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 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, is the crucial parameter for assessing the condition 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 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 can be an all-in-one instrument for the web monitoring of 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 and when remedial measures must be taken. Subsequently, maintenance work or gas treatment is only undertaken when action is really needed. Predictive maintenance thus replaces the sequence of regular maintenance intervals that has been previously necessary to avoid ecological and safety risks.
An excessive amount of 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 results in corrosive reaction products that can damage internal components and shorten the service life. If such substances escape, there is an additional danger to people?s health.
SF6 moisture measurement parameters
Measurement of SF6 moisture is therefore indispensable. In most cases, the dew or frost point is used as a parameter. This can be the temperature of which the air humidity begins to condense. In the case of 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 having an internationally valid reference standard. However, the measuring instrument can also 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 choice insulating gases N2, CF4, O2, CO2 and 3MTM NovecTM 4710.
Note
Cataclysmic on the GDHT-20 sensor can be found on the WIKA website. Assuming you have any questions, your contact will gladly assist you to.
Also read Sizzlingly of sulphur hexafluoride
You can also find out more about WIKA?s SF6 expertise in the next video:

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