Chemistry Reference
In-Depth Information
7.5
Sulfur Hexafluoride, SF
6
7.5.1
SF
6
as Insulating Gas for Electrical Equipment
Solvay's sulfur hexafluoride is a nontoxic, inert, insulating and cooling gas of high
dielectric strength and thermal stability [40]. For more than 40 years the gas has been
used for high and medium voltage applications.
It is particularly suitable for application in both high-voltage and medium-high voltage
power circuit breakers (Gas Insulated Switch Gear: GIS) as well as in high-voltage cables
(Gas Insulated Lines: GIL), transformers, transducers, particle accelerators (insulation of
Van der Graaf generator and high-voltage GIS), X-ray equipment and UHF transmission
systems and with 99.999 % purity as an etching and chamber cleaning gas in the semi-
conductor and photovoltaic industry.
The construction of new equipment with higher capacity and improved performance has
been made possible by the excellent electrical, thermal and chemical properties of SF
6
.
Changing from conventional dielectrics to sulfur hexafluoride, which is a nonflammable
chemically inactive and nontoxic gas with high density, results in considerable space and
weight savings. Improvements in the operational safety of converted equipment can also
be achieved [41, 42].
Electrical discharges appearing during switching processes or generated by fault electric
arcs lead to the formation of gaseous decomposition products and dusty metal compounds.
Gaseous decomposition products of SF
6
exhibit very characteristic warning signs even at
low concentrations. These warning signs are for example pungent or unpleasant odours
like ''rotten eggs'', or irritation of nose, mouth and eyes. Such irritation occurs within
seconds, well in advance of any danger arising from poisoning.
When handling such contaminated SF
6
care must be taken not to breathe in gaseous or
dusty decomposition products. In case this cannot be achieved by technical safety mea-
sures like good ventilation, personal protective equipment must be worn. This personal
protective equipment needs to include items of protection for the eyes, body and breathing.
Due to the ecological and economical aspects, any SF
6
that is released during main-
tenance work or when electrical systems are decommissioned should be contained and
returned to the economic cycle. This limits emissions of SF
6
into the atmosphere to the
extremely low leakage rate of the systems.
Solvay Fluor GmbH, as a leading producer of SF
6
, developed the SF
6
-ReUse
concept at the beginning of the 1990s in order to provide SF
6
users with virtually
unlimited possibilities to reuse SF
6
and, consequently, to eliminate emissions as far as
possible.
7.5.2
SF
6
Applications in Metallurgy
SF
6
/ inert gas mixtures are used in the production of magnesium and magnesium
alloys and the cleaning of aluminium melts. It functions as a protective gas to prevent
ignition, oxidation and nitride formation as well as for removing oxides and solid
inclusions.
