A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. Chemical substances can be chemical compounds, or alloys. Chemical elements may not be included in the definition, depending on expert viewpoint. Chemical substances are called'pure' to set them apart from mixtures. A common example of a chemical substance is pure water. Other chemical substances encountered in pure form are diamond, table salt and refined sugar. However, in practice, no substance is pure, chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, gases, or plasma, may change between these phases of matter with changes in temperature or pressure. Chemical substances may be converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, are thus not "substances" in this regard.
A chemical substance may well be defined as "any material with a definite chemical composition" in an introductory general chemistry textbook. According to this definition a chemical substance can either be a pure chemical element or a pure chemical compound. But, there are exceptions to this definition; the chemical substance index published by CAS includes several alloys of uncertain composition. Non-stoichiometric compounds are a special case that violates the law of constant composition, for them, it is sometimes difficult to draw the line between a mixture and a compound, as in the case of palladium hydride. Broader definitions of chemicals or chemical substances can be found, for example: "the term'chemical substance' means any organic or inorganic substance of a particular molecular identity, including – any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature". In geology, substances of uniform composition are called minerals, while physical mixtures of several minerals are defined as rocks.
Many minerals, mutually dissolve into solid solutions, such that a single rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are a common example: anorthoclase is an alkali aluminum silicate, where the alkali metal is interchangeably either sodium or potassium. In law, "chemical substances" may include both pure substances and mixtures with a defined composition or manufacturing process. For example, the EU regulation REACH defines "monoconstituent substances", "multiconstituent substances" and "substances of unknown or variable composition"; the latter two consist of multiple chemical substances. For example, charcoal is an complex polymeric mixture that can be defined by its manufacturing process. Therefore, although the exact chemical identity is unknown, identification can be made to a sufficient accuracy; the CAS index includes mixtures. Polymers always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance.
However, the polymer may be defined by a known precursor or reaction and the molar mass distribution. For example, polyethylene is a mixture of long chains of -CH2- repeating units, is sold in several molar mass distributions, LDPE, MDPE, HDPE and UHMWPE; the concept of a "chemical substance" became established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate. He deduced; this is now known as the law of constant composition. With the advancement of methods for chemical synthesis in the realm of organic chemistry. However, there are some controversies regarding this definition because the large number of chemical substances reported in chemistry literature need to be indexed. Isomerism caused much consternation to early researchers, since isomers have the same composition, but differ in configuration of the atoms. For example, there was much speculation for the chemical identity of benzene, until the correct structure was described by Friedrich August Kekulé.
The idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction; this is so, beca
Overhead power line
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy along large distances. It consists of one or more conductors suspended by poles. Since most of the insulation is provided by air, overhead power lines are the lowest-cost method of power transmission for large quantities of electric energy. Towers for support of the lines are made of wood, steel or aluminum and reinforced plastics; the bare wire conductors on the line are made of aluminum, though some copper wires are used in medium-voltage distribution and low-voltage connections to customer premises. A major goal of overhead power line design is to maintain adequate clearance between energized conductors and the ground so as to prevent dangerous contact with the line, to provide reliable support for the conductors, resilience to storms, ice loads and other potential damage causes. Today overhead lines are operated at voltages exceeding 765,000 volts between conductors. Overhead power transmission lines are classified in the electrical power industry by the range of voltages: Low voltage – less than 1000 volts, used for connection between a residential or small commercial customer and the utility.
Medium voltage -- between 1000 volts and 69 kV, used for distribution in rural areas. High voltage, used for sub-transmission and transmission of bulk quantities of electric power and connection to large consumers. Extra high voltage – from 345 kV, up to about 800 kV, used for long distance high power transmission. Ultra high voltage – higher than 800 kV; the Financial Times reported UHV lines are a "game changer", making a global electricity grid feasible. StateGrid said that compared to conventional lines, UHV enables the transmission of five times more power, over six times the distance. Structures for overhead lines take a variety of shapes depending on the type of line. Structures may be as simple as wood poles directly set in the earth, carrying one or more cross-arm beams to support conductors, or "armless" construction with conductors supported on insulators attached to the side of the pole. Tubular steel poles are used in urban areas. High-voltage lines are carried on lattice-type steel towers or pylons.
