GASES AS INSULATING MEDIUM :

• Few years ago, most of the electrical apparatus are used air as a insulating medium.
• Now a days, various gases are used for insulating medium such as nitrogen (N2), freon (CCl2F2) and sulphur hexafluoride (SF6).
• During testing when applied voltage is low, small currents flow between the conducting electrodes and the insulation keep its electrical properties.
• Whereas, if applied voltage is high, the large amount of current flowing through the insulation between electrodes and an electrical breakdown occurs.
• The maximum voltage applied to the insulation at the moment of breakdown occur is known as breakdown voltage.
• Two types of electrical discharge in gases :

1. Non-sustaining discharge
2. Self-sustaining discharge

• There are the various physical conditions of gases, like pressure, temperature, electrode field configuration, nature of electrode surfaces and the availibility of initial conducting particles are called the ionization processes.