Electrostatic machine

The electrostatic machine is thus named because it calls upon the laws of electrostatics to the difference of the machines known as electromagnetic. Although driving electrostatic were imagined (they function on the principle of the reciprocity of the electrostatic generators), they did not have success (but the nanotechnologies could propose such electrostatic “nanomoteurs”); on the other hand, as a generating of very high voltage, the electrostatic machines know their principal application in the field of the accelerators of ions or electrons. They transform the mechanical energy into electrical energy whose characteristics are very the continuous high voltage and the microampérage. The power of the machines of the 18th century and the 19th century was indeed negligible (a few Watts) and mechanical frictions left them only one very bad output. The reason is that the maximum density of energy of the electric field in the air is very low. The electrostatic machines cannot be usable (in an industrial way) only if they function in a medium where the density of energy of the electric field is raised enough, i.e. practically a compressed gas, which is generally the sulfur hydrogen or hexafluoride (SF₆), under pressures ranging between 10 and 30 atmospheres.

Machines with friction

It is electrification by triboelectrification which generates the electric charges.

The first electrostatic generators are called machines with friction (or with friction ) because of the use of friction in the process of generation of loads. In 1600, William Gilbert, private doctor of the Queen Elizabeth, published a Latin treaty, De Magnete , on the magnetism and the properties of attraction of the Ambre. It found many other substances which, rubbed, behaved like amber. It called them “electric”. The primitive shape of electric machine with friction was built about 1663 by Otto von Guericke, of Magdeburg, by using a sulfur sphere in rotation rubbed with the hand . Isaac ''' Newton ''' suggested the use of a sphere of glass instead of a sulfur sphere; in 1707, Francis Hauksbee built such a Gas-discharge lamp.

About 1740, the hands were replaced by mechanical wipers, leather bearings, the sphere was replaced by cylinders of glass. It is necessary to await 1730 and Stephen Gray to include/understand electric conduction . It draws up an insulating list of conducting and , supplementing that of the electric made by Gilbert, the insulators appearing among the best electric ones. Gray discovered by chance that the electric charges do not fill a body but are entirely on its surface. Charles-François Of Fay with the assistance of the ''' abbot Nollet ''' discovers vitreous electricity and resinous electricity: the loads of a species attract those of the other species. The similar loads are pushed back. The bodies noncharged should contain a quantity equalizes each one. The invention of the electric condenser in the form of the Leyden jar (by E. - G. Kleist, Van Musschenbroek and its Cuneus pupil, improved by sir William Watson, 1745-1747) makes it possible to reinforce the intensity of the discharges. 1768, machine of ''' Ramsden ''' . 1784, the machine of ''' Van Marum '''. 1785, the machine of NR. Rouland (one of the ancestors of the generator VAN DE GRAAFF). 1840, the machine of Woodward was developed like an improvement of the machine of Ramsden (placing the principal driver above the discs). 1840, the hydroelectric machine of Armstrong was developed by employing the vapor like charge carrier. Instrument of physics, the generating with friction was to remain it until the end (demonstrations of electrostatics in the schools until 1905).

Induction machines

A model improved considerably of generator of load, the induction machine (or static induction), was developed before 1800. Canton described the principle in 1750 of it, but the machines were produced only later. The machine with induction was doubly important: on the one hand, it rested on the clear comprehension of electricity positive or negative, on the other hand, it could accumulate theoretically unlimited loads (with essential insulation). This unlimited capacity came to supplement that of the Leyden jar. The first induction machines employed rotary discs of glass, often in multiple form.

electrostatic induction or electrostatic induction

When one approaches a body has electrically neutral a body B electrified (conducting or insulator), it occurs on the body has an electrification such as loads of opposite signs accumulate compared to the body B. As the body has does not receive nor does not yield any load, of the loads of opposite signs are distributed on the surface of the body has with a predilection for curved or pointed surfaces of the ends.

the electrophorus of Volta (Alessandro Volta, about 1775): It is composed of a cast resin cake in a mould and of a brass disc provided with an insulating handle. It is a source of electricity created by influence. One strikes the resin cake with a skin of cat, then one lays out the conducting disc above, without there being contact: the negative electricity of the resin develops by influence positive electricity on the lower face of the disc and negative electricity on the higher face. One then touches the disc with the finger, negative electricity runs out towards the ground via the human body. One then ceases the contact with the finger: the disc which one moves away, by holding it by the insulating handle, is then in charge of positive electricity. The disc thus charged makes it possible to make spout out a spark between him and any conducting body.

The induction machines can be regarded as temporarily perpetual electrophori by addition of loads. The mechanical energy is transformed into electrical energy by the additional contribution of loads to a small initial load.

