Source: Energy & Management Powernews, November 10 2022
Tennet is building the world's first gas-insulated switchgear at extra-high voltage level that does not use the climate-damaging insulating gas sulfur hexafluoride (SF6).
The SF6-free switchgear is to be built by Hitachi Energy at the Erzhausen substation (Lower Saxony) by 2024. It is part of the largest AC grid expansion project of the transmission system operator Tennet from Wahle (Lower Saxony) to Mecklar (Hesse). Although the sulfur hexafluoride previously used in encapsulated switchgear is considered an ideal insulating gas, it is extremely harmful to the climate (see info box below for details).
"By using an alternative gas mixture instead of SF6, the global warming potential of the insulating gas of this new switchgear will be only about 1 percent of conventional plants," Tennet COO Tim Meyerjürgens explained in a company statement. The goal, he said, is to gradually move to using natural gases for insulation in new electrical switchgear to reduce this value to zero in perspective. From 2025 onward, one-third and from 2030 onward, two-thirds of new projects are to meet this criterion. "With the commissioning, we are sending a strong signal to the market to develop SF6-free switchgear at extra-high voltage level," Meyerjürgens said.
Natural gases are less powerful insulators, and the plants will have to be built larger and thus more complex, they added. On the way to widespread use of SF6-free switchgear, it is first necessary to gain experience in pilot projects in order to safely test the new technologies and optimize them for regular operation,
Criticism of EU plans
The four German transmission system operators (TSOs) therefore also take a critical view of current EU plans to quickly abandon SF6 switchgear. The alternative technologies, they point out, would have to have the same very high reliability. To ensure that alternative solutions are available for all applications in the transmission grid in the future, various technologies must be considered and, if possible, tested in pilot projects, the TSOs demand in a joint position paper. Important are about
- protection of existing SF6 plants already installed,
- the consideration of technology security and market availability
- as well as planning security with regard to the energy transition.
Otherwise, the network operators fear a "significant delay and security risk" in the expansion of the transmission networks. After all, a decisive success factor for the decarbonization of the European economies by 2045/2050 is the trouble-free operation and targeted expansion of the transport networks. This in turn requires large procurement volumes of proven plants and equipment. It would be several years before these volumes are available.
Sulfur hexafluoride
SF6 is the most potent greenhouse gas known. According to the United Nations, its global warming potential is 25,200 times that of CO2. In addition, SF6 degrades very slowly. Heavy, high-density, non-toxic, chemically inert, non-flammable - for a long time, SF6 seemed to be the perfect gas for many high-voltage applications and to offer only advantages. But since 2007, SF6 applications have been banned in the EU - with one exception: in the electrical industry, sulfur hexafluoride continues to be permitted because it was previously without alternative.
SF6 is mainly used in high-voltage equipment, both for insulation and for power interruption. However, SF6 does not have the climate-damaging effect in normal use, but only when it escapes into the environment. Emissions cannot be completely eliminated, however, because the gas cannot be 100 percent sealed off in the application. Tennet currently puts SF6 emissions from its operating equipment in Germany at less than 0.1 percent.
Author: Günter Drewnitzky
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