Main applications

The gas SF6 (Sulphur hexafluoride) has proven to be essential in its main application in high and medium voltage switchgear stations and circuit breakers. Switchgear is a basic part of energy supply network. Many of today's technical, economic and environmental requirements for high and medium voltage switchgear can only be met by the use of SF₆. About 70-80 % of the global SF₆ production is used in this sector.

Gas insulated switchgears (GIS) using SF₆ as an arc quenching and insulation medium provide considerable environmental advantages over air insulated switchgear (AIS) as clearly shown in a Life Cycle Assessment taking into account the complete chain including primary energy consumption, area requirement and contribution to global warming.

An earlier life cycle assessment (LCA) (1) on high-voltage (110kV to 380kV) switchgear had demonstrated clear advantages from SF₆ insulation technology in a power supply network This assessment was taking into account present practices of minimising leakage and handling losses and of recycling consistently SF₆.
This showed that the focus on the global warming potential (GWP) of SF₆ (LINK) is misleading and that a global approach is necessary to fully appraise the total environmental benefits of SF₆ in the systems in which it is used.

However, in medium-voltage (MV) applications this global performance of SF₆ still needed to be demonstrated. Therefore, a LCA study was commissioned by a group of companies (equipment manufacturers, grid operators, producer) and subject to critical and independent peer-review.

The study covers MV (between 1 and 30kV) switchgear used in systems including transformer substations, ring-main units, consumer substations. Again and despite a high GWP, SF₆ was shown to be environmentally preferable to alternative technologies. The results confirm also the need of a "system approach" to adequately evaluate the performance in such applications.

Source: Mersiowsky I., "Life Cycle Assessment - SF₆-GIS Technology for Power Distribution - Medium Voltage", November 2003.

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Power supply fulfils an essential role in our economy. But what about the contribution of electriciy distribution grids to Germany's greenhourse gas emission burden? This new Life Cycle Assessment (LCA) study investigates the environmental profile of medium-voltage equipment, with a comparison between air-insulated and SF₆-insulated switchgear.

Summary report in  1,7 MB ()

Summary report in  2,15 MB ()

Technical and safety aspects

Technical

The gas SF₆ provides a combination of favourable properties such as high dielectric strength, excellent arc quenching ability, chemical inertness, high thermal stability, non-flammability and very low toxicity. It is colourless and odourless.
The excellent quenching and insulating properties of SF₆ have permitted the construction of completely new types of high-voltage circuit breakers and switching stations with outstanding features:

• compact and space-saving design
• low noise levels
• protection against accidental contact of live parts
• protection against intrusion of impurities
• elimination of fire hazard

Substations using SF₆ are particularly in demand where, on account of limited space, a compact design is required. These substations occupy only 10-15 % of the space required by conventional units. New SF₆ filled equipment can thus be installed in densely-populated areas where site costs would prohibit the use of traditional methods. Thanks to their insensitivity to polluted air, enclosed outdoor versions of SF₆-insulated substations are installed in the chemical industry, in desert regions and in coastal areas.

Safety aspects

SF₆ is non-flammable and has very low toxicity. It is transported as a pressurized liquified gas.

Pure (new) SF₆ according to IEC 376:

Potential hazard: Asphyxiation
Protective measures: Natural and forced ventilation

Contaminated SF₆ (e.g. caused by electrical discharges):

Potential hazard: Formation of small quantities of toxic gaseous decomposition products could have occured.

Technical and safety aspects If health hazards associated with the handling of contaminated SF₆ cannot be totally excluded with the aid of technical safety measures, then personal protective clothing must be worn

Recovery and recycling

SF₆ is securely contained in switchgears, which are hermetically sealed or closed systems. Leakage is generally less than 0.5 % per annum due to the technology used. Additional emissions occur during handling. Total emission from equipment in service in the EU in 1995 was about 3 % of the about 4000 tonnes installed according to the result of a comprehensive inquiry by switchgear manufacturers and utilities. These around 2.5 % handling losses (plus 0,5% leakage losses) can be considered as the highest limit, since recovery processes and handling procedures are constantly being improved.
Additionally "ReUse" concepts of SF₆ producers ensure that a closed product cycle is established including reclamation of contaminated gas to original quality in cases when on-site recycling is impossible due to the kind or concentration of impurities.

See also 

"News section":  01/11/2003: "SF₆ Sustainability: The SF₆ Reuse Programme" and

"The SF₆ ReUse Program-A Case Study" San Diego, CA. November 2002. - D.C. Lauzon    138 KB

Economic aspects

SF₆ is currently produced by two companies in the EU: Ausimont and Solvay.
A third company (Honeywell) participates in the EU market for SF₆, but has its production site in the US.

As the export share of the main four European switchgear manufacturers is significant, a corresponding SF₆ quantity is exported with the systems, too.