For remote areas, aluminum towers may be placed by helicopters. Concrete poles have been used. Poles made of reinforced plastics are available, but their high cost restricts application; each structure must be designed for the loads imposed on it by the conductors. The weight of the conductor must be supported, as well as dynamic loads due to wind and ice accumulation, effects of vibration. Where conductors are in a straight line, towers need only resist the weight since the tension in the conductors balances with no resultant force on the structure. Flexible conductors supported at their ends approximate the form of a catenary, much of the analysis for construction of transmission lines relies on the properties of this form. A large transmission line project may have several types of towers, with "tangent" towers intended for most positions and more constructed towers used for turning the line through an angle, dead-ending a line, or for important river or road crossings. Depending on the design criteria for a particular line, semi-flexible type structures may rely on the weight of the conductors to be balanced on both sides of each tower.
More rigid structures may be intended to remain standing if one or more conductors is broken. Such structures may be installed at intervals in power lines to limit the scale of cascading tower failures. Foundations for tower structures may be large and costly if the ground conditions are poor, such as in wetlands; each structure may be stabilized by the use of guy wires to counteract some of the forces applied by the conductors. Power lines and supporting structures can be a form of visual pollution. In some cases the lines are buried to avoid this, but this "undergrounding" is more expensive and therefore not common. For a single wood utility pole structure, a pole is placed in the ground three crossarms extend from this, either staggered or all to one side; the insulators are attached to the crossarms. For an "H"-type wood pole structure, two poles are placed in the ground a crossbar is placed on top of these, extending to both sides; the insulators are attached in the middle. Lattice tower structures have two common forms.
One has a pyramidal base a vertical section, where three crossarms extend out staggered. The strain insulators are attached to the crossarms. Another has a pyramidal base. On top of this a horizontal truss-like structure is placed. A grounded wire is sometimes strung along the tops of the towers to provide lightning protection. An optical ground wire is a more advanced version with embedded optical fibers for communication. Overhead wire markers can be mounted on the ground wire to meet International Civil Aviation Organization recommendations; some markers include flashing lamps for night-time warning. A single-circuit transmission line carries conductors for only one circuit. For a three-phase system, this implies. A double-circuit transmission line has two circuits. For three
A windmill is a structure that converts the energy of wind into rotational energy by means of vanes called sails or blades. Centuries ago, windmills were used to mill grain, pump water, or both. There are windmills; the majority of modern windmills take the form of wind turbines used to generate electricity, or windpumps used to pump water, either for land drainage or to extract groundwater. Windmills first appeared in Persia in the 9th century AD, were independently invented in Europe; the windwheel of the Greek engineer Hero of Alexandria in the first century is the earliest known instance of using a wind-driven wheel to power a machine. Another early example of a wind-driven wheel was the prayer wheel, used in Tibet and China since the fourth century; the first practical windmills had sails. According to Ahmad Y. al-Hassan, these panemone windmills were invented in eastern Persia, or Khorasan, as recorded by the Persian geographer Estakhri in the ninth century. The authenticity of an earlier anecdote of a windmill involving the second caliph Umar is questioned on the grounds that it appears in a tenth-century document.
Made of six to 12 sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, were quite different from the European vertical windmills. Windmills were in widespread use across the Middle East and Central Asia, spread to China and India from there. A similar type of horizontal windmill with rectangular blades, used for irrigation, can be found in thirteenth-century China, introduced by the travels of Yelü Chucai to Turkestan in 1219. Horizontal windmills were built, in small numbers, in Europe during the 18th and nineteenth centuries, for example Fowler's Mill at Battersea in London, Hooper's Mill at Margate in Kent; these early modern examples seem not to have been directly influenced by the horizontal windmills of the Middle and Far East, but to have been independent inventions by engineers influenced by the Industrial Revolution. Due to a lack of evidence, debate occurs among historians as to whether or not Middle Eastern horizontal windmills triggered the original development of European windmills.