1788, William Nicholson proposed her turning lapping machine, which can be regarded as first revolving induction machine. 1795, T. Cavallo, John Lu, Charles Bernard Desormes, and Jean Nicolas Pierre Hatchet, developed various forms of revolving lapping machines . 1798, Gottlieb Christoph Bohnenberger describes the machine of Bohnenberger, with several other lapping machines of Simpleton; 1831, Giuseppe Belli developed a simple symmetrical lapping machine of it. 1867, Lord Kelvin and the replenisher . 1860, c.f. Varley made patent a more modern type of induction machine. Between 1864 and 1880, W.T.B. Holtz built and described a great number of induction machines considered as the most advanced time. The machine of Holtz is made up of a disc of glass assembled on a horizontal axis made to turn at a considerable speed by reduction. Another disc, motionless, carries notches in which pass from small conducting legs which make it possible the inductors to discharge. In 1865, J.I. Toepler developed an induction machine which is made up of two discs fixed on the same axis and turning in the same direction. They are variable capacitators charged and discharged by contact with brushes. The small machine excites the large one and conversely, from where automatic priming due to the tensions of contact. In 1868, the machine of Schwedoff had a curious structure to amplify the current of exit.

Always in 1868, several machines combine friction and influence: the machine of Kundt and the machine of Square . In 1866, the machine of Piche (or the machine of Bertsch). In 1869, H. Jules Smith received an American patent for a portable and hermetic electrostatic device which was designed to fire the powder. Always in 1869, of the machines without sector in Germany were studied by Poggendorff .

The action and the effectiveness of the induction machines were studied further by F. Rossetti, A. Righi , and F.W.G. Kohlrausch. E.E. NR. Mascart , A. Roiti, and E. Bouchotte also examined the effectiveness and the power of the produced currents of the induction machines. In 1871, machines without sector were studied by Musaeus (precursory of the invention of the machine of Wimshurst). In 1872, the electrometer of Righi was developed and was one of the first ancestors of the generator of VAN DE GRAAFF. In 1873, Leyser developed the machine of Leyser, a variation of the machine of Holtz . In 1880, Robert Voss (a manufacturer of instruments of Berlin) conceived the shape of machine in which he claimed that the principles of Toepler and Holtz were combined. The same structure becomes also known under the name of machine of Toepler-Holtz. In 1878, the English inventor James Wimshurst improves the machine of Holtz and that of Musaeus, in a powerful version with the multiple discs. The traditional machine of Wimshurst, becomes the most popular model of the induction machines. In 1885, one of the largest machines of Wimshurst was built in England (it is now with the museum of Chicago of Science and Industry). In 1885, the German Walter Hempel notes that the operation of the machines of Toepler is improved when the air is pressurized. The current increases proportionally with the pressure (tests to 3 bars). Unfortunately it does not make an experiment on the effects of the pressure on the tension. In 1887, Weinhold modified the machine of Leyser with a system of vertical inductors. Mr. L. Lebiez described the machine of Lebiez, as being primarily a simplified machine of Voss ( the Electrician , April 1895, pp. 225-227). In 1894, Bonetti designed a machine with the structure of the machine of Wimshurst, but without the metal sectors on the discs. This machine is appreciably more powerful than the version with sectors, but it is not car-amorçante. In 1898, the machine of Pidgeon was developed with a single installation by W.R. Pidgeon.

Machines with multiple discs, electrostatic machines “ plywood ” (generating with three discs) were also developed intensively with the turning of the century. In 1900, F. Tudsbury discovered (independently of Walter Hempel) that by locking up a generator in a metal room containing of the compressed air, or better carbonic gas, one improves the performances (insulation and tension).

In 1903, Alfred Wehrsen made patent a rotary ebonite disc having the sectors included with contacts on the face of the disc. In 1907, Heinrich Wommelsdorf (1877-1945) brought back a variation of the machine of Holtz. It also developed several electrostatic generators with raised output, of which most known were its machines with condenser (1920). They was machines with multiple discs, using metal sectors enchased accessible by the section from the disc.

At the beginning of the XXe century, the electrostatic generators with influence reach tensions between 80 000 and 100 000 volts (80 to 100 kilovolts).

Machine of Wimshurst

Generator of VAN DE GRAAFF

Generator of Felici

In France, between the years 1940 and 1960, No5el Felici, collaborator of Louis Néel at the electrostatic laboratory of of CNRS stuck to a systematic study of the electrostatic generators, in order to extract the maximum from the energy point of view from it. This research led to a model different from the machine with belt of the VAN DE GRAAFF type because the mobile body is a cylinder hollow and the compressed gas of insulation of pure hydrogen. Compared to the generator VAN DE GRAAFF, the belt is replaced by a cylinder isolating with thin walls (a few millimetres) turning at high speed (up to 80 meters a second) around a slightly conducting cylindrical stator, leaving a very weak interstice (fraction of millimetre), and which plays the part of distributer of potential (equipotential rings) of the column of the machines with belt. The load and the discharge of the cylinder are ensured by thin steel blades, laid out outside the cylinder parallel to its axis, and influenced by metal inductors being inside the stator. When it is multipolar (2, 4,6,16 poles), it can give relatively intense currents. Hydrogen under pressure facilitates commutation, reduced frictions and improves cooling. It is to date the electrostatic machine which had the best output. Marketed until in the years 1970 by the SAMES in Grenoble, these compact industrial electrostatic generators could be used for electric tests, electrostatic projections, particle accelerators (ions or electrons), ionic implantateurs, x-rays. It is a machine of this type (Series KR300.10, 300 Kv and 10 µA) which is the generator in demonstration with the Palais of discovered the in Paris. This type of machine is replaced today by multipliers of tension of the type Greinacher (Tandetron, Singletron, of mark HVEE, or Dynamitron) where electrostatics is replaced by the association of cascades diodes/condensing).

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