SF6 is no longer the gas of choice. Here’s what could replace it.

In Bergen, a transformer station supplies electricity to Norway's largest port for cruise ships. Since in recent years the number of ships docking there had been rising sharply, two years ago the regional electricity network operator BKK Nett decided to upgrade the station from 45 kV to 132 kV. The upgraded station has a special feature: for its high-voltage switches it uses clean air as an insulating gas - instead of sulfur hexafluoride (SF₆), which has been the standard for more than fifty years to prevent short circuits and arcs in substations.

Within the power grid, from power generation to the end consumer, transformer stations with gas-insulated switchgear connect extra-high-, medium- and low-voltage in the smallest possible space. In recent years, demand for such systems has risen sharply. This is due to decentralized renewable energy production, the global rise in electricity consumption and increased urbanization which increases demand for small substation and hence for compact switchgear. With this, the demand for SF₆ has grown, as it is the gas mostly used in switchgear. After all it’s largely safe to handle and allows for space-saving switchgear-designs.

But more and more often, SF₆ is no longer the gas of choice. For a simple reason: if the gas escapes, it contributes to climate change. It is around 23,500 times more warming than the greenhouse gas CO₂ and has a life span of 3,200 years in the earth's atmosphere. According to the Intergovernmental Panel on Climate Change IPCC, abandoning SF₆ completely could contribute 1.5 percent to achieving no more than 2 degrees Celsius global warming by 2100. In recent years, the potential climate impact of SF₆ has led to a steady increase in demand for SF₆ alternatives. Most prominent among available options are “clean air” solutions, i.e. purified air, and gas mixtures that both have a fraction of the climate impact of SF₆. 

Hermetically sealed systems with clean air as an insulating gas take up more space than SF₆, but combined with digitalised current and voltage transformers these systems can be built as small as current SF₆ systems. In addition, they are durable and can be used without any problems at the lowest temperatures - down to -50 degrees Celsius. And if the purified air escapes, there is no danger to the environment whatsoever. The use of vacuum switching also results in increased performance. And a shorter arcing time – compared to SF₆ – leads to less wear and tear on the system. 

Unsurprisingly, many new construction projects rely on insulation with purified air and vacuum switching technology. For the medium- and high-voltage range, they are mainly offered by Siemens Energy, which actually equipped the substation in Bergen. "Clean air solutions are not only environmentally sound, they're also future-proof for users, since no restrictions are to be expected," says Ulf Katschinski, Managing Director for high-voltage switching technology at Siemens Energy. "Compared to SF₆ and other mixed gases, air is available in abundance and completely easy to handle". 

Another option are certain fluorinated gas mixtures that also have less greenhouse gas potential than SF₆.  For example, the Zurich-based energy supplier EWZ has been using such a solution since 2015, and in 2019 a 380 kV plant was erected in Bavaria, Germany. However, these gas mixtures lose their effectiveness at very low temperatures. There is also a risk that equipment parts wear out more quickly, which in turn reduces switching capacity. Furthermore, with these gases being rather new, there is still no comprehensive clarity about their health risks. Their handling is also more complex than that of clean air, and service requirements are correspondingly higher.

A hurdle to these solutions, though, are currently higher production costs compared to SF₆. This is why it is mainly energy suppliers in rich countries such as Norway or Germany who choose this more environmentally friendly technology. However over time cost should become lower thanks to economies of scale. Furthermore, government and international regulations can accelerate the process. In any case, there is no way around these innovations for a sustainable energy supply in the long term.