In northwestern Europe, the horizontal-axis or vertical windmill is believed to date from the twelfth and thirteenth centuries in the triangle of northern France, eastern England and Flanders. The earliest certain reference to a windmill in Europe dates from 1185, in the former village of Weedley in Yorkshire, located at the southern tip of the Wold overlooking the Humber Estuary. A number of earlier, but less dated, twelfth-century European sources referring to windmills have been found; these earliest mills were used to grind cereals. The evidence at present is that the earliest type of European windmill was the post mill, so named because of the large upright post on which the mill's main structure is balanced. By mounting the body this way, the mill is able to rotate to face the wind direction; the body contains all the milling machinery. The first post mills were of the sunken type, where the post was buried in an earth mound to support it. A wooden support was developed called the trestle.
This was covered over or surrounded by a roundhouse to protect the trestle from the weather and to provide storage space. This type of windmill was the most common in Europe until the nineteenth century, when more powerful tower and smock mills replaced them. In a hollow-post mill, the post on which the body is mounted is hollowed out, to accommodate the drive shaft; this makes it possible to drive machinery below or outside the body while still being able to rotate the body into the wind. Hollow-post mills driving scoop wheels were used in the Netherlands to drain wetlands from the fourteenth century onwards. By the end of the thirteenth century, the masonry tower mill, on which only the cap is rotated rather than the whole body of the mill, had been introduced; the spread of tower mills came with a growing economy that called for larger and more stable sources of power, though they were more expensive to build. In contrast to the post mill, only the cap of the tower mill needs to be turned into the wind, so the main structure can be made much taller, allowing the sails to be made longer, which enables them to provide useful work in low winds.
The cap can be turned into the wind either by winches or gearing inside the cap or from a winch on the tail pole outside the mill. A method of keeping the cap and sails into the wind automatically is by using a fantail, a small windmill mounted at right angles to the sails, at the rear of the windmill; these are fitted to tail poles of post mills and are common in Great Britain and English-speaking countries of the former British Empire and Germany but rare in other places. Around some parts of the Mediterranean Sea, tower mills with fixed caps were built because the wind's direction varied little most of the time; the smock mill is a development of the tower mill, where the masonry tower is replaced by a wooden framework, called the "smock", thatched, boarded or covered by other materials, such as slate, sheet metal, or tar paper. The smock is of octagonal plan, though there are examples with different numbers of sides; the lighter weight than tower mills make smock mills practical as drainage mills, which had t
Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter. Different sources define different frequency ranges as microwaves. A more common definition in radio engineering is the range between 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations; the prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range. Rather, it indicates that microwaves are "small", compared to the radio waves used prior to microwave technology; the boundaries between far infrared, terahertz radiation and ultra-high-frequency radio waves are arbitrary and are used variously between different fields of study. Microwaves travel by line-of-sight. At the high end of the band they are absorbed by gases in the atmosphere, limiting practical communication distances to around a kilometer.
Microwaves are used in modern technology, for example in point-to-point communication links, wireless networks, microwave radio relay networks, radar and spacecraft communication, medical diathermy and cancer treatment, remote sensing, radio astronomy, particle accelerators, industrial heating, collision avoidance systems, garage door openers and keyless entry systems, for cooking food in microwave ovens. Microwaves occupy a place in the electromagnetic spectrum with frequency above ordinary radio waves, below infrared light: In descriptions of the electromagnetic spectrum, some sources classify microwaves as radio waves, a subset of the radio wave band; this is an arbitrary distinction. Microwaves travel by line-of-sight paths. Although at the low end of the band they can pass through building walls enough for useful reception rights of way cleared to the first Fresnel zone are required. Therefore, on the surface of the Earth, microwave communication links are limited by the visual horizon to about 30–40 miles.
Microwaves are absorbed by moisture in the atmosphere, the attenuation increases with frequency, becoming a significant factor at the high end of the band. Beginning at about 40 GHz, atmospheric gases begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies. Above 100 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is in effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges. In a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal; this technique has been used at frequencies between 0.45 and 5 GHz in tropospheric scatter communication systems to communicate beyond the horizon, at distances up to 300 km.
