The Southeast Steam Plant , formerly known as the Twin City Rapid Transit Company Steam Power Plant , is a combined heat and power plant on the Mississippi River in the city of Minneapolis, Minnesota in the United States owned by the University of Minnesota .
125-533: The plant was constructed in 1903 to provide electricity for the Twin City Rapid Transit street railway system . It supported the area's major form of public transportation for 50 years. Minneapolis converted to buses in 1949–1954, and in the early 1950s, Northern States Power Company (now Xcel Energy ) acquired the building. The University of Minnesota purchased the plant in 1976 for $ 1. The facility heats 94 buildings (nearly all of
250-455: A conductor 's surface, since otherwise there would be a force along the surface of the conductor that would move the charge carriers to even the potential across the surface. The electric field was formally defined as the force exerted per unit charge, but the concept of potential allows for a more useful and equivalent definition: the electric field is the local gradient of the electric potential. Usually expressed in volts per metre,
375-461: A force on each other, an effect that was known, though not understood, in antiquity. A lightweight ball suspended by a fine thread can be charged by touching it with a glass rod that has itself been charged by rubbing with a cloth. If a similar ball is charged by the same glass rod, it is found to repel the first: the charge acts to force the two balls apart. Two balls that are charged with a rubbed amber rod also repel each other. However, if one ball
500-737: A magnetic field . In most applications, Coulomb's law determines the force acting on an electric charge. Electric potential is the work done to move an electric charge from one point to another within an electric field, typically measured in volts . Electricity plays a central role in many modern technologies, serving in electric power where electric current is used to energise equipment, and in electronics dealing with electrical circuits involving active components such as vacuum tubes , transistors , diodes and integrated circuits , and associated passive interconnection technologies. The study of electrical phenomena dates back to antiquity, with theoretical understanding progressing slowly until
625-427: A renewable resource that would reduce each student's fees by about $ 21. Four boilers are operational. A fluidized bed boiler (CFB) is seven stories high and capable of burning fuel oil, coal, wood, oat hulls or natural gas. There are two natural gas boilers, and one pulverized coal boiler, that can also fire fuel oil. There is a spreader stoker coal boiler, also capable of burning fuel oil and possibly oat hulls that
750-409: A steady state current, but instead blocks it. The inductor is a conductor, usually a coil of wire, that stores energy in a magnetic field in response to the current through it. When the current changes, the magnetic field does too, inducing a voltage between the ends of the conductor. The induced voltage is proportional to the time rate of change of the current. The constant of proportionality
875-432: A charge of Q coulombs every t seconds passing through an electric potential ( voltage ) difference of V is where Electric power is generally supplied to businesses and homes by the electric power industry . Electricity is usually sold by the kilowatt hour (3.6 MJ) which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using electricity meters , which keep
1000-418: A chute into a wagon, wheelbarrow, or open pile. When closed, the forage continues past the opening and onward to other parts of the conveyor. Computer automation and a conveyor running the length of a feeding stall can permit the silage to be automatically dropped from above to each animal, with the amount dispensed customized for each location. Silos are hazardous, and people are killed or injured every year in
1125-516: A common reference point to which potentials may be expressed and compared is useful. While this could be at infinity, a much more useful reference is the Earth itself, which is assumed to be at the same potential everywhere. This reference point naturally takes the name earth or ground . Earth is assumed to be an infinite source of equal amounts of positive and negative charge and is therefore electrically uncharged—and unchargeable. Electric potential
1250-430: A considerable engineering analysis of the system. Flexible Silos are the most versatile and cost-effective solution for the storage of bulk powder and granules. Manufactured from trevira tissue, a tough non-toxic fabric, the silos can handle particle size down to 2 microns and can be pneumatically loaded without the need for a dust collector. The 45-degree fabric silo cone flexes freely when the product discharges, enabling
1375-472: A current of one amp. The capacitor is a development of the Leyden jar and is a device that can store charge, and thereby storing electrical energy in the resulting field. It consists of two conducting plates separated by a thin insulating dielectric layer; in practice, thin metal foils are coiled together, increasing the surface area per unit volume and therefore the capacitance . The unit of capacitance
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#17327979768691500-494: A dampened kite string and flown the kite in a storm-threatened sky . A succession of sparks jumping from the key to the back of his hand showed that lightning was indeed electrical in nature. He also explained the apparently paradoxical behavior of the Leyden jar as a device for storing large amounts of electrical charge in terms of electricity consisting of both positive and negative charges. In 1775, Hugh Williamson reported
1625-526: A disadvantage for items like chopped wood. The tower silo was invented by Franklin Hiram King . In Canada , Australia and the United States, many country towns or the larger farmers in grain-growing areas have groups of wooden or concrete tower silos, known as grain elevators , to collect grain from the surrounding towns and store and protect the grain for transport by train, truck or barge to
1750-402: A fabric bag suspended within a rigid, structural frame. Polyester based fabrics are often used for fabrication of the bag material, with specific attention given to fabric pore size. Upper areas of silo fabric are often manufactured with slightly larger pore size, with the design intent of acting as a vent filter during silo filling. Some designs include metal thread within the fabric, providing
1875-418: A large comb -shaped tines to push forage into the bag. The forage is pushed in through a large opening, and as the teeth rotate back out, they pass between the comb tines. The cam-shaped auger teeth essentially wipe the forage off using the steel tines, keeping the forage in the bag. Before filling begins, the entire bag is placed onto the loader as a bunched-up tube folded back on itself in many layers to form
