Presented By:
Dr. Yannick Kieffel
Materials R&D and Eco-Design Manager, Consulting Engineer
GE Grid Solutions
For many years, SF6 has been the preferred dielectric medium in electrical power applications, particularly in high voltage gas-insulated equipment. However, with the recognition that SF6 has an extremely long atmospheric lifetime of 3200 years and a global warming potential (GWP) of 23,500, making it the most potent greenhouse gas identified to date, governments have pursued emission reductions from gas-filled equipment. The electrical power industry has responded to this environmental challenge applying SF6 -free technologies to an expanding range of applications which have traditionally used SF6, including gas-insulated switchgear, gas-insulated circuit breakers, and gas-insulated lines or bus bars.
In this regard, in partnership with the 3M™ Company, GE Grid Solutions has developed g3, a mixture based on carbon dioxide, oxygen, and 3M™ Novec™ 4710. g3is an optimal solution for high voltage switchgear applications meeting requirements of minimum outdoor temperatures as defined in international standards (like -25°C or -30°C).
This paper presents the return of experience gained over the past years with g3products and highlights recent development dedicated to the 60 Hz market segment. The benefits of the g3technology to end-users will be clearly emphasized.
Introduction
In recent years, extensive work has been done on SF6-free gaseous environmentally-friendly solutions presenting the advantage of a high dielectric strength and switching current capabilities close or equal to SF6 with the benefit of a low global warming potential (GWP). Beyond SF6, it has been evidenced that CO2 is the most promising arc quenching gas. However, CO2 shows dielectric performance which is quite low compared to SF6 making the use of pure CO2 not feasible in High Voltage switchgear unless changing drastically the dimension and/or the nominal pressure of CO2 as function of SF6 equivalent equipment. CO2 dielectric performance must therefore be improved with an additive that has superior dielectric strength.
In this regard, GE Grid Solutions, in partnership with the 3M™ Company, has developed a gas mixture, based on heptafluoro-iso-butyronitrile (CF3)2-CF-CN (or fluoronitrile), also known as 3M™ Novec™ 4710 Dielectric Fluid [1] and mixed with carbon dioxide and oxygen. Gas mixtures of this fluoronitrile with CO2 and O2 were found to be an optimal solution for switchgear applications. This specific gas mixture called “g3” has been proved to be the most technically and economically promising solution with the advantage of meeting requirements of minimum outdoor temperatures as defined in international standards (like -25°C or -30°C) [2, 3, 4].
High voltage (HV) electrical transmission equipment developed for and filled with the g3 mixture features the same ratings and same dimensional footprint as the state-of-the-art SF6 ones, with a drastic change of the gas environmental impact: its GWP (Global Warming Potential) is reduced by more than 99% compared to SF6 which has a GWP 23,500 times greater than CO2 and a lifetime in the atmosphere of 3,200 years, putting it at the top of the Kyoto Protocol list [5].
Characteristics And Behavior Of g3
The physicochemical characteristics of the fluoronitrile/CO2/O2 mixture, said g3, have been determined through a wide range of investigations. They showed for instance that the homogeneity and the composition of the gas is stable over time and the behavior of the mixture at low temperatures and liquefaction temperature of the mixture depends on the partial pressure of the different components. Regarding electrical behavior, the fluoronitrile i.e. (CF3)2-CF-CN, provides the dielectric strength to the mixture thanks to its nitrile triple function combined with fluorine. CO2 handles the arc interruption process [6]. O2 plays a major role in the gas chemical decomposition especially in case of heavy arc interruption. The influence of O2 content into g3has been the target of several investigations focusing on gas decomposition and the formation of powders [7]. For instance, the amount of carbon monoxide is lowered by 2 or 3 depending on O2 ratio and the formation rate of other gaseous by products is also significantly reduced. Furthermore, the oxygen content also positively reduces the solid powders composition formed in the breaker after power arc interruption.
