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In 1822, Peter Barlow built what can be regarded as the first electrical motor of the history: the “Wheel of Barlow” which is a simple metal disc cut out out of star and whose ends plunge in a cup containing of the mercury which ensures the arrival of the current.

The first switch usable in experiments was invented in 1832 by William Sturgeon. The first engine has D.C. current manufactured with the intention to be marketed was invented by Thomas Davenport in 1834 then patented in 1837. These engines did not experience industrial development because of the cost of the batteries at the time.

One owes the practical checking of the reversibility of the electric machines to the Italian physicist Antonio Pacinotti in 1864.

1869 the Belgian inventor Zénobe Gram, makes possible the realization of the generators to D.C. current by imagining the collector. It improves the first antiquated versions of alternators (1867) and becomes famous by finding the principle of ring armature of Pacinotti. In 1871, it will present to the Academy of Science of Paris the first industrial generator of D.C. current, which one called machine of Gram and which was in fact a magneto.

The paternity of the asynchronous machine is discussed between three inventors: in 1887, Nikola Tesla deposits a patent on the asynchronous machine, then in May of the following year five other patents. For the same period Galileo Ferraris publishes treaties on the revolving machines, with an experimentation in 1885, then a theory on the asynchronous motor in April 1888. In 1889, Michail Ossipowitsch Doliwo-Dobrowolski, German electrician of Russian origin, invents the first asynchronous motor with three-phase current with squirrel-cage which will be built industrially as from 1891.

Revolving machines

Machine with D.C. current

See also: Machine with D.C. current

Like all the revolving machines, the electric machines with D.C. current consist of a stator and a rotor. The stator creates a fixed longitudinal magnetic field using rollings up or of permanent magnets. The rotor consists of a whole of reels connected to a rotary collecting . The rotary collector makes it possible to reverse the polarity of the magnetic field created by the stator before this one is not in phase with that created by the rotor. Thanks to this device, the fields rotor and stator are always in squaring thus causing the rotation of the rotor.

The principal advantage of the machines with D.C. current lies in their simple adaptation to the means making it possible to regulate or vary their speed, their couple and their direction of rotation: the variable speed transmissions. And even their direct connection with the source of energy: pile, accumulator batteries, etc

The principal defect of the machine with D.C. current lies as a whole balas/collecting rotary which wears, is complex to realize and consumes energy. Another problem limits high speeds of use of these engines when the rotor is wound, it is the phenomenon of “hoop removing”, the centrifugal force ending up breaking the bonds ensuring the behavior of the whole of whorls (hooping).

A certain number of these disadvantages were partially solved by achievements of engines without iron to the rotor, like the engines “discs” or the engines “bells”, which nevertheless always have brushes.

The disadvantages above were radically eliminated thanks to technology from the driving '' brushless '', also called “engine with D.C. current without brushes”, or engine without brushes.

Machines with Alternative course

These alternate engines are declined in three types:

• the universal engines ;
• the asynchronous engines ;
• the synchronous engines .

Universal engines

See also: Driving universal

A universal driving is a Machine with D.C. current with excitation series: the rotor is connected in series with the field winding. The couple of the machine is independent of the direction of flow of the current (couple proportional to the square of the current) and can thus be fed in alternative course. To limit the eddy current which appear systematically in all the massive metal zones subjected to alternate magnetic fields, his Stator is laminated.

The universal engines are used in devices requiring a couple rather extremely, such as a food processor, the électroportatif tools of low power (until 1200  W) or Suction S. The Speed of rotation of these engines can be easily regulated by an inexpensive device such as a Gradateur (variator being used to regulate the luminous intensity of the Luminaire S).

Synchronous machines

See also: synchronous Machine

The synchronous machine is often used like generating. It is called then alternator . Put aside for the realization of Generator of low power, this machine is generally three-phase. For the electrical production, the powerplants use alternators whose powers can border the 1500  MW.

