In Electricity Generation, an Electric Generator Is a Device

Electric author Inelectricity genesis, anelectric generatoris a device that converts mechanised energytoelectrical energy. A generator forceselectric charge(usually carried byelectrons) to flow through an externalelectrical circuit. It is analogous to a water pump, which causes water to flow ( further does not create water). Thesource of mechanical energy may be a reciprocating or turbinesteam engine, water falling through aturbine or waterwheel, aninternal combustion engine, a horn in turbine, a handcrank,compressed airor any other source of mechanical energy.The override conversion of electrical energy into mechanical energy is done by anelectric motor, and motors and generators stomach many similarities. In fact many motors clear be mechanically driven to generate electricity, and really frequently make acceptable generators. -Historical developments Before the connection betweenmagnetismandelectricitywas discovered,electrostatic generatorswere invented that usedelectrostati cprinciples. These generated very senior high schoolvoltagesand lowstreams.They operated by using movingelectrically chargedbelts, plates and disks to carry charge to a high potential electrode. The charge was generated using every of two mechanisms * Electrostatic induction * Thetriboelectric effect, where the contact between two insulators leaves them charged. Because of their inefficiency and the difficulty ofinsulating apparatuss producing very high voltages, electrostatic generators had low strength ratings and were never used for generation of commercially signifi female genitalst quantities of electric power.TheWimshurst machineandVan de Graaff generatorare examples of these machines that have survived. Faradays disk In the years of 18311832,Michael Faradaydiscovered the operating principle of electromagnetic generators. The principle, subsequently calledFaradays legal philosophy, is that anelectromotive forceis generated in an electrical conductor that encircles a varying magnetic flux. He also built the first electromagnetic generator, called theFaraday disk, a reference ofhomopolar generator, using acopperdisc rotating between the poles of a horseshoemagnet. It produced a littler DC voltage.This design was inefficient due to self-cancelling counterflows of veritable in regions not under the forge of the magnetic field. While current was induced directly underneath the magnet, the current would circulate backwards in regions outside the influence of the magnetic field. This counterflow limits the power end product to the pickup wires and induces waste heating of the copper disc. Later homopolar generators would solve this problem by using an array of magnets arranged round the disc perimeter to maintain a steady field effect in one current-flow direction.Another disadvantage was that the output voltage was very low, due to the virtuoso current path through the magnetic flux. Experimenters found that using multiple turns of wire in a coil coul d produce higher more utilitarian voltages. Since the output voltage is proportional to the number of turns, generators could be easily designed to produce any desired voltage by varying the number of turns. telegraph windings became a basic feature of all subsequent generator designs. Dynamo Thedynamowas the first electrical generator capable of delivering power for industry.The dynamo useselectromagneticprinciples to convert mechanical gyration intopulsed DCthrough the use of acommutator. The first dynamo was built byHippolyte Pixiiin 1832. Through a series of accidental discoveries, the dynamo became the source of many later inventions, including the DCelectric motor, the ACalternator, the ACsynchronous motor, and therotary converter. A dynamo machine consists of a stationary structure, which provides a ceaseless magnetic field, and a club of rotating windings which turn inwardly that field.On small machines the constant magnetic field may be provided by one or more permanen t magnets larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils. Large power generation dynamos are instanter rarely seen due to the now nearly universal use of change currentfor power distribution andsolid stateelectronic AC to DC power conversion. But before the principles of AC were discovered, very large direct-current dynamos were the only means of power generation and distribution.Now power generation dynamos are mostly a curiosity. Alternator Without acommutator, a dynamo becomes analternator, which is asynchronous singly fed generator. When used to feed anelectric power grid, an alternator must always operate at a constant speed that is precisely synchronized to the electrical frequency of the power grid. A DC generator can operate at any speed within mechanical limits, but always outputs direct current. Typical alternators use a rotating field winding excited with direct current, and a stationary (stat or) winding that produces alternating current.Since the rotor field only requires a tiny fraction of the power generated by the machine, the brushes for the field contact can be relatively small. In the shell of a brushless exciter, no brushes are used at all and the rotor shaft carries rectifiers to excite the main field winding. MHD generator Main articleMHD generator A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery. MHD generators were originally developed because the output of a plasma MHD generator is a flame, well able to heat the boilers of asteampower plant.The first practical design was the AVCO Mk. 25, developed in 1965. The U. S. government funded substantial development, culminating in a 25 MW demonstration plant in 1987. In theSoviet Unionfrom 1972 until the late 1980s, the MHD plant U 25 was in regular commercial operation on the Moscow power system wi th a rating of 25 MW, the largest MHD plant rating in the human race at that time. 2MHD generators operated as atopping cycleare currently (2007) less efficient than combined-cyclegas turbines. - Terminology The two main parts of a generator or motor can be described in either echanical or electrical terms. Mechanical * Rotor The rotating part of anelectrical machine * Stator The stationary part of an electrical machine Electrical * Armature The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electric current. The armature can be on either the rotor or the stator. * Field The magnetic field component of an electrical machine. