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69-410: Today, the simpler alternator dominates large scale power generation , for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator . Also, converting alternating to direct current using rectifiers (such as vacuum tubes or more recently via solid state technology) is effective and usually economical. The operating principle of electromagnetic generators

138-423: A French instrument maker. It used a permanent magnet which was rotated by a crank. The spinning magnet was positioned so that its north and south poles passed by a piece of iron wrapped with insulated wire. Pixii found that the spinning magnet produced a pulse of current in the wire each time a pole passed the coil. However, the north and south poles of the magnet induced currents in opposite directions. To convert

207-406: A combination of series and parallel (shunt) field windings, which are directly supplied power by the rotor through the commutator in a regenerative manner. They are started and operated in a manner similar to modern portable alternating current electric generators, which are not used with other generators on an electric grid. There is a weak residual magnetic field that persists in the metal frame of

276-419: A magnetic field around the rotor. This was also the discovery of the principle of dynamo self-excitation , which replaced permanent magnet designs. The dynamo was the first electrical generator capable of delivering power for industry. The modern dynamo, fit for use in industrial applications, was invented independently by Sir Charles Wheatstone , Werner von Siemens and Samuel Alfred Varley . Varley took out

345-552: A patent on 24 December 1866, while Siemens and Wheatstone both announced their discoveries on 17 January 1867, by delivering papers at the Royal Society . The "dynamo-electric machine" employed self-powering electromagnetic field coils rather than permanent magnets to create the stator field. Wheatstone's design was similar to Siemens', with the difference that in the Siemens design the stator electromagnets were in series with

414-411: A power plant, unless either the rotor or field wiring or the mechanical drive systems are coupled together in certain special combinations. Dynamos were used in motor vehicles to generate electricity for battery charging. An early type was the third-brush dynamo . They have, again, been replaced by alternators . Dynamos still have some uses in low power applications, particularly where low voltage DC

483-414: A pulsing direct current is produced. The earliest dynamos used permanent magnets to create the magnetic field. These were referred to as "magneto-electric machines" or magnetos . However, researchers found that stronger magnetic fields — and thus more power — could be produced by using electromagnets (field coils) on the stator. These were called "dynamo-electric machines" or dynamos. The field coils of

552-415: A replacement for batteries. The commutator is essentially a rotary switch . It consists of a set of contacts mounted on the machine's shaft, combined with graphite-block stationary contacts, called "brushes," because the earliest such fixed contacts were metal brushes. The commutator reverses the connection of the windings to the external circuit when the potential reverses — so instead of alternating current,

621-415: A rotating magnet, called the rotor , turns within a stationary set of conductors, called the stator , wound in coils on an iron core. The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical input causes the rotor to turn. The rotating magnetic field induces an AC voltage in the stator windings. Since the currents in the stator windings vary in step with

690-405: A set of rotating windings called the armature which turn within that field. Due to Faraday's law of induction, the motion of the wire within the magnetic field creates an electromotive force , which pushes on the electrons in the metal, creating an electric current in the wire. On small machines, the constant magnetic field may be provided by one or more permanent magnets ; larger machines have

759-406: A small DC voltage . This was not a dynamo in the current sense, because it did not use a commutator . This design was inefficient, due to self-cancelling counterflows of current in regions of the disk that were not under the influence of the magnetic field. While current was induced directly underneath the magnet, the current would circulate backwards in regions that were outside the influence of

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828-416: A small amount of electricity, just enough to excite the field coils of the connected alternator to generate electricity. A variation of this system is a type of alternator that uses direct current from a battery for initial excitation upon start-up, after which the alternator becomes self-excited. This method of excitation consists of a smaller alternating-current (AC) generator fixed on the same shaft as

897-490: Is N = 120 f / P {\displaystyle N=120f/P} , where f {\displaystyle f} is the frequency in Hz (cycles per second). P {\displaystyle P} is the number of poles (2, 4, 6, …), and N {\displaystyle N} is the rotational speed in revolutions per minute (r/min). Old descriptions of alternating current systems sometimes give

966-442: Is a type of alternator that uses direct current from a battery for initial excitation upon start-up, after which the alternator becomes self-excited. This method depends on residual magnetism retained in the iron core to generate a weak magnetic field, which would allow a weak voltage to be generated. This voltage is used to excite the field coils so the alternator can generate stronger voltage as part of its build up process. After

1035-429: Is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current . For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature . Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually,

