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Alternator

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  • geronaapril
    An alternator is an electromechanical device that converts mechanical energy to alternating current electrical energy. Most alternators use a rotating magnetic
    Message 1 of 4 , Aug 23, 2007
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      An alternator is an electromechanical device that converts mechanical
      energy to alternating current electrical energy. Most alternators use
      a rotating magnetic field but linear alternators are occasionally
      used. In principle, any AC generator can be called an alternator, but
      usually the word refers to small rotating machines driven by
      automotive and other internal combustion engines.
    • sheilamarieflores_03
      Alternator From Wikipedia, the free encyclopedia • Find out more about navigating Wikipedia and finding information •Jump to: navigation, search Early 20th
      Message 2 of 4 , Sep 29, 2007
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        Alternator
        From Wikipedia, the free encyclopedia
        • Find out more about navigating Wikipedia and finding
        information •Jump to: navigation, search

        Early 20th century Alternator made in Budapest, Hungary, in the
        power generating hall of a hydroelectric station.An alternator is an
        electromechanical device that converts mechanical energy to
        alternating current electrical energy. Most alternators use a
        rotating magnetic field but linear alternators are occasionally
        used. In principle, any AC generator can be called an alternator,
        but usually the word refers to small rotating machines driven by
        automotive and other internal combustion engines.

        Contents [hide]
        1 History
        2 Theory of operation
        3 Automotive alternators
        4 Marine alternators
        5 Brushless Alternators
        5.1 Terminology
        5.2 Construction
        5.3 Exciter
        5.4 Main Alternator
        5.5 Control System
        5.6 AVR
        6 Hybrid automobiles
        7 Radio alternators
        8 Notes
        9 See also
        10 References



        [edit] History
        Alternating current generating systems were known in simple forms
        from the discovery of the magnetic induction of electric current.
        The early machines were developed by pioneers such as Michael
        Faraday and Hippolyte Pixii. Faraday developed the "rotating
        rectangle", whose operation was heteropolar.[1] The first public
        demonstration of a more robust "alternator system" took place in
        1886.[2] Large two-phase alternating current generators were built
        by a British electrician, J.E.H. Gordon, in 1882. Lord Kelvin and
        Sebastian Ferranti also developed early alternators, producing
        frequencies between 100 and 300 hertz. In 1891, Nikola Tesla
        patented a practical "high-frequency" alternator (which operated
        around 15,000 hertz).[3] After 1891, polyphase alternators were
        introduced to supply currents of multiple differing phases.[4] Later
        alternators were designed for varying alternating-current
        frequencies between sixteen and about one hundred hertz, for use
        with arc lighting, incandescent lighting and electric motors.[5]


        [edit] Theory of operation
        Alternators generate electricity by the same principle as DC
        generators, namely, when the magnetic field around a conductor
        changes, a current is induced in the conductor. Typically, a
        rotating magnet called the rotor turns within a stationary set of
        conductors wound in coils on an iron core, called the stator. The
        field cuts across the conductors, generating an electrical current,
        as the mechanical input causes the rotor to turn.

        The rotor magnetic field may be produced by induction (in
        a "brushless" alternator), by permanent magnets (in very small
        machines), or by a rotor winding energized with direct current
        through slip rings and brushes. The rotor magnetic field may even be
        provided by stationary field winding, with moving poles in the
        rotor. Automotive alternators invariably use a rotor winding, which
        allows control of the alternator generated voltage by varying the
        current in the rotor field winding. Permanent magnet machines avoid
        the loss due to magnetizing current in the rotor, but are restricted
        in size, owing to the cost of the magnet material. Since the
        permanent magnet field is constant, the terminal voltage varies
        directly with the speed of the generator. Brushless AC generators
        are usually larger machines than those used in automotive
        applications.

        A rotating magnetic field is a magnetic field which periodically
        changes direction. This is a key principle to the operation of
        alternating-current motor. In 1882, Nikola Tesla identified the
        concept of the rotating magnetic field. In 1885, Galileo Ferraris
        independently researched the concept. In 1888, Tesla gained U.S.
        Patent 0,381,968 for his work. Also in 1888, Ferraris published his
        research in a paper to the Royal Academy of Sciences in Turin.