2000-407: A large brake shoe pressure regulator, holding back two large winch drums on either side of the loader. Cables from the drum extend to the rear of the bag where a large mesh basket holds the rear end of the bag shut. To prevent molding and to assure an airtight seal during fermentation, the ends of the silo bag tube are gathered, folded, and tied shut to prevent oxygen from entering the bag. Removal of
2125-420: A large heavy sheet of silo plastic which seals out oxygen and permits the entire pile to begin to ferment in the autumn. In the winter when animals must be kept indoors, the silo plastic is removed, the unloader is lowered down onto the top of the silage pile, and a hinged door is opened on the side of the silo to permit the silage to be blown out. There is an array of these access doors arranged vertically up
2250-425: A large lightning cloud may be as high as 100 MV and have discharge energies as great as 250 kWh. The field strength is greatly affected by nearby conducting objects, and it is particularly intense when it is forced to curve around sharply pointed objects. This principle is exploited in the lightning conductor , the sharp spike of which acts to encourage the lightning strike to develop there, rather than to
2375-488: A local historic preservation award, presented to the university and Miller Dunwiddie Architects, McGough Construction, Hess Roise Historical Consultants, Meyer Borgman Johnson , Michaud Cooley Erickson, INSPEC, Akiba Architects, and Kimley Horn. Among the "cleanest burning power plants in the country," the high temperature fires almost completely consume its fuels— natural gas , fuel oil, coal , and wood waste. The plant has tested and been approved for oat hull biofuel ,
2500-402: A millimetre per second, the electric field that drives them itself propagates at close to the speed of light , enabling electrical signals to pass rapidly along wires. Current causes several observable effects, which historically were the means of recognising its presence. That water could be decomposed by the current from a voltaic pile was discovered by Nicholson and Carlisle in 1800,
2625-553: A more reliable source of electrical energy than the electrostatic machines previously used. The recognition of electromagnetism , the unity of electric and magnetic phenomena, is due to Hans Christian Ørsted and André-Marie Ampère in 1819–1820. Michael Faraday invented the electric motor in 1821, and Georg Ohm mathematically analysed the electrical circuit in 1827. Electricity and magnetism (and light) were definitively linked by James Clerk Maxwell , in particular in his " On Physical Lines of Force " in 1861 and 1862. While
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#17327979768692750-416: A plug, the forage needs to be forked out into an even layer around the unloader so that the unloader does not immediately dig into the pile and plug itself again. All during this process the farmer is standing on or near a machine that could easily kill them in seconds if it were to accidentally start up. This could happen if someone in the barn were to unknowingly switch on the unloading mechanism while someone
2875-425: A positive current is defined as having the same direction of flow as any positive charge it contains, or to flow from the most positive part of a circuit to the most negative part. Current defined in this manner is called conventional current . The motion of negatively charged electrons around an electric circuit , one of the most familiar forms of current, is thus deemed positive in the opposite direction to that of
3000-891: A practical generator, but it showed the possibility of generating electric power using magnetism, a possibility that would be taken up by those that followed on from his work. An electric circuit is an interconnection of electric components such that electric charge is made to flow along a closed path (a circuit), usually to perform some useful task. The components in an electric circuit can take many forms, which can include elements such as resistors , capacitors , switches , transformers and electronics . Electronic circuits contain active components , usually semiconductors , and typically exhibit non-linear behaviour, requiring complex analysis. The simplest electric components are those that are termed passive and linear : while they may temporarily store energy, they contain no sources of it, and exhibit linear responses to stimuli. The resistor
3125-406: A process now known as electrolysis . Their work was greatly expanded upon by Michael Faraday in 1833. Current through a resistance causes localised heating, an effect James Prescott Joule studied mathematically in 1840. One of the most important discoveries relating to current was made accidentally by Hans Christian Ørsted in 1820, when, while preparing a lecture, he witnessed the current in
3250-418: A processor or to an export port. In bumper crop times, the excess grain is stored in piles without silos or bins, causing considerable losses. Concrete stave silos are constructed from small precast concrete blocks with ridged grooves along each edge that lock them together into a high strength shell. Concrete is much stronger in compression than tension , so the silo is reinforced with steel hoops encircling
3375-471: A rapidly changing one. Electric power is the rate at which electric energy is transferred by an electric circuit . The SI unit of power is the watt , one joule per second . Electric power, like mechanical power , is the rate of doing work , measured in watts , and represented by the letter P . The term wattage is used colloquially to mean "electric power in watts." The electric power in watts produced by an electric current I consisting of
3500-489: A relatively large stock of wheat was preserved in some hundreds of pits (silos) cut in the rock. A single silo stored from 60 to 80 tons of wheat, which, with proper precautions, kept in good condition for four years or more. The first modern silo, a wooden and upright one filled with grain , was invented and built in 1873 in Spring Grove, Illinois by Fred Hatch of McHenry County, Illinois , US. Forage silo filling
3625-489: A resistance is directly proportional to the potential difference across it. The resistance of most materials is relatively constant over a range of temperatures and currents; materials under these conditions are known as 'ohmic'. The ohm , the unit of resistance, was named in honour of Georg Ohm , and is symbolised by the Greek letter Ω. 1 Ω is the resistance that will produce a potential difference of one volt in response to
3750-595: A running total of the electric energy delivered to a customer. Unlike fossil fuels , electricity is a low entropy form of energy and can be converted into motion or many other forms of energy with high efficiency. Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes , transistors , diodes , sensors and integrated circuits , and associated passive interconnection technologies. The nonlinear behaviour of active components and their ability to control electron flows makes digital switching possible, and electronics
3875-431: A scientific curiosity into an essential tool for modern life. In 1887, Heinrich Hertz discovered that electrodes illuminated with ultraviolet light create electric sparks more easily. In 1905, Albert Einstein published a paper that explained experimental data from the photoelectric effect as being the result of light energy being carried in discrete quantized packets, energising electrons. This discovery led to