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator.Because power transferred into the field circuit is much less than in the armature circuit, AC generators nearly always have the field winding on the rotor and the stator as the armature winding. Only a small amount of field current must be transferred to the moving rotor, usingslip rings. Direct current machines (dynamos) require acommutatoron the rotating shaft to convert thealternating currentproduced by the armature todirect current, so the armature winding is on the rotor of the machine. - ExcitationAn electric generator or electric motor that uses field coils rather than permanent magnets requires a current to be present in the field coils for the device to be able to work. If the field coils are not powered, the rotor in a generator can spin without producing any usable electrical energy, while the rotor of a motor may not spin at all. Smaller generators are sometimesself-excited, which means the field coils are powered by the current produced by the generator itself. The field coils are connected in series or twin with the armature winding.When the generator first starts to turn, the small amount ofremane nt magnetismpresent in the iron core provides a magnetic field to get it started, generating a small current in the armature. This flows through the field coils, creating a larger magnetic field which generates a larger armature current. This bootstrap process continues until the magnetic field in the core levels off due tosaturationand the generator reaches a steady state power output. Very large power station generators often go for a separate smaller generator to excite the field coils of the larger.In the event of a severe widespreadpower outagewhereislandingof power stations has occurred, the stations may need to perform ablack startto excite the fields of their largest generators, in order to restore customer power service. - Equivalent circuit The homogeneous circuit of a generator and load is shown in the diagram to the right. The generatorsVGandRGparameters can be determined by cadence the winding resistance (corrected to operating temperature), and measuring the open-ci rcuit and loaded voltage for a defined current load. editVehicle-mounted generators Early motor vehicles until about the 1960s tended to use DC generators with electromechanical regulators. These have now been replaced byalternatorswith organicrectifiercircuits, which are less costly and lighter for equivalent output. Moreover, the power output of a DC generator is proportional to rotational speed, whereas the power output of an alternator is case-by-case of rotational speed. As a result, the charging output of an alternator at engine idle speed can be much greater than that of a DC generator.Automotive alternators power the electrical systems on the vehicle and recharge thebatteryafter starting. Rated output will normally be in the range 50-100 A at 12 V, depending on the designed electrical load within the vehicle. Some cars now have electrically poweredsteering assistanceandair conditioning, which places a high load on the electrical system. Large commercial vehicles are more likely to use 24 V to give sufficient power at thestarter motorto turn over a largediesel engine.Vehicle alternators do not use permanent magnets and are typically only 50-60% efficient over a wide speed range. 4Motorcycle alternators often use permanent magnetstatorsmade withrare earthmagnets, since they can be made smaller and lighter than other types. See alsohybrid vehicle. Some of the smallest generators commonly found power roulette wheel lights. These tend to be 0. 5 ampere, permanent-magnet alternators supplying 3-6 W at 6 V or 12 V. Being powered by the rider, efficiency is at a premium, so these may incorporaterare-earth magnetsand are designed and make with great precision.Nevertheless, the maximum efficiency is only around 80% for the best of these generators60% is more typicaldue in part to the rolling clash at thetyregeneratorinterface from poor alignment, the small size of the generator, bearing losses and cheap design. The use of permanent magnets means that effic iency falls even further at high speeds because the magnetic field strength cannot be controlled in any way. Hub dynamosremedy many of these flaws since they are internal to the bicycle hub and do not require an interface between the generator and tyre. Until recently, these generators have been expensive and hard to find.Major bicycle component manufacturers like Shimano and SRAM have only moreover entered this market. However, significant gains can be expected in future as cycling becomes more mainstream transportation and LED technology allows brighter lighting at the reduced current these generators are capable of providing. Sailing yachts may use a water or wind powered generator to trickle-charge the batteries. A smallpropeller,wind turbineorimpelleris connected to a low-power alternator and rectifier to supply currents of up to 12 A at typical cruising speeds. Still smaller generators are used inmicropowerapplications. Engine-generator Anengine-generatoris the confederacy of an electrical generator and anengine(prime mover) mounted together to form a single piece of self-contained equipment. The engines used are usually piston engines, but gas turbines can also be used. Many different versions are available ranging from very small portablepetrolpowered sets to large turbine installations. - human beings powered electrical generators A generator can also be driven by human muscle power (for instance, in field piano tuner station equipment).Human powered direct current generators are commercially available, and have been the project of someDIYenthusiasts. Typically operated by means of pedal power, a reborn bicycle trainer, or a foot pump, such generators can be practically used to charge batteries, and in some cases are designed with an constituent(a) inverter. The average adult could generate about 125-200 watts on a pedal powered generator, but at a power of 200 W, a typical healthy human will reach complete exhaustion and fail to produce any more power after approximately 1. 3 hours. 6Portable receiving set receivers with a crank are made to reduce battery purchase requirements, seeclockwork radio. During the mid 20th century, pedal powered radios were used throughout the Australian outback, to provide schooling,(school of the air) medical and other needs in remote stations and towns. - Linear electric generator In the simplest form of linear electric generator, a slidingmagnetmoves back and forth through asolenoid a spool of copper wire. Analternating currentis induced in the loops of wire byFaradays law of inductioneach time the magnet slides through.This type of generator is used in theFaraday flashlight. Larger linear electricity generators are used in curl powerschemes. - Tachogenerator Tachogenerators are frequently used to powertachometersto measure the speeds of electric motors, engines, and the equipment they power. Generators generate voltage roughly proportional to shaft speed. With precise construction and design, generators can be built to produce very precise voltages for certain ranges of shaft speeds