Gases as one of the three states of matter are composed of neutral molecules with sufficient kinetic energy to overcome the intermolecular force. They constitute a naturally insulating medium and hence are used in various applications. Extensive studies of gas discharges over the years have contributed significantly to the understanding of the atomic structure of the elements. They also lead to a variety of applications in various fields, lighting, insulation, current interruption, etc. Air, a natural mixture of nitrogen and oxygen, has good dielectric properties and has been extensively used as the insulating medium for overhead lines and other high-voltage equipment, to provide the most economical way of transmitting a large amount of electric energy over long distances, and hence constitutes the backbone of power transmission and distribution systems worldwide. Sulfur hexafluoride (SF6), on the other hand, is a synthetic gas with superior dielectric properties and good arc-quenching capability. It has been widely used as the insulating medium of gas-insulated equipment and as an arc-quenching medium for current interruption devices. These proprieties of SF6 have significantly influenced the development of gas-insulated equipment and cables and promoted their application in gas-insulated substations (GIS).