The short wavelengths of microwaves allow omnidirectional antennas for portable devices to be made small, from 1 to 20 centimeters long, so microwave frequencies are used for wireless devices such as cell phones, cordless phones, wireless LANs access for laptops, Bluetooth earphones. Antennas used include short whip antennas, rubber ducky antennas, sleeve dipoles, patch antennas, the printed circuit inverted F antenna used in cell phones, their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. Therefore, beams of microwaves are used for point-to-point communication links, for radar. An advantage of narrow beams is that they don't interfere with nearby equipment using the same frequency, allowing frequency reuse by nearby transmitters. Parabolic antennas are the most used directive antennas at microwave frequencies, but horn antennas, slot antennas and dielectric lens antennas are used. Flat microstrip antennas are being used in consumer devices.
Another directive antenna practical at microwave frequencies is the phased array, a computer-controlled array of antennas which produces a beam which can be electronically steered in different directions. At microwave frequencies, the transmission lines which are used to carry lower frequency radio waves to and from antennas, such as coaxial cable and parallel wire lines, have excessive power losses, so when low attenuation is required microwaves are carried by metal pipes called waveguides. Due to the high cost and maintenance requirements of waveguide runs, in many microwave antennas the output stage of the transmitter or the RF front end of the receiver is located at the antenna; the term microwave has a more technical meaning in electromagnetics and circuit theory. Apparatus and techniques may
Hydraulics is a technology and applied science using engineering and other sciences involving the mechanical properties and use of liquids. At a basic level, hydraulics is the liquid counterpart of pneumatics, which concerns gases. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation and transmission of power by the use of pressurized liquids. Hydraulic topics range through some parts of science and most of engineering modules, cover concepts such as pipe flow, dam design and fluid control circuitry; the principles of hydraulics are in use in the human body within the vascular system and erectile tissue. Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in rivers, lakes and seas, its sub-field open-channel flow studies the flow in open channels. The word "hydraulics" originates from the Greek word ὑδραυλικός which in turn originates from ὕδωρ and αὐλός.
Early uses of water power date back to Mesopotamia and ancient Egypt, where irrigation has been used since the 6th millennium BC and water clocks had been used since the early 2nd millennium BC. Other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient Central Asia; the Greeks constructed sophisticated water and hydraulic power systems. An example is the construction by Eupalinos, under a public contract, of a watering channel for Samos, the Tunnel of Eupalinos. An early example of the usage of hydraulic wheel the earliest in Europe, is the Perachora wheel; the construction of the first hydraulic automata by Ctesibius and Hero of Alexandria is notable. Hero describes a number of working machines using hydraulic power, such as the force pump, known from many Roman sites as having been used for raising water and in fire engines; the Persians constructed an intricate system of water mills and dams known as the Shushtar Historical Hydraulic System.
The project, commenced by Achaemenid king Darius the Great and finished by a group of Roman engineers captured by Sassanian king Shapur I, has been referred to by UNESCO as "a masterpiece of creative genius." They were the inventors of the Qanat, an underground aqueduct. Several of Iran's large, ancient gardens were irrigated thanks to Qanats. In ancient China there was Sunshu Ao, Ximen Bao, Du Shi, Zhang Heng, Ma Jun, while medieval China had Su Song and Shen Kuo. Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron. Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation. In ancient Sri Lanka, hydraulics were used in the ancient kingdoms of Anuradhapura and Polonnaruwa; the discovery of the principle of the valve tower, or valve pit, for regulating the escape of water is credited to ingenuity more than 2,000 years ago. By the first century AD, several large-scale irrigation works had been completed.
Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control and recreational water courses and retaining structures and cooling systems were in place in Sigiriya, Sri Lanka. The coral on the massive rock at the site includes cisterns for collecting water. Large ancient reservoirs of Sri Lanka are Kalawewa, Parakrama Samudra, Tisa Wewa, Minneriya In Ancient Rome, many different hydraulic applications were developed, including public water supplies, innumerable aqueducts, power using watermills and hydraulic mining, they were among the first to make use of the siphon to carry water across valleys, used hushing on a large scale to prospect for and extract metal ores. They used lead in plumbing systems for domestic and public supply, such as feeding thermae. Hydraulic mining was used in the gold-fields of northern Spain, conquered by Augustus in 25 BC; the alluvial gold-mine of Las Medulas was one of the largest of their mines. It was worked by at least 7 long aqueducts, the water streams were used to erode the soft deposits, wash the tailings for the valuable gold content.