Regulations
Europe
The European regulation No 517/2014 [8] on fluorinated greenhouse gasses (said the F-gas regulation) is addressing the use of SF6 in High-Voltage equipment and gives instruction about training, labeling, and reporting. Intentional SF6 release is prohibited, recovery after use is mandatory. Leakages are measured and should be minimized. In its Article 21, the Commission had set a target to assess whether cost-effective, technically feasible, energy-efficient, and reliable alternatives exist, which make the replacement of fluorinated greenhouse gasses (F-gasses) possible in new medium voltage secondary switchgear.
The report issued by the Commission in September 2020 [9] assesses whether cost-effective, technically feasible, energy-efficient, and reliable alternatives exist. The report was finally not limited to medium voltage and addressed also high voltage equipment. The report is confirming the availability of alternatives and therefore opening the door for a future ban of SF6. It is also providing very positive feedback on g3 technology and associated products: “Gas blends based on fluoronitriles and SF6-based solutions are equivalent in terms of dimensions and electrical ratings. On the other hand, models with gas blends based on fluoroketones and natural gasses, require larger physical dimensions compared to SF6 models”.
UK
In terms of National Regulations, UK TSOs and DSOs are aligned with the EU and there are no other national measures presently in place. UK TSOs (and DSOs) are all regulated by OFGEM and each has funded asset interventions and pain/gain incentive mechanisms associated directly with SF6 emission reduction against a target value. Target is 50% emission reduction by 2030 from the 2018/2019 benchmark. These arrangements form part of the transmission licenses of the individual companies. Incentive arrangements are included in the special license conditions, along with a lot of other items, additional to the standard license conditions.
This regulation has demonstrated to be very effective to accelerate the implementation of SF6 alternatives. UK is currently hosting a larger number of SF6-free equipment.
USA
The U.S. Environmental Protection Agency (U.S. EPA) started a voluntary greenhouse gas reporting program in 1999. In 2011, the program became mandatory for use and manufacture of electrical T&D equipment. The program requires users to report annual SF6 emissions if their equipment nameplate capacity exceeds 7838 kg SF6. Similarly, manufacturers are required to report emissions if their annual SF6 purchase exceeds 10433 kg. EPA is now considering a revision of the program in response to industry trends since 2011.
The state of California, via the California Air Resources Board (CARB), has implemented the “Regulation for Reducing SF6 Emissions from Gas Insulated Switchgear” since 2011. In addition to SF6 emissions reporting, the regulation imposes progressively lower annual emission rate limits, starting with 10% in 2011 and dropping to 1.0% annually after 2020. A revision has been released on January 2022 that expands the scope to, “Greenhouse Gas Emissions from Gas Insulated Equipment” where greenhouse gas is defined as any gas with a GWP > 1 and emissions are reported in megatons of CO2 equivalent. Also, the purchase of new SF6 equipment is proposed to be phased out in stages by rating and application starting in 2025. The phase-out details is given in Table 9.3.
The state of Massachusetts also operates its own SF6 regulation. Emissions are both reported annually and limited from 3.5%/yr. (2015) to 1.0%/yr. (2020 and beyond). In addition, major utilities in Massachusetts have absolute limits placed upon their SF6 emissions from 2018 to 2020 and beyond. The SF6 & Alternatives Coalition, affiliated with the National Electrical Manufacturers Association (NEMA), maintains a website with current information on regulatory activity and other topics related to SF6 and alternatives. Other states considering broad regulatory action on greenhouse gasses which may include SF6 are, Colorado, Maryland, Montana, New Hampshire, New Jersey, New Mexico, New York, Oregon, Rhode Island, Texas, and Washington.