        Sine wave current in each of the coils produces sine varying
        magnetic field on the rotation axis. Magnetic fields add as
        vectors.
        Vector sum of the magnetic field vectors of the stator coils
        produces a single rotating vector of resulting rotating magnetic
        field.





        U.S. Patent 381968: Mode and plan of operating electric motors by
        progressive shifting; Field Magnet; Armature; Electrical conversion;
        Economical; Transmission of energy; Simple construction; Easier
        construction; Rotating magnetic field principles.Symmetric rotating
        magnetic field can be produced with as little as three coils. Three
        coils will have to be driven by a symmetric 3-phase AC sine current
        system, thus each phase will be shifted 120 degrees in phase from
        the others. For the purpose of this example, magnetic field is taken
        to be the linear function of coil's current.

        Result of adding three 120-degrees phased sine waves on the axis of
        the motor is a single rotating vector. Rotor (having a constant
        magnetic field driven by DC current or a permanent magnet) will
        attempt to take such position that N pole of the rotor is adjusted
        to S pole of the stator's magnetic field, and vice versa. This
        magneto-mechanical force will drive rotor to follow rotating
        magnetic field in a synchronous manner.

        A permanent magnet in such a field will rotate so as to maintain its
        alignment with the external field. This effect was utilised in early
        alternating current electric motors. A rotating magnetic field can
        be constructed using two orthogonal coils with 90 degrees phase
        difference in their AC currents. However, in practice such a system
        would be supplied through a three-wire arrangement with unequal
        currents. This inequality would cause serious problems in
        standardization of the conductor size and in order to overcome it,
        three-phase systems are used where the three currents are equal in
        magnitude and have 120 degrees phase difference. Three similar coils
        having mutual geometrical angles of 120 degrees will create the
        rotating magnetic field in this case.The ability of the three phase
        system to create a rotating field utilized in electric motors is one
        of the main reasons why three phase systems dominated in the world
        electric power supply systems. Because magnets degrade with time,
        synchronous motors and induction motors use short-circuited rotors
        (instead of a magnet) following rotating magnetic field of
        multicoiled stator. (Short circuited turns of rotor develop eddy
        currents in rotating field of stator which (currents) in turn move
        the rotor by Lorentz force).

        Note that the rotating magnetic field can actually be produced by
        two coils, with phases shifted about 90 degrees, but such field
        would not be symmetric due to difference between magnetic
        susceptibility of ferromagnetic materials of pole and air. In case
        two phases of sine current are only available, four poles are
        commonly used.


        [edit] Automotive alternators
        Alternators are used in automobiles to charge the battery and to
        power a car's electric system when its engine is running.
        Alternators have the great advantage over direct-current generators
        of not using a commutator, which makes them simpler, lighter, less
        costly, and more rugged than a DC generator. The stronger
        construction of automotive alternators allows them to use a smaller
        pulley so as to turn twice as fast as the engine, improving output
        when the engine is idling. The availability of low-cost solid-state
        diodes from about 1960 allowed auto manufacturers to substitute
        alternators for DC generators. Automotive alternators use a set of
        rectifiers (diode bridge) to convert AC to DC. To provide direct
        current with low ripple, automotive alternators have a three-phase
        winding.

        Typical passenger vehicle and light truck alternators use Lundell or
        claw-pole field construction, where the field north and south poles
        are all energized by a single winding, with the poles looking rather
        like fingers of two hands interlocked with each other. Larger
        vehicles may have salient-pole alternators similar to larger
        machines. The automotive alternator is usually belt driven at 2-3
        times the engine crankshaft speed.

        Modern automotive alternators have a voltage regulator built into
        them. The voltage regulator operates by modulating the small field
        current in order to produce a constant voltage at the stator output.
        The field current is much smaller than the output current of the
        alternator; for example, a 70-amp alternator may need only 2 amps of
        field current.

        Efficiency of automotive alternators is limited by fan cooling loss,
        bearing loss, iron loss, copper loss, and the voltage drop in the
        diode bridges; at part load, efficiency is between 50-62% depending
        on the size of alternator, and varies with alternator speed.[6] In
        comparison, the best permanent magnet generators, such as those used
        for bicycle lighting systems, achieve an efficiency of around only
        60%.