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4000-575: A series of experiments to the Royal Society on the shocks delivered by the electric eel ; that same year the surgeon and anatomist John Hunter described the structure of the fish's electric organs . In 1791, Luigi Galvani published his discovery of bioelectromagnetics , demonstrating that electricity was the medium by which neurons passed signals to the muscles. Alessandro Volta 's battery, or voltaic pile , of 1800, made from alternating layers of zinc and copper, provided scientists with
4125-515: A series of observations on static electricity around 600 BCE, from which he believed that friction rendered amber magnetic , in contrast to minerals such as magnetite , which needed no rubbing. Thales was incorrect in believing the attraction was due to a magnetic effect, but later science would prove a link between magnetism and electricity. According to a controversial theory, the Parthians may have had knowledge of electroplating , based on
4250-546: A set of equations that could unambiguously describe the interrelationship between electric field, magnetic field, electric charge, and electric current. He could moreover prove that in a vacuum such a wave would travel at the speed of light , and thus light itself was a form of electromagnetic radiation. Maxwell's equations , which unify light, fields, and charge are one of the great milestones of theoretical physics. Storage silo A silo (from Ancient Greek σιρός ( sirós ) 'pit for holding grain')
4375-477: A solid crystal (such as a germanium crystal) to detect a radio signal by the contact junction effect. In a solid-state component, the current is confined to solid elements and compounds engineered specifically to switch and amplify it. Current flow can be understood in two forms: as negatively charged electrons , and as positively charged electron deficiencies called holes . These charges and holes are understood in terms of quantum physics. The building material
4500-471: A static conductive path from the surface of the fabric to ground. The frame of a fabric silo is typically constructed of steel . Fabric silos are an attractive option because of their relative low cost compared to conventional silos. However, when fabric silos are used to store granular or particulate combustible materials, conventional practices prescribed by established industry consensus standards addressing combustible dust hazards can not be applied without
4625-409: A thick pile of plastic. Because the plastic is minimally elastic, the loader mechanism filling chute is slightly smaller than the final size of the bag, to accommodate this stack of plastic around the mouth of the loader. The plastic slowly unfurls itself around the edges of the loader as the tube is filled. The contents of the silo bag are under pressure as it is filled, with the pressure controlled by
4750-534: A traveling sled driven from the PTO of a tractor left in neutral and which is gradually pushed forward as the bag is filled. The steering of the tractor controls the direction of bag placement as it fills, but bags are normally laid in a straight line. The bag is loaded using the same forage harvesting methods as the tower, but the forage wagon must be moved progressively forward with the bag loader. The loader uses an array of rotating cam-shaped spiraled teeth associated with
4875-578: A wide variety of polyethylene plastics. The silos are light weight and make for great small scale storage for farmers with livestock and grain operations. The light weight design and cost effective materials make plastic silos a great alternative to traditional steel bins. Unlike fabric silos, which "tend to be prone to grain rot and pests which have left many farmers frustrated", plastic silos are more safe and secure, keeping grain fresh and unspoiled. They can be designed to be stationary hopper bottom bins or portable pallet bins. Fabric silos are constructed of
5000-511: A wire disturbing the needle of a magnetic compass. He had discovered electromagnetism , a fundamental interaction between electricity and magnetics. The level of electromagnetic emissions generated by electric arcing is high enough to produce electromagnetic interference , which can be detrimental to the workings of adjacent equipment. In engineering or household applications, current is often described as being either direct current (DC) or alternating current (AC). These terms refer to how
5125-448: A wire suspended from a pivot above the magnet and dipped into the mercury. The magnet exerted a tangential force on the wire, making it circle around the magnet for as long as the current was maintained. Experimentation by Faraday in 1831 revealed that a wire moving perpendicular to a magnetic field developed a potential difference between its ends. Further analysis of this process, known as electromagnetic induction , enabled him to state
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5250-402: A wire. The informal term static electricity refers to the net presence (or 'imbalance') of charge on a body, usually caused when dissimilar materials are rubbed together, transferring charge from one to the other. Charge can be measured by a number of means, an early instrument being the gold-leaf electroscope , which although still in use for classroom demonstrations, has been superseded by
5375-584: Is a scalar quantity . That is, it has only magnitude and not direction. It may be viewed as analogous to height : just as a released object will fall through a difference in heights caused by a gravitational field, so a charge will 'fall' across the voltage caused by an electric field. As relief maps show contour lines marking points of equal height, a set of lines marking points of equal potential (known as equipotentials ) may be drawn around an electrostatically charged object. The equipotentials cross all lines of force at right angles. They must also lie parallel to
5500-411: Is a vector field . The study of electric fields created by stationary charges is called electrostatics . The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field. This concept was introduced by Faraday, whose term ' lines of force ' still sometimes sees use. The field lines are the paths that a point positive charge would seek to make as it
5625-497: Is a structure for storing bulk materials . Silos are commonly used for bulk storage of grain, coal , cement , carbon black , woodchips , food products and sawdust . Three types of silos are in widespread use today: tower silos, bunker silos, and bag silos. Silos are used in agriculture to store fermented feed known as silage . Storage silos are cylindrical structures, typically 10 to 90 ft (3 to 27 m) in diameter and 30 to 275 ft (10 to 90 m) in height with