In 1619 Benedetto Castelli, a student of Galileo Galilei, published the book Della Misura dell'Acque Correnti or "On the Measurement of Running Waters", one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e. management of rivers in the Papal States, beginning in 1626. Blaise Pascal studied fluid hydrodynamics and hydrostatics, centered on the principles of hydraulic fluids, his discovery on the theory behind hydraulics led to the invention of the hydraulic press by Joseph Bramah, which multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure at both locations. Pascal's law or principle states that for an incompressible fluid at rest, the difference in pressure is proportional to the difference in height and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force.
This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other point in the containe
A transformer is a static electrical device that transfers electrical energy between two or more circuits. A varying current in one coil of the transformer produces a varying magnetic flux, which, in turn, induces a varying electromotive force across a second coil wound around the same core. Electrical energy can be transferred between the two coils, without a metallic connection between the two circuits. Faraday's law of induction discovered in 1831 described the induced voltage effect in any coil due to changing magnetic flux encircled by the coil. Transformers are used for increasing or decreasing the alternating voltages in electric power applications, for coupling the stages of signal processing circuits. Since the invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission and utilization of alternating current electric power. A wide range of transformer designs is encountered in electric power applications. Transformers range in size from RF transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect the power grid.
An ideal transformer is a theoretical linear transformer, lossless and coupled. Perfect coupling implies infinitely high core magnetic permeability and winding inductances and zero net magnetomotive force. A varying current in the transformer's primary winding attempts to create a varying magnetic flux in the transformer core, encircled by the secondary winding; this varying flux at the secondary winding induces a varying electromotive force in the secondary winding due to electromagnetic induction and the secondary current so produced creates a flux equal and opposite to that produced by the primary winding, in accordance with Lenz's law. The windings are wound around a core of infinitely high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With a voltage source connected to the primary winding and load impedance connected to the secondary winding, the transformer currents flow in the indicated directions and the core magnetomotive force cancels to zero.
According to Faraday's law, since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of windings. Thus, referring to the equations shown in the sidebox at right, according to Faraday's law, we have primary and secondary winding voltages defined by eq. 1 & eq. 2, respectively. The primary EMF is sometimes termed counter EMF; this is in accordance with Lenz's law, which states that induction of EMF always opposes development of any such change in magnetic field. The transformer winding voltage ratio is thus shown to be directly proportional to the winding turns ratio according to eq. 3. However, some sources use the inverse definition. According to the law of conservation of energy, any load impedance connected to the ideal transformer's secondary winding results in conservation of apparent and reactive power consistent with eq. 4. The ideal transformer identity shown in eq. 5 is a reasonable approximation for the typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio.
By Ohm's law and the ideal transformer identity: the secondary circuit load impedance can be expressed as eq. 6 the apparent load impedance referred to the primary circuit is derived in eq. 7 to be equal to the turns ratio squared times the secondary circuit load impedance. The ideal transformer model neglects the following basic linear aspects of real transformers: Core losses, collectively called magnetizing current losses, consisting of Hysteresis losses due to nonlinear magnetic effects in the transformer core, Eddy current losses due to joule heating in the core that are proportional to the square of the transformer's applied voltage. Unlike the ideal model, the windings in a real transformer have non-zero resistances and inductances associated with: Joule losses due to resistance in the primary and secondary windings Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance. Similar to an inductor, parasitic capacitance and self-resonance phenomenon due to the electric field distribution.