1104-399: Is called a hub dynamo , although these are invariably AC devices, and are actually magnetos . The electric dynamo uses rotating coils of wire and magnetic fields to convert mechanical rotation into a pulsing direct electric current through Faraday's law of induction . A dynamo machine consists of a stationary structure, called the stator , which provides a constant magnetic field , and

1173-505: Is distributed by electric power grids . Alternating current generating systems were known in simple forms from the discovery of the magnetic induction of electric current in the 1830s. Rotating generators naturally produced alternating current, but since there was little use for it, it was normally converted into direct current via the addition of a commutator in the generator. The early machines were developed by pioneers such as Michael Faraday and Hippolyte Pixii . Faraday developed

1242-409: Is fed into the rotating field coils through the voltage regulator (VR). This increases the magnetic field around the field coils, which induces a greater voltage in the armature coils. Thus, the output voltage is brought back up to its original value. Alternators used in central power stations also control the field current to regulate reactive power and to help stabilize the power system against

1311-698: Is referred to as flashing the field . Both types of self-excited generator, which have been attached to a large external load while it was stationary, will not be able to build up voltage even if the residual field is present. The load acts as an energy sink and continuously drains away the small rotor current produced by the residual field, preventing magnetic field buildup in the field coil. Dynamos, usually driven by steam engines , were widely used in power stations to generate electricity for industrial and domestic purposes. They have since been replaced by alternators . Large industrial dynamos with series and parallel (shunt) windings can be difficult to use together in

1380-454: Is required, since an alternator with a semiconductor rectifier can be inefficient in these applications. Hand cranked dynamos are used in clockwork radios , hand powered flashlights and other human powered equipment to recharge batteries . The generator used for bicycle lighting may be called a "dynamo" but these are almost always AC devices and so, strictly, would be called "alternators". Alternator An alternator

1449-448: Is that a small DC exciter current indirectly controls the output of the main alternator. Another way to classify alternators is by the number of phases of their output voltage. The output can be single phase or polyphase. Three-phase alternators are the most common, but polyphase alternators can be two-phase, six-phase, or more. The revolving part of alternators can be the armature or the magnetic field. The revolving armature type has

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1518-480: The Alexanderson alternator were developed as longwave radio transmitters around World War 1 and used in a few high power wireless telegraphy stations before vacuum tube transmitters replaced them. A conductor moving relative to a magnetic field develops an electromotive force (EMF) in it ( Faraday's Law ). This EMF reverses its polarity when it moves under magnetic poles of opposite polarity. Typically,

1587-401: The prime mover turns an alternator which provides electricity for the traction motors (AC or DC). The traction alternator usually incorporates integral silicon diode rectifiers to provide the traction motors with up to 1,200 volts DC. The first diesel electric locomotives, and many of those still in service, use DC generators as, before silicon power electronics, it was easier to control

1656-478: The "rotating rectangle", whose operation was heteropolar – each active conductor passed successively through regions where the magnetic field was in opposite directions. Lord Kelvin and Sebastian Ferranti also developed early alternators, producing frequencies between 100 and 300 Hz . The late 1870s saw the introduction of the first large-scale electrical systems with central generation stations to power Arc lamps , used to light whole streets, factory yards, or

1725-505: The Greek word dynamis (δύναμις), meaning force or power) was originally another name for an electrical generator , and still has some regional usage as a replacement for the word generator. The word was coined in 1831 by Michael Faraday , who utilized his invention toward making many discoveries in electricity (Faraday discovered electrical induction) and magnetism . The original "dynamo principle" of Werner von Siemens referred only to

1794-557: The West Side IRT subway in Manhattan into the late 1960s, and possibly some years later. They were powered by 25 Hz AC, and provided DC at 600 volts for the trains. Direct current machines like dynamos and commutated DC motors have higher maintenance costs and power limitations than alternating current (AC) machines due to their use of the commutator . These disadvantages are: Although direct current dynamos were

1863-420: The alternating current to DC, Pixii invented a commutator , a split metal cylinder on the shaft, with two springy metal contacts that pressed against it. This early design had a problem: the electric current it produced consisted of a series of "spikes" or pulses of current separated by none at all, resulting in a low average power output. As with electric motors of the period, the designers did not fully realize

1932-442: The alternator. The AC stator generates a small amount of field coil excitation current, which is induced in the rotor and rectified to DC by a bridge rectifier built in to the windings where it excites the field coils of the larger connected alternator to generate electricity. This system has the advantage of not requiring brushes, which increases service life, although with a slightly lower overall efficiency. A variation of this system