Canada
At the Federal level, there are no constraints concerning the use of SF6 and CF4, just a voluntary declaration of emissions. However, Federal regulation provide requirements with regard to the accidental release of SF6 and its storage. At the provincial level (Quebec), recycled and emitted SF6 quantities are strictly controlled: The calculation methodology is provided by the provincial authorities. For example, users should provide the capacity of each SF6 and CF4 insulated equipment, track the recovery gas cylinders that can be used in operation, track the additional gas required for leaking equipment. If the emissions exceed a defined threshold: a “cap-and-trade system” applies, and allocations are purchased on the joint carbon market with California and Ontario. This is the case for the owners of T&D equipment. Also, all accidental release of contaminants, including gas such as SF6 and CF4, must be declared without any delay. Furthermore, there has been an update in the “Regulation regarding the environmental impact assessment and review of certain projects”. This new regulation requires, for each phase of a project, an environmental impact assessment which includes an estimate of the greenhouse gas emissions and possible reduction measures.
South-Korea
No specific public regulation of SF6. A self-imposed greenhouse emission gas reduction by Korean Electric Power Company is in place. This includes the use of SF6 insulated switchgear of up to 170 kV and 362 kV GIS. All major switchgear manufacturers are encouraged to develop 170 kV “Eco GIS”, and several companies have succeeded in development of 170 kV GIS, and pilot operations have been in progress since 2020. For 362 kV GIS, a government-funded research and development project is in the planning stage and is targeted for use in the late 2020s.
Technical Committees And Standardization
CIGRE
Cigré WGB3-45, Technical Brochure 802 “Application of non-SF6 gasses or gas-mixtures in medium and high voltage gas-insulated switchgear” [10]
This brochure describes the needs for adaptations or new requirements for the safe, reliable, and sustainable application of non-SF6 gasses and gas mixtures in gas-insulated switchgear. It also describes the given and available properties of the non-SF6 gasses and gas mixtures which have been investigated and applied to gas-insulated switchgear. Topics covered by this Brochure are:
- Quality and purity requirements
- Aging aspects
- Gas handling and filling accuracy
- Tightness requirements
- Minimum functional gas composition
- Health, Safety, Environmental aspects
- Maintenance and life-cycle aspects including end-of-life considerations/reuse concepts
The Brochure also covers ongoing development of alternatives for SF6 and application restrictions and issues of the pilot projects applying alternative gasses. It summarizes today’s state of the art and collects and describes principles to range gasses and gas mixtures. Those principles can be used to characterize any kind of alternative gasses to SF6 which might come up in the future. The feasibility for large-scale application of alternative gasses depends on the developments, the results of the pilot projects, the availability of the alternative gasses, and the reliability and health, safety, and environment aspects of these new solutions.
Cigré WGD1-67 “Electric performance of new non-SF6 gasses and gas mixtures for gas-insulated systems”
The present working group focused on the technical properties of new insulation gas mixture for the purpose of electrical insulation. The arc quenching performance and its specific requirements are not discussed in this report, it is the task of WG A3.41. Other alternative insulation technologies, as pressurized air (which was treated by WG D1.51) and solid or fluid insulation, are not considered in this work as well.
Cigré WGA3-41 “Current Interruption in SF6-free Switchgear”
This Working Group is currently delivering an overview of the impact of application of SF6 alternatives on switchgear functions and listing the various ongoing utility applications with the equipment discussed. It focuses on natural origin gasses and their mixture with fluoronitrile (C4-FN), fluoroketone (C5-FK), and technical-air insulated vacuum circuit breakers as mainstream upcoming SF6-free technology.
IEEE
PC37.100.7 “Draft Guide for the Evaluation of Performance Characteristics of Non-Sulfur Hexafluoride Insulation and Arc Quenching Media for Switchgear Rated above 1000 V”
This guide reviews existing standards and performance criteria for switchgear rated above 1000 V. Each aspect of performance is discussed within the context of Sulfur Hexafluoride alternatives, how their behavior may differ from existing technologies and how this behavior may lead to changes in the qualification process. Relevant analytical, numerical, and test methods are discussed which may contribute to the process of performance evaluation and evolution of the standards.