5750-452: Is an important difference. Gravity always acts in attraction, drawing two masses together, while the electric field can result in either attraction or repulsion. Since large bodies such as planets generally carry no net charge, the electric field at a distance is usually zero. Thus gravity is the dominant force at distance in the universe, despite being much weaker. An electric field generally varies in space, and its strength at any one point
5875-401: Is charged by the glass rod, and the other by an amber rod, the two balls are found to attract each other. These phenomena were investigated in the late eighteenth century by Charles-Augustin de Coulomb , who deduced that charge manifests itself in two opposing forms. This discovery led to the well-known axiom: like-charged objects repel and opposite-charged objects attract . The force acts on
6000-728: Is decommissioned. During May and October, the periods of lowest demand, the CFB boiler is not in use. The CFB controls emissions of the acid gases sulfur dioxide , hydrogen chloride and hydrogen fluoride and particulate matter (PM) with limestone injection and a fabric filter. The pulverized coal and spreader stoker boilers are equipped with dry gas scrubbers (spray dryers). Two boilers have no control equipment but have flue gas recirculation to limit nitrogen oxide emission. The plant emits almost zero sulfur and mercury . The unloading terminal for rail cars and its conveyors are enclosed and equipped with baghouse filters. The outdoor coal bunker
6125-473: Is defined as negative, and that by protons is positive. Before these particles were discovered, Benjamin Franklin had defined a positive charge as being the charge acquired by a glass rod when it is rubbed with a silk cloth. A proton by definition carries a charge of exactly 1.602 176 634 × 10 coulombs . This value is also defined as the elementary charge . No object can have a charge smaller than
6250-483: Is defined as the force (per unit charge) that would be felt by a stationary, negligible charge if placed at that point. The conceptual charge, termed a ' test charge ', must be vanishingly small to prevent its own electric field disturbing the main field and must also be stationary to prevent the effect of magnetic fields . As the electric field is defined in terms of force , and force is a vector , having both magnitude and direction , it follows that an electric field
6375-413: Is immune to atmospheric pressure changes over time. Instead, the silo structure is open to the atmosphere but outside air is separated from internal air by large impermeable bags sealed to the silo breather openings. In the warmth of the day when the silo is heated by the sun, the gas trapped inside the silo expands and the bags "breathe out" and collapse. At night the silo cools, the air inside contracts and
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#17327979768696500-401: Is in the silo working on the unloader. Often, when unloading grain from an auger or other opening at the bottom of the silo, another worker will be atop the grain "walking it down", to ensure an even flow of grain out of the silo. Sometimes unstable pockets in the grain will collapse beneath the worker doing the walking; this is called grain entrapment as the worker can be completely sunk into
6625-531: Is integral to applications spanning transport , heating , lighting , communications , and computation , making it the foundation of modern industrial society. Long before any knowledge of electricity existed, people were aware of shocks from electric fish . Ancient Egyptian texts dating from 2750 BCE described them as the "protectors" of all other fish. Electric fish were again reported millennia later by ancient Greek , Roman and Arabic naturalists and physicians . Several ancient writers, such as Pliny
6750-406: Is mediated by the magnetic field each current produces and forms the basis for the international definition of the ampere . This relationship between magnetic fields and currents is extremely important, for it led to Michael Faraday's invention of the electric motor in 1821. Faraday's homopolar motor consisted of a permanent magnet sitting in a pool of mercury . A current was allowed through
6875-415: Is most often a crystalline semiconductor . Solid-state electronics came into its own with the emergence of transistor technology. The first working transistor, a germanium -based point-contact transistor , was invented by John Bardeen and Walter Houser Brattain at Bell Labs in 1947, followed by the bipolar junction transistor in 1948. By modern convention, the charge carried by electrons
7000-413: Is performed using a forage harvester which may either be self-propelled with an engine and driver's cab, or towed behind a tractor that supplies power through a PTO . The harvester contains a drum-shaped series of cutting knives which shear the fibrous plant material into small pieces no more than an inch long, to facilitate mechanized blowing and transport via augers. The finely chopped plant material
7125-403: Is perhaps the simplest of passive circuit elements: as its name suggests, it resists the current through it, dissipating its energy as heat. The resistance is a consequence of the motion of charge through a conductor: in metals, for example, resistance is primarily due to collisions between electrons and ions. Ohm's law is a basic law of circuit theory , stating that the current passing through
7250-436: Is related to magnetism , both being part of the phenomenon of electromagnetism , as described by Maxwell's equations . Common phenomena are related to electricity, including lightning , static electricity , electric heating , electric discharges and many others. The presence of either a positive or negative electric charge produces an electric field . The motion of electric charges is an electric current and produces
7375-549: Is shielded from the wind by concrete retaining walls. Storage silos for ash have fabric filters. Environmental groups including the Save Our Riverfront Coalition and Friends of the Mississippi Inc. attempted and failed to move the plant off the river in 1996. Elected officials Phyllis Kahn and Larry Pogemiller, Arne Carlson who was governor of Minnesota , and Sharon Sayles Belton who
7500-531: Is subjected to transients , such as when first energised. The concept of the electric field was introduced by Michael Faraday . An electric field is created by a charged body in the space that surrounds it, and results in a force exerted on any other charges placed within the field. The electric field acts between two charges in a similar manner to the way that the gravitational field acts between two masses , and like it, extends towards infinity and shows an inverse square relationship with distance. However, there
7625-406: Is termed the inductance . The unit of inductance is the henry , named after Joseph Henry , a contemporary of Faraday. One henry is the inductance that will induce a potential difference of one volt if the current through it changes at a rate of one ampere per second. The inductor's behaviour is in some regards converse to that of the capacitor: it will freely allow an unchanging current, but opposes
