Electrostatic generator

Electrostatic generators are mechanical devices for generating electrical power with means of electrostatics by the separation of electric charges. Generally, they are likely to reach high pressure, but can not deliver high performance. The achievable voltages are limited only by insulation problems such as leakage current and peak discharges.

History

The first electrostatic generators were working on the principle of static electricity and were referred to the end of the 19th century as a electrical machines. 1883 generators have been developed which operate on the principle of induction. These generators are called influence machines.

Otto von Guericke built in 1663 a sulfur sphere with an axis of rotation which rubbed by hand should demonstrate the cosmic potencies ( virtutes mundanae ). Such a sulfur ball he sent to interested contemporaries, as well as 1671 to Gottfried Wilhelm von Leibniz, who thus produced a first artificial electric spark. Early 18th century began the systematic study of electricity. Francis Hauksbee developed in 1706 a Reibungselektrisiermaschine whose ball was not built more of sulfur, but made ​​of glass. Electrostatic generators were through to the development of the voltaic pile, in 1800 by Alessandro Volta, the only source of artificially generated electricity.

For educational purposes and in particle accelerators or Van de Graaff generators and tape Pelletron be used currently. For small band generators, the initial charge separation occurs by friction, so they are more advanced electrical machines. With the large Van de Graaff accelerators, the initial charge separation is effected by means of peak discharge voltage obtained from the mains, at Pelletron by induction. The increase in the voltage is then, in both cases with an electric -static agents.

Operation

Electrostatic generators can be divided into two classes:

• Electrostatic generators, which operate on the principle of frictional electricity;
• Influence machines that use the effect of the electric induction.

Characteristic of electrical machines is the friction between insulators ( for example, sulfur, glass, wood and rubber). In contrast, influence machines which charge is produced by induction in metal parts.

Electrical machines

By mechanical friction between two materials with different electron affinity, the electrons are distributed on their surfaces to varying degrees between them. In the electrostatic generators thus obtained, depending on the design either positive or negative charge is derived and collected in capacitors, such as Leyden jars.

Static electricity is a special case of the contact or contact electricity. By the frictional contact between the materials is greater, and the exchange of carriers intense than the mere contact.

The most common construction consists of one or more glass twills in the form of hollow spheres, rolls or sheets of glass. Rotating the vitreous Reibzeuge be pressed, for example leather pad having a coating of amalgam.

At one point behind the nip point of the Reibzeuge takes a konduktor ( an electrical conductor, such as a small metallic brush ) the electric charge from the glass surface and passes them directly to an experiment or in a capacitor from. The Reibzeuge are generally grounded so that the charge derived from the konduktor is compensated. Some machines work according to the reverse principle, wherein the konduktor is grounded, and the electric charge is removed on the Reibzeugen, and there was machines which could be changed between konduktor and Reibzeugerdung.

In addition to glass wood and rubber were used for windows of electrical machines. In the first place of electrical machines and rasp konduktor served at the same time to rub the human hand and to hold the electric charge. The Grinding was " electrified ", leading electrical machine to the label.

The largest disc electrostatic generator ( the diameter of the glass is 1.65 m) is in Teylers Museum in Haarlem and was Martinus van Marum of the physician ( 1750-1837 ) in 1785 presented to the public. On construction also an instrument maker from Amsterdam Cuthbertson was involved. Van Marum was then just become director of Teylers Museum and dealt for over 10 years still in Groningen with the improvement of electrical machines, with which he wanted to make new discoveries in the field of electricity and which he founded Oersted and 1781/2 Volta presented. You can generate sparks in a spark gap distance of up to 61 cm. In 1881 she received an honorary medal at the World Exhibition in Paris. An exact replica, which was built at the University of Eindhoven, 1968 ( Prof. HJ de Weyer ) can generate voltages in excess of 500,000 volts. It was presented as the Dutch contribution to the 200- year celebration of the United States 1976/7.

Influence machines

The charge separation is at influence reached not by friction, but by the effect of the electric induction. When a conductive body is spaced apart from one another, with respect to this electrically charged body, increases at constant charge, the voltage between two electrically charged bodies. The mechanical work to overcome the electrostatic attraction is converted into energy of the electrical field. If the accumulated charge on the distant bodies electrically derived, one can see at a very high voltage ( up to 100 kV), low power (some 10 uA ).

The body made ​​of insulating metal foils applied to segments at influence, on the same principle, however, other shapes and body are used. The maximum voltage is limited by the number and spacing of the segments and by the wheel diameter.

Critical to the function of a Wimshurst machine, the existence and mobility of charge carriers. For this reason, metals are used for influence machines. The steps

Take place repeated with each revolution.

The Wimshurstmaschine uses the detached electric charge in addition to the amplification of the electric field of the inductor and thereby enhances the effect of steadily. Through this self- reinforcement they need, unlike the machines from Töpler / Holtz, no initial charge of their inducers, since the beginning of operation at least a small difference in charge is always present.

The principle of the influence machine can be reversed also, by a similar arrangement is supplied with high voltage and then works as a motor.

A very unusual Influenzmaschine is the Kelvin or water droplet generator, the water drops influenziert and they used to transport the electric charge. He also does not require initial charging and achieved solely by two separately running water jets after 20 to 30 s, a voltage 4-6 kV.

A small Holtzsche Influenzmaschine provides typical currents of 10 uA, thus resulting in a Leyden jar with a capacity of 10 nF in 30 s can recharge to 30 kV. That's enough to let in a parallel sphere gap of 1 cm skip popping sparks. The sparks take approximately 1 microseconds and thus have a maximum current of 300 A.

History

The study of electricity and the development of electrostatic generators were of 17 closely linked to the mid- 19th century. Discoveries in electricity research led to improvements of the generators, and improved generators allowed new insights into the nature of electricity.

The following table will give a brief overview of the mutually beneficial history:

Curiosities

The " electric kiss " to 1740

Treatment of dental pain with electricity

After since 1730 the notoriety of the experiments and research on electricity increased significantly ( weekly science journals now regularly reported above) ensured after a short time curiosities and attractions for attention. Very popular was the " electric kiss ". At the entrance to some establishments the visitors expected an electrically charged lady. Gave her the visitor a kiss on the lips, he received a small electric shock.

For practical considerations, the beer glass generator of Johann Heinrich Winkler was born. Electrostatic generators of glass were in the circles of the experimenters usual ( because cost ). The use of beer glasses made ​​the construction of an electrical machine a little cheaper and spare parts was no shortage. By setting this could hardly design. Nevertheless, she founded his own line of development of roller- electrostatic generators, where glass rollers were used.

New uses for electricity were sought, inter alia, the treatment of toothache was attempted with power surges. With what success this happened is not known. Around the same time (around 1740-1750 ) were first animals killed by artificially generated electricity and the treatment of people was first abandoned.