        The field windings are initially supplied via the ignition switch
        and charge warning light, which is why the light glows when the
        ignition is on but the engine is not running. Once the engine is
        running and the alternator is generating, a diode feeds the field
        current from the alternator main output, thus equalizing the voltage
        across the warning light which goes out. The wire supplying the
        field current is often referred to as the "exciter" wire. The
        drawback of this arrangement is that if the warning light fails or
        the "exciter" wire is disconnected, no priming current reaches the
        alternator field windings and so the alternator will not generate
        any power. However, some alternators will self-excite when the
        engine is revved to a certain speed. The driver may check for a
        faulty exciter-circuit by ensuring that the warning light is glowing
        with the engine stopped.

        Very large automotive alternators used on buses, heavy equipments or
        emergency vehicles may produce 300 amperes. Very old automobiles
        with minimal lighting and electronic devices may have only a 30
        ampere alternator. Typical passenger car and light truck alternators
        are rated around 70 amperes, though higher ratings are becoming more
        common. Very large automotive alternators may be water-cooled or oil-
        cooled.

        Many alternators are also linked to the vehicle's on board computer
        system, and in recent years many other factors including air flow
        are considered in adjusting the battery charging voltage supplied by
        the alternator.


        [edit] Marine alternators
        Marine alternators as used in yachts are normally versions of
        automotive alternators, with appropriate adaptations to the salt-
        water environment. They may be 12 or 24 volt depending on the type
        of system installed. Larger marine diesels may have two or more
        alternators to cope with the heavy electrical demand of a modern
        yacht. On single alternator circuits the power is split between the
        engine starting battery and the domestic battery (or batteries) by
        use of a split-charge diode or a mechanical switch. Because the
        alternator only produces power when running engine control panels
        are typically fed directly from the alternator by means of an
        auxiliary terminal. Other typical connections are for charge control
        circuits[[1]].


        [edit] Brushless Alternators

        [edit] Terminology
        The stationary part of a motor or alternator is called the stator
        and the rotating part is called the rotor. The coils of wire that
        are used to produce a magnetic field are called the field and the
        coils that produce the power are called the armature. The coils of
        wire that are used to create the field and the armature are
        sometimes referred to as the "windings".



        [edit] Construction
        A brushless alternator is composed of two alternators built end-to-
        end on one shaft. Smaller brushless alternators may look like one
        unit but the two parts are readily identifiable on the large
        versions. The larger of the two sections is the main alternator and
        the smaller one is the exciter. The exciter has stationary field
        coils and a rotating armature (power coils). The main alternator
        uses the opposite configuration with a rotating field and stationary
        armature.



        [edit] Exciter
        The exciter field coils are on the stator and its armature is on the
        rotor. The AC output from the exciter armature is fed through a set
        of diodes that are also mounted on the rotor to produce a DC
        voltage. This is fed directly to the field coils of the main
        alternator, which are also located on the rotor. With this
        arrangement, brushes and slip rings are not required to feed current
        to the rotating field coils. This can be contrasted with a simple
        automotive alternator where brushes and slip rings are used to
        supply current to the rotating field.



        [edit] Main Alternator
        The main alternator has a rotating field as described above and a
        stationary armature (power generation windings). With the armature
        stationary, the high current output does not have to go through
        brushes and slip rings. Although the electrical design is more
        complex, it results in a very reliable alternator because the only
        parts subject to wear are the bearings.



        [edit] Control System
        Varying the amount of current through the stationary exciter field
        coils controls the strength of the magnetic field in the exciter.
        This in turn controls the output from the exciter. The exciter
        output is fed into the rotating field of the main alternator to
        supply the magnetic field for it. The strength of the magnetic field
        in the main alternator then controls its output. The result of all
        this is that a small current, in the field of the exciter indirectly
        controls the output of the main alternator and none of it has to go
        through brushes and slip-rings.


        [edit] AVR
        AVR is an abbreviation for Automatic Voltage Regulator. An AVR
        serves the same function as the "voltage regulator" in an automobile
        or the "regulator" or "controller" in a home power system.


        [edit] Hybrid automobiles
        Hybrid automobiles replace the separate alternator and starter motor
        with a combined motor/generator that performs both functions,
        cranking the internal combustion engine when starting, providing
        additional mechanical power for accelerating, and charging a large
        storage battery when the vehicle is running at constant speed. These
        rotating machines have considerably more powerful electronic devices
        for their control than the simple automotive alternator described
        above.