C37.122.XX “Guide for Handling Non-SF6 Gas Mixtures for High Voltage Equipment”
This guide describes the on-site handling of non-SF6 gasses and their gas mixtures used in electric power equipment. This includes gas mixing, filling, analysis, recovery, reclamation, and recycling.
IEC
IEC 62271-4 “High-Voltage Switchgear and Control gear – Part 4: Handling procedures for gasses for insulation and/or switching”
This part of IEC 62271 applies to the procedures for handling of gasses for insulation and/or switching during installation, commissioning, repair, overhaul, normal and abnormal operations, and disposal at the end-of-life of high-voltage switchgear and control gear. These procedures are regarded as minimum requirements to ensure the reliability of electric power equipment, the safety of personal working with these gasses, and to minimize the impact on the environment. Additional requirements could be given or specified in the operating instruction manual of the manufacturer.
For each gas, which is known to be used in electric power equipment at the date of the publication of this document, a separate annex describes specifications, handling procedures, safety measures, etc. For gasses not covered by these annexes, the electric power equipment manufacturer should provide the information needed, following the structure of these annexes. Such gasses should also be described in a next edition or in amendments to this edition.
IEC 63360 “Fluids for electrotechnical application: Alternative to SF6”
The IEC TC10 WG41 is preparing that document that will specify the quality for technical grade alternatives to SF6 for use in electric power equipment. Detection techniques, covering both laboratory and in-situ portable instrumentation, applicable to the analysis of alternatives to SF6 prior to the introduction of these gasses into the electric power equipment will also be described in this document.
IEC 63359 “Fluids for electrotechnical application: Specifications for the re-use of mixtures of gasses alternative to SF6”
This document will provide an international standard for the reuse of lower GWP alternative gasses to SF6 after recovery and reclaiming from electrical equipment (e.g., for maintenance, at the end-of-life). These gasses are now in application in the industry and the criteria for the reuse of such gasses are required. This document should cover the different solutions in use for medium and high voltage equipment. This standard is intended to be the counterpart to IEC 60480 for SF6.
Information about alternatives to SF6 by-products and the procedure for evaluating the potential effects of alternatives to SF6 and its by-products on human health will be covered by IEC 63359, their handling and disposal being carried out according to international and local regulations with regard to the impact on the environment.
This document will provide an international standard for the reuse of lower GWP alternative gasses to SF6 after recovery and reclaiming from electrical equipment (e.g. for maintenance, at the end-of-life). These gasses are now in application in the industry and the criteria for the reuse of such gasses are required. This document should cover the different solutions in use for medium and high voltage equipment. This standard is intended to be the counterpart to IEC 60480 for SF6.
Information about alternatives to SF6 by-products and the procedure for evaluating the potential effects of alternatives to SF6 and its by-products on human health will be covered by IEC 63359, their handling and disposal being carried out according to international and local regulations with regard to the impact on the environment.
Return Of Experience With g3 Equipment
420kV GIL
In a typical 420 kV substation, the GIL represents quite often 50% of the total quantity of gas used in the GIS project [11]. Hence utilities paid attention to limit the use of SF6 in such arrangements and have decided to replace some GIL sections normally filled with SF6 by GIL connections filled with alternative gas mixture based on g3. The first utility to make the move was National Grid in England. They decided in 2016 to replace SF6 on the Sellindge project [12]. Two feeders out of five using g3 solution are in service since 2017, totalizing 230 meters. For this project (see Fig 1), about 40 bottles of B50 type have been used, cumulating more than 750 kg of gas mixture. This represented a total of about 38,000 liters distributed in 15 compartments of different volumes (120 liters to 4600 liters). GIL equipment was filed during wintertime with ambient outdoor conditions around 10 to 15°C.