As the name indicates it, the number of revolutions of these machines is always proportional to the Fréquence currents which cross them. This type of machine can be used to raise the power-factor of an installation. One calls this one a Synchronous condenser .

The synchronous machines are also used in the systems of traction (such TGV). These machines are associated with inverters of currents, which makes it possible to fix the constant average engine torque with a minimum of current. One speaks about autopilotage (control of the stator currents compared to the position of the rotor).

Engines without brushes

See also: Driving without brushes

An engine without brushes, or “driving brushless ”, is a synchronous motor, whose rotor consists of one or several permanent magnets and to which is assistant a rotor position encoder (Capteur with Hall effect, synchro-synchro-transmitter, incremental coder for example). Seen outside, it functions in D.C. current. Its name Brushless comes owing to the fact that this type of engine does not contain any balas. On the other hand an electronic system of order must ensure the commutation of the current in the stator windings. This device can be either integrated into the engine, for the small powers, or outside. The role of the sensor-electronics unit of order is to ensure the car-piloting of the engine i.e. the orthogonality of rotor flow compared to stator flow, role formerly reserved for the brush-collector unit on a machine with D.C. current.

The engines brushless equip in particular the hard drives and the engravers with DVD of our computers. It also are very much used in model making to make be driven small-scale models of planes, helicopters and cars. They are also utisés in industry in particular in the servomechanisms of the machine tools and in Robotique.

Asynchronous machines

See also: asynchronous Machine

The asynchronous machine , also known under the “Anglo-Saxon” term of machine to induction , is a machine with Alternative course without connection between the Stator and the Rotor. The asynchronous term comes owing to the fact that the speed of these machines is not inevitably proportional to the Fréquence of the currents which cross them.

The asynchronous machine a long time was strongly competed with by the synchronous Machine in the fields of strong power, until the advent of the electronic of power. One finds it today in many applications, in particular in the Transport (subway, trains, propulsion of the ships), of the Industrie (machine tools), in the electric household appliances. They in the beginning were only used out of engine but, always thanks to the electronics of power, they are more and more often used out of generator. It is for example the case in the wind S.

To function while running Single-phase current, these machines require a system of starting. For the applications of power, beyond some kilowatts, the asynchronous motors are only supplied by systems of currents Triphasé S

The machines autosynchrones

Characteristics common of the machines to alternative course

L exists a large variety of driving hybrids (for example “asynchronous synchronized” in the pumps of dishwasher).

Engines step by step

See also: Driving step by step

Another kind of electrical motor is the driving step by step . A rotor interns containing permanent magnets is moved by a whole of electromagnets placed in the stator commutated by an electronics of power. The food or not of each one defines a different angular position (the sequence allows the movement). The engines step by step simple have a limited number of positions, but the engines step by step with order proportional (variable food of the reels) can be extremely precise. One speaks then about “micro step” since the engine can balance between two steps.

These engines ordered by a numerical electronic are one of the most flexible forms of the systems of positioning, in particular in the bodies servos numerically: example, the engines of positioning of the read/write heads of the hard drives of Ordinateur were positioned a long time by this type of engine, from now on too slow for this application, they were replaced by linear motor with impulse much faster.

Linear motors

A linear motor is primarily an electrical motor which “was unrolled” so that instead of producing a couple (rotation), it produces a linear force over its length by installing an electromagnetic field of displacement. They are as well divided into those with weak acceleration used in transport the Transrapid as the SkyTrain, and those with fast acceleration in the weapons like the magnetic Canon and the space engines.

In the same category the Electromagnetic pumps appear in induction which make it possible to convey a conducting fluid . The first tests of this type of machine were carried out with mercury then NAK (mixture of Sodium/Potassium). The great industrial achievements relate to the circulation du sodium in certain types of nuclear reactors and of the proportioning pumps of Aluminum liquid.

• Magnetohydrodynamic electromagnet

• electromagnetic Lift
• (MHD)

Appendices