Arc discharge and dielectric breakdown - are these the same phenomena?
With the subtle distinction, arc discharge generally occurs in the gaseous state and dielectric breakdown in condensed matter.
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Essentially they are the same phenomenon in the sense that both are avalanche effects of excessive voltage. In the field of dielectric strength testing of insulation both gases like air and solids are considered electric insulation.
The main difference is gases are considered renewable insulation, meaning they recover after the voltage is removed. Repeating the test generally results in the same voltage level to cause breakdown. The insulation qualities of solids on the other hand are usually permanently degraded as a result of dielectric breakdown.
Hope this helps
Dielectric breakdown occurs when a material which usually behaves as an insulator suddenly starts conducting current on being subject to a sufficiently high voltage. It occurs when the electric field is increased so much as to pull the outer valence electrons away from their atoms. The electrons become mobile, and the heat created by their collisions releases additional electrons, which helps in conduction.
Arc discharge which is the electric breakdown of a gas, occurs when current flows through a non-conductive medium such as air producing plasma. The electrical arc is subject to resistance which produces heat and ionizes more gas molecules. The electric field accelerates the small number of free electrons naturally present. When they collide with gas molecules they knock additional electrons out of them, ionizing more molecules creating more free electrons and ions in a chain. Current in the arc is maintained by thermionic emission and field emission of electrons at the cathode.