without utility grid service, off-grid solar-electric systems can work anywhere. These systems operate independently from the grid to provide all of a household’s electricity. That means no electric bills and no blackouts—at least none caused by grid failures. People choose to live off-grid for a variety of reasons, including the prohibitive cost of bringing utility lines to remote homesites, the appeal of an independent lifestyle, or the general reliability a solar-electric system provides. Those who choose to live off-grid often need to make adjustments to when and how they use electricity, so they can live within the limitations of the system’s design. This doesn’t necessarily imply doing without, but rather is a shift to a more conscientious use of electricity.
The following illustration includes the primary components of any off grid solar electric system. See our Solar Electric System Components section for an introduction to the function(s) of each component.

See also the following Home Power feature articles:
Postmodern PV Pioneers
Solar Comfort in the Idaho Wilderness: Off-Grid PV
All Creatures Under the Sun—My Solar Powered Barn
Green Half-Acre: Off-Grid Country Living – In the City

System Components

Electrical

The word is from the New Latin ēlectricus, "amber-like", coined in the year 1600 from the Greek ήλεκτρον (electron) meaning amber (hardened plant resin), because static electricity effects were produced classically by rubbing amberElectricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge.Electrical phenomena have been studied since antiquity, though advances in the science were not made until the seventeenth and eighteenth centuries.

Adding microprocessors to field instruments has transformed them into data acquisition systems and transmission terminals. Now technicians can use well-designed software to see what is happening inside plant instrumentation.

When asset management software is used, devices that need service can signal the operator or maintenance shop before they fail, lowering maintenance or repair costs and reducing the risk of unscheduled shutdown.

Instrumentation technicians responsible for reliable operation of thousands of field devices commonly receive calls from operators who are having trouble controlling a piece of production equipment, a reactor for example. If the plant is equipped with state-of-the-art asset management software, the technician can quickly determine which devices are associated with that reactor and which ones could be causing problems. Rather than going into the plant, the technician can evaluate each smart device from a personal computer in the instrument shop. For example, a quick computer check of the condition of each field device serving that reactor might reveal a travel deviation alert from one control valve, indicating a significant difference between the valve set point and its actual position--a situation requiring attention. The technician is spared long hours of checking out individual devices on the plant floor and knows exactly what must be done to correct the problem.
Although the poorly functioning valve in the reactor is hypothetical, the solution to this common problem is not. Up to 60 percent of instrument maintenance labor dollars are spent on devices where no problem exists or for routine checks to verify the condition of properly functioning devices. These requests often occur because an operator has no means of checking on the health and validity of field instrumentation and therefore calls the instrument shop when a problem is suspected. The most time-consuming and expensive service calls are those that conclude with no problem found.
Now, instrumentation technicians have a way to see what is happening inside plant instrumentation by using well-designed software in conjunction with intelligent field devices and new standard communications. These technologies allow technicians to

• Make sure field devices deliver optimum performance
• Use predictive maintenance to maximize service and repair resources
• Perform configurations and calibrations in half the normal time
• Document maintenance as required by industry regulators.

