Dilo SF6 - Page 58

Dry filter revision | 3-899-R…
www.dilo-gmbh.com | C 1978-03 | Page 4 / 8
The solid particles that can be found in the decomposed SF
6
like tungsten trioxide (WO
3
), cupric fluoride
(CuF
2
) and others are effectively retained in particle filters 3-377-R001 that are placed behind.
The absorbing capacity of the filter cartridge for decomposition products is different and depends on the
substance. For sulphur dioxide (SO
2
) and thionyl fluoride (SOF
2
) it is about 15-20 % by weight, that
means 90-120 g (2.6 - 3.9 ounces) for each filter cartridge.
Note:
The absorption of humidity and decomposition products generates an exothermic reaction in the filter.
Therefore a dry filter can become hot if these substances are fed in high concentrations.
2. Revision intervals
There is no formula to determine the revision intervals generally as it depends on the substances the
filter is fed with. Therefore it is important to control the efficiency of the dry filter from time to time using a
moisture measuring device and a decomposition products measuring device.
a) If it is known that the dry filter had been admitted with decomposed SF
6
the filter cartridge must be
exchanged in any case.
b) Example:
When drying SF
6
a dew point temperature of less than -50 C (-58 °F) is obtained with a
practically new filter cartridge.
A dew point temperature of -20 °C (-4 °F) is measured for SF
6
-gas, filled into a storage tank. Now
the question is: How much SF
6
can be dried to a dew point temperature of less than
-50 °C (-58 °F) with one filter cartridge?
A dew point temperature of -20 C (-4 °F at atmosphere) at 1 bar is 1000 ppm
V
and
thus
1000
81
123 5
,
,
ppm
m
. Thus the moisture content of the gas is 123.5 mg/kg. With one filter
cartridge can therefore be dried a gas quantity of
120
0 1235
971
g
g
kg
,

kg (2140 lbs) .
c) If the filter had been charged with decomposed SF
6
as a consequence of max. 1.700 kJ arc energy
(= arc current x arc voltage x duration of the arc) the filter cartridge must be exchanged.
Investigations showed that SOF
2
is the most abundant decomposition product as a consequence of
electric arcs and spark discharge. Other decomposition products appear in considerably lower
concentrations. The production rate of SOF
2
directly depends on the arc energy that affects the SF
6
.
If SF
6
that was exposed to such an arc energy had been led over a dry filter the filter cartridge has to
be exchanged.