2001-438: The armature wound on the rotor, where the winding moves through a stationary magnetic field. The revolving armature type is not often used. The revolving field type has a magnetic field on the rotor to rotate through a stationary armature winding. The advantage is that then the rotor circuit carries much less power than the armature circuit, making the slip ring connections smaller and less costly; only two contacts are needed for

2070-410: The battery to adjust the charging voltage and an over-temperature sensor on the actual alternator to protect it from overheating. High-frequency alternators of the variable-reluctance type were applied commercially to radio transmission in low-frequency radio bands. These were used for transmitting Morse code and, experimentally, for transmitting voice and music. In the Alexanderson alternator , both

2139-547: The coil was continually passing by the magnets, smoothing out the current. The Woolrich Electrical Generator of 1844, now in Thinktank, Birmingham Science Museum , is the earliest electrical generator used in an industrial process. It was used by the firm of Elkingtons for commercial electroplating . In 1827, independently of Faraday, Hungarian inventor Ányos Jedlik started experimenting with electromagnetic rotating devices which he called electromagnetic self-rotors . In

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2208-598: The constant magnetic field provided by one or more electromagnets , which are usually called field coils . The commutator is needed to produce direct current . When a loop of wire rotates in a magnetic field, the magnetic flux through it—and thus the potential induced in it—reverses with each half turn, generating an alternating current . However, in the early days of electric experimentation, alternating current generally had no known use. The few uses for electricity, such as electroplating , used direct current provided by messy liquid batteries . Dynamos were invented as

2277-610: The constant voltage generator that could produce a stated output voltage, regardless of the value of the actual load. The introduction of transformers in the mid-1880s led to the widespread use of alternating current and the use of alternators needed to produce it. After 1891, polyphase alternators were introduced to supply currents of multiple differing phases. Later alternators were designed for various alternating current frequencies between sixteen and about one hundred hertz for use with arc lighting, incandescent lighting, and electric motors. Specialized radio frequency alternators like

2346-446: 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 than those used in automotive applications. An automatic voltage control device controls the field current to keep the output voltage constant. If the output voltage from the stationary armature coils drops due to an increase in demand, more current

2415-410: The device when it is not operating, which has been imprinted onto the metal by the field windings. The dynamo begins rotating while not connected to an external load. The residual magnetic field induces a very small electrical current into the rotor windings as they begin to rotate. Without an external load attached, this small current is then fully supplied to the field windings, which in combination with

2484-505: The direct current generators which use exclusively the self-excitation (self-induction) principle to generate DC power. The earlier DC generators which used permanent magnets were not considered "dynamo electric machines". The invention of the dynamo principle (self-induction) was a major technological leap over the old traditional permanent magnet based DC generators. The discovery of the dynamo principle made industrial scale electric power generation technically and economically feasible. After

2553-418: The direct-current rotor, whereas often a rotor winding has three phases, and multiple sections which would each require a slip-ring connection. The stationary armature can be wound for any convenient medium voltage level, up to tens of thousands of volts; manufacture of slip ring connections for more than a few thousand volts is costly and inconvenient. Many alternators are cooled by ambient air, forced through

2622-401: The effects of momentary faults . Often, there are three sets of stator windings, physically offset so that the rotating magnetic field produces a three phase current, displaced by one-third of a period with respect to each other. One cycle of alternating current is produced each time a pair of field poles passes over a point on the stationary winding. The relation between speed and frequency

2691-463: The enclosure by an attached fan on the shaft that drives the alternator. In vehicles such as transit buses, a heavy demand on the electrical system may require a large alternator to be oil-cooled. In marine applications water-cooling is also used. Expensive automobiles may use water-cooled alternators to meet high electrical system demands. Most power generation stations use synchronous machines as their generators. The connection of these generators to

2760-526: The field winding and armature winding are stationary, and current is induced in the armature by the changing magnetic reluctance of the rotor (which has no windings or current-carrying parts). Such machines were made to produce radio frequency current for radio transmissions, although the efficiency was low. Jedlik%27s dynamo Too Many Requests If you report this error to the Wikimedia System Administrators, please include

2829-447: The first source of electric power for industry, they had to be located close to the factories that used their power. Electricity could only be distributed over distances economically as alternating current (AC), through the use of the transformer . With the 1890s conversion of electric power systems to alternating current, during the 20th century dynamos were replaced by alternators , and are now almost obsolete. The word 'dynamo' (from

