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SF6, critical temp
2

SF6, critical temp

SF6, critical temp

(OP)
What happens to SF6 above 45.6 deg.C, since this is stated as a critical temp for use in a SF6 CB?

Audun

RE: SF6, critical temp

General definition: The critical temperature is the temperature above which it is no longer possible to liquify the substance in question by increasing the pressure.

RE: SF6, critical temp

2
Sulfur Hexafluoride (SF6) is chemically inert and is completely stable in the presence of most materials to temperatures of about +204°C at 28 bar, (+400°F at 392 psig ). It is shipped as a liquefied compressed gas at its vapor pressure of 298 psig at +70°F (21.5 bar at +21.3°C).

The SF6 critical parameters are as follow:

1- Critical temperature:    +114.0ºF, (+45.55ºC) .            .

2- Critical pressure:    544.3 psia, (37.53 bar), (36.557 atm)

3- Critical density:    45.8 lb/ft3, (734 kg/m3 ), (0.755 g/mL)



The operational pressure on a typical SF6 dead-tank circuit breaker vessel is as follow:

Operational Pressure             Temp=20oC        Temp=45.50C

Rated……………………...   87 psig              95 psig

Alarm…………. …………    75 psig              83 psig

Minimum/cut-out…………72 psig              78 psig

    
CASE I: Breaker without operation at ambient temperature.
At rated filled pressure equivalent to 95 psig at 45.5oC there will not be any condensation since this is produced at critical pressure of 544.3 psig.

CASE II: Circuit breaker interruption operation at rated SC.
Temperature above 5000K converts the gas in stage of conductive plasma. After rapid cooling to 1500K, the material starts recovering the gas estate.

CASE III: During freezing condition.
For temperatures bellow –25C there is risk of condensation. Thermal insulated blanket with heater and mix with other dielectric gases could be used for critical cases with temperatures down to –50C.

  

RE: SF6, critical temp

Another great detailed post, cuky...
You're a star in my book.

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