Increasing demand for electrical power and the technical capacities of SF6 Sustainable concepts, that allow for being sparing with the environment and natural
resources, are needed for ensuring the supply of electricity. Humanity needs sufficient quantities of electrical power, provided from reliable sources, in an environmentally compatible and economically viable manner. Sulfur hexafluoride (SF6) makes a substantial contribution to all this. As an insulating and arc-quenching medium in high-voltage and medium-voltage switchgear, SF6 has enabled constant advances in the transmission and distribution of electricity since 1960 like no other technology. 
Discussions of environmental aspects
In the last few years, discussions of the use of SF6 have extended beyond engineering circles to the political level. Until now, these discussions have almost exclusively dealt with the greenhouse effect of SF6 emissions. For example, the signatories to the Kyoto Protocol to the 'United Nations Framework Convention on Climate Change' have undertaken to slow the increase in the greenhouse effect caused by anthropogenic emissions. Besides carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs), the measures concerned also involve sulfur hexafluoride (SF6). Pursuant to the Kyoto Protocol, the differing greenhouse potentials of these gases are to be allowed for by means of CO2 equivalents.
| Calculations based on atmospheric measurements show that the total worldwide emissions of SF6 contribute only about 0.1 percent of the overall anthropogenic greenhouse effect. This includes both the SF6 emissions from the major area of use in high-voltage and medium-voltage switchgear, and those from all other uses. Despite this small quantity, some people view the use of SF6 as involving a conflict between its technological advantages and ecologically questionable aspects - especially since they often wrongly only consider the much higher greenhouse potential, weight for weight, of sulfur hexafluoride as compared to carbon dioxide. The environmental benefits resulting from the use of SF6 in the transmission and distribution of electrical power are ignored in such a consideration. | | 
In gas-insulated, metal-enclosed high-voltage switchgear, SF6 is used as an insulating and arc-quenching medium. |
Environmental protection measures and life cycle assessment
Aware of their responsibility, the German manufacturers and users of SF6 switchgear
- represented by their trade associations, ZVEI and VDEW - and the SF6 producer Solvay Fluor GmbH already in February 1997 undertook voluntarily suitable measures in the manufacture, installation, operation and maintenance of switchgear to prevent or minimize SF6 emissions according to the state of the art. The most important measure is to reclaim and re-use used SF6 on site. If this is not possible, the manufacturer, Solvay Fluor GmbH, will take back the SF6 and reprocess it to a good-as-new quality, or guarantee proper environmentally compatible disposal, if necessary.
The development and implementation of these closed cycles of SF6 use ('SF6 -ReUse-Concept') is a matter of cooperation between equipment manufacturers, power utilities, and the SF6 producer, Solvay Fluor GmbH. In a joint project, ABB, PreussenElektra Netz, RWE Energie, Siemens, and Solvay Fluor GmbH have now taken a further step along the line of product responsibility: in order to overcome the one-sided view that is restricted to the material-based greenhouse potential, they have prepared a life cycle assessment.
A realistic electricity supply system was completely analyzed, taking into account the criteria of primary energy consumption, area required, greenhouse potential, acidification potential, and nutrification potential. This is intended to create a basis for a well-founded environmental discussion, on the one hand, and to show the companies involved possibilities for further environmental optimization, on the other hand. The life cycle assessment was performed according to the specifications of the international standard DIN EN ISO 14040, and was followed and evaluated by an external independent expert from TÜV NORD.
Design of the life cycle assessment
The life cycle assessment is oriented to conditions in Germany; the technologies considered reflect the present state of the art. The study compares various switchgear technologies, with and without SF6 , at the bay level and at the system level of a real urban power supply system, with respect to primary energy consumption, area required, greenhouse potential, acidification potential, and nutrification potential.
At the switchgear bay level, the following are examined: - conventional outdoor installation without SF6
- outdoor installation with SF6 equipment (circuit breakers and instrument transformers)
- SF6 -insulated, metal-enclosed switchgear.
At the system level, two alternative supply models are compared, based on the given load profile of a German city about 40 km2 large, with about 130,000 inhabitants, a peak load of 120 MW, and a consumption of 400 GWh during the first year of the period (and an annual increase in load of 1.5 percent): - The electric power is fed into four air-insulated 110/20-kV transformer substations (AIS) on the outskirts, occupying a correspondending surface area, and distributed via the 20-kV network. The 110-kV transformer substations are connected by means of overhead lines.
- The electric power is fed via 110-kV cables into three SF6 -insulated 110/20-kV transformer substations (GIS) close to the consumers, and distributed via the 20-kV network.
 In both cases, the electric power is taken from the regional grid in a 380/110-kV transformer substation on the outskirts. Both systems are designed such that the quality of supply to the consumers is equal: differing failure probabilities of the different types of equipment are taken into account and compensated for in the planning of the power system. The design of the systems is optimized from the commercial point of view. The period considered is thirty years, the typical service life of air-insulated high-voltage switchgear, in order to be fair to all the versions of switchgear considered. SF6 -insulated switchgear can usually be used for at least ten years more.
Outdoor-type transformer substation
with SF6 equipment 
Topology of the power system variants: System with AIS technology (left) and system with GIS technology (right) for a distribution voltage of 20 kV. 'UW' stands for transformer substation. The left hand illustration shows that, in the AIS version, the four air-insulated substations are located on the outskirts. In the GIS version shown on the right, the three SF6 -insulated substations are positioned within the city, and thus close to the consumers. ? Thick lines represent 110-kV high-voltage overhead lines or underground cables; thin lines stand for 20-kV medium- voltage cables. While the 110-kV overhead transmission lines of the AIS version (without SF6) circle the city, the 110-kV cables of the GIS version (with SF6) stretch into the city, resulting in a reduction in transmission losses.
Results of the life cycle assessment Even at the bay level, the use of SF6 technology offers advantages for four of the five criteria of the life cycle assessment study: primary energy consumption, area required, acidification potential, and nutrification potential. Switchgear with a high utilization factor and/or the low rates of SF6 loss achievable today provide an ecological advantage even for the greenhouse potential.
At the level that counts in the end, namely the power supply system considered, the following results are obtained: designing a power supply network with GIS technology (using SF6) results in a reduction of about 27 percent in the primary energy consumption, of about 86 percent in the area required, of about 21 percent in the greenhouse potential (GWP), of about 21 percent in the acidification potential (AP), and of about 29 percent in the nutrification potential (NP), compared to designing the same network with AIS technology (without SF6). The transferability of the results from this sample network has been tested in extensive scenario calculations.
The major reasons for this reduced environmental impact are: since SF6 has considerably better insulating and quenching properties than air, substations and equipment can be made with less material and energy than in the SF6 -free AIS alternative. Furthermore, due to the compact design of the GIS components, the 110/20-kV transformer substations can be built directly at the (downtown) load centers. So the energy is transmitted at high voltage with low losses to the city centers, and distributed from there to the consumers via short medium-voltage lines. 
The use of GIS switchgear in the power supply system considered reduces all the potential environmental impacts studied. The diagram shows the relative environmental impact potentials during the first year of use of the power system variant (orange bars = AIS version, green bars = GIS/SF6 version). An increase in the system?s supply capacities by about 50 percent (i.e. increased utilization of the system) results in a further reduction of about 5 percent each in the parameters primary energy consumption, greenhouse potential (GWP), acidification potential (AP), and nutrification potential (NP), due to SF6 technology.
Conclusions The use of SF6 technology leads to considerable environmental advantages over the use of SF6 -free switchgear. Therefore, SF6 technology makes sense for electric power supplies, even from the environmental viewpoint. This requires the use of GIS installations that ensure appropriately low SF6 emissions, on the one hand, and rigorous application of the SF6 -ReUse-Concept of a closed SF6 cycle, on the other. The technical and logistical prerequisites for this effort are already available. It is also very clear that an environmental view limited to the greenhouse potential of a unit of weight of SF6 cannot provide an environmental assessment of the use of SF6 in high-voltage and medium-voltage equipment. A comprehensive consideration of entire power supply system with the help of a life cycle assessment, directed to all relevant environmental criteria, provides dependable results that are positive for SF6 use.
The Responsible Care Programme for SF6
SF6 - a reusable commodity
SF6 is a user-friendly product which besides its many other positive characteristics can be recycled as well. This is increasingly the important, particularly today. This is why Solvay Fluor GmbH together with the producer of SF6 maintenance equipment DILO Armaturen und Anlagen GmbH developed a common concept for the re-use of SF6 , based on many years of experience. The practical side of this approach is illustrated by the following diagram. As an additional service, an analysis can be conducted on your used SF6 gas. Detailed information can be found in the brochure 'Analysis of Used SF6'. You will find further information in the brochure 'Concept of Reuse of Used SF6 gas', available upon request.
Life cycle assessment studies for the use of SF6 in high and medium-voltage applications Solvay Fluor GmbH, as a producer of SF6 and the manufacturers and operators of SF6 switchgear take the ecological issues associated with the use of this product very seriously. Because of this, switchgear manufacturers, power generation companies, trade associations and Solvay Fluor und Derivate established an SF6 ReUse Concept several years ago, which meets the basic requirements for the implementation of a closed product cycle for the majority of SF6 in use. With respect to the Kyoto Protocol, switchgear manufacturers, operators and SF6 producers saw the necessity of going one step further with regard to their product responsibility. For the first time, they quantified the environmental profile of the use of SF6 as an insulating and arc-quenching medium in high and medium-voltage circuit breakers and switchgear by means of life cycle assessments. One of the main reasons behind this was the need to get away from the prevailing, one-sided focus on the substance-related global warming potential of SF6 by analysing all the relevant environmental criteria in connection with the use of SF6 in the power generation industry. Criteria for this comparison include the potential environmental effects, primary energy requirements, space requirements, global warming potential, acidification potential and nutrification potential. The life cycle assessments were performed according to the ISO 14040-43 standards by a working group including scientists and other stakeholders, as well as a critical review by an external, independent verifier from TÜV NORD CERT.
