Mositure testing in GIS
Mositure testing in GIS
(OP)
I have a question from all respected memebers. The pressure in GIS is always above atmospheric pressure (6.5 bar in Circuit Breakers and Isolators and 5.5 in VT/PT and Busbars), while atmospheric is always less (say 1 atm). In case of leakage, it is confirm that always SF6 will be released into atmosphere and air cannot go inside GIS. My question is:
When we check the dew point of SF6 gas and some times results are not good. So from where does the moisture enters the GIS?
Kindly answer dear engineers.
When we check the dew point of SF6 gas and some times results are not good. So from where does the moisture enters the GIS?
Kindly answer dear engineers.






RE: Mositure testing in GIS
RE: Mositure testing in GIS
The tendency of gaseous contaminants to diffuse from one side of a barrier to the other is a function of the partial pressures of that contaminant on either side of the barrier - not of the total pressures. The partial pressure of water vapour in atmospheric air can be quite high and the desired partial pressure on the dry gas side of the system remarkably low.
Water is a very small molecule compared to SF6, which means that, for a given temperature, the average speed of water vapour molecules is much higher than that of those of the rest of the gas.
Where you have leaks, the first factor creates a preference for water vapour to diffuse through them into a dry system. The second makes it possible for that tendency to overcome the flushing effect of the general outflow of gas.
That all ignores the ability of water vapour to adsorb onto surfaces (like the inside of hoses) exposed to atmosphere and later outgas into a dry gas stream (for instance when you use the hose to connect your hygrometer to your GIS).
A.
RE: Mositure testing in GIS
Anecdote: The dryouts were once deferred for too long; the fog and mist that appeared when a breaker subsequently operated during a contingency was so pronounced that the operators began to jocularly ask up the chain of command when we had started installing water-blast breakers...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Mositure testing in GIS
are there any chances that moisture is contained by solid components inside the bay like copper contacts, insulators etc all which are packed inside the GIS bays.