SF6 Gas Density Monitoring Very low temperature and liquefaction situation with Trafag 87X6 SF6 gas density monitor 05.02.07/ nip

The Reference Gas Principle (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“ 05.02.07/ nip

The Density Monitor with Reference Chamber (Picture shows the “older” 87x0 density monitor generation) Tappet moves when SF6 leaks from tank and triggers alarm switch ...inside the monitor Reference chamber filled with gas SF6 gas inlet (connection to tank) 05.02.07/ nip

Behavior of bimetalic-compensated Systems Contact 1, falling (bimetal comp, non-Trafag) True isochor Tolerance band of Trafag DM for calibration Contact 2, falling (bimetal comp, non-Trafag) True isochor Tolerance band of Trafag DM for calibration The accuracy of the alarm levels 05.02.07/ nip

Density Monitor at temperature 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 05.02.07/ nip

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 monitor 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 05.02.07/ nip