After filling GIL compartments, the gas quality was checked, and values were in line with the criteria fixed for this type of gas mixture. Humidity content was also below the value required for this project (-35°C dew point at atmospheric pressure). Purity was recorded above 99%. Partial discharges were measured during HV tests and no specific PD signals were recorded. The substation was energized in April 2017 and is operating well since. In 2017, SP Energy Networks also decided to implement this alternative gas on a newly built substation at Kilmarnock in Scotland, with one GIL circuit out of three using g3solution, totalizing 177 meters. It is now energized. For the installation of this second GIL (see fig. 2), weather conditions were severe with heavy rains, snow, wind, and colder temperatures (below 0°C). Gas filling of the 30 bottles (representing more than 600 kg of gas) could be managed properly using again the same filling gas cart as used for the first application.
After filling gas quality was checked. All recorded values were again with the acceptable criteria and the GIL feeders are now energized. In 2018, Tennet of Netherlands decided to implement the alternative gas at one of its existing substations, with the addition of 76 meters of g3 GIL. The equipment has been installed and is expected to be energized in 2022. In 2018, SSEN Transmission also decided to implement alternative gas on all the feeders of both new substations, New Deer and Fort Augustus in Scotland. This represents more than 1500 meters of g3 GIL. New Deer has been energized in 2021 and Fort Augustus will be in 2022. Early December 2020, SSEN Transmission also announced the future implementation of g3equipment at its Kintore 420 kV substation, not only for GIL but for full GIS, including circuit-breaker.
145kV GIS and Live Tank Breaker
A full g3 145 kV/40 kA GIS, including all relevant components, has been developed on the base of the existing 145 kV GIS keeping exactly the same footprint as the original SF6 switchgear, this allows to secure a high standardization in the parts, the production, and overall processes. The worldwide first g3substation, including all major GIS components, built as H-Schematic with two incoming feeders connected via cables and two feeders to the transformer connected via outdoor GIB is based on the mixture of 6% C4F7N, 5% O2 and 89% CO2 (g3) was energized in 2018 for the utility Axpo Power in Switzerland. The application temperature is – 25°C … 40°C. Since then, 25 substations have been ordered for 20 different customers. A total amount of more than 150 Circuit Breaker bays are therefore spread in Denmark, Finland, France, Germany, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom. By end of 2021 already 13 substations were energized and fully operational. The example in Figure 3 is showing a full 145kV rated substation in Zernez for the utility EKW OEE after energization in 2019 and is distributing 100% locally produced renewable energy in the region of the Swiss National Park. A further example is shown in Figure 4, this double busbar substation was installed in Grimaud in France within the network of RTE. During the commissioning, all the methods for the gas treatment and gas analysis have been approved.
The gas mixture is delivered on-site, premixed in cylinders to ease the installation. Dedicated g³ service carts from two different manufacturers may be used for the installation and commissioning phase to fill the GIS. The gas handling of g³ is similar to the gas handling of SF6. An additional step of heating the cylinder to bring the mixture from liquid into the gaseous phase is required. After filling, the C4F7N content, O2 content, and humidity in each 5 compartment were confirmed by using gas analyzers available from two different manufacturers. A repetition of the gas quality measurement has been performed in 2020 after three years operational time in the first energized substation in Switzerland. Those measurements have been done with portable gas analyzers, that allow to measure the C4F7N and O2 concentrations as well as the humidity content. No deviations were found for the composition of the gas mixture beside the expected measuring uncertainties.
In addition to GIS, 145kV 40kA Live Tank Circuit Breaker has been developed and is fully type-tested according to IEC 62271-100. It corresponds to a higher energy over volume rate (25kJ / litre) and is based on a 3.5% C4F7N, 13% O2, and 83.5% CO2 gas mixture that allows achieving -30°C [4], see Figure 5.
