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 having an accuracy of �2 K.
Moisture, along with 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 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 instead of regular maintenance intervals
The model GDHT-20 sensor can be an all-in-one instrument for the online tabs on SF6-insulated switchgear. It works 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 and when remedial measures should be taken. Consequently, maintenance work or gas treatment is only undertaken when action is really 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, this is usually a consequence of 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 may damage internal components and shorten the service life. If such substances escape, there is an additional danger to people?s health.
Promote of SF6 moisture is therefore indispensable. Usually, the dew or frost point can be used as a parameter. This can be the temperature of 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 even be configured for other parameters (dew point, ppmv, ppmw and relative humidity). The brand new version of the sensor also features greater application flexibility. The GDHT-20 is now also ideal for density monitoring of the alternative insulating gases N2, CF4, O2, CO2 and 3MTM NovecTM 4710.
Note
Further information on the GDHT-20 sensor are available on the WIKA website. Assuming you have any questions, your contact will gladly assist you to.
Also read our post
Responsible handling of sulphur hexafluoride
You can also find out more about WIKA?s SF6 expertise in the next video:

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