Three kinds of parasitic capacitance are considered and the closed-loop equations are provided Capacitance between adjacent turns in any one layer. However, the capacitance effect can be measured by comparing open-circuit inductance, i.e. the inductance of a primary winding when the secondary circuit is open, to a short-circuit inductance when the secondary winding is shorted. The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths; such flux is termed leakage flux, results in leakage inductance in series with the mutually coupled transformer windings. Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply, it is not directly a power loss, but results in inferior voltage regulation, causing the secondary voltage not to be directly proportional to the primary voltage under heavy load. Transformers are therefore designed to have low
Pumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low-lying land, the removal of sewage to processing sites. A pumping station is, by definition, an integral part of a pumped-storage hydroelectricity installation. In countries with canal systems, pumping stations are frequent; because of the way the system of canal locks work, water is lost from the upper part of a canal each time a vessel passes through. Most lock gates are not watertight, so some water leaks from the higher levels of the canal to those lower down; the water has to be replaced or the upper levels of the canal would not hold enough water to be navigable. Canals are fed by diverting water from streams and rivers into the upper parts of the canal, but if no suitable source is available, a pumping station can be used to maintain the water level. An excellent example of a canal pumping station is the Claverton Pumping Station on the Kennet and Avon Canal in southern England, United Kingdom.
This pumps water from the nearby River Avon to the canal using pumps driven by a waterwheel, powered by the river. Where no external water supply is available, back pumping systems may be employed. Water is extracted from the canal below the lowest lock of a flight and is pumped back to the top of the flight, ready for the next boat to pass through; such installations are small.. When low-lying areas of land are drained, the general method is to dig drainage ditches. However, if the area is below sea level it is necessary to pump the water upwards into water channels that drain into the sea; the Victorians understood this concept, in the United Kingdom they built pumping stations with water pumps, powered by steam engines to accomplish this task. In Lincolnshire, large areas of wetland at sea level, called The Fens, were turned into rich arable farmland by this method; the land is full of nutrients because of the accumulation of sedimentary mud that created the land initially. Elsewhere, pumping stations are used to remove water that has found its way into low-lying areas as a result of leakage or flooding.
In more recent times, a "package pumping station" provides an efficient and economic way of installing a drainage system. They are suitable for mechanical building services collection and pumping of liquids like surface water, wastewater or sewage from areas where drainage by gravity is not possible. A package pumping station is an integrated system, built in a housing manufactured from strong, impact-resistant materials such as precast concrete, polyethylene, or glass-reinforced plastic; the unit is supplied with internal pipework fitted, pre-assembled ready for installation into the ground, after which the submersible pumps and control equipment are fitted. Features may include controls for automatic operation. Traditional site constructed systems have the valve vault components installed in a separate structure. Having two structural components can lead to serious site problems such as uneven settling between components which results in stress on, failure of the pipes and connections between components.
The development of a packaged pump station system combined all components into a single housing which not only eliminates uneven settling issues, but pre-plumbing and outfitting each unit prior to installation can reduce the cost and time involved with civil work and site labor. Pumping stations in sewage collection systems are designed to handle raw sewage, fed from underground gravity pipelines. Sewage is fed into and stored in a pit known as a wet well; the well is equipped with electrical instrumentation to detect the level of sewage present. When the sewage level rises to a predetermined point, a pump will be started to lift the sewage upward through a pressurized pipe system called a sewer force main if the sewage is transported some significant distance; the pumping station may be called a lift station if the pump discharges into a nearby gravity manhole. From here the cycle starts all over again until the sewage reaches its point of destination—usually a treatment plant. By this method, pumping stations are used to move waste to higher elevations.
In the case of high sewage flows into the well additional pumps will be used. If this is insufficient, or in the case of failure of the pumping station, a backup in the sewer system can occur, leading to a sanitary sewer overflow—the discharge of raw sewage into the environment. Sewage pumping stations are designed so that one pump or one set of pumps will handle normal peak flow conditions. Redundancy is built into the system so that in the event that any one pump is out of service, the remaining pump or pumps will handle the designed flow; the storage volume of the wet well between the "pump on" and "pump off" settings is designed to minimize pump starts and stops, but is not so long a retention time as to allow the sewage in the wet well to go septic. Sewage pumps are always end-suction centrifugal pumps with open impellers and are specially designed with a large open passage so as to avoid clogging with debris or winding stringy debris onto the impeller. A four pole or six pole AC induction motor drives the pump.
Rather than provide large open passages, some pumps smaller sewage pumps macerate any solids within the