electrostatic generator - Description, Related machines, Fringe science and devices

A device for producing a large electric charge, usually by the repetition of an induction process and the successive accumulation of the charge produced. An important 19th-c type was the Wimshurst machine (1878), devised by British engineer James Wimshurst (1832–1903). Modern, very high voltage machines are versions of the Van de Graaff belt-operated generator (1929).

An electrostatic generator is a mechanical device that produces very high voltage and very low continuous current -- which is measured in Mega Volts and micro Amperes. The development of electrostatic machines did not begin in earnest until the 18th Century. Electrostatic generators operate by using manual (or other) power to transform mechanical work into electric energy. Electrostatic generators develop electrostatic charges of opposite sign rendered to divided conductors.

Description

Electrostatic machines are used for generating high voltages, using either friction or electrostatic induction to accumulate electrical charges. Electrostatic generators are typically used in science classrooms to safely demonstrate electrical forces and high voltage phenomena (because these devices produce very high voltage at very low current). Electrostatic generators such as the Van de Graaff generator, and variations as the Pelletron and the tandem generator, also find use in physics research.

Electrostatic generators are of two kinds: friction machines, and influence machines.

Friction machines

History

Some electrostatic generators are called friction machines because of the friction in the generation process. A primitive form of frictional electrical machine was constructed at about 1663 by Otto von Guericke, using a rotating sulphur globe rubbed by hand. In the latter part of the 18th Century, Benjamin Franklin, Ewald Jürgen Georg von Kleist, and Pieter van Musschenbroek (the last two the inventors of the Leyden jar) made several important discoveries concerning electrostatic machines. In 1746, Watson's machine had a large wheel turning several glass globes with a sword and a gun barrel suspended from silk cords for its prime conductors. By 1784, the van Marum machine could produce voltage with any polarity. Also in 1784, Van Marum constructed a rather large electrostatic machine of high quality (currently on display at the Teylers Museum in the Netherlands). Rouland constructed a silk belted machine which rubbed two grounded hare fur covered tubes. Edward Nairne developed an electrostatic generator in 1787 which introduced the ability to generate either positive or negative electricity, the first named being collected from the prime conductor carrying the collecting points and the second from the prime conductor carrying the cushion. The Winter machine possessed higher efficiency than earlier friction machines. In the 1830s, Georg Ohm possessed a machine similar to the van Marum machine for his research (which is now at the Deutches Museum, Munich, Germany). In 1840, the Woodward machine was developed from improving the Ramsden machine (placing the prime conductor above the disk(s)). Also in 1840, the Armstrong hydroelectric machine was developed and used steam as a charge carrier.

The Van de Graaff generator was developed, starting in 1929, at MIT. The first machine used a silk ribbon bought at a five and dime store as the charge transport belt. Tesla stated, "I believe that when new types [of Van de Graaff generators] are developed and sufficiently improved a great future will be assured to them". Note that the presence of electric current does not detract from the electrostatic forces nor from the sparking, from the corona discharge, or other phenomena.

Influence machines

History

Frictional machines were, in time, gradually superseded by the second class of instrument mentioned above, namely, influence machines. These operate by electrostatic induction and convert mechanical work into electrostatic energy by the aid of a small initial charge which is continually being replenished or reinforced. The first suggestion of an influence machine appears to have grown out of the invention of Volta's electrophorus. The electrophorus is a single-plate capacitor used to produce imbalances of electric charge via the process of electrostatic induction. "Doublers" were the first rotating influence machines. He developed the idea for the "rotating double" instrument which by turning a winch produced the two states of electricity without friction or communication with the earth. Cavallo (who developed the Cavallo multiplier in 1795), John Read, Charles Bernard Desormes, and Jean Nicolas Pierre Hachette, developed further various forms of rotating doubler. In 1798, The German scientist and preacher Gottlieb Christoph Bohnenberger, developed the Bohnenberger machine. Bohnenberger also, in the "Annalen der Physik" (1801), described an electrostatic machine based on the operation of the Bennet's doubler. Giuseppe Belli, in 1831, developed a widely used and simpler doubler which consisted of two curved metal plates between which revolved a pair of balls carried on an insulating stem. It was the first symmetrical influence machine. Lord Kelvin also devised a combined influence machine and electromagnetic machine, commonly called a mouse mill, for electrifying the ink in connection with his siphon recorder. Lord Kelvin also developed, between 1858 and 1867, a water-drop electrostatic generator, which he called the "water-dropping condenser". Varley patented a more modern type of influence machine. Toepler developed an influence machine that consisted of two disks fixed on the same shaft and rotating in the same direction. In 1868, the Schwedoff machine was one of the stranger machines developed. Also in 1868, several mixed friction-influence machine were developed, including the Kundt machine and the Carré machine. Holtz constructed and described a large number of influence machines which were considered the most advanced developments of the time. In one form, the Holtz machine consisted of a glass disk mounted on a horizontal axis which could be made to rotate at a considerable speed by a multiplying gear, interacting with induction plates mounted in a fixed disk close to it. In 1866, the Piche machine (or Bertsch machine) was developed. Also in 1869, sectorless machines in Germany were investigated by Poggendorff.

