SF
6
-Aciditor
11
5 Introduction
The increased application of SF
6
in gas-insulated electrical equipment, such as switchgear or
transmission lines, has led to many recent analytical investigations on the stability and
decomposition of SF
6
. Although SF
6
shows great chemical inertness it decomposes under
electrical stress, in the presence of arcs, sparks or partial discharges. Among the products
found are species such as SOF
2
, SO
2
F
2
, SOF
4
, S
2
F
10
, SO
2
, HF, SiF
4
and others.
The decomposition of SF
6
further
depends on gas pressure,
electrode materials and the inner
surface materials of the
equipment. Despite the proven
reliability of such components in
the electrical power distribution
systems, failures occur due to the
above mentioned SF
6
aging under
electrical stress.
The laboratory analysis of
decomposition products were carried out by gas chromatography, gas chromatography/
mass spectrometry or infrared spectroscopy. The methods described above are complicated,
expensive, require specially trained personnel and can only be used in a laboratory.
Using ion mobility spectrometer (IMS) a good quality assessment of the SF
6
in SF
6
-filled
compartment can be achieved. The IMS is calibrated to measure all kind of decomposition
products in sum and in combination with a moisture sensor and SF
6
percentage sensor a
comprehensive monitoring of the SF
6
can be achieved. For monitoring the quality of SF
6
G.A.S. recommends to use a multi-functional device with a combination of the above
mentioned sensors such as, the SF
6
-Analyser or SF6-Breaker-Analyser, that allows to
implement a Condition Based Maintenance (CBM) and a fault detection at an early stage via
a gas analytical approach (see www.gas-dortmund.de).
