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53-693: Pearl Street Station consumed coal for fuel; it began with six 100 kW dynamos , and it started generating electricity on September 4, 1882, serving an initial load of 400 lamps to 82 customers. By 1884, Pearl Street Station was serving 508 customers with 10,164 lamps. Electricity was supplied at 110V DC. The station was originally powered by custom-made Porter-Allen high-speed steam engines designed to provide 175 horsepower at 700 rpm, but these proved to be unreliable with their sensitive governors. They were removed and replaced with new engines from Armington & Sims that proved to be much more suitable for Edison's dynamos. Pearl Street Station served what

106-409: 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 , a French instrument maker. It used a permanent magnet which was rotated by a crank. The spinning magnet

159-406: 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

212-412: 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 They have, again, been replaced by alternators .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

265-417: 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

318-415: 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,

371-405: 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

424-399: A surface of vector area S is Φ B = B ⋅ S = B S cos ⁡ θ , {\displaystyle \Phi _{B}=\mathbf {B} \cdot \mathbf {S} =BS\cos \theta ,} where B is the magnitude of the magnetic field (the magnetic flux density) having the unit of Wb/m ( tesla ), S is the area of the surface, and θ is

477-497: Is an electrical generator that creates direct current using a commutator . Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor , the alternating-current alternator , and the rotary converter . Today, the simpler alternator dominates large scale power generation , for efficiency, reliability and cost reasons. A dynamo has

530-400: 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

583-455: 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 a small DC voltage . This was not a dynamo in the current sense, because it did not use a commutator . This design

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636-632: Is now kept in the Greenfield Village Museum in Dearborn, Michigan. It was rebuilt, and ran till 1895, when it was decommissioned, since larger and more efficient plants had been built nearby. In 1929 the Edison Company constructed three scale working models of the station. When a button was pushed, a motor turned the engines, generators, and other equipment in the model. A set of lamps connected to labelled buttons identified

689-399: Is proportional to the number of field lines passing through that surface (in some contexts, the flux may be defined to be precisely the number of field lines passing through that surface; although technically misleading, this distinction is not important). The magnetic flux is the net number of field lines passing through that surface; that is, the number passing through in one direction minus

742-698: 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

795-485: 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". Magnetic flux In physics , specifically electromagnetism ,

848-400: 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 the prototype of the single-pole electric starter, both the stationary and

901-432: Is the statement: for any closed surface S . While the magnetic flux through a closed surface is always zero, the magnetic flux through an open surface need not be zero and is an important quantity in electromagnetism. When determining the total magnetic flux through a surface only the boundary of the surface needs to be defined, the actual shape of the surface is irrelevant and the integral over any surface sharing

954-615: 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 the rotor, but in Wheatstone's design they were in parallel. The use of electromagnets rather than permanent magnets greatly increased

1007-812: The Smithsonian Institution 's National Museum of American History in Washington, D.C.; at the Consolidated Edison Learning Center in Long Island City , New York; and at the Henry Ford Museum in Dearborn, Michigan. Up to 31 people worked on constructing the models which took about 6 months to complete. 40°42′28″N 74°00′17″W  /  40.70778°N 74.00472°W  / 40.70778; -74.00472 Dynamo A dynamo

1060-485: The line integral is taken over the boundary of the surface S , which is denoted ∂ S . Gauss's law for magnetism , which is one of the four Maxwell's equations , states that the total magnetic flux through a closed surface is equal to zero. (A "closed surface" is a surface that completely encloses a volume(s) with no holes.) This law is a consequence of the empirical observation that magnetic monopoles have never been found. In other words, Gauss's law for magnetism

1113-465: The magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted Φ or Φ B . The SI unit of magnetic flux is the weber (Wb; in derived units, volt–seconds or V⋅s), and the CGS unit is the maxwell . Magnetic flux is usually measured with a fluxmeter , which contains measuring coils , and it calculates

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1166-528: The EMF are, firstly, the work per unit charge done against the Lorentz force in moving a test charge around the (possibly moving) surface boundary ∂Σ and, secondly, as the change of magnetic flux through the open surface Σ . This equation is the principle behind an electrical generator . By way of contrast, Gauss's law for electric fields, another of Maxwell's equations , is where The flux of E through

