Alstom FKG1X - Page 83

Description and operation
SF
6
gas
monitor
ing
M20
-
-0
02EN03
4/10
02--2011
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ion contained in
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representati
on or
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 GRID
Gas pressure and density
Introduction
 The
el
ec
tri
ca
l
ch
ara
cte
ris
tic
s
of
sw
itc
hg
ea
r
de
pe
nd
on
the
de
ns
ity
of
SF
6
gas
i.e. the mass of gas pumped into a compartment of a given capacity.
Constant
temperature
At
constan
t
temperatur
e,
an
increa
se
of
gas
density results
in a
higher gas
pressure against the walls of compartment.
Constant density
At
constant
density
, w
ith a
n
invaria
ble
compartme
nt
volume,
the
pressur
e
cha
nge
s
in
the
same
way
as
the te
mpe
ratu
re.
Sin
ce th
e
gas
den
sity
rema
ins
invariable owing to the fact that no modification occurs in the quantity of gas
or
the
vol
ume
of
the
rele
van
t
comp
artme
nt,
the
ele
ctric
al
cha
racte
rist
ics
of
the
switchgear will remain unchanged.
Conclusion
Since
it
is
difficult
to
measure
the
gas
density
directly
,
it
is
essentia
l
to
know
accurately its absolute pressure and temperature.