Life cycle assessment study for SF6 in high-voltage applications
'Power supply using SF6 technology' The study was carried out as a joint project by ABB, PreussenElektra Netz, RWE Energie, Siemens and Solvay Fluor und Derivate and relates to conditions in Germany. In the study, conventional and SF6 technologies were compared on a switch panel level. The study also compared urban power supplies using air-insulated and SF6 gas-insulated switchgear with no change in the quality of the supply. The use of GIS switchgear in the public grid reduced all the potential environmental effects that were investigated. Figure 44 shows the relative potential environmental effects in the first year of using the grid variants (blue bar = AIS variant, green bar = GIS / SF6 variant). Increasing the supply to the grid by around 50 per cent (that is, improving grid capacity utilisation) led to a further reduction for the parameters of primary energy requirements, global warming potential (GWP), acidification potential (AP) and nutrification potential (NP) of around 5 per cent in each case as a result of the SF6 technology. 
Fig. 44
Potential environmental effects for SF6 in high-voltage applications for AIS and GIS Have a full screen of the graph.
Life cycle assessment study for SF6 in medium-voltage applications
'SF6 GIS technology in energy distribution' The study was commissioned as a joint project by ABB, AREVA T&D (formerly ALSTOM), SIEMENS, EnBW, E.ON Hanse, RWE and Solvay Fluor und Derivate. During the study, data was gathered for a representative mix of medium-voltage switchgear: transformer stations, ring-main units (RMU, network stations) and customer substations. The data included electrical key figures (in particular ohmic loss), material data from disassembly analy-ses as well as load ratios and life times. To determine the quantity structures, the systems were examined at both a grid and a switchgear level. Grid level - contribution of the public grid to the greenhouse effect When the contribution made by distribution grids to the greenhouse effect (Global Warming Potential, GWP) in Germany is analysed, it can be seen that by far the greatest share of this can be attributed to ohmic losses in cables, transmission lines and transformers (Fig. 45). At present, SF6 emissions from medium-voltage switchgear contribute less than 0.005 % to the greenhouse effect in Germany. 
Fig. 45
Observation of the total global warming potential (GWP) of a representative urban grid Have a full screen of the graph. Switchgear level - comparison between AIS and GIS technologies Analysis of the switchgear level in figure 46 comparing air-insulated (AIS) and SF6 insulated technologies, illustrates the advantages of the SF6 GIS technology with regard to primary energy requirements, acidification potential (acid rain), nutrification potential (over-fertilisation of waterways) and global warming potential (GWP). It was shown that the determining factors impacting on the greenhouse effect are in fact the load ratios in the grid and the switchgear. The current trend towards higher capacity utilisation of the grids increases the advantages of SF6 -insulated switchgear. Thus, to develop any noticeable climatic protection potential it would appear that load flow management in grids is a further way of optimising switchgear design. In principle, the results of this life cycle assessment could be transferred to other European countries. A sensitivity analysis shows that the selection of primary energy carriers used for electricity generation (as the most significant regional impacting factor) only has minor effects on the results. 
Fig. 46
Overview of the environmental categories that were examined in the study at switchgear level. Have a full screen of the graph.
Summary of life cycle assessment studies The use of SF6 technology provides ecological advantages compared with the use of SF6 -free switchgear and equipment. One condition for this is that GIS switchgear guaranteing the corresponding low SF6 emissions is used, and on the other hand, it is important that the SF6 ReUse concept for a closed SF6 cycle is applied consistently. A narrow-based environmental study focussed exclusively on the global warming potential of SF6 is not sufficient to provide an ecological assessment of the use of SF6 in high and medium-voltage technologies. As a result of the life cycle assessments that were carried out, it can be seen that bans and application restrictions on the use of SF6 -insulated high and medium-voltage switchgear cannot be justified from an ecological point of view.
Product stewardship for SF6 Solvay Fluor - well known as a global supplier of new SF6 gas according to IEC 376 - cares for the environment. We are your partner for the SF6 ReUse concept and full technical services. The SF6 ReUse concept of Solvay Fluor GmbH includes: - environmental consulting
- analytical services of used SF6
- packaging and transportof used SF6
- reclaiming of used SF6
Solvay Fluor GmbH is the only company worldwide delivering such a complete range, to fullfil the requirements of the responsible care programme. For further information, please refer to our SF6 ReUse Folder.
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