High-accuracy moisture measurement in SF6 switchgear

Meticulous 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, 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 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 can be an all-in-one instrument for the web 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 once the SF6 will reach a critical state so when remedial measures must be taken. As a result, maintenance work or gas treatment is only undertaken when action is actually 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 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 results in corrosive reaction products that can damage internal components and shorten the service life. If such substances escape, there’s yet another danger to people?s health.
SF6 moisture measurement parameters
Measurement of SF6 moisture is therefore indispensable. Generally, the dew or frost point can be used as a parameter. This can be a temperature of which the air humidity begins to condense. Regarding SF6, the atmospheric dew point specified by IEC 60376 is -36 �C.
Banned 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 brand new version of the sensor also features greater application flexibility. The GDHT-20 is currently also ideal for density monitoring of the alternative insulating gases N2, CF4, O2, CO2 and 3MTM NovecTM 4710.
Note
More info on the GDHT-20 sensor are available on the WIKA website. If you have any questions, your contact will gladly help you.
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