Advances in eco-friendly gas insulating medium for next-generation SF6-free equipment

Newswise — The power industry has extensively employed gas-insulated equipment (GIE), which relies on sulfur hexafluoride (SF6), the most potent greenhouse gas, as an insulation and arc-quenching medium. However, to achieve the "net-zero" objective and promote sustainable development, there is a crucial need to explore environmentally friendly alternatives that offer advanced performance for the next generation of SF6-free GIE.

On March 31, 2023, a team of researchers, led by Xiaoxing Zhang from Hubei University of Technology in China, collaborated with scientists from Wuhan University, Southeast University, North China Electric Power University, Université de Toulouse, Xi'an University of Technology, Schneider Electric, and South China University of Technology, to compile a comprehensive summary of the latest developments in eco-friendly gas insulating mediums for the next generation of SF6-free equipment. This review report was published as the cover article in the journal iEnergy.

To emphasize the importance of finding eco-friendly insulating gases, the initial section of the overview focused on providing insights into SF6-based gas-insulated equipment (GIE), along with an examination of emission and reduction policies pertaining to SF6. Professor Zhang highlighted, "SF6 is recognized as one of the most potent greenhouse gases, possessing a global warming potential of 25,200 and an atmospheric lifetime of 3,200 years. The power industry is responsible for 80% of SF6 consumption, with China alone consuming over 7,000 tons of this gas. Various countries have implemented regulations governing the use, recovery, and treatment of SF6, which have stimulated the development of eco-friendly insulating gases."

The overview put forward fundamental criteria for eco-friendly gases, encompassing environmental attributes, insulation and arc-quenching performance, stability, material compatibility, and biosafety. It then proceeded to present the main categories of such gases, which include traditional options like CO2, N2, and air, as well as Perfluorocarbons and Trifluoroiodomethane. Additionally, the overview introduced Fluorinated-nitrile (C4F7N), Fluorinated-ketones (C5F10O, C6F12O), and Hydrofluro-Olefins (HFO-1234ze(E), HFO-1336mzz(E)) as alternative eco-friendly gas options. Furthermore, the overview included information on the molecular design methodology employed for the development of eco-friendly gases.

The recent advancements in eco-friendly insulating gases were highlighted, focusing on key aspects such as dielectric insulation (including AC/DC breakdown, LI breakdown, partial discharge, and surface flashover), arc-quenching (comprising particle compositions, thermodynamic properties, transport coefficients, radiation coefficients, and post-arc dielectric breakdown properties), stability and decomposition (encompassing thermal and discharge stability, as well as decomposition mechanisms), materials compatibility (including metal, epoxy resin, elastomer, and adsorbent), and biosafety (evaluated in terms of LC50, target organ toxicity, and toxicity of by-products). These progressions shed light on the performance and characteristics of various eco-friendly insulating gases.

Furthermore, the overview summarized the recent applications of eco-friendly insulating gases in medium-voltage (MV) and high-voltage (HV) scenarios, along with relevant maintenance-related technologies. Professor Zhang highlighted, "Since 2016, GE and ABB have developed gas-insulated switchgear, gas-insulated transmission lines, and ring main units utilizing C4F7N/CO2 and C5F10O/air as the base gases. These advancements have showcased the potential of fluorinated-free technologies. Additionally, there is a growing focus on the utilization of technical air combined with vacuum interruption in the roadmap for future developments."

Despite considerable progress in the field, there are still noteworthy challenges that necessitate additional solutions for the realization of next-generation SF6-free gas-insulated equipment (GIE) in the future. Enhancing stability, interruption capacity, and material compatibility are crucial objectives. Additionally, focusing on SF6 control and recycling, insulation coordination, and scientific management of per- and polyfluoroalkyl substances (PFAS) are anticipated to guide the advancement of eco-friendly insulating gases and GIE. These areas of focus hold promise for driving sustainable development and achieving the desired goals in the field.

Currently serving as the Dean of the School of Electrical and Electronic Engineering at Hubei University of Technology, Professor Zhang's research expertise lies in the field of high voltage engineering and low-carbon electrical materials. His research interests include eco-friendly gases, SF6 disposal and resource conversion, as well as degradable dielectric materials. Notably, he was honored with the National Award for Technological Invention in 2014 and was selected for the esteemed Cheungkong Scholars Program in 2020, recognizing his outstanding contributions in his field.

The term "iEnergy" encompasses multiple meanings such as intelligent energy, innovation for energy, internet of energy, and electrical energy, with the "i" symbolizing the current. As a quarterly publication, iEnergy serves as a cross-disciplinary journal dedicated to sharing the latest technological advancements and solutions in the field of power and energy. The journal focuses on original research that explores various aspects of power and energy, encompassing technologies and applications related to power generation, transmission, distribution, conversion, utilization, and storage. By providing a platform for the dissemination of cutting-edge scientific and technological developments, iEnergy contributes to shaping the future-generation power and energy systems.