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#17327979768697750-415: Is the farad , named after Michael Faraday , and given the symbol F : one farad is the capacitance that develops a potential difference of one volt when it stores a charge of one coulomb. A capacitor connected to a voltage supply initially causes a current as it accumulates charge; this current will however decay in time as the capacitor fills, eventually falling to zero. A capacitor will therefore not permit
7875-427: Is then blown by the harvester into a forage wagon which contains an automatic unloading system. Tower forage filling is typically performed with a silo blower which is a very large fan with paddle-shaped blades. Material is fed into a vibrating hopper and is pushed into the blower using a spinning spiral auger . There is commonly a water connection on the blower to add moisture to the plant matter being blown into
8000-529: Is therefore 0 at all places inside the body. This is the operating principal of the Faraday cage , a conducting metal shell which isolates its interior from outside electrical effects. The principles of electrostatics are important when designing items of high-voltage equipment. There is a finite limit to the electric field strength that may be withstood by any medium. Beyond this point, electrical breakdown occurs and an electric arc causes flashover between
8125-422: Is typically lowered only a half-inch or so at a time by the operator, and the unloader picks up only a small amount of material until the winch cable has become taut and the unloader is not picking up any more material. The operator then lowers the unloader another half-inch or so and the process repeats. If lowered too far, the unloader can pull up much more material than it can handle, which can overflow and plug up
8250-410: Is typically much shorter than a silo, and is typically used for holding dry matter such as cement or grain. Grain is often dried in a grain dryer before being stored in the bin. Bins may be round or square, but round bins tend to empty more easily due to a lack of corners for the stored material to become wedged and encrusted. The stored material may be powdered, as seed kernels, or as cob corn. Due to
8375-409: Is usually measured in volts , and one volt is the potential for which one joule of work must be expended to bring a charge of one coulomb from infinity. This definition of potential, while formal, has little practical application, and a more useful concept is that of electric potential difference , and is the energy required to move a unit charge between two specified points. An electric field has
8500-536: Is widely used in information processing , telecommunications , and signal processing . Interconnection technologies such as circuit boards , electronics packaging technology, and other varied forms of communication infrastructure complete circuit functionality and transform the mixed components into a regular working system . Today, most electronic devices use semiconductor components to perform electron control. The underlying principles that explain how semiconductors work are studied in solid state physics , whereas
8625-721: The Neo-Latin word electricus ("of amber" or "like amber", from ἤλεκτρον, elektron , the Greek word for "amber") to refer to the property of attracting small objects after being rubbed. This association gave rise to the English words "electric" and "electricity", which made their first appearance in print in Thomas Browne 's Pseudodoxia Epidemica of 1646. Isaac Newton made early investigations into electricity, with an idea of his written down in his book Opticks arguably
8750-594: The United States . The shaped is based on natural shape formed when piling solids. The dome is made of prefabricated wood panels with shingles installed on a circular reinforced concrete base. Open canopy entrance allows for front end loaders to fill and retrieve easily. These are usually found along major highway or key primary roads. Plastic silos, also known as hopper bottom tanks, are manufactured through various processes such as: injection molding , rotational molding, and blow molding . They are constructed using
8875-423: The electromagnetic force , one of the four fundamental forces of nature. Experiment has shown charge to be a conserved quantity , that is, the net charge within an electrically isolated system will always remain constant regardless of any changes taking place within that system. Within the system, charge may be transferred between bodies, either by direct contact, or by passing along a conducting material, such as
9000-522: The quantum revolution. Einstein was awarded the Nobel Prize in Physics in 1921 for "his discovery of the law of the photoelectric effect". The photoelectric effect is also employed in photocells such as can be found in solar panels . The first solid-state device was the " cat's-whisker detector " first used in the 1900s in radio receivers. A whisker-like wire is placed lightly in contact with
9125-476: The slipform and Jumpform concrete silos being the larger diameter and taller silos. They can be made of many materials. Wood staves, concrete staves, cast concrete, and steel panels have all been used, and have varying cost, durability, and airtightness tradeoffs. Silos storing grain, cement and woodchips are typically unloaded with air slides or augers. Silos can be unloaded into rail cars, trucks or conveyors. Tower silos containing silage are usually unloaded from
9250-452: The strong interaction , but unlike that force it operates over all distances. In comparison with the much weaker gravitational force , the electromagnetic force pushing two electrons apart is 10 times that of the gravitational attraction pulling them together. Charge originates from certain types of subatomic particles , the most familiar carriers of which are the electron and proton . Electric charge gives rise to and interacts with
9375-541: The 17th and 18th centuries. The development of the theory of electromagnetism in the 19th century marked significant progress, leading to electricity's industrial and residential application by electrical engineers by the century's end. This rapid expansion in electrical technology at the time was the driving force behind the Second Industrial Revolution , with electricity's versatility driving transformations in both industry and society. Electricity
9500-545: The 1936 discovery of the Baghdad Battery , which resembles a galvanic cell , though it is uncertain whether the artifact was electrical in nature. Electricity would remain little more than an intellectual curiosity for millennia until 1600, when the English scientist William Gilbert wrote De Magnete , in which he made a careful study of electricity and magnetism, distinguishing the lodestone effect from static electricity produced by rubbing amber. He coined
9625-656: The Elder and Scribonius Largus , attested to the numbing effect of electric shocks delivered by electric catfish and electric rays , and knew that such shocks could travel along conducting objects. Patients with ailments such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them. Ancient cultures around the Mediterranean knew that certain objects, such as rods of amber , could be rubbed with cat's fur to attract light objects like feathers. Thales of Miletus made