Recent research and development on HV range up to 245kV 63kA on single break unit:
Following CO2/O2/C4F7N gas mixture optimum definition for product and demonstration of its capability at 145kV 40 kA, 145 kV 63 kA, and 170 kV 50 kA, recent research has been focused on the achievement of higher performances [13, 14]. Using -25°C gas mixture, this research focuses on the development of a single chamber metal-enclosed circuit-breaker reaching 245 kV 63 kA performance. Starting with 245 kV 63 kA SF6 design, optimization has been made within the SF6 enclosure (same dimensions and footprint) to test and demonstrate several standard test duties, such as Terminal Faults, Short-Line Fault, and Capacitive switching. To prove g3gas mixture capability at high voltage and short-circuit current levels, optimized design was tested at low and high current levels, with the highest TRVs from normative standard applied on the circuit-breaker, based on 245 kV 63 kA kpp = 1.5 networks (non-effectively earthed neutral system). Those tests, performed on several prototypes, resulted in the demonstration of complete arcing window according to IEC62271-100 Ed2.2 and IEC62271-101 full test sequence of T10 and T30 test duties.
Technology Acceptation
On April 21st, 2021, GE and Hitachi ABB Power Grids (now Hitachi Energy) announced the signature of a non-exclusive, cross-licensing agreement enabling Hitachi Energy to use g3type mixture as an alternative gas to SF6 in high voltage equipment [15].
Under this landmark agreement announced just before Earth Day 2021 between two global leaders in power technologies – both companies will share complementary intellectual property related to their respective SF6-free solutions. This will help accelerate the use of g3eco-efficient insulation and switching gas in high-voltage equipment as an alternative to SF6. This historic agreement paves the way for a standard SF6-free solution for high-voltage equipment in the coming years. This would enable utilities and industries to accelerate their reduction of greenhouse gas emissions while facilitating their ability to plan, as well as operate and maintain their networks thanks to standardized services and the use of the same auxiliary equipment.
The two companies will keep the product development, manufacturing, sales, marketing, and service activities of their gas solutions fully independent. Each company will continue to independently grant and set terms of licenses to its respective intellectual property, hence preserving supplier base diversity for the industry and fair competition.
Environmental Benefit Of The Solution
A comparative Life Cycle Assessment (LCA) of two products, F35-145kV SF6, and F35g 145kV g3complete bays was carried out to evaluate the environmental impact of the g3solution on 16 environmental indicators compare to SF6. The results are presented on Figure 7.
The comparative LCA shows that F35g-145kV brings a huge reduction on the climate change impact compared to the SF6 product. Indeed, as the Global Warming Potential (GWP) of g3gas mixture is drastically reduced compared to SF6 (467 versus 23’500 for SF6), the impact of gas emissions during the use phase is reduced by 99%. This is of course the main advantage that is brought by the g3solution. What it is here interesting to see is that even considering the complete product over its whole life cycle, and not only the gas itself but the reduction on the climate change impact is also still of -73% compared to SF6 (considering 0.2% of leakage rate per year – the reduction will be even bigger if we considered a more important leakage rate in the study).
The ozone depletion indicator is the only indicator where the F35g-145kV (SF6-free) is more impacting than its SF6 pendant. As seen in the previous section, the main impact on this indicator comes from the production of PTFE material that is used in the circuit breakers. Yet, the SF6-free product has 1kg more PTFE than the SF6 product. That’s why the F35g-145kV is 15 % more impacting than the F35-145kV on ozone depletion on the global life cycle of the product. This may seem high at first glance, however, when considering the absolute result, the increase is only 2.8 g of CFC-11 equivalent over the whole life cycle of the product of 40 years. Overall it can be concluded that the increase of this indicator is not significant because the SF6 switchgear was already using very low quantities of PTFE.
On the 13 other indicators, the difference of the impact of the two products is less than 5 %, below the range of the uncertainty of the LCA analyses.
This study allows to demonstrate that there is no pollution transfer due to the shift on g3 technology: the impact on climate change indicator has been reduced by 73% compared to SF6 product, without increasing impact on other indicators like resource depletion. This has been achieved thanks to the fact that there is no oversizing of the g3product compared to SF6 one (it uses the same enclosures, resulting in the same overall footprint of the switchgear) while maintaining the same performances.