1219-507: 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

1272-557: 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

1325-477: The angle between the magnetic field lines and the normal (perpendicular) to S . For a varying magnetic field, we first consider the magnetic flux through an infinitesimal area element d S , where we may consider the field to be constant: d Φ B = B ⋅ d S . {\displaystyle d\Phi _{B}=\mathbf {B} \cdot d\mathbf {S} .} A generic surface, S , can then be broken into infinitesimal elements and

1378-598: 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

1431-438: 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 the magnetic flux. Faraday and others found that higher, more useful voltages could be produced by winding multiple turns of wire into

1484-410: 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

1537-506: 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

1590-414: 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 was discovered in the years 1831–1832 by Michael Faraday . The principle, later called Faraday's law , is that an electromotive force

1643-447: 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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1696-402: 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

1749-471: 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 was a better path for the magnetic flux , by filling

1802-487: The magnetic flux from the change of voltage on the coils. The magnetic interaction is described in terms of a vector field , where each point in space is associated with a vector that determines what force a moving charge would experience at that point (see Lorentz force ). Since a vector field is quite difficult to visualize, introductory physics instruction often uses field lines to visualize this field. The magnetic flux through some surface, in this simplified picture,

1855-427: The number passing through in the other direction (see below for deciding in which direction the field lines carry a positive sign and in which they carry a negative sign). More sophisticated physical models drop the field line analogy and define magnetic flux as the surface integral of the normal component of the magnetic field passing through a surface. If the magnetic field is constant, the magnetic flux passing through

1908-399: 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 was developed consisted of a stationary structure, which provides

1961-490: 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 a patent on 24 December 1866, while Siemens and Wheatstone both announced their discoveries on 17 January 1867, by delivering papers at

2014-445: 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

2067-405: 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 a magnetic field around the rotor. This was also the discovery of

2120-410: 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

2173-790: The same boundary will be equal. This is a direct consequence of the closed surface flux being zero. For example, a change in the magnetic flux passing through a loop of conductive wire will cause an electromotive force (emf), and therefore an electric current, in the loop. The relationship is given by Faraday's law : E = ∮ ∂ Σ ( E + v × B ) ⋅ d ℓ = − d Φ B d t , {\displaystyle {\mathcal {E}}=\oint _{\partial \Sigma }\left(\mathbf {E} +\mathbf {v} \times \mathbf {B} \right)\cdot d{\boldsymbol {\ell }}=-{\frac {d\Phi _{B}}{dt}},} where: The two equations for

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2226-501: 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

2279-507: 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 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

2332-498: 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 the heart of all modern dynamos. Charles F. Brush assembled his first dynamo in

2385-517: 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 the coil was continually passing by the magnets, smoothing out the current. The Woolrich Electrical Generator of 1844, now in Thinktank, Birmingham Science Museum ,

2438-418: 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

2491-558: 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

2544-640: The total magnetic flux through the surface is then the surface integral Φ B = ∬ S B ⋅ d S . {\displaystyle \Phi _{B}=\iint _{S}\mathbf {B} \cdot d\mathbf {S} .} From the definition of the magnetic vector potential A and the fundamental theorem of the curl the magnetic flux may also be defined as: Φ B = ∮ ∂ S A ⋅ d ℓ , {\displaystyle \Phi _{B}=\oint _{\partial S}\mathbf {A} \cdot d{\boldsymbol {\ell }},} where

2597-418: The various areas of the building. Cut-outs in the side of the model building allowed examination of the boilers on the first level, reciprocating steam engines and dynamos on the reinforced second level, and the control and test gear on the third and fourth levels. The models were constructed to a scale of 1:24 and were 62 inches long, 34 inches high and 13 inches wide. The models still exist and are on display at

2650-399: 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 the magnetic field. This counterflow limited the power output to the pickup wires, and induced waste heating of

2703-576: Was known as the "First District" (bounded clockwise from north by Spruce Street , the East River , Wall Street , and Nassau Street ). This was the world's first underground urban network. The district, so named because of its importance in the history of electric power, contained several other power stations such as the Excelsior Power Company Building . The station burned down in 1890, destroying all but one dynamo that

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2756-704: 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

2809-405: 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 the alternating current to DC, Pixii invented a commutator , a split metal cylinder on

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