9750-607: The U of M to operate it from 1992 to 2016, when Veolia North America took over. Just upstream is the Hennepin Island Hydroelectric Plant operated by Xcel Energy . The university's Saint Paul, Minnesota campus three miles (5 km) away has its own plant. In addition the university has generators , pumps and boilers powered by diesel and natural gas, most used only in emergencies, with 11 used as peak shaving units. Before pipes were reinsulated, employees needed breaks once an hour to work in
9875-427: The amount of material to be stored. They are packed using a machine made for the purpose, and sealed on both ends. They are unloaded using a tractor and loader or skid-steer loader . The bag is discarded in sections as it is torn off. Bag silos require little capital investment. They can be used as a temporary measure when growth or harvest conditions require more space, though some farms use them every year. A bin
10000-412: The bag loader can be hazardous to bystanders since the pressure must be released and the rear end allowed to collapse onto the ground. A silo unloader specifically refers to a special cylindrical rotating forage pickup device used inside a single tower silo. The main operating component of the silo unloader is suspended in the silo from a steel cable on a pulley that is mounted in the top-center of
10125-482: The bags "breathe in" and expand again. While the iconic blue Harvestore low-oxygen silos were once very common, the speed of its unloader mechanism was not able to match the output rates of modern bunker silos, and this type of silo went into decline. Unloader repair expenses also severely hurt the Harvestore reputation, because the unloader feed mechanism is located in the bottom of the silo under tons of silage. In
10250-408: The beginning of the field theory of the electric force. Further work was conducted in the 17th and early 18th centuries by Otto von Guericke , Robert Boyle , Stephen Gray and C. F. du Fay . Later in the 18th century, Benjamin Franklin conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a metal key to the bottom of
10375-416: The blower, outlet spout, and the unloader tube, resulting in a time-wasting process of having to climb up the silo to clear the blockages. Once silage has entered the conveyor system, it can be handled by either manual or automatic distribution systems. The simplest manual distribution system uses a sliding metal platform under the pickup channel. When slid open, the forage drops through the open hole and down
10500-400: The blower. The farmer must continually move around in this highly hazardous environment of spinning shafts and high-speed conveyors to check material flows and adjust speeds, and to start and stop all the equipment between loads. Preparation for filling a silo requires winching the unloader to the top, and any remaining forage at the base that the unloader could not pick up must be removed from
10625-419: The building it serves to protect. The concept of electric potential is closely linked to that of the electric field. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires work . The electric potential at any point is defined as the energy required to bring a unit test charge from an infinite distance slowly to that point. It
10750-454: The campus buildings and would be enough to heat 55,000 homes. Each student pays about $ 200 for energy and those in residence halls pay $ 375 a year for heat and air conditioning, water heating and dining services. The plant is university building #059. The university's Energy Management department, part of Facilities Management, oversees the plant. Foster Wheeler Twin Cities was contracted with
10875-426: The charged particles themselves, hence charge has a tendency to spread itself as evenly as possible over a conducting surface. The magnitude of the electromagnetic force, whether attractive or repulsive, is given by Coulomb's law , which relates the force to the product of the charges and has an inverse-square relation to the distance between them. The electromagnetic force is very strong, second only in strength to
11000-450: The charged parts. Air, for example, tends to arc across small gaps at electric field strengths which exceed 30 kV per centimetre. Over larger gaps, its breakdown strength is weaker, perhaps 1 kV per centimetre. The most visible natural occurrence of this is lightning , caused when charge becomes separated in the clouds by rising columns of air, and raises the electric field in the air to greater than it can withstand. The voltage of
11125-418: The contents in a low-oxygen atmosphere at all times, to keep the fermented contents in a high quality state, and to prevent mold and decay, as may occur in the top layers of a stave silo or bunker. Low-oxygen silos are only opened directly to the atmosphere during the initial forage loading, and even the unloader chute is sealed against air infiltration. It would be expensive to design such a huge structure that
11250-411: The current varies in time. Direct current, as produced by example from a battery and required by most electronic devices, is a unidirectional flow from the positive part of a circuit to the negative. If, as is most common, this flow is carried by electrons, they will be travelling in the opposite direction. Alternating current is any current that reverses direction repeatedly; almost always this takes
11375-516: The design and construction of electronic circuits to solve practical problems are part of electronics engineering . Faraday's and Ampère's work showed that a time-varying magnetic field created an electric field, and a time-varying electric field created a magnetic field. Thus, when either field is changing in time, a field of the other is always induced. These variations are an electromagnetic wave . Electromagnetic waves were analysed theoretically by James Clerk Maxwell in 1864. Maxwell developed
11500-833: The dry nature of the stored material, it tends to be lighter than silage and can be more easily handled by under-floor grain unloaders. To facilitate drying after harvesting, some grain bins contain a hollow perforated or screened central shaft to permit easier air infiltration into the stored grain. There are different types of cement silos such as the low-level mobile silo and the static upright cement silo, which are used to hold and discharge cement and other powder materials such as pulverised fuel ash (PFA). The low-level silos are fully mobile with capacities from 100 to 750 tons. They are simple to transport and are easy to set up on site. These mobile silos generally come equipped with an electronic weighing system with digital display and printer. This allows any quantity of cement or powder discharged from
11625-478: The early 19th century had seen rapid progress in electrical science, the late 19th century would see the greatest progress in electrical engineering . Through such people as Alexander Graham Bell , Ottó Bláthy , Thomas Edison , Galileo Ferraris , Oliver Heaviside , Ányos Jedlik , William Thomson, 1st Baron Kelvin , Charles Algernon Parsons , Werner von Siemens , Joseph Swan , Reginald Fessenden , Nikola Tesla and George Westinghouse , electricity turned from