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2898-407: The frequency in terms of alternations per minute, counting each half-cycle as one alternation ; so 12,000 alternations per minute corresponds to 100 Hz. An alternator's output frequency depends on the number of poles and the rotational speed. The speed corresponding to a particular frequency is called the synchronous speed . This table gives some examples: Alternators may be classified by

2967-640: The heart of all modern dynamos. Charles F. Brush assembled his first dynamo in the summer of 1876 using a horse-drawn treadmill to power it. Brush's design modified the Gramme dynamo by shaping the ring armature like a disc rather than a cylinder shape. The field electromagnets were also positioned on the sides of the armature disc rather than around the circumference. After dynamos and motors were found to allow easy conversion back and forth between mechanical or electrical power, they were combined in devices called rotary converters , rotating machines whose purpose

3036-432: The initial AC voltage buildup, the field is supplied with rectified voltage from the alternator. A brushless alternator is composed of two alternators built end-to-end on one shaft. Until 1966, alternators used brushes with rotating field. With the advancement in semiconductor technology, brushless alternators are possible. Smaller brushless alternators may look like one unit, but the two parts are readily identifiable in

3105-481: The interior of large warehouses. Some, such as Yablochkov arc lamps introduced in 1878, ran better on alternating current, and the development of these early AC generating systems was accompanied by the first use of the word "alternator". Supplying the proper amount of voltage from generating stations in these early systems was left up to the engineer's skill in "riding the load". In 1883 the Ganz Works invented

3174-402: The invention of the alternator and that alternating current can be used as a power supply, the word dynamo became associated exclusively with the ' commutated direct current electric generator', while an AC electrical generator using either slip rings or rotor magnets would become known as an alternator . A small electrical generator built into the hub of a bicycle wheel to power lights

3243-429: The large versions. The main alternator is the larger of the two sections, 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. A bridge rectifier , called the rotating rectifier assembly, is mounted on the rotor. Neither brushes nor slip rings are used, which reduces

3312-415: The magnetic field. This counterflow limited the power output to the pickup wires, and induced waste heating of the copper disc. Later homopolar generators would solve this problem by using an array of magnets arranged around 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 single current path through

3381-438: The magnetic flux. Faraday and others found that higher, more useful voltages could be produced by winding multiple turns of wire into a coil. Wire windings can conveniently produce any voltage desired by changing the number of turns, so they have been a feature of all subsequent generator designs, requiring the invention of the commutator to produce direct current. The first commutated dynamo was built in 1832 by Hippolyte Pixii ,

3450-446: The method of excitation, number of phases, the type of rotation, cooling method, and their application. There are two main ways to produce the magnetic field used in the alternators: by using permanent magnets , which create their persistent magnetic field, or by using field coils . The alternators that use permanent magnets are specifically called magnetos . In other alternators, wound field coils form an electromagnet to produce

3519-435: The number of wearing parts. The main alternator has a rotating field and a stationary armature (power generation windings). Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and hence alternator output. The result

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3588-440: The position of the rotor, an alternator is a synchronous generator. The rotor's magnetic field may be produced by permanent magnets or by a field coil electromagnet. Automotive alternators use a rotor winding, which allows control of the alternator's 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 due to

3657-531: The power may be split between the engine starting battery and the domestic or house battery (or batteries) by use of a split-charge diode ( battery isolator ) or a voltage-sensitive relay. Due to the high cost of large house battery banks, Marine alternators generally use external regulators. Multistep regulators control the field current to maximize the charging effectiveness (time to charge) and battery life. Multistep regulators can be programmed for different battery types. Two temperature sensors can be added: one for

3726-412: The prototype of the single-pole electric starter, both the stationary and the revolving parts were electromagnetic. Around 1856, six years before Siemens and Wheatstone , Ányos formulated the concept of the dynamo, but did not patent it as he thought he was not the first to realize the idea. Instead of permanent magnets, his dynamo used two electromagnets placed opposite to each other in order to induce

3795-445: The residual field, cause the rotor to produce more current. In this manner, the self-exciting dynamo builds up its internal magnetic fields until it reaches its normal operating voltage. When it is able to produce sufficient current to sustain both its internal fields and an external load, it is ready to be used. A self-excited dynamo with insufficient residual magnetic field in the metal frame will not be able to produce any current in

3864-417: The rotating magnetic field. A device that uses permanent magnets to produce alternating current is called a permanent magnet alternator (PMA). A permanent magnet generator (PMG) may produce either alternating current or direct current if it has a commutator . This method of excitation consists of a smaller direct-current (DC) generator fixed on the same shaft as the alternator. The DC generator generates