Last development In EU And In USA (EU Life and ARPA-e programs)
The EU Commission supports GE Grid Solutions to develop g3based switchgear. The co-funding reflects the EU’s commitment to accelerate the decarbonization of Europe’s electrical grids and help them get ready for the EU’s stricter fluorinated F-gas regulation, which aims to cut F-gas emissions by two-thirds by 2030.
EU co-funded 420kV/63kA g3 GIS Circuit Breaker
The European Commission is currently co-funding since 2019 the development of the g3 420 kV 63 kA GIS circuit-breaker under its LIFE Climate action program called LIFEGRID (LIFE18 CCM/FR/001096) aiming at the completion of the 420 kV 63 kA GIS [16].
LIFEGRID project integrates two 245 kV 63 kA chambers in series in a double break architecture. Despite a double-break circuit breaker arrangement, the new complete GIS bay based on C4-FN gas mixture offers the same footprint compared to its equivalent in SF6. As a result of innovative design progress in both the GIS bay and the circuit breaker, the bay width remains the same as the existing single break SF6 architecture. Figure 8 shows the circuit-breaker illustrating the compactness of the active part for the double-break to maintain the same outer dimension of the enclosure.
245kV interrupting unit offers the advantage to be more compact compared to the existing SF6 single break version. This allows the integration of grading capacitors in the tank with no impact on the bay width. Such compact arrangement of the active parts of the circuit breaker generated constraints on the dielectric withstand design and on the breaking unit design with successful results as presented below.
EU co-funded 245kV/50kA g3 Live Tank Circuit Breaker
In 2021, the European Commission’s LIFE climate action program as awarded again GE Grid Solutions for the development of a sulfur hexafluoride SF₆-free 245 kilovolts (kV) g³ live tank circuit-breaker [17]. The new circuit-breaker will rely on GE’s industry-leading g³ gas technology to deliver the same high performance and compact dimensional footprint as a traditional SF₆ circuit-breaker.
The new 245 kV g³ live tank circuit-breaker, which will be based on International Electrotechnical Commission (IEC) standards, is the second g³ gas project co-funded by the EU. The EU’s co-funding of a g³ 245 kV live tank circuit-breaker will help demonstrate the applicability of GE’s g³ gas for this commonly used voltage level by transmission operators around the world, as well as outdoor applications down to -30°C and the new g³ 245 kV live tank circuit breakers, once ramped up together with 420 kV voltage level, will help avoid the addition of some 52,000 tons of CO₂ equivalent annually on to the European grid alone and more – as we expect other continents to adopt our g³ gas technology.
ARPA-e funded g3 project with University of Connecticut
GE’s Global Research Center has been awarded by ARPA-e as part of project led by the University of Connecticut – to focus on the life cycle management of g3products, mainly gas leakages, byproduct detection, and monitoring tools [18]. The University of Connecticut, in partnership with GE Research, proposes to develop a life-cycle management framework to accelerate and safeguard the transition of the US power grid towards an SF6-free green power network.
This three-year program will advance the proposed framework for SF6-free lifecycle management.
ARPA-e funded 245kV g3 Dead Tank Circuit Breaker for 60Hz Market
Technical advancements are still necessary to achieve a functional and reliable outdoor g3circuit breaker rated at or above 245 kV, 63 kA, 4,000 A, 60 Hz. Improvements to the performance of the interrupting chamber are necessary since thermal and arc quenching properties of g3differ from those of SF6. Fault and load current switching tests must comply with domestic IEEE standards, which incorporate specific requirements related to US network conditions. Resiliency must be addressed to withstand system voltage under loss of pressure conditions, recovery from cold conditions after a blackout as well as voltage and current overload conditions.
This marks our first g3funding award in the U.S. The g3 245 kV dead tank circuit-breaker leverages the expertise acquired in g3by Grid Solutions’ technology research center in Villeurbanne, France, and the know-how of its manufacturing site in Charleroi, Pennsylvania, where the new g3circuit-breaker will be developed and built [18].