11750-427: The effect was reciprocal: a current exerts a force on a magnet, and a magnetic field exerts a force on a current. The phenomenon was further investigated by Ampère , who discovered that two parallel current-carrying wires exerted a force upon each other: two wires conducting currents in the same direction are attracted to each other, while wires containing currents in opposite directions are forced apart. The interaction
11875-634: The efficient flow of hard to handle products such as sugar, flour, calcium carbonate etc., minimally assisted by a small vibrator fitted to the discharge transition. The trevira tissue is able to breathe, preventing condensation from forming on its internal walls. This eliminates lumping and caking of the product. With sizes ranging from 2m to over 1000m , Rigid Silos cover an extreme range of applications and they can be constructed from various materials. Rigid silos can be provided with more than one vertical partition to compartmentalize it for different grades of product. The 5th millennium BC site of Tel Tsaf in
12000-448: The electronic electrometer . The movement of electric charge is known as an electric current , the intensity of which is usually measured in amperes . Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current. Electric current can flow through some things, electrical conductors , but will not flow through an electrical insulator . By historical convention,
12125-416: The electrons. However, depending on the conditions, an electric current can consist of a flow of charged particles in either direction, or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation. The process by which electric current passes through a material is termed electrical conduction , and its nature varies with that of the charged particles and
12250-428: The elementary charge, and any amount of charge an object may carry is a multiple of the elementary charge. An electron has an equal negative charge, i.e. −1.602 176 634 × 10 coulombs . Charge is possessed not just by matter , but also by antimatter , each antiparticle bearing an equal and opposite charge to its corresponding particle. The presence of charge gives rise to an electrostatic force: charges exert
12375-592: The event of cutter chain breakage, it can cost up to US$ 10,000 to perform repairs. The silo may need to be partially or completely emptied by alternate means, to unbury the broken unloader and retrieve broken components lost in the silage at the bottom of the structure. In 2005 the Harvestore company recognized these issues and worked to develop new unloaders with double the flow rate of previous models to stay competitive with bunkers, and with far greater unloader chain strength. They are now also using load sensing soft-start variable frequency drive motor controllers to reduce
12500-413: The floor of the silo. This job requires that the farmer work directly underneath a machine weighing several tons suspended fifty feet or more overhead from a small steel cable. Should the unloader fall, the farmer will likely be killed instantly. Unloading also poses its own special hazards, due to the requirement that the farmer regularly climb the silo to close an upper door and open a lower door, moving
12625-495: The form of a sine wave . Alternating current thus pulses back and forth within a conductor without the charge moving any net distance over time. The time-averaged value of an alternating current is zero, but it delivers energy in first one direction, and then the reverse. Alternating current is affected by electrical properties that are not observed under steady state direct current, such as inductance and capacitance . These properties however can become important when circuitry
12750-543: The likelihood of mechanism breakage, and to control the feeder sweep arm movement. Bunker silos are trenches, usually with concrete walls, that are filled and packed using tractors and loaders. The filled trench is covered with a plastic tarp to make it airtight. These silos are usually unloaded with a tractor and loader. They are inexpensive and especially well suited to very large operations. Bag silos are heavy plastic tubes, usually around 8 to 12 ft (2.4 to 3.6 m) in diameter, and of variable length as required for
12875-400: The material through which they are travelling. Examples of electric currents include metallic conduction, where electrons flow through a conductor such as metal, and electrolysis , where ions (charged atoms ) flow through liquids, or through plasmas such as electrical sparks. While the particles themselves can move quite slowly, sometimes with an average drift velocity only fractions of
13000-428: The principle, now known as Faraday's law of induction , that the potential difference induced in a closed circuit is proportional to the rate of change of magnetic flux through the loop. Exploitation of this discovery enabled him to invent the first electrical generator in 1831, in which he converted the mechanical energy of a rotating copper disc to electrical energy. Faraday's disc was inefficient and of no use as
13125-418: The process of filling and maintaining them. The machinery used is dangerous, and workers can fall from a tower silo's ladder or work platform. Several fires have occurred over the years. Filling a silo requires parking two tractors very close to each other, both running at full power and with live PTO shafts , one powering the silo blower and the other powering a forage wagon unloading fresh-cut forage into
13250-414: The roof of the silo. The vertical positioning of the unloader is controlled by an electric winch on the exterior of the silo. For the summer filling of a tower silo, the unloader is winched as high as possible to the top of the silo and put into a parking position. The silo is filled with a silo blower , which is literally a very large fan that blows a large volume of pressurized air up a 10-inch tube on
13375-405: The side of the silo, with an unloading tube next to the doors that has a series of removable covers down the side of the tube. The unloader tube and access doors are normally covered with a large U-shaped shield mounted on the silo, to protect the farmer from wind, snow, and rain while working on the silo. The silo unloader mechanism consists of a pair of counter-rotating toothed augers which rip up
13500-403: The side of the silo. A small amount of water is introduced into the air stream during filling to help lubricate the filling tube. A small adjustable nozzle at the top, controlled by a handle at the base of the silo directs the silage to fall into the silo on the near, middle, or far side, to facilitate evenly layered loading. Once completely filled, the top of the exposed silage pile is covered with
13625-425: The silo blower attached to the silo at all times to use it when necessary to ventilate the silo with fresh air, or to have a dedicated electric fan system to blow fresh air into the silo, before anyone attempts to enter it. In the event that the unloader mechanism becomes plugged, the farmer must climb the silo and directly stand on the unloader, reaching into the blower spout to dig out the soft silage. After clearing