The action and efficiency of influence machines were further investigated by F. Bouchotte also examined the efficiency and current producing power of influence machines. In 1871, sectorless machines were investigated by Musaeus. In 1872, Righi's electromer was developed and was one of the first antecedents of the Van de Graaff generator. In 1873, Leyser developed the Leyser machine to avoid polarity reversals. In 1880, Robert Voss (a Berlin instrument maker) devised a form of machine in which he claimed that the principles of Toepler and Holtz were combined. In 1885, one of the largest Wimshurst machine was built in England (and is now at the Chicago Museum of Science and Industry). In 1887, Weinhold developed a system that possessed vertical metal bar inductors with wooden cylinders close to the disk for avoiding polarity reversals. Lebiez described a machine similar to the that of the Holtz and Voss machines, being a simplified Voss machine (L'Électricien, April 1895, pp. 225-227)

In 1898, the Pidgeon machine was developed with a unique setup by W. In October 28 of that year, Pidgeon presented this machine to the Physical Society after several years of investigation into influence machines (beginning at the start of the decade). Pidgeon machines possess fixed inductors arranged in a manner that increases the electrical induction effect (and it electrical output is at least double that of typical machines of this type [except when it is overtaxed]). The essential features of the Pidgeon machine are, one, the combination of the rotating support and the fixed support for inducing charge, and, two, the improved insulation of all parts of the machine (but more especially of the generator's carriers). Pidgeon machines are a combination of a Wimshurst Machine and Voss Machine, with special features adapted to reduce the amount of charge leakage. Pidgeon machines excite themselves more readily than the best of these types of machines. In addition, Pidgeon investigated higher current "triplex" section machines (or "double machines with a single central disk") with enclosed sectors (and would receive British Patent 22517 (1899) for this type of machine).

Double disk machines and "triplex" electrostatic machines, with classical structure, were also developed extensively around the turn of the century. "Wehrsen machine"). In 1907, Heinrich Wommelsdorf reported a similar variation of the Holtz machine.

Related machines

In 1991, G. It is a triboelectric machine operating with rolling friction, consisting of four cylinders with the two central ones made of different insulating materials and the two outer ones metallic.

Fringe science and devices

These generators have been used, sometimes inappropriately and with some controversy, to support various fringe science investigations. In 1911, George Samuel Piggott received a patent for a compact double machine enclosed within a pressurized box for his experiments concerning radiotelegraphy and "antigravity". Testatika is an electromagnetic generator based on the 1889 Pidgeon electrostatic machine, said to produce "free energy" available directly from the environment and which cannot be depleted (so it is available in effectively unlimited quantity). Jefimenko (Editor), "Electrostatic Experiments: An Encyclopedia of Early Electrostatic Experiments, Demonstrations, Devices, and Apparatus". Johnson, "Modern High-Speed Influence Machines; Simon, "Quantitative Theory of the Influence Electrostatic Generator". Gray, "Electrical Influence Machines, Their Historical Development and Modern Forms [with instruction on making them]" (London, I903). Thompson, The Influence Machine from Nicholson -1788 to 1888, Journ. American Museum of Radio: Electrostatic Machines The Bakken Museum: frictional generators "Articles on Electrostatics from those that actually made the discoveries". Sir William Thomson (Lord Kelvin), "On Electric Machines Founded on Induction and Convection". M Hill and D J Jacobs, "A novel Kelvin Electrostatic Generator". (PDF) Paolo Brenni (Author) and Willem Hackmann (Editor), "The Van de Graaff Generator: An Electrostatic Machine for the 20th Century".