3933-527: The rotor, but in Wheatstone's design they were in parallel. The use of electromagnets rather than permanent magnets greatly increased the power output of a dynamo and enabled high power generation for the first time. This invention led directly to the first major industrial uses of electricity. For example, in the 1870s Siemens used electromagnetic dynamos to power electric arc furnaces for the production of metals and other materials. The dynamo machine that

4002-410: The rotor, regardless of what speed the rotor spins. This situation can also occur in modern self-excited portable generators, and is resolved for both types of generators in a similar manner, by applying a brief direct current battery charge to the output terminals of the stopped generator. The battery energizes the windings just enough to imprint the residual field, to enable building up the current. This

4071-414: The salt-water environment. Marine alternators are designed to be explosion proof (ignition protected) so that brush sparking will not ignite explosive gas mixtures in an engine room environment. Depending on the type of system installed, they may be 12 or 24 volts. Larger marine diesels may have two or more alternators to cope with the heavy electrical demand of a modern yacht. On single alternator circuits,

4140-501: The same time. The size and mass of the rotor was made large so that the rotor would act as a flywheel to help smooth out any sudden surges or dropouts in the applied power. The technology of rotary converters was replaced in the early 20th century by mercury-vapor rectifiers , which were smaller, did not produce vibration and noise, and required less maintenance. The same conversion tasks are now performed by solid state power semiconductor devices . Rotary converters remained in use in

4209-465: The seriously detrimental effects of large air gaps in the magnetic circuit. Antonio Pacinotti , an Italian physics professor, solved this problem around 1860 by replacing the spinning two-pole axial coil with a multi-pole toroidal one, which he created by wrapping an iron ring with a continuous winding, connected to the commutator at many equally spaced points around the ring; the commutator being divided into many segments. This meant that some part of

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4278-506: The speed of DC traction motors. Most of these had two generators: one to generate the excitation current for a larger main generator. Optionally, the generator also supplies head-end power (HEP) or power for electric train heating . The HEP option requires a constant engine speed, typically 900 r/min for a 480 V 60 Hz HEP application, even when the locomotive is not moving. Marine alternators used in yachts are similar to automotive alternators, with appropriate adaptations to

4347-418: The stator were originally separately excited by a separate, smaller, dynamo or magneto. An important development by Wilde and Siemens was the discovery (by 1866) that a dynamo could also bootstrap itself to be self-excited , using current generated by the dynamo itself. This allowed the growth of a much more powerful field, thus far greater output power. Self-excited direct current dynamos commonly have

4416-407: The term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses a permanent magnet for its magnetic field is called a magneto . Alternators in power stations driven by steam turbines are called turbo-alternators. Large 50 or 60 Hz three-phase alternators in power plants generate most of the world's electric power, which

4485-482: The utility grid requires synchronization conditions to be met. Alternators are used in modern internal combustion engine automobiles to charge the battery and to power the electrical system when its engine is running. Until the 1960s, automobiles used DC dynamo generators with commutators . With the availability of affordable silicon-diode rectifiers, alternators were used instead. In later diesel-electric locomotives and diesel electric multiple units ,

4554-466: Was a better path for the magnetic flux , by filling the space occupied by the magnetic field with heavy iron cores and minimizing the air gaps between the stationary and rotating parts. The Gramme dynamo was one of the first machines to generate commercial quantities of power for industry. Further improvements were made on the Gramme ring, but the basic concept of a spinning endless loop of wire remains at

4623-483: Was developed consisted of a stationary structure, which provides the magnetic field, and a set of rotating windings which turn within that field. On larger machines the constant magnetic field is provided by one or more electromagnets, which are usually called field coils. Zénobe Gramme reinvented Pacinotti's design in 1871 when designing the first commercial power plants operated in Paris . An advantage of Gramme's design

4692-474: Was discovered in the years 1831–1832 by Michael Faraday . The principle, later called Faraday's law , is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux . He also built the first electromagnetic generator, called the Faraday disk , a type of homopolar generator , using a copper disc rotating between the poles of a horseshoe magnet . It produced

4761-704: Was not to provide mechanical power to loads but to convert one type of electric current into another, for example DC into AC . They were multi-field single-rotor devices with two or more sets of rotating contacts (either commutators or sliprings, as required), one to provide power to one set of armature windings to turn the device, and one or more attached to other windings to produce the output current. The rotary converter can directly convert, internally, any type of electric power into any other. This includes converting between direct current (DC) and alternating current (AC), three phase and single phase power, 25 Hz AC and 60 Hz AC, or many different output voltages at

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