This design will become the basis for a broad range of products covering the entire voltage range of the US Grid. The specificities of the US grid and consecutive IEEE standards represent unique challenges for the breaker successful design. On the other hand, the always increasing constraints in the US Grid make it more difficult than ever for utilities to decrease the required performance of their outdoor breakers. Thus, the challenge is here to successfully develop an outdoor high voltage dead-tank circuit breaker that is SF6-free while at the same time offering high short-circuit-current (63 kA) and definite purpose switching capability, per relevant IEEE standards with 0 psig line to ground dielectric withstand capability. That development is critical as a first step in developing a fully performing SF6-free HV outdoor solution to then allow going after higher performances needed such as 362 kV and 550 kV all at 63 kA.
Conclusion
High voltage (HV) electrical transmission equipment developed for and filled with the g3 mixture features the same ratings and same dimensional footprint as the state-of-the-art SF6 equipment, with more than 99% CO2 equivalent reduction compared to SF6 and the environmental benefit of the g3 based HV product fully is demonstrated through a life cycle assessment with a reduced impact on climate change, without pollution transfer.
The handling specificities of the gas mixture is managed using specifically designed gas carts, considering the supercritical properties of the carbon dioxide buffer gas. The on-site experience on several projects has proven the efficiency of the process, even in severe climatic conditions.
The g3 equipment portfolio is enlarged, with equipment covering the HV range from 145kV to 420kV and 30 leading utilities have decided to move forward and to install g3equipment. GE has a number of projects on more than 40 sites that together will reduce the impact of the installed gas masses by more than 1,000,000 tons of CO2 equivalent. These projects include 150+ bays of 145 kV GIS, 5000+ meters of 420 kV GIL, and 100+ 145 kV Live Tank breakers.
New developments are ongoing and will start co-funded by EU/Life program and DOE ARPA E to enlarge the g3product portfolio towards higher voltage and 60Hz segment for US market.
References:
[1] https://multimedia.3m.com/mws/media/1132124O/3m-novec-4710-insulating-gas.pdf.
[2] Kieffel, Y, et al. “SF6 alternative development for high voltage switchgears”, Cigré Paper D1- 305, Paris, 2014.
[3] Kieffel, Y., et al. “Green Gas to Replace SF6 in Electrical Grids” IEEE Power and Energy Magazine 14 (2), p. 32-39, 2016.
[4] M. Walter, D. Leguizamon, L. Maksoud, T. Berteloot, et al. “Low temperature behaviour and dielectric performance of C4F7N/CO2/O2 mixture”, Cigré Paper D1-213, Paris, E-session 2020.
[5] IPCC Fifth Assessment Report: Climate Change 2013 (AR5).
[6] P Robin-Jouan, K Bousoltane, Y Kieffel, JY Trepanier, R Camarero, et Al. “Analysis of last development results for high voltage circuit-breakers using new g3 gas”, PLASMA PHYSICS AND TECHNOLOGY 4 (2), 157-160.
[7] K. Bousoltane et al. “Investigation on the influence of the O2 content in Fluoronitrile/CO2/O2 (g3) mixtures on the breaking in high voltage circuit breakers” Gas Discharges GD2018 Novi Sad, 2018.
[8] Regulation (EU) N° 517/2014 of The European Parliament and of The Council of 16 April 2014 on fluorinated greenhouse gasses.
[9] https://ec.europa.eu/clima/system/files/2020-09/c_2020_6635_en.pdf.
[10] https://e-cigre.org/publication/802-application-of-non-sf6-gasses-or-gas-mixtures-in medium-and-high-voltage-gas-insulated-switchgear.
[11] Y. Kieffel, E. Laruelle, G. Gaudart, F. Biquez, et al., “g3– The alternative to SF6 for HV equipment”, MATPOST, Lyon, 2015.
