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High-accuracy moisture measurement in SF6 switchgear

Moisture measurement in SF6-insulated switchgear is vital. That?s why WIKA has improved the performance of the GDHT-20 sensor for this industry. The transmitter, which also provides values for gas density, pressure and temperature, now measures the dew/frost point having an accuracy of �2 K.
Moisture, alongside density, may be the crucial parameter for assessing the condition of the SF6 gas used. The GDHT-20 continuously monitors its content in the gas. The information from the online monitoring forms the input for a downstream trend analysis. The more precise both the density and the moisture measurement are, the more precise this analysis will be.
Predictive maintenance instead of regular maintenance intervals
The model GDHT-20 sensor is an all-in-one instrument for the online monitoring of SF6-insulated switchgear. It works with three temperature sensors (red), a pressure sensor (blue) and a humidity sensor (yellow).
The analysis shows the operator once the SF6 will reach a crucial state and when remedial measures should be taken. Subsequently, maintenance work or gas treatment is undertaken when action is in fact needed. Predictive maintenance thus replaces the sequence of regular maintenance intervals that has been previously necessary to avoid ecological and safety risks.
Too much moisture in the gas compartment is one of these risks. In older plants, moisture mainly increases because of permeation through sealing materials. In younger plant, normally, this is due to moisture remaining on metal surfaces or in insulation materials during tank assembly, due to incomplete evacuation before initial filling with SF6.
Excessive moisture content leads to corrosive reaction products that can damage internal components and shorten the service life. If such substances escape, there is yet another danger to people?s health.
SF6 moisture measurement parameters
Measurement of SF6 moisture is therefore indispensable. In most cases, the dew or frost point can be used as a parameter. Here is the temperature at which the air humidity begins to condense. Regarding SF6, the atmospheric dew point specified by IEC 60376 is -36 �C.
The accuracy of the GDHT-20 of �2 K for moisture measurement is validated at the frost point with an internationally valid reference standard. However, the measuring instrument can also be configured for other parameters (dew point, ppmv, ppmw and relative humidity). diaphragm seal of the sensor also features greater application flexibility. The GDHT-20 is now also suitable for density monitoring of the alternative insulating gases N2, CF4, O2, CO2 and 3MTM NovecTM 4710.
Note
More info on the GDHT-20 sensor can be found on the WIKA website. Should you have any questions, your contact will gladly help you.
Also read our post
Responsible handling of sulphur hexafluoride
There are also out more about WIKA?s SF6 expertise in the following video: