Practical Considerations in using Gases for Insulation Purpose

Practical Considerations in using Gases for Insulation Purpose

• Air has great advantage of being low in cost, therefore it found some application at increased pressure in condensers, cables and other insulation constructions.
• But it does not satisfy the second requirement, since ionization of air is accompanied by emission of ozone, nitrous and nitric oxides causing intensive corrosion of all metallic parts of the apparatus and oxidation of organic insulation, which causes gradual lowering of its insulating properties.
• Therefore nitrogen is often used instead of air. Nitrogen has equal electric strength, low cost and is inert

• Last two gases have very high electric strength. But (CCI₄) decomposes by emitting carbon which forms a conducting layer on the surface of solid dielectric and chlorine which corrodes metallic parts of the construction on account of high liquefaction temperature and chemical activeness in presence of ionization (CCI₃F) Tri-chloro-flouro Methane, having electric strength 4.5 times higher than that of air also, did not find application.
• Two gases Freon and Sulphur hexa-Floride (SF₆) are most widely used as insulating medium.
• Breakdown voltage : It is also defined as the maximum voltage which material withstands without destruction. Its unit is kV or MV.

Electrons as Best lonizers

    Electrons contribute to ionization process by virtue of moving towards anode and in the process collide with many neutral atoms and thus act as best ionizers by providing more and more electrons and therefore positive ions.