Transporting Electricity – The Environmentally-Friendly Way

Upgrade: Renewable electricity must flow through a high-performance grid at the highest possible voltage and has to be transformed in transformer stations.

Sulfur hexafluoride (SF₆) is one protective gas that meets these requirements well. It is fed into the switch at high pressure and features a very high dielectric strength when used as an insulation material – as a compressed gas, it can separate one electric charge from another reliably even under high voltage. It also extinguishes any potential electric arc immediately. An SF₆ molecule consists of one sulfur atom and six fluorine atoms and is relatively large. Even that is an advantage since the molecule is not inclined to migrate through rubber – and therefore through the O-rings and special seals that, for example, seal the passage of the power lines through a switch housing. Freudenberg Sealing Technologies has developed seals that coexist with the protective gas in switches for many years. It is only when the gas pressure in the switch falls below a certain level that the SF₆ has to be replenished during maintenance.

But this protective gas has a major disadvantage. It is more damaging to the climate than CO₂ by a factor of 22,800. Experts call this capacity to damage the environment the global warming potential (GWP). Even if the gas takes a while to migrate through the sealing material, it will arrive in the atmosphere sooner or later. In 2014, in legislation to reduce fluorinated greenhouse gases, the EU began gradually limiting the available quantities of gases such as SF₆, encouraging the search for alternatives. Meanwhile, a handful of potential materials have been identified that are all based on CO₂ and, in some cases, are enriched with other ingredients. They are far more climate-friendly but have a major disadvantage: They migrate much more easily through sealing materials. “It is like a balloon,” said Dr. Robert Rotzoll, material developer at Freudenberg Sealing Technologies. “At first, it is filled to bursting, but over time the air or the helium escapes through the rubber surface.” Permeation is the process by which a gas penetrates or migrates through a solid body. And it is much greater for small CO₂ molecules than it is for SF₆.