13750-607: The silo to be controlled and also provides an accurate indication of what remains inside the silo. The static upright silos have capacities from 200 to 800 tons. These are considered a low-maintenance option for the storage of cement or other powders. Cement silos can be used in conjunction with bin-fed batching plants . Sand and salt for winter road maintenance are stored in conical dome-shaped (clear truss roof) silos. These are more common in North America , namely in Canada and
13875-422: The silo. The blower may be driven by an electric motor but it is more common to use a spare tractor instead. A large slow-moving conveyor chain underneath the silage in the forage wagon moves the pile towards the front, where rows of rotating teeth break up the pile and drop it onto a high-speed transverse conveyor that pours the silage out the side of the wagon into the blower hopper. Silo bags are filled using
14000-601: The southern Levant contain the earliest known silos. Archaeological ruins and ancient texts show that silos were used in ancient Greece as far back as the late 8th century BC; the term silo is derived from the Greek σιρός ( siros ), "pit for holding grain". The silo pit, as it has been termed, has been a favorite way of storing grain from time immemorial in Asia. In Turkey and Persia, insurance agents bought stores of wheat or barley whilst comparatively cheap, and store it in hidden pits against seasons of dearth. In Malta
14125-454: The special property that it is conservative , which means that the path taken by the test charge is irrelevant: all paths between two specified points expend the same energy, and thus a unique value for potential difference may be stated. The volt is so strongly identified as the unit of choice for measurement and description of electric potential difference that the term voltage sees greater everyday usage. For practical purposes, defining
14250-426: The surface of the silage and pull it towards the center of the unloader. The toothed augers rotate in a circle around the center hub, evenly chewing the silage off the surface of the pile. In the center, a large blower assembly picks up the silage and blows it out the silo door, where the silage falls by gravity down the unloader tube to the bottom of the silo, typically into an automated conveyor system. The unloader
14375-498: The three years necessary for testing and the approval process lost the source of the hulls. General Mills , makers of the oat cereal Cheerios , had signed a contract by then with U.S. Steel for use in their facility on the Iron Range in northern Minnesota. Electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge . Electricity
14500-482: The top but become progressively more closely spaced towards the bottom to prevent seams from opening and the contents leaking out. Concrete stave silos are built from common components designed for high strength and long life. They have the flexibility to have their height increased according to the needs of the farm and purchasing power of the farmer, or to be completely disassembled and reinstalled somewhere else if no longer needed. Low-oxygen silos are designed to keep
14625-410: The top of the pile, originally by hand using a silage fork—which has many more tines than the common pitchfork; 12 vs 4—and in modern times using mechanical unloaders. Bottom silo unloaders are utilized at times, but have problems with difficulty of repair. An advantage of tower silos is that the silage tends to pack well due to its own weight, except in the top few feet. However, this may be
14750-426: The tower and compressing the staves into a tight ring. The vertical stacks are held together by intermeshing of the ends of the staves by a short distance around the perimeter of each layer, and hoops which are tightened directly across the stave edges. The static pressure of the material inside the silo pressing outward on the staves increases towards the bottom of the silo, so the hoops can be spaced wide apart near
14875-497: The tunnels which reached 115 °F (46 °C). Insulation reduced the ambient temperature to 80 °F (27 °C), and the loss of energy from 10% to 4%, and over time resulted in a 25% campus-wide decrease in energy consumption. The university closed the Southeast plant to gut and rebuild the interior, and in 2000, reopened it and closed down its old coal-burning power plant. Completed in 2005, exterior rehabilitation won
15000-418: The two forces of nature then known. The force on the compass needle did not direct it to or away from the current-carrying wire, but acted at right angles to it. Ørsted's words were that "the electric conflict acts in a revolving manner." The force also depended on the direction of the current, for if the flow was reversed, then the force did too. Ørsted did not fully understand his discovery, but he observed
15125-489: The university's Minneapolis campus), provides electricity to cool 19 of those buildings, and provides steam to the University of Minnesota Medical Center , Minnesota State Board of Health and Cedar Riverside People's Center. Captured as the steam leaves the plant, pressure powers the plant and provides 20% of the university's electricity. The plant's steam is transported through an 18-mile (29 km) network of tunnels to
15250-412: The unloader chute from door to door in the process. The fermentation of the silage produces methane gas which over time will outgas and displace the oxygen in the top of the silo. A farmer directly entering a silo without any other precautions can be asphyxiated by the methane, knocked unconscious, and silently suffocate to death before anyone else knows what has happened. It is either necessary to leave
15375-417: The vector direction of the field is the line of greatest slope of potential, and where the equipotentials lie closest together. Ørsted's discovery in 1821 that a magnetic field existed around all sides of a wire carrying an electric current indicated that there was a direct relationship between electricity and magnetism. Moreover, the interaction seemed different from gravitational and electrostatic forces,
15500-412: Was mayor of Minneapolis supported the move. Concerned about potential emissions and noise from deliveries, some neighborhood associations and a condominium developer at the nearby Pillsbury "A" Mill criticized the plant's 2005 application to amend its permit to allow tests of alternative fuels. The Minnesota Pollution Control Agency approved use of biomass fuels, specifically oat hulls in 2006 but
15625-543: Was forced to move within the field; they are however an imaginary concept with no physical existence, and the field permeates all the intervening space between the lines. Field lines emanating from stationary charges have several key properties: first, that they originate at positive charges and terminate at negative charges; second, that they must enter any good conductor at right angles, and third, that they may never cross nor close in on themselves. A hollow conducting body carries all its charge on its outer surface. The field
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