From a broader perspective, the integration and use of information acquired from intelligent field devices eliminates unexpected shutdowns, reduces downtime, and improves overall equipment performance.
Intelligent field devices
The process control system is designed for tight control of valves, motors, heaters, etc., in real time to manage feed stocks and make quality products. However, to increase the reliability and maintainability of plant instrumentation and process equipment and to lower the mean time between failures and time to accomplish repairs, a vast amount of information is needed about the condition and status of field equipment. The increase in smart instruments throughout the process industry makes it both practical and economical to use all the information they generate. It is estimated that 30 times more information is available from smart instruments than the simple variables required for process control.
Consider a smart pressure transmitter. Beyond providing basic pressure data, it can produce information relative to an overpressure condition (which can lead to inaccurate readings), an overtemperature condition (which can cause premature failure), a loss of signal, a stuck signal, and more. In the case of a control valve, the number of times the valve has cycled is a key indicator of how much work it has done and can be used in predicting its useful life. As the reactor example mentioned previously suggests, the internal position of a valve stem versus where it is supposed to be is critically important to the reliable operation of that piece of equipment. Smart valves routinely provide this kind of information.
The accuracy of field measurements and the reliability of field instrumentation are influenced by internal conditions that can be reported only by intelligent devices, and those conditions can have a direct impact on the availability or reliability of the process itself. Demand to make use of such data is growing. The acquired information must be made available well beyond the process control system.
Communicating the data
Automation architectures are evolving to deliver information from intelligent field devices, acting as information servers, around the control system to computers where the information can be used for diagnostic and maintenance purposes, for reliability analysis, for purchasing and inventory control systems, and for the overall management of plant assets.
General-purpose field communications protocols capable of transmitting large volumes of information for these purposes are currently in use. Today, the Highway Addressable Remote Transducer (HART) protocol offers the broadest range of user benefits and is supported by a wide range of vendors. Unlike proprietary communications technologies that lock users into field devices from a single manufacturer, the HART protocol is an open communications standard that works alongside any control system without interrupting the flow of process data.
Whereas HART transmits both analog and digital signals, the emerging Foundation Fieldbus protocol will be used with all-digital systems. Profibus is another new protocol under development. These sophisticated protocols are capable of carrying complex messages. Their use enables technicians to examine an instrument's self-diagnostics and also run extensive diagnostics programs on each device.
Using the information
For field data to be turned into useful knowledge, a reliable method of receiving, processing, and presenting it is required. Maintenance personnel require information on the condition of equipment, while operations personnel want other information and purchasing or inventory control requires something different. Each group needs information tailored to specific requirements. For example, the enhancement most desired by maintenance supervisors is seamless access to maintenance-related data. Advanced software applications are performing that function now.
Monitoring the intelligent devices installed in a plant and viewing their self-diagnostics probably are the most common functions of the instrumentation technician. Most smart instruments provide extensive information about their own health. Access to on-line device status provides a way to monitor and ensure proper device performance. The technician calls up the information device by device to see if any faults are flagged.
Automatic alert monitoring also is available to automatically scan devices on a user-determined schedule. If device problems exist, the information is posted to an alert monitor list. If no specific problems are found but something is suspected, it may be possible, depending on the software package, to use on-demand diagnostics. Certain operating parameters may be changed slightly to see if the device responds. For example, safety valves might be moved slightly to determine that the valve is not stuck and actuator pressures are sufficient to move the valve.
Automatic scanning of devices requires a higher level of sophistication. Such scans may uncover devices that need immediate attention, or they might generate lists of devices due for calibration. Some software is designed to interface with computerized maintenance management systems that track maintenance schedules and alert technicians when maintenance is due. Sophisticated software that identifies a need for instrument calibration combined with intelligent calibrators may also be able to automatically perform configurations and calibrations in a fraction of the time required for conventional calibrations.
Advanced, maintenance-oriented software permits maximum use of the information transmitted through a general-purpose protocol. The more advanced software receives the data, organizes it into open databases, and makes it available to other applications within the organization. Predictive maintenance is one of the key attributes of such systems. When the software makes a prediction about the expected service life of any piece of equipment, knowledgeable decisions can be made as to when repair or replacement will cause the least disruption to production.
Decisions such as run until failure, continue to run at reduced load, run until a scheduled shutdown, or repair immediately are based on highly reliable information, including the importance of the piece of equipment to the process. This approach helps focus limited resources on problems that warrant attention rather than wasting time on devices expected to continue working properly. In this way, instruments and control systems can be maintained in a high state of continued reliability.
What to look for
It is not difficult to obtain a communications and software package capable of accessing information generated by smart instruments, but not all software is created equal. First, potential buyers should be sure that nothing done with this ancillary information degrades the performance of the control system. Users of heavily loaded control systems may want to reserve all remaining control system capacity for future process control needs. Solutions available from various vendors of HART-compatible devices will carry the information through multiplexing, through intrinsic safety barrier panels, and through intelligent termination panels where information can be accessed by computers without using control system communications and computation resources.
However, data acquisition by itself does not provide the cost and time-saving benefits most maintenance managers are seeking. A flexible, maintenance-oriented, modular software platform that is both expandable and scalable must be found. Such software can provide access to a single device or to highly integrated client/server solutions for large multi-instrument plants.
In addition, the software should use device descriptions (DD), which are essentially files of field device attributes residing in the host application. The DD is essential to the interoperability of devices, allowing users to choose those that best meet their needs, regardless of manufacturer. As each new device is introduced, the description of attributes and capabilities is loaded into the host, providing complete data about each device in the plant. The DD technology is fundamental to the HART and Fieldbus protocols.
To be most useful, the software must accommodate the broadest range of field devices. It should support virtually all current HART and future Fieldbus devices, not just those manufactured by one company. In other words, the company should choose a technology to accommodate the widest range of applications needed to meet current and future plant and business needs. A number of good solutions are available. However, many tend to focus on a specific vendor's field instrumentation, which does not generally solve the problem of the large multi-instrument user.
Finally, it must be possible to integrate data from the field management software with any computerized maintenance management system the plant is running. An integrated solution is essential to realize the greatest value from information derived from intelligent field devices, transported through a state-of-the-art data highway, and processed in sophisticated, maintenance-oriented software.
Estimates show that one-third of all dollars spent on maintenance are wasted because of unnecessary work or ineffective practices. This trend can be reversed through the application of information generated by intelligent field devices and acceptance of the concept of predictive maintenance. The result can be a significant contribution to a plant's profitability.
It is not necessary to totally restructure maintenance practices. A plant can start small and expand the use of process floor information as needs dictate and budgets allow. The key is to begin building a database from the smart devices now in operation and expand the use of the available information as the number of such devices grows. A scalable and expandable platform can grow into a plantwide system that supports the reliability and maintainability of all field instrumentation. MT