        [edit] Radio alternators
        Main article: Alexanderson alternator
        Extending Tesla's work on high-frequency alternators, high frequency
        alternators of the variable-reluctance type were applied
        commercially to radio transmission in the low-frequency radio bands.
        These were used for transmission of Morse code and, experimentally,
        for transmission of voice and music.


        [edit] Notes
        ^ Thompson, Sylvanus P., Dynamo-Electric Machinery. pp. 7
        ^ Blalock, Thomas J., "Alternating Current Electrification, 1886".
        IEEE History Center, IEEE Milestone. (ed. first practical
        demonstration of a dc generator - ac transformer system.)
        ^ US patent 447921, Tesla, Nikola, "Alternating Electric Current
        Generator".
        ^ Thompson, Sylvanus P., Dynamo-Electric Machinery. pp. 17
        ^ Thompson, Sylvanus P., Dynamo-Electric Machinery. pp. 16
        ^ Horst Bauer (ed.) Automotive Handbook 4th Edition, Robert Bosch
        GmbH, Stuttgart, 1996, ISBN 0-8376-0333-1, page 813

        [edit] See also
        Electrical generator as in pre-1960 motor cars
        Linear alternator

        [edit] References
        Thompson, Sylvanus P., Dynamo-Electric Machinery, A Manual for
        Students of Electrotechnics, Part 1, Collier and Sons, New York,
        1902
        White, Thomas H.,"Alternator-Transmitter Development (1891-1920)".
        EarlyRadioHistory.us.
        Alternators
        "Alternators". Integrated Publishing (TPub.com).
        "Wooden Low-RPM Alternator". ForceField, Fort Collins, Colorado,
        USA.
        "Understanding 3 phase alternators". WindStuffNow.
        Author unknown, "Alternator secrets". date unknown.
        "Alternator, Arc and Spark. The first Wireless Transmitters". The
        G0UTY Homepage.
        Tesla, Nikola, "The Ewing High-Frequency Alternator and Parson's
        Steam Engine". 12-17-1892. (Pepe's Tesla Pages, DOC)
        First practical alternating current with transformers system
        demonstrated (by William Stanley)
        Retrieved from "http://en.wikipedia.org/wiki/Alternator"
        Categories: Electrical generators | Energy conversion

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      • sheilamarieflores_03
        Alternator From Wikipedia, the free encyclopedia • Have questions? Find out how to ask questions and get answers. •Jump to: navigation, search Early 20th
        Message 3 of 4 , Oct 11, 2007
        View Source
        • 0 Attachment
          Alternator
          From Wikipedia, the free encyclopedia
          • Have questions? Find out how to ask questions and get
          answers. •Jump to: navigation, search

          Early 20th century Alternator made in Budapest, Hungary, in the
          power generating hall of a hydroelectric station.An alternator is an
          electromechanical device that converts mechanical energy to
          alternating current electrical energy. Most alternators use a
          rotating magnetic field but linear alternators are occasionally
          used. In principle, any AC generator can be called an alternator,
          but usually the word refers to small rotating machines driven by
          automotive and other internal combustion engines.

          Contents [hide]
          1 History
          2 Theory of operation
          3 Automotive alternators
          4 Marine alternators
          5 Brushless Alternators
          5.1 Terminology
          5.2 Construction
          5.3 Exciter
          5.4 Main Alternator
          5.5 Control System
          5.6 AVR
          6 Hybrid automobiles
          7 Radio alternators
          8 Notes
          9 See also
          10 References



          [edit] History
          Alternating current generating systems were known in simple forms
          from the discovery of the magnetic induction of electric current.
          The early machines were developed by pioneers such as Michael
          Faraday and Hippolyte Pixii. Faraday developed the "rotating
          rectangle", whose operation was heteropolar.[1] The first public
          demonstration of a more robust "alternator system" took place in
          1886.[2] Large two-phase alternating current generators were built
          by a British electrician, J.E.H. Gordon, in 1882. Lord Kelvin and
          Sebastian Ferranti also developed early alternators, producing
          frequencies between 100 and 300 hertz. In 1891, Nikola Tesla
          patented a practical "high-frequency" alternator (which operated
          around 15,000 hertz).[3] After 1891, polyphase alternators were
          introduced to supply currents of multiple differing phases.[4] Later
          alternators were designed for varying alternating-current
          frequencies between sixteen and about one hundred hertz, for use
          with arc lighting, incandescent lighting and electric motors.[5]


          [edit] Theory of operation
          Alternators generate electricity by the same principle as DC
          generators, namely, when the magnetic field around a conductor
          changes, a current is induced in the conductor. Typically, a
          rotating magnet called the rotor turns within a stationary set of
          conductors wound in coils on an iron core, called the stator. The
          field cuts across the conductors, generating an electrical current,
          as the mechanical input causes the rotor to turn.

          The rotor magnetic field may be produced by induction (in
          a "brushless" alternator), by permanent magnets (in very small
          machines), or by a rotor winding energized with direct current
          through slip rings and brushes. The rotor magnetic field may even be
          provided by stationary field winding, with moving poles in the
          rotor. Automotive alternators invariably use a rotor winding, which
          allows control of the alternator generated voltage by varying the
          current in the rotor field winding. Permanent magnet machines avoid
          the loss due to magnetizing current in the rotor, but are restricted
          in size, owing to the cost of the magnet material. Since the
          permanent magnet field is constant, the terminal voltage varies
          directly with the speed of the generator. Brushless AC generators
          are usually larger machines than those used in automotive
          applications.

          A rotating magnetic field is a magnetic field which periodically
          changes direction. This is a key principle to the operation of
          alternating-current motor. In 1882, Nikola Tesla identified the
          concept of the rotating magnetic field. In 1885, Galileo Ferraris
          independently researched the concept. In 1888, Tesla gained U.S.
          Patent 0,381,968 for his work. Also in 1888, Ferraris published his
          research in a paper to the Royal Academy of Sciences in Turin.


          Sine wave current in each of the coils produces sine varying
          magnetic field on the rotation axis. Magnetic fields add as
          vectors.
          Vector sum of the magnetic field vectors of the stator coils
          produces a single rotating vector of resulting rotating magnetic
          field.





          U.S. Patent 381968: Mode and plan of operating electric motors by
          progressive shifting; Field Magnet; Armature; Electrical conversion;
          Economical; Transmission of energy; Simple construction; Easier
          construction; Rotating magnetic field principles.Symmetric rotating
          magnetic field can be produced with as little as three coils. Three
          coils will have to be driven by a symmetric 3-phase AC sine current
          system, thus each phase will be shifted 120 degrees in phase from
          the others. For the purpose of this example, magnetic field is taken
          to be the linear function of coil's current.

          Result of adding three 120-degrees phased sine waves on the axis of
          the motor is a single rotating vector. Rotor (having a constant
          magnetic field driven by DC current or a permanent magnet) will
          attempt to take such position that N pole of the rotor is adjusted
          to S pole of the stator's magnetic field, and vice versa. This
          magneto-mechanical force will drive rotor to follow rotating
          magnetic field in a synchronous manner.

          A permanent magnet in such a field will rotate so as to maintain its
          alignment with the external field. This effect was utilised in early
          alternating current electric motors. A rotating magnetic field can
          be constructed using two orthogonal coils with 90 degrees phase
          difference in their AC currents. However, in practice such a system
          would be supplied through a three-wire arrangement with unequal
          currents. This inequality would cause serious problems in
          standardization of the conductor size and in order to overcome it,
          three-phase systems are used where the three currents are equal in
          magnitude and have 120 degrees phase difference. Three similar coils
          having mutual geometrical angles of 120 degrees will create the
          rotating magnetic field in this case.The ability of the three phase
          system to create a rotating field utilized in electric motors is one
          of the main reasons why three phase systems dominated in the world
          electric power supply systems. Because magnets degrade with time,
          synchronous motors and induction motors use short-circuited rotors
          (instead of a magnet) following rotating magnetic field of
          multicoiled stator. (Short circuited turns of rotor develop eddy
          currents in rotating field of stator which (currents) in turn move
          the rotor by Lorentz force).

          Note that the rotating magnetic field can actually be produced by
          two coils, with phases shifted about 90 degrees, but such field
          would not be symmetric due to difference between magnetic
          susceptibility of ferromagnetic materials of pole and air. In case
          two phases of sine current are only available, four poles are
          commonly used.


