High-accuracy moisture measurement in SF6 switchgear

Moisture measurement in SF6-insulated switchgear is essential. That?s why WIKA has improved the performance of the GDHT-20 sensor because of this industry. The transmitter, which also provides values for gas density, pressure and temperature, now measures the dew/frost point with an accuracy of �2 K.
Moisture, along with density, is the crucial parameter for assessing the health of the SF6 gas used. The GDHT-20 continuously monitors its content in the gas. The info from the web monitoring forms the input for a downstream trend analysis. The more precise both density and the moisture measurement are, the more precise this analysis will be.
Predictive maintenance rather than regular maintenance intervals
The model GDHT-20 sensor is an all-in-one instrument for the online tabs on SF6-insulated switchgear. It works together with three temperature sensors (red), a pressure sensor (blue) and a humidity sensor (yellow).
The analysis shows the operator when the SF6 will reach a crucial state so when remedial measures should be taken. Consequently, maintenance work or gas treatment is undertaken when action is in fact needed. Predictive maintenance thus replaces the sequence of regular maintenance intervals that was 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 due to permeation through sealing materials. In younger plant, normally, this is due to moisture remaining on metal surfaces or in insulation materials during tank assembly, because of incomplete evacuation before initial filling with SF6.
Cash in corrosive reaction products that can damage internal components and shorten the service life. If such substances escape, there’s an additional danger to people?s health.
SF6 moisture measurement parameters
Measurement of SF6 moisture is therefore indispensable. Typically, the dew or frost point can be used as a parameter. This can be a 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). The new version of the sensor also features greater application flexibility. The GDHT-20 is now also suitable for density monitoring of the choice insulating gases N2, CF4, O2, CO2 and 3MTM NovecTM 4710.
Note
Further information on the GDHT-20 sensor are available on the WIKA website. Should you have any questions, your contact will gladly help you.
Also read our post
Responsible handling of sulphur hexafluoride
You can also find out more about WIKA?s SF6 expertise in the following video:

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