Description and operation
SF
6
gas monitoring
L20--001EN/04
2/6
01--2003
E ALSTOM
Gas pressure and density
Introduction
The electrical characteristics of switchgear depend on the density of SF
6 gas
i.e. the mass of gas pumped into a compartment of a given volume.
Constant
temperature
At constant temperature
, an increase of gas density results in a higher gas
pressure against the walls of compartment.
Constant density
At constant density
, with an fixed compartment volume, the pressure
changes in the same way as the temperature. Since the gas density re-
mains invariable owing to the fact that no modification occurs in the quanti-
ty of gas or the volume of the relevant compartment, the electrical charac-
teristics of the switchgear will remain unchanged.
Conclusion
Since it is difficult to measure the gas density directly, it is essential to
know accurately its absolute pressure and temperature.
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