What Is Dielectric Gas?

Dielectric gas is a form of gas used in industrial applications as an electrical insulator. Common types of gasses used include air, nitrogen, and sulfur hexafluoride. Various types of electrical components such as transformers and circuit breakers require the presence of a dielectric gas to prevent damage to a circuit in the case of an electrical discharge. In routine applications, air is often the dielectric gas of choice because it doesn't require a pressurized, sealed system, and is ubiquitous.

The type of dielectric gas used depends largely on the voltage level of the device and circuit, as well as fundamental properties of the gas, such as its inert chemical nature, and thermal properties, such as its boiling point and ability to transfer heat. The level of toxicity and flammability of the dielectric gas under certain conditions must also be considered. An electrical short circuit can cause a component like a high-voltage transformer to physically degrade to the point that the gas is released into the surrounding environment. For this reason, air and nitrogen gasses are often used as they are largely inert and nonreactive.

Sulfur hexafluoride is used as a dielectric gas in high-voltage switchgear such as industrial circuit breakers that connect generators to step-up voltage transformers. It is also used in areas of high voltage electric power systems that require gas insulators, such as transmission lines, transformers and substations. Around 80% of all the sulfur hexafluoride manufactured is commonly used in electrical power plants and substations throughout the world due to its superior insulating qualities and ability to suppress radio wave and sound wave transmission from electrical equipment. It also has the highest level of breakdown voltage for any insulating gas, which is the level of voltage necessary for a dielectric gas to begin conducting current and fail to act as an insulator.

Disadvantages to using sulfur hexafluoride as a dielectric gas are significant, however, and, for this reason, attempts are being made to combine it with safer gasses, such as nitrogen, carbon dioxide, or perfluorocarbon compounds. It is estimated that sulfur hexafluoride is 22,800 to 23,900 times more of a contributing factor to global warming when released into the atmosphere as compared to an equivalent amount of carbon dioxide. It also endures in the atmosphere as a stable greenhouse gas for much longer than other greenhouse gasses as well, lasting for 800 to 3,200 years before it degrades. The compound also poses serious health risks upon human exposure, such as causing respiratory problems, and it often combines with other compounds when released into the air that can lead to fluoride contamination of the body and a variety of ailments.