An electric arc is a high-current, low-voltage electrical discharge between electrodes in the presence of gases. In an electric arc, electrons are emitted from a heated cathode. Arcs can be formed in high, atmospheric, or low pressures, and in various gases. They have wide uses as highly luminous lamps, as furnaces for heating, cutting and welding, and as tools for spectrochemical analysis.
Gases consist of neutral molecules, and are, therefore, good insulators. Yet under certain conditions, a breakdown of the insulating property occurs, and current can pass through the gas. Several phenomena are associated with the electric discharge in gases; among them are spark, dark (Townsend) discharge, glow, corona, and arc. In order to conduct electricity, two conditions are required. First, …
The electric arc was first detected in 1808 by British chemist Humphry Davy. He saw a brilliant luminous flame when two carbon rods conducting a current were separated, and the convection current of hot gas deflected it in the shape of an arc. Typical characteristics of an arc include a relatively low potential gradient between the electrodes (less than a few tens of Volts), and a high current den…
There are many types of arc devices. Some operate at atmospheric pressure and may be open, and others operate at low pressure and are therefore closed in a container, like glass. The property of high current in the arc is used in the mercury arc rectifiers, like the thyratron. An alternate potential difference is applied, and the arc transfers the current in one direction only. The cathode is heat…
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