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SF6 Gas Density Monitoring

Very low temperature and liquefaction situation with

Trafag 87X6 SF6 gas

density monitor

SF6 Gas Density Monitoring

Very low temperature and liquefaction situation with

Trafag 87X6 SF6 gas

density monitor

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The Reference Gas PrincipleThe Reference Gas Principle(Theory)(Theory)

SF6 filled switchgear

SF6 filled reference chamber

separating membrane

DM

The temperatures of the gas in the switchgear and the gas in the reference chamber of 87x6 density monitor are „the same“ (depends on the mounting situation)

Conclusion: „fully temperature compensation over the whole temperature range“

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The Density Monitor with Reference The Density Monitor with Reference ChamberChamber

(Picture shows the “older” 87x0 density monitor generation)(Picture shows the “older” 87x0 density monitor generation)

Reference chamber filled with gasReference chamber filled with gas

Tappet moves whenTappet moves whenSFSF66 leaks from tank and leaks from tank and triggers alarm switchtriggers alarm switch

SFSF66 gas inlet gas inlet (connection to tank)(connection to tank)

...inside the monitor...inside the monitor

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Behavior of bimetalic-Behavior of bimetalic-compensated Systemscompensated Systems

Isochoren von xyz No. 06397

3.000bar

3.500bar

4.000bar

4.500bar

5.000bar

5.500bar

6.000bar

6.500bar

7.000bar

7.500bar

8.000bar

-40.0°C -30.0°C -20.0°C -10.0°C 0.0°C 10.0°C 20.0°C 30.0°C 40.0°C 50.0°C 60.0°C

Schalter 1 sinkend

Schalter 2 sinkend

Isochore 5 bar

Isochore 6,4 bar

-8 kPa

+8 kPa

-8 kPa

+8 kPa

Contact 1, falling(bimetal comp, non-Trafag)

Contact 2, falling(bimetal comp, non-Trafag)

True isochor

Tolerance band of TrafagDM for calibration

True isochor

Tolerance band of TrafagDM for calibration

The accuracy of the alarm levels

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Density Monitor at temperature Density Monitor at temperature below -55C below -55C •Due to the mechanical system the density monitor will still operate below -55°C•May be the specifications like accuracy and so on are out of the from Trafag specified values on the datasheets•The tolerances of the mechanical system may be are to high for a proper function

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Liquefaction?Liquefaction?•The reference chamber of 87x6 density monitor is filled at previous alarm density level (1. stage)•In regular operation the density at switch breaker is higher (somewhere between filling pressure and previous alarm level) as previous alarm level in reference chamber of 87x6 density monitor•Therefore, the liquefaction in switch breaker starts at higher temperature (that means earlier) as in the reference chamber of 87x6 gas density monitorBenefits:• Small local liquefaction in the

switch breaker will not be detected by the 87x6 density monitor

• Serious liquefaction which can create a critical situation for the switch breaker get detected by the 87x6 density monitor