SF

6

Gas Density Monitoring

Very low temperature and liquefaction situation with Trafag 87X6 SF

6

gas density monitor

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The Reference Gas Principle (Theory) SF 6 filled switchgear SF 6 filled reference chamber DM

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separating membrane 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“

The Density Monitor with Reference Chamber (Picture shows the “older” 87x0 density monitor generation)

...inside the monitor Tappet moves when SF 6 leaks from tank and triggers alarm switch Reference chamber filled with gas SF 6 gas inlet (connection to tank) 05.02.07/ nip

Behavior of bimetalic compensated Systems

Isochoren von xyz No. 06397

8.000bar

7.500bar

7.000bar

6.500bar

6.000bar

5.500bar

5.000bar

4.500bar

4.000bar

Contact 1, falling (bimetal comp, non-Trafag) True isochor Tolerance band of Trafag DM for calibration Schalter 1 sinkend Contact 2, falling Isochore 6,4 bar +8 kPa -8 kPa Tolerance band of Trafag DM for calibration

The accuracy of the alarm levels

3.500bar

-40.0°C -30.0°C -20.0°C 3.000bar

-10.0°C 0.0°C 10.0°C 20.0°C 30.0°C 40.0°C 50.0°C 60.0°C 05.02.07/ nip

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Density Monitor at temperature below -55C

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Due to the mechanical system the density monitor will still operate below -55 °C

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May be the specifications like accuracy and so on are out of the from Trafag specified values on the datasheets

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The tolerances of the mechanical system may be are to high for a proper function

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Liquefaction?

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The reference chamber of 87x6 density monitor is filled at previous alarm density level (1. stage)

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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

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Therefore, the liquefaction in switch breaker starts at higher temperature (that means earlier) as in the reference chamber of 87x6 gas density monitor

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Benefits: 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