Electric arc

General information

An electric arc is a visible Electric current in an insulating medium (gas, air, empty…). The discovery of the principles governing this phenomenon is due to the English chemist and physicist to sir Humphry Davy in 1813. The electric arc concerns a very complex physics.

Simple explanation

A simple explanation would be to say that the arc is created by a Ionization of the insulating matter, this ionization takes place all the more easily as conducting surfaces are close.

Once ionized, the gas creates a conducting channel which involves the remainder of the load present on the starting surface. The arc continues then, even if surfaces deviate one from the other and in so far as the potential difference remains sufficient, but several orders of magnitude compared to the critical Electric field are necessary to ionize the air.

Indeed, the disruptive Champ of the air is estimated at 3600 V/mm for dry air with the atmospheric pressure and to the sea level, it can go down to a threshold from 1000 V/mm in an air saturated with moisture, this for distances close inter-electrodes (about the millimetre or centimetre). For larger distances, this disruptive field is even higher.

The position of an electric arc is stable: once it found the way shortest, it remains there (principle of minimal energy). All the difficulty for a welding the arc is thus to control the arc of a continuous motion to make him keep the form which one wishes in spite of the fact that surface transmitting (or more rarely receiving) is sometimes an acute angle.

A current crossing an electric arc is generally intense (see Amperage) and variable. This is why an electric arc causes strong electromagnetic disturbances, an electric sensor can find its place in its proximity with difficulty.

The establishment of an electric arc can be favoured by emission Thermoïonique, in particular in the vacuum, by heating of the conducting electrode S (the electrons more often leave surface by tunnel effect).

The dissipation of the current in the ionized matter emits a radiation of Lumière of which the spectrum is characteristic of the nature of gas, and with a least degree, of that of the electrodes if these last are fusible. In the general case, the arcs emit a great proportion of particularly aggressive Ultraviolet for the eyes.

This ionization and the flow of an electric current which follows generates noises due to the brutal expansion of gas following its heating quite as brutal.

Transfer of matter

The scientists observed that the electric arcs electrically remain neutral. As there is a flow of electron S of the negative potential to the positive potential, there must obligatorily be transfers of Ion S in the direction opposed to maintain neutrality electric. This flow of ions (thus of materials solid) is called transfer of matter .

Examples

the Foudre is a large-sized electric arc which allows the flow of the electric charges between the Nuage S or enter the clouds and the Ground.
the gas-discharge lamps use the properties of the electric arcs for the production of light (public lighting, projectors, etc).
the electric welding with the arc produces a great quantity of localized Chaleur generating the fusion materials, which carries out resistant connections after cooling.
the furnaces with arc are used in Métallurgie for the fusion of metals.
the cut of a current, obtained by separation of contacts, can involve the production of a more or less important electric arc, small spark with that of the arc furnace. The extinction of an arc can be obtained by cooling or lengthening, such as for example in the circuit breakers with high voltage, or by other methods.

See too

External bonds

Electric arc - Video 1 - Videos 2 (These vidéos can be read with VLC)
association-arc-electric
Electric arc in the vacuum
Soudeur.com: The French-speaking site gate of the welder, the welding and welding

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