SULPHUR hexafluoride, SF6, is the most common compressed gas used in high voltage power equipment since the 1950s and in HV transmissions and substations applications (GIS, GCB, GIL …), SF6 holds a prominent place because of its dielectric and chemical performance (high dielectric strength, non-toxicity, low condensation temperature, thermal stability, non-flammability, chemical inactivity with the other constituent materials of the apparatus, availability and moderate cost). It is one of the best insulators gas known today.