          [edit] Automotive alternators
          Alternators are used in automobiles to charge the battery and to
          power a car's electric system when its engine is running.
          Alternators have the great advantage over direct-current generators
          of not using a commutator, which makes them simpler, lighter, less
          costly, and more rugged than a DC generator. The stronger
          construction of automotive alternators allows them to use a smaller
          pulley so as to turn twice as fast as the engine, improving output
          when the engine is idling. The availability of low-cost solid-state
          diodes from about 1960 allowed auto manufacturers to substitute
          alternators for DC generators. Automotive alternators use a set of
          rectifiers (diode bridge) to convert AC to DC. To provide direct
          current with low ripple, automotive alternators have a three-phase
          winding.

          Typical passenger vehicle and light truck alternators use Lundell or
          claw-pole field construction, where the field north and south poles
          are all energized by a single winding, with the poles looking rather
          like fingers of two hands interlocked with each other. Larger
          vehicles may have salient-pole alternators similar to larger
          machines. The automotive alternator is usually belt driven at 2-3
          times the engine crankshaft speed.

          Modern automotive alternators have a voltage regulator built into
          them. The voltage regulator operates by modulating the small field
          current in order to produce a constant voltage at the stator output.
          The field current is much smaller than the output current of the
          alternator; for example, a 70-amp alternator may need only 2 amps of
          field current.

          Efficiency of automotive alternators is limited by fan cooling loss,
          bearing loss, iron loss, copper loss, and the voltage drop in the
          diode bridges; at part load, efficiency is between 50-62% depending
          on the size of alternator, and varies with alternator speed.[6] In
          comparison, the best permanent magnet generators, such as those used
          for bicycle lighting systems, achieve an efficiency of around only
          60%.


          A typical automotive alternator mounted in a spacious pickup truck
          engine bay.The field windings are initially supplied via the
          ignition switch and charge warning light, which is why the light
          glows when the ignition is on but the engine is not running. Once
          the engine is running and the alternator is generating, a diode
          feeds the field current from the alternator main output, thus
          equalizing the voltage across the warning light which goes out. The
          wire supplying the field current is often referred to as
          the "exciter" wire. The drawback of this arrangement is that if the
          warning light fails or the "exciter" wire is disconnected, no
          priming current reaches the alternator field windings and so the
          alternator will not generate any power. However, some alternators
          will self-excite when the engine is revved to a certain speed. The
          driver may check for a faulty exciter-circuit by ensuring that the
          warning light is glowing with the engine stopped.

          Very large automotive alternators used on buses, heavy equipments or
          emergency vehicles may produce 300 amperes. Very old automobiles
          with minimal lighting and electronic devices may have only a 30
          ampere alternator. Typical passenger car and light truck alternators
          are rated around 70 amperes, though higher ratings are becoming more
          common. Very large automotive alternators may be water-cooled or oil-
          cooled.

          Many alternators are also linked to the vehicle's on board computer
          system, and in recent years many other factors including air flow
          are considered in adjusting the battery charging voltage supplied by
          the alternator.


          [edit] Marine alternators
          Marine alternators as used in yachts are normally versions of
          automotive alternators, with appropriate adaptations to the salt-
          water environment. They may be 12 or 24 volt depending on the type
          of system installed. Larger marine diesels may have two or more
          alternators to cope with the heavy electrical demand of a modern
          yacht. On single alternator circuits the power is split between the
          engine starting battery and the domestic battery (or batteries) by
          use of a split-charge diode or a mechanical switch. Because the
          alternator only produces power when running engine control panels
          are typically fed directly from the alternator by means of an
          auxiliary terminal. Other typical connections are for charge control
          circuits[[1]].


          [edit] Brushless Alternators

          [edit] Terminology
          The stationary part of a motor or alternator is called the stator
          and the rotating part is called the rotor. The coils of wire that
          are used to produce a magnetic field are called the field and the
          coils that produce the power are called the armature. The coils of
          wire that are used to create the field and the armature are
          sometimes referred to as the "windings".



          [edit] Construction
          A brushless alternator is composed of two alternators built end-to-
          end on one shaft. Smaller brushless alternators may look like one
          unit but the two parts are readily identifiable on the large
          versions. The larger of the two sections is the main alternator and
          the smaller one is the exciter. The exciter has stationary field
          coils and a rotating armature (power coils). The main alternator
          uses the opposite configuration with a rotating field and stationary
          armature.



          [edit] Exciter
          The exciter field coils are on the stator and its armature is on the
          rotor. The AC output from the exciter armature is fed through a set
          of diodes that are also mounted on the rotor to produce a DC
          voltage. This is fed directly to the field coils of the main
          alternator, which are also located on the rotor. With this
          arrangement, brushes and slip rings are not required to feed current
          to the rotating field coils. This can be contrasted with a simple
          automotive alternator where brushes and slip rings are used to
          supply current to the rotating field.



          [edit] Main Alternator
          The main alternator has a rotating field as described above and a
          stationary armature (power generation windings). With the armature
          stationary, the high current output does not have to go through
          brushes and slip rings. Although the electrical design is more
          complex, it results in a very reliable alternator because the only
          parts subject to wear are the bearings.



          [edit] Control System
          Varying the amount of current through the stationary exciter field
          coils controls the strength of the magnetic field in the exciter.
          This in turn controls the output from the exciter. The exciter
          output is fed into the rotating field of the main alternator to
          supply the magnetic field for it. The strength of the magnetic field
          in the main alternator then controls its output. The result of all
          this is that a small current, in the field of the exciter indirectly
          controls the output of the main alternator and none of it has to go
          through brushes and slip-rings.By varying excitation only reactive
          power is controlled , system voltage is improved .


          [edit] AVR
          AVR is an abbreviation for Automatic Voltage Regulator. An AVR
          serves the same function as the "voltage regulator" in an automobile
          or the "regulator" or "controller" in a home power system.


          [edit] Hybrid automobiles
          Hybrid automobiles replace the separate alternator and starter motor
          with a combined motor/generator that performs both functions,
          cranking the internal combustion engine when starting, providing
          additional mechanical power for accelerating, and charging a large
          storage battery when the vehicle is running at constant speed. These
          rotating machines have considerably more powerful electronic devices
          for their control than the simple automotive alternator described
          above.


          [edit] Radio alternators
          Main article: Alexanderson alternator
          Extending Tesla's work on high-frequency alternators, high frequency
          alternators of the variable-reluctance type were applied
          commercially to radio transmission in the low-frequency radio bands.
          These were used for transmission of Morse code and, experimentally,
          for transmission of voice and music.


          [edit] Notes
          ^ Thompson, Sylvanus P., Dynamo-Electric Machinery. pp. 7
          ^ Blalock, Thomas J., "Alternating Current Electrification, 1886".
          IEEE History Center, IEEE Milestone. (ed. first practical
          demonstration of a dc generator - ac transformer system.)
          ^ US patent 447921, Tesla, Nikola, "Alternating Electric Current
          Generator".
          ^ Thompson, Sylvanus P., Dynamo-Electric Machinery. pp. 17
          ^ Thompson, Sylvanus P., Dynamo-Electric Machinery. pp. 16
          ^ Horst Bauer (ed.) Automotive Handbook 4th Edition, Robert Bosch
          GmbH, Stuttgart, 1996, ISBN 0-8376-0333-1, page 813

          [edit] See also
          Electrical generator as in pre-1960 motor cars
          Linear alternator

          [edit] References
          Thompson, Sylvanus P., Dynamo-Electric Machinery, A Manual for
          Students of Electrotechnics, Part 1, Collier and Sons, New York,
          1902
          White, Thomas H.,"Alternator-Transmitter Development (1891-1920)".
          EarlyRadioHistory.us.
          Alternators
          "Alternators". Integrated Publishing (TPub.com).
          "Wooden Low-RPM Alternator". ForceField, Fort Collins, Colorado,
          USA.
          "Understanding 3 phase alternators". WindStuffNow.
          Author unknown, "Alternator secrets". date unknown.
          "Alternator, Arc and Spark. The first Wireless Transmitters". The
          G0UTY Homepage.
          Tesla, Nikola, "The Ewing High-Frequency Alternator and Parson's
          Steam Engine". 12-17-1892. (Pepe's Tesla Pages, DOC)
          First practical alternating current with transformers system
          demonstrated (by William Stanley)
          Retrieved from "http://en.wikipedia.org/wiki/Alternator"
          Categories